Stumble @WOT

[texas69bee]

I would stay with the 35 but like old bee said, you may have to change the cam. At this point is when I would contact Don from 4secondsflat.com
I'm not sure if he is still giving tech advice on Quickfuel since they sold to Holley.

 

[Jcharger]

The cam determines how the gas is sent in as the throttle is rotated through its cycle. It also affects how much gas is delivered. The squirter affects how fast it takes for the gas to get there and I suspect may have a slight effect on the amount, but only because of inefficiencies.

What color cam do you have on now? You can look up a graph to get an idea of what the different ones do.

 

[rebootej]

First of thank you so much for the help this far I would be so lost.

Okay so I have the pink cam on my carb now. Looks like any other cam is going to give me a quicker shot. Thinking maybe the green or red or white? Any preference? I know my father has a few extras at his house, I'll check out which ones he has. Leaning maybe white or red first?

I've read a few of Don's pieces very informative. Ill try to email him and see if he's still giving advice.

 

[rebootej]

Rich usually sounds more in exhaust, lean through carburetor. Follow the link below and practice up on patience and note taking for each change and the result it produces. I'm proof that any fool can do this, I'm sure you will excel.
http://www.4secondsflat.com/Spark_plug_reading.html

How often do can you check the plugs?

these are my plugs from a month ago

This was the old carb. Looks like slightly too much advance, not a hot enough plug? Am i reading these right?

 

[Belle66]

How often do can you check the plugs?

Every few months once fuel and timing are set.
For primary jet size, right after a few miles at steady cruise speeds...and repeat until the jets size is good.
For secondary jetting right after several WOT runs at drag strip....and repeat until the jet size is good.

 

[Belle66]

How often do can you check the plugs?

these are my plugs from a month ago
View attachment 424740 View attachment 424741

This was the old carb. Looks like slightly too much advance, not a hot enough plug? Am i reading these right?

Can't promise this will work for you or saying this is the only way, this is how i go about it. This process takes time and patience.

• During the first couple of steps adjust the timing to the photos in the 4seconds flat link.
• Keep detailed notes of jet sizes, squirter sizes and cam sizes at the beginning and note how the engine performs
• Continue detailed notes including any changes to the carb and how the performance has changed.
• Adjust the idle mixture screws to obtain max intake manifold vacuum and then back of 1/8 turn every time you change the jets.
• After making some adjustments, I usually drive the car to and from work or on errands to make sure it has good street manners.

1)Get new plugs and some spares. Be certain that they are the manufacturer recommended plugs. These will be the correct heat range or very close.
2)Watch the Holley videos.
3)Drive and check plugs for primary jetting. inspect white insulator.
4)Disable secondary and drive WOT for response to determine squirter size.
5)Drive WOT and change cams for best throttle response
6)Enable secondary and make WOTs for secondary jetting inspect white insulator
7)Drive WOT for response to determine secondary squirter size. you may need to adjust the primary squirter too.
8)Drive WOT and change secondary cam for best throttle response. you may need to change the primary too.

 

[Belle66]

How often do can you check the plugs?

these are my plugs from a month ago
View attachment 424740 View attachment 424741

This was the old carb. Looks like slightly too much advance, not a hot enough plug? Am i reading these right?

Yeah I don't see any color change on the strap which means it's cold. Find out what Mopar recommends and buy that specific manufacturer and model spark plug...it should get you close.

 

[texas69bee]

Can't promise this will work for you or saying this is the only way, this is how i go about it. This process takes time and patience.

• During the first couple of steps adjust the timing to the photos in the 4seconds flat link.
• Keep detailed notes of jet sizes, squirter sizes and cam sizes at the beginning and note how the engine performs
• Continue detailed notes including any changes to the carb and how the performance has changed.
• Adjust the idle mixture screws to obtain max intake manifold vacuum and then back of 1/8 turn every time you change the jets.
• After making some adjustments, I usually drive the car to and from work or on errands to make sure it has good street manners.

1)Get new plugs and some spares. Be certain that they are the manufacturer recommended plugs. These will be the correct heat range or very close.
2)Watch the Holley videos.
3)Drive and check plugs for primary jetting. inspect white insulator.
4)Disable secondary and drive WOT for response to determine squirter size.
5)Drive WOT and change cams for best throttle response
6)Enable secondary and make WOTs for secondary jetting inspect white insulator
7)Drive WOT for response to determine secondary squirter size. you may need to adjust the primary squirter too.
8)Drive WOT and change secondary cam for best throttle response. you may need to change the primary too.

