6 pak slow return idle/poor throttle response

[mac]

any updates?

 

[tak419]

any updates?

Hey mac. I've been on vacation and busy with a few other projects but yes a few updates. I rebuilt the center carb and corrected the accelerator pump issue. Again checked for vacuum leaks but still same issue. Let me recap. The car starts great, idles great, good vacuum at 13-14lbs, now revs up good but when it comes down it gets to around 1500 and then a lot slower to the 850 idle. That is the issue is the last slow part. And I've disconnected the throttle cable to eliminate a cable issue. Also note when the choke is closed the throttle is super crisp and goes completely to idle so that tells me it's a lean condition. The outboards are at 1/2 out and centers 2- 2 1/4 out. That is where the highest vacuum is. I'm still thinking vacuum leak somewhere. What do you think ? I had a small vacuum leak on my motorcycle that cause a slight miss issue and was almost impossible to find. Was the throttle body to head boot.

 

[mac]

i would still like to see your initial timing at 16 degrees at least. no more than 34 total. after that i would turn all 4 idle screws to 3/4 of a turn on outboard carbs and readjust center carb for idle. also, can you confirm that the float levels have been checked? i have an A/F meter and my idle was not consistent and cruise had a stumble. found out that both situations were very lean. opened the outboard carbs a little and it was all good. outboard carbs always contribute fuel even when closed so i believe a small adjustment may help.

 

[Johnpat]

Check your throttle plate,might be binding & slow
To return to shut position.

Pull Back by hand at carb to see if it makes a difference.
Had this happen to me.
Binding throttle shaft.

 

[tak419]

Just checked. Definitely not the issue. All good and free.

 

[tak419]

It revs up quick, idle good. Starts good, but coming down off of a good rev it gets to about 1500 and then slowly down to the idle speed.

 

[mac]

It revs up quick, idle good. Starts good, but coming down off of a good rev it gets to about 1500 and then slowly down to the idle speed.

maybe not enough spring in the distributor to pull weights back in. also, i still would increase initial timing. try it in the garage. you can boost it up and give the throttle a couple of cracks and see how it behaves. if it likes the added timing then check the total to make sure it is not too much before you take it to the street..

 

[tak419]

I've played with the timing anywhere from 7-18 initial. It makes a difference just not in the problem I'm having. I've thought about the distributor springs. Is there a way to check that and also would the choke being closed when cold it's snappy and goes right down to idle as it should. I was told that is a lean condition which I kind knew. Back to the distributor, if I set it at 15* initial and set the idle back to 850. As I raise the speed doesn't the mechanical advance start to work almost immediately ? I can definitely understand coming down out of the rpms if the springs are week the weights won't want to snap back as fast. This is a Mopar kit sold around 2000 or so and I believe the springs in it now are purple.

 

[wyrmrider]

you have to limit the total mech advance when you do this- kit a kit
electronic or points- may be the same I don't remember dual points are different

 

[mac]

if you have a dial back timing light it should be a piece of cake. get it warmed up and check your timing at idle. then using the idle speed screw, go up in 500 rpm increments and write down what you get until it stops advancing. with today's fuel, i would try and make it start advancing at 1500 rpm and all in at 3000 rpm. then return to idle and see if it returns to the original timing you started with.

 

[mac]

you have to limit the total mech advance when you do this- kit a kit
electronic or points- may be the same I don't remember dual points are different

all the things i am suggesting is done parked. only when you know that it is limited to around 34 degrees total, then go for a ride under load. no load tests in park are not a problem.

 

[biomedtechguy]

outboard carbs always contribute fuel even when closed so i believe a small adjustment may help.

THIS was an epiphany for me in getting my 6bbl way better:

 

[mac]

i know this is a commercial to sell their product, but still the process is a good reference to getting car setup with a good ignition curve.