Good info...
Just curious, this is a 318. Is there any mods that were made that aren't listed. Compression, fuel pump, intake??? What octane of fuel?

 

[Belle66]

Good info...
Just curious, this is a 318. Is there any mods that were made that aren't listed. Compression, fuel pump, intake??? What octane of fuel?

Last tuning session was on my poly after putting in a mid range cam, new valve springs, and replaced a singe plane intake with a dual plane and higher stall torque converter.
Good point on the fuel pump always good to know that it's pumping enough and that you're not runninf low on gas at WOT.

 

[rebootej]

Okay. so for the engine. i rebuilt it myself, had the local napa clean it up and order the parts and i assembled. Its a 1974 318 with a 360 equivalent comp camp, headers, eldelbrock performer intake (spreadbore-adapted to square) mopar performance orange box ignition. Running premium pump gas.

The fuel pump is a stock style Napa or Oreilly, havent checked flow rate but its PSI is steady at 7. But when i had the 625 Demon on the engine it never had this problem making me think its not the pump? but i have debated upgrading to a better one...

Ive actually never checked my compression to see what my compression was after I assembled. Ive been meaning to do that lately. I just keep forgetting..

 

[rebootej]

Can't promise this will work for you or saying this is the only way, this is how i go about it. This process takes time and patience.

• During the first couple of steps adjust the timing to the photos in the 4seconds flat link.
• Keep detailed notes of jet sizes, squirter sizes and cam sizes at the beginning and note how the engine performs
• Continue detailed notes including any changes to the carb and how the performance has changed.
• Adjust the idle mixture screws to obtain max intake manifold vacuum and then back of 1/8 turn every time you change the jets.
• After making some adjustments, I usually drive the car to and from work or on errands to make sure it has good street manners.

1)Get new plugs and some spares. Be certain that they are the manufacturer recommended plugs. These will be the correct heat range or very close.
2)Watch the Holley videos.
3)Drive and check plugs for primary jetting. inspect white insulator.
4)Disable secondary and drive WOT for response to determine squirter size.
5)Drive WOT and change cams for best throttle response
6)Enable secondary and make WOTs for secondary jetting inspect white insulator
7)Drive WOT for response to determine secondary squirter size. you may need to adjust the primary squirter too.
8)Drive WOT and change secondary cam for best throttle response. you may need to change the primary too.

This is great! Im willing to give it a try. and see what i get. Chasing this thing is frustrating. but i am definitely learning alot about carbs. How quick will the timing marks show up on the spark plugs? A couple runs?

 

[Belle66]

This is great! Im willing to give it a try. and see what i get. Chasing this thing is frustrating. but i am definitely learning alot about carbs. How quick will the timing marks show up on the spark plugs? A couple runs?

When you pull the plugs after your first drive for primary jetting you will know timing and heat range.
Tuning can be frustrating and tedious lotsa patience and taking breaks helps me. During the breaks is when I drive it for street manners.

 

[rebootej]

Okay, ill give it a try.. yes its frustrating for sure! Is it possiable I went the wrong way on the squirter? I need a longer shot, not a quicker fat shot?

Did the paper clip test and my leaning out at wot is not from the secondaries opening.. and it revs for half a second then falls on its face. Would a longer shot keep it from falling on its face?

Lost confused and tired.

 

[Belle66]

primary jets first, watch the holley videos. Gotta start with a firm foundation.

 

[Jcharger]

Belle66 gives good advice. Let me recap what I understand.

You have an O2 sensor and it sounds like you have your main jets dialed in OK if you are at 12.8-13.1 A/F on WOT acceleration. I am assuming you have the idle set up OK to. I would think the pink cam would be sufficient for your purposes, but won't hurt to try various configurations, but Keep notes, especially of the starting point because you may want to go back. Also the points made above about the health of the ignition are critical. Early on, I chased what I thought was a problem with the caruburetor and it was an issue with the points. (Vacuum will often get better with RPM and RPM will often increase with timing, so make sure you make comparisons at the same RPM).

I assume you are tuned to max vacuum at idle and then 1/8 turn rich on the idle mixture screws. I assume your idle is somewhere in the 13-14 range for A/F (Apologize if I missed that). I assume your cruise is somewhere in the 14-15 range. And you see a lean spike and stumble as you hit the throttle (do you see the switch to rich when the accelerator pump puts the gas in. You also have made this a little better with a stronger spring in the VS and a larger pump nozzle. One thing I do not know is if you are doing your tests starting a very low RPM (lower than you normally would ever be operating) or if it is at a reasonable RPM. This can make things appear that don't matter in the real world. The other thing is that carburetors have their limits. They have three basic settings to cont (main jets, cruise, and idle) - that the demon worked suggests that there is something that can be tweaked.