Many cooling issues like this can be cured by getting your tune up right, it's way cheaper and it permanently solves the issues rather than spending a bunch of money trying to put a band-aid on it.
Look at this solution to getting enough timing in it to burn pump gas:
eBay item# 323099910935 $29.00 or direct from FBO Ignition for $25.00

This plate allows you to add more initial timing to the engine without exceeding the 34* total timing as they were engineered to run most efficiently at under load. Then connect a vacuum can to the constant manifold vacuum port to get it even higher at idle and part throttle/cruise to get the best mileage and cleanest burn. An engine that gets good mileage is an engine that is tuned properly.

This plate and a correctly adjusted and calibrated vacuum canister will correct your timing events so it can burn all the fuel it's getting and get rid of that rich stinky idle. If your having problems with your carb not responding to your adjustments its usually timing events and not a carb issue.

How much initial timing?
Start your engine, warm it up, pull the vacuum line off and plug it so you don't create a vacuum leak'
Hopefully you have a dial-back type timing light? Start out by advancing it to 18* at idle.
Now shut it off and let it heat soak for 2-3 minutes.
Try starting it by just bumping the key.
Did it fire right off? Or did it drag the starter down? Or kick backwards and maybe even kick back through the carb?
My guess is it fired right up with no issues.
Now repeat this procedure adding 2* at a time until it kicks back or drags the starter down, at this point lets say it's kicks at 22, back it up 2* to 20, should be a huge improvement in how quick it now starts and idle quality, exhaust smell should have improved noticeably.
So we have established that the engine will handle 20* initial timing but with that much timing you'll be at probably 45* under load and it WILL detonate, so don't attempt to drive it set like this. You can crack the throttle and see how much the throttle response has improved, it'll be crisp and clean. Don't be afraid to whack that throttle it won't detonate. It takes 2 conditions to make a engine detonate "Heat" and "Pressure (load)", if one of these conditions is not present (load) then it won't detonate, like I said Don't try and drive it.
Using the FBO Plate now you can install it using the 14* slot which will limit the mechanical advance to 14* + the 20* initial for a total of 34* under load, Perfect!

Now you can set your vacuum can up using your dial back timing light.

First I want to explain these vacuum cans.... The SAE standard adjustable vacuum can has a large hex shape molded into the metal can this is how you can tell the difference between the adjustable and non-adjustable varieties. Non-adjustable cans are for Emissions Vehicles and Adjustable are for pre-emissions or your Hot Rod engines.

This has always been the way its been done it in America, until the Chinese imports flooded the market, and they are tricky folks always trying to deceive you by making it cheaper and claiming "Sam ting but much cheapa" they ARE NOT the same. Mail order houses and mass merchandisers are notorious for always trying to have the lowest price, the quality and functionality suffers drastically. They make vacuum cans with the SAE standard hex design... but they are NOT adjustable, what we call the piston that moves inside the can to increase the pressure on the internal spring is plastic instead of steel so they easily strip the threads if its actually an adjustable type can, they use a one spring fits all so unless your making 12" of vacuum or more at idle you can't get the can adjusted even if it is an adjustable type. Then they top it off by using an assortment of Allen wrench sizes mostly in metric, USA standard is a 3/16 Allen. The screw is such poor quality even if you find a metric Allen you'll usually strip the head out trying to adjust it. Many of these imported distributors are of such low quality we won't even work on them, in this business the last guy to touch it it is responsible for the warranty, we won't be the warranty dumping ground for these low end units, Spectra being the worst of them all.

So the object here is to get the idle timing up to 30-32 with the vacuum connected to a constant manifold vacuum port on the carb or directly to a manifold source.
Using your dial-back timing light simply plug in the vac can and check your timing, experiment by checking, then adjust, check and adjust until it effectively brings the timing up to 28-32 at idle, remember that the adjustment only changes the sensitivity and not the total amount of timing.

Vacuum timing degrees are controlled by the arm, if its a good USA Made vacuum can it will have a number stamped on the arm, take that number and double it for distributor degrees, a common one is a 6.5 which gives you 13* when fully engaged. There's not much you can do with your vacuum can if you want less or more than amount stamped on the can, we have a propriety method of setting limiters up on the vacuum cans to limit the amount of advance that the canister will generate.

So now you have the initial timing set up, the mechanical advance limiter in place, the vacuum canister adjusted correctly so what happens when you drive the car?

Its now got plenty of initial timing to light the fire when you hit the key, as soon as the engine lights off you have plenty of timing to burn unleaded ethanol infused so called Gasoline, so now you have nice clean idle, very crisp throttle response, and your completely burning the fuel in the combustion process so you exhaust is clean and your eyes stop watering from the stink of UN-burned fuel.

Spring rate or "Mechanical Curve"
Forget about the factory specs they mean nothing, you've probably changed the cam, heads, intake, converted to electronic ignition, added headers and the most relevant of all the oil company's have changed the FUEL formulations. We can't buy 1968-69 fuel anymore, today's fuel formulations are complex and loaded with ethanol, fuel pump lubricants for in tank fuel pumps on injected vehicles, injector cleaners and a multitude of other additives that are not designed in any way to burn in your old style push rod motors. Most of them don't even burn, they are designed to to vaporize under the extreme combustion chamber temperatures that are developed in the new injected, computer controlled vehicles to achieve the highest fuel economy. So bringing your timing in at 1600 or 2000 RPM is not longer an viable option. Why would you need all that timing when you cam does't even start making power until 3500? If your convertor is a 3000 stall what would be the point? If your hammering your 4 speed to 6200 why do you need the timing in so low... all it going to do is create excessive cylinder pressure and heat before the engine gets into it's power-band, causing detonation, carbon build up and lousy bottom end tork. Where it needs to "All In" depends on the cam duration, compression ratio, gearing, trans type, head type and the weight of the car. There's no formula or rate chart that can read all these variables and give you a definitive number, only experience and knowledge of how to read everything as package can determine that number. Between Jim and I we have been doing this for over 100 years... I think we have it kinda figured out.

Now lets go for a ride, at part throttle cruise at 65 MPH you have the carb throttle blades open maybe 10% and your spinning the motor at 2400-3000 RPM depending on the gear so you have good RPM but the carb is restricting the air flow so the motor is making lots of vacuum. So now you'll have your 20* initial, maybe another 10* of mechanical and vacuum can is pulling another 13, add those all together and you'll be at 43* of timing, awesome! At cruise your only running on the primary side of the carburetor which is by design delivery a very lean mixture (hence the power valve or a vacuum secondary) Lean mixtures take longer to burn than rich mixtures as the fuel particles are further apart so the flame front speed is reduced. With this is mind its only common sense that you need more timing at cruise to optimize the combustion process. Anywhere from 40-48* at cruise is fine. new computer controlled cars will run easily as high as 60* or more under certain circumstances of course all controlled by the computer and the information it receives from 15 to 30 or more different sensors feeding it information at 100-1000 samples per second. just slightly more sophisticated than our old analog systems.

So now you have invested your time and money in getting your distributor dialed in, please don't plug it in to a transistor type box (Orange, Blue, Green or pink) and expect it to perform, all those old design, slow transistor type stock boxes will retard your timing by 8* starting at 3200 and by 5200 or less they have retarded the timing by 8* or more. The (Proclaimed) 7500 RPM will hold timing better but it will drop out put to about 8KV , you need at least 35KV to keep the fire burning correctly.

Mopar Performance hasn't made a orange or any other ignition control box or distributor for over a decade, don't be fooled by someone in China who bought a licensing agreement on a part number.

There's more to it than what I have time to type here but I hope that it gives you guidance and gets you going in the right direction.

You can email questions to me at [email protected] or visit our website and read more articles in the tech section.

 

[biomedtechguy]

i know this is a commercial to sell their product, but still the process is a good reference to getting car setup with a good ignition curve.


Many cooling issues like this can be cured by getting your tune up right, it's way cheaper and it permanently solves the issues rather than spending a bunch of money trying to put a band-aid on it.
Look at this solution to getting enough timing in it to burn pump gas:
eBay item# 323099910935 $29.00 or direct from FBO Ignition for $25.00

This plate allows you to add more initial timing to the engine without exceeding the 34* total timing as they were engineered to run most efficiently at under load. Then connect a vacuum can to the constant manifold vacuum port to get it even higher at idle and part throttle/cruise to get the best mileage and cleanest burn. An engine that gets good mileage is an engine that is tuned properly.