Also have you checked the level of the fuel in the fuel bowls.

 

[oldbee]

Post #33 got me thinking of float level also, if too low will delay getting into main fuel circuit.

 

[rebootej]

primary jets first, watch the holley videos. Gotta start with a firm foundation.

I've been watching the videos, Ill pull plugs tonight and post pics. This acceleration problem is really affecting the car drivability. Even if its not WOT the car still leans wayyy out if Im doing anything more then a gentle acceleration.

 

[rebootej]

Belle66 gives good advice. Let me recap what I understand.

You have an O2 sensor and it sounds like you have your main jets dialed in OK if you are at 12.8-13.1 A/F on WOT acceleration. I am assuming you have the idle set up OK to. I would think the pink cam would be sufficient for your purposes, but won't hurt to try various configurations, but Keep notes, especially of the starting point because you may want to go back. Also the points made above about the health of the ignition are critical. Early on, I chased what I thought was a problem with the caruburetor and it was an issue with the points. (Vacuum will often get better with RPM and RPM will often increase with timing, so make sure you make comparisons at the same RPM).

I assume you are tuned to max vacuum at idle and then 1/8 turn rich on the idle mixture screws. I assume your idle is somewhere in the 13-14 range for A/F (Apologize if I missed that). I assume your cruise is somewhere in the 14-15 range. And you see a lean spike and stumble as you hit the throttle (do you see the switch to rich when the accelerator pump puts the gas in. You also have made this a little better with a stronger spring in the VS and a larger pump nozzle. One thing I do not know is if you are doing your tests starting a very low RPM (lower than you normally would ever be operating) or if it is at a reasonable RPM. This can make things appear that don't matter in the real world. The other thing is that carburetors have their limits. They have three basic settings to cont (main jets, cruise, and idle) - that the demon worked suggests that there is something that can be tweaked.

Also have you checked the level of the fuel in the fuel bowls.

Yes Jcharger you are right with the wide band O2 sensor, and once the engine recovers from its stumble, WOT is right around 13.0 Idle is a little rich, Ive got air bleeds coming to help bring this down.

Im going to put a notebook in the car and start taking better notes. I really want to nail down the timing on this car, its up at about 18 degrees right now. Side note I also replaced the cap and rotor last night. Currently I have the orange cam in.. not noticing a big difference.

Yes thats how i set my carb up using those steps, 1/8 turn back, it is a little rich closer to 12.0, air bleeds should help that out. I could lean the idle more but then my cruise was lean too.

I am not seeing a rich spike on gauge if i punch it, the only time I ever see a rich spike is if I blip the throttle. Punch it then let off right way.

As far as RPM it falls on its face all over the board. Either from idle ~550rpm in gear or if im already rolling 1000rpm.

I did check the floats and i adjusted them both down a little bit so that they lined up with the center line on the sight glass, should i bring them back up a little bit?

 

[oldbee]

Don't know the QF's but regular Holleys were fuel just barely trickling out at bottom of plug threads.

 

[Belle66]

Yes Jcharger you are right with the wide band O2 sensor, and once the engine recovers from its stumble, WOT is right around 13.0 Idle is a little rich, Ive got air bleeds coming to help bring this down.

Im going to put a notebook in the car and start taking better notes. I really want to nail down the timing on this car, its up at about 18 degrees right now. Side note I also replaced the cap and rotor last night. Currently I have the orange cam in.. not noticing a big difference.

Yes thats how i set my carb up using those steps, 1/8 turn back, it is a little rich closer to 12.0, air bleeds should help that out. I could lean the idle more but then my cruise was lean too.

I am not seeing a rich spike on gauge if i punch it, the only time I ever see a rich spike is if I blip the throttle. Punch it then let off right way.

As far as RPM it falls on its face all over the board. Either from idle ~550rpm in gear or if im already rolling 1000rpm.

I did check the floats and i adjusted them both down a little bit so that they lined up with the center line on the sight glass, should i bring them back up a little bit?

I also have a 79 corvette with a ZZ355 motor with an ACCEL DFI system. I used a wideband for tuning and ended up still reading plugs at the end to get the last bit. An AFR number doesn't mean the engine is happy but usually close to happy.