This plate and a correctly adjusted and calibrated vacuum canister will correct your timing events so it can burn all the fuel it's getting and get rid of that rich stinky idle. If your having problems with your carb not responding to your adjustments its usually timing events and not a carb issue.

How much initial timing?
Start your engine, warm it up, pull the vacuum line off and plug it so you don't create a vacuum leak'
Hopefully you have a dial-back type timing light? Start out by advancing it to 18* at idle.
Now shut it off and let it heat soak for 2-3 minutes.
Try starting it by just bumping the key.
Did it fire right off? Or did it drag the starter down? Or kick backwards and maybe even kick back through the carb?
My guess is it fired right up with no issues.
Now repeat this procedure adding 2* at a time until it kicks back or drags the starter down, at this point lets say it's kicks at 22, back it up 2* to 20, should be a huge improvement in how quick it now starts and idle quality, exhaust smell should have improved noticeably.
So we have established that the engine will handle 20* initial timing but with that much timing you'll be at probably 45* under load and it WILL detonate, so don't attempt to drive it set like this. You can crack the throttle and see how much the throttle response has improved, it'll be crisp and clean. Don't be afraid to whack that throttle it won't detonate. It takes 2 conditions to make a engine detonate "Heat" and "Pressure (load)", if one of these conditions is not present (load) then it won't detonate, like I said Don't try and drive it.
Using the FBO Plate now you can install it using the 14* slot which will limit the mechanical advance to 14* + the 20* initial for a total of 34* under load, Perfect!

Now you can set your vacuum can up using your dial back timing light.

First I want to explain these vacuum cans.... The SAE standard adjustable vacuum can has a large hex shape molded into the metal can this is how you can tell the difference between the adjustable and non-adjustable varieties. Non-adjustable cans are for Emissions Vehicles and Adjustable are for pre-emissions or your Hot Rod engines.

This has always been the way its been done it in America, until the Chinese imports flooded the market, and they are tricky folks always trying to deceive you by making it cheaper and claiming "Sam ting but much cheapa" they ARE NOT the same. Mail order houses and mass merchandisers are notorious for always trying to have the lowest price, the quality and functionality suffers drastically. They make vacuum cans with the SAE standard hex design... but they are NOT adjustable, what we call the piston that moves inside the can to increase the pressure on the internal spring is plastic instead of steel so they easily strip the threads if its actually an adjustable type can, they use a one spring fits all so unless your making 12" of vacuum or more at idle you can't get the can adjusted even if it is an adjustable type. Then they top it off by using an assortment of Allen wrench sizes mostly in metric, USA standard is a 3/16 Allen. The screw is such poor quality even if you find a metric Allen you'll usually strip the head out trying to adjust it. Many of these imported distributors are of such low quality we won't even work on them, in this business the last guy to touch it it is responsible for the warranty, we won't be the warranty dumping ground for these low end units, Spectra being the worst of them all.

So the object here is to get the idle timing up to 30-32 with the vacuum connected to a constant manifold vacuum port on the carb or directly to a manifold source.
Using your dial-back timing light simply plug in the vac can and check your timing, experiment by checking, then adjust, check and adjust until it effectively brings the timing up to 28-32 at idle, remember that the adjustment only changes the sensitivity and not the total amount of timing.

Vacuum timing degrees are controlled by the arm, if its a good USA Made vacuum can it will have a number stamped on the arm, take that number and double it for distributor degrees, a common one is a 6.5 which gives you 13* when fully engaged. There's not much you can do with your vacuum can if you want less or more than amount stamped on the can, we have a propriety method of setting limiters up on the vacuum cans to limit the amount of advance that the canister will generate.

So now you have the initial timing set up, the mechanical advance limiter in place, the vacuum canister adjusted correctly so what happens when you drive the car?

Its now got plenty of initial timing to light the fire when you hit the key, as soon as the engine lights off you have plenty of timing to burn unleaded ethanol infused so called Gasoline, so now you have nice clean idle, very crisp throttle response, and your completely burning the fuel in the combustion process so you exhaust is clean and your eyes stop watering from the stink of UN-burned fuel.

Spring rate or "Mechanical Curve"
Forget about the factory specs they mean nothing, you've probably changed the cam, heads, intake, converted to electronic ignition, added headers and the most relevant of all the oil company's have changed the FUEL formulations. We can't buy 1968-69 fuel anymore, today's fuel formulations are complex and loaded with ethanol, fuel pump lubricants for in tank fuel pumps on injected vehicles, injector cleaners and a multitude of other additives that are not designed in any way to burn in your old style push rod motors. Most of them don't even burn, they are designed to to vaporize under the extreme combustion chamber temperatures that are developed in the new injected, computer controlled vehicles to achieve the highest fuel economy. So bringing your timing in at 1600 or 2000 RPM is not longer an viable option. Why would you need all that timing when you cam does't even start making power until 3500? If your convertor is a 3000 stall what would be the point? If your hammering your 4 speed to 6200 why do you need the timing in so low... all it going to do is create excessive cylinder pressure and heat before the engine gets into it's power-band, causing detonation, carbon build up and lousy bottom end tork. Where it needs to "All In" depends on the cam duration, compression ratio, gearing, trans type, head type and the weight of the car. There's no formula or rate chart that can read all these variables and give you a definitive number, only experience and knowledge of how to read everything as package can determine that number. Between Jim and I we have been doing this for over 100 years... I think we have it kinda figured out.

Now lets go for a ride, at part throttle cruise at 65 MPH you have the carb throttle blades open maybe 10% and your spinning the motor at 2400-3000 RPM depending on the gear so you have good RPM but the carb is restricting the air flow so the motor is making lots of vacuum. So now you'll have your 20* initial, maybe another 10* of mechanical and vacuum can is pulling another 13, add those all together and you'll be at 43* of timing, awesome! At cruise your only running on the primary side of the carburetor which is by design delivery a very lean mixture (hence the power valve or a vacuum secondary) Lean mixtures take longer to burn than rich mixtures as the fuel particles are further apart so the flame front speed is reduced. With this is mind its only common sense that you need more timing at cruise to optimize the combustion process. Anywhere from 40-48* at cruise is fine. new computer controlled cars will run easily as high as 60* or more under certain circumstances of course all controlled by the computer and the information it receives from 15 to 30 or more different sensors feeding it information at 100-1000 samples per second. just slightly more sophisticated than our old analog systems.

So now you have invested your time and money in getting your distributor dialed in, please don't plug it in to a transistor type box (Orange, Blue, Green or pink) and expect it to perform, all those old design, slow transistor type stock boxes will retard your timing by 8* starting at 3200 and by 5200 or less they have retarded the timing by 8* or more. The (Proclaimed) 7500 RPM will hold timing better but it will drop out put to about 8KV , you need at least 35KV to keep the fire burning correctly.

Mopar Performance hasn't made a orange or any other ignition control box or distributor for over a decade, don't be fooled by someone in China who bought a licensing agreement on a part number.

There's more to it than what I have time to type here but I hope that it gives you guidance and gets you going in the right direction.

You can email questions to me at [email protected] or visit our website and read more articles in the tech section.

All GREAT info! I switched out my Chrysler electronic ignition for the FBO system from Don @ FBO. The only problem I've had is my initial timing under vacuum (direct manifold) is a little under what Don set it up to be and as hard as I've tried I can't get an Allen wrench to grab to make adjustments to the vacuum can. If you read this post, PM me so maybe we can address this. If not, I'll call you soon because I will be re-tuning my motor when my Promax modded carbs come in.
The FBO ignition system is great, the built in rev limiter is reliable and easy to set, and gave me the courage to power shift my 3 pedal 6bbl 440, resulting in much better 1/4 mile times.

 

[Paul_G]

i know this is a commercial to sell their product, but still the process is a good reference to getting car setup with a good ignition curve.


Many cooling issues like this can be cured by getting your tune up right, it's way cheaper and it permanently solves the issues rather than spending a bunch of money trying to put a band-aid on it.
Look at this solution to getting enough timing in it to burn pump gas:
eBay item# 323099910935 $29.00 or direct from FBO Ignition for $25.00

This plate allows you to add more initial timing to the engine without exceeding the 34* total timing as they were engineered to run most efficiently at under load. Then connect a vacuum can to the constant manifold vacuum port to get it even higher at idle and part throttle/cruise to get the best mileage and cleanest burn. An engine that gets good mileage is an engine that is tuned properly.

This plate and a correctly adjusted and calibrated vacuum canister will correct your timing events so it can burn all the fuel it's getting and get rid of that rich stinky idle. If your having problems with your carb not responding to your adjustments its usually timing events and not a carb issue.

How much initial timing?
Start your engine, warm it up, pull the vacuum line off and plug it so you don't create a vacuum leak'
Hopefully you have a dial-back type timing light? Start out by advancing it to 18* at idle.
Now shut it off and let it heat soak for 2-3 minutes.
Try starting it by just bumping the key.
Did it fire right off? Or did it drag the starter down? Or kick backwards and maybe even kick back through the carb?
My guess is it fired right up with no issues.
Now repeat this procedure adding 2* at a time until it kicks back or drags the starter down, at this point lets say it's kicks at 22, back it up 2* to 20, should be a huge improvement in how quick it now starts and idle quality, exhaust smell should have improved noticeably.
So we have established that the engine will handle 20* initial timing but with that much timing you'll be at probably 45* under load and it WILL detonate, so don't attempt to drive it set like this. You can crack the throttle and see how much the throttle response has improved, it'll be crisp and clean. Don't be afraid to whack that throttle it won't detonate. It takes 2 conditions to make a engine detonate "Heat" and "Pressure (load)", if one of these conditions is not present (load) then it won't detonate, like I said Don't try and drive it.
Using the FBO Plate now you can install it using the 14* slot which will limit the mechanical advance to 14* + the 20* initial for a total of 34* under load, Perfect!

Now you can set your vacuum can up using your dial back timing light.

First I want to explain these vacuum cans.... The SAE standard adjustable vacuum can has a large hex shape molded into the metal can this is how you can tell the difference between the adjustable and non-adjustable varieties. Non-adjustable cans are for Emissions Vehicles and Adjustable are for pre-emissions or your Hot Rod engines.

This has always been the way its been done it in America, until the Chinese imports flooded the market, and they are tricky folks always trying to deceive you by making it cheaper and claiming "Sam ting but much cheapa" they ARE NOT the same. Mail order houses and mass merchandisers are notorious for always trying to have the lowest price, the quality and functionality suffers drastically. They make vacuum cans with the SAE standard hex design... but they are NOT adjustable, what we call the piston that moves inside the can to increase the pressure on the internal spring is plastic instead of steel so they easily strip the threads if its actually an adjustable type can, they use a one spring fits all so unless your making 12" of vacuum or more at idle you can't get the can adjusted even if it is an adjustable type. Then they top it off by using an assortment of Allen wrench sizes mostly in metric, USA standard is a 3/16 Allen. The screw is such poor quality even if you find a metric Allen you'll usually strip the head out trying to adjust it. Many of these imported distributors are of such low quality we won't even work on them, in this business the last guy to touch it it is responsible for the warranty, we won't be the warranty dumping ground for these low end units, Spectra being the worst of them all.

So the object here is to get the idle timing up to 30-32 with the vacuum connected to a constant manifold vacuum port on the carb or directly to a manifold source.
Using your dial-back timing light simply plug in the vac can and check your timing, experiment by checking, then adjust, check and adjust until it effectively brings the timing up to 28-32 at idle, remember that the adjustment only changes the sensitivity and not the total amount of timing.

Vacuum timing degrees are controlled by the arm, if its a good USA Made vacuum can it will have a number stamped on the arm, take that number and double it for distributor degrees, a common one is a 6.5 which gives you 13* when fully engaged. There's not much you can do with your vacuum can if you want less or more than amount stamped on the can, we have a propriety method of setting limiters up on the vacuum cans to limit the amount of advance that the canister will generate.

So now you have the initial timing set up, the mechanical advance limiter in place, the vacuum canister adjusted correctly so what happens when you drive the car?

Its now got plenty of initial timing to light the fire when you hit the key, as soon as the engine lights off you have plenty of timing to burn unleaded ethanol infused so called Gasoline, so now you have nice clean idle, very crisp throttle response, and your completely burning the fuel in the combustion process so you exhaust is clean and your eyes stop watering from the stink of UN-burned fuel.

Spring rate or "Mechanical Curve"
Forget about the factory specs they mean nothing, you've probably changed the cam, heads, intake, converted to electronic ignition, added headers and the most relevant of all the oil company's have changed the FUEL formulations. We can't buy 1968-69 fuel anymore, today's fuel formulations are complex and loaded with ethanol, fuel pump lubricants for in tank fuel pumps on injected vehicles, injector cleaners and a multitude of other additives that are not designed in any way to burn in your old style push rod motors. Most of them don't even burn, they are designed to to vaporize under the extreme combustion chamber temperatures that are developed in the new injected, computer controlled vehicles to achieve the highest fuel economy. So bringing your timing in at 1600 or 2000 RPM is not longer an viable option. Why would you need all that timing when you cam does't even start making power until 3500? If your convertor is a 3000 stall what would be the point? If your hammering your 4 speed to 6200 why do you need the timing in so low... all it going to do is create excessive cylinder pressure and heat before the engine gets into it's power-band, causing detonation, carbon build up and lousy bottom end tork. Where it needs to "All In" depends on the cam duration, compression ratio, gearing, trans type, head type and the weight of the car. There's no formula or rate chart that can read all these variables and give you a definitive number, only experience and knowledge of how to read everything as package can determine that number. Between Jim and I we have been doing this for over 100 years... I think we have it kinda figured out.

Now lets go for a ride, at part throttle cruise at 65 MPH you have the carb throttle blades open maybe 10% and your spinning the motor at 2400-3000 RPM depending on the gear so you have good RPM but the carb is restricting the air flow so the motor is making lots of vacuum. So now you'll have your 20* initial, maybe another 10* of mechanical and vacuum can is pulling another 13, add those all together and you'll be at 43* of timing, awesome! At cruise your only running on the primary side of the carburetor which is by design delivery a very lean mixture (hence the power valve or a vacuum secondary) Lean mixtures take longer to burn than rich mixtures as the fuel particles are further apart so the flame front speed is reduced. With this is mind its only common sense that you need more timing at cruise to optimize the combustion process. Anywhere from 40-48* at cruise is fine. new computer controlled cars will run easily as high as 60* or more under certain circumstances of course all controlled by the computer and the information it receives from 15 to 30 or more different sensors feeding it information at 100-1000 samples per second. just slightly more sophisticated than our old analog systems.

So now you have invested your time and money in getting your distributor dialed in, please don't plug it in to a transistor type box (Orange, Blue, Green or pink) and expect it to perform, all those old design, slow transistor type stock boxes will retard your timing by 8* starting at 3200 and by 5200 or less they have retarded the timing by 8* or more. The (Proclaimed) 7500 RPM will hold timing better but it will drop out put to about 8KV , you need at least 35KV to keep the fire burning correctly.

Mopar Performance hasn't made a orange or any other ignition control box or distributor for over a decade, don't be fooled by someone in China who bought a licensing agreement on a part number.

There's more to it than what I have time to type here but I hope that it gives you guidance and gets you going in the right direction.

You can email questions to me at [email protected] or visit our website and read more articles in the tech section.

Fantastic read and 100% correct. I have been fidling with my 72 Charger with an iron headed mild built 360 for 5 years trying to control engine overheating, detonating, hesitations, poor idle quality, lack of power, etc. I have stumbled in to all the fixes you just just stated, except I did it the hard way, by trial and error.

 

[mac]

all fixed?

 

[biomedtechguy]

all fixed?