440 still idles with screws turned in

[Moparnocar]

If the idle screws are fully in there is no idle fuel except from an exposed transfer slot or some other fuel leak. If it also has a vacuum leak that means it would be really lean and I am not sure how it could idle. Once you turn off motor is there any fuel residue around the carb top and air valve pockets?

No, that's the odd thing, and usually you can see it off the mains, must be off the transfer slots. The random increase in idle was odd too. I never touched the idle speed screw

 

[turbine68rt]

Get the FBO limiter plate. Well worth it.

 

[RemCharger]

Post #9.
The idea of getting idle timing correct is so that the carb idle cct can be tuned. Once that is known, THEN a centri curve can be organised.

Best quote in thread.

 

[Dragon Slayer]

I meant the idle mixture screw, not idle screw. But as stated with proper timing at idle you should be able to lower idle with idle screw to just have blades cracked open. Mixture screws should have an effect on idle quality and rpm.

 

[Moparnocar]

Get the FBO limiter plate. Well worth it.

That's what I'm gonna try and get him to order it

 

[Dan64]

No, that's the odd thing, and usually you can see it off the mains, must be off the transfer slots. The random increase in idle was odd too. I never touched the idle speed screw

I'm not sure that i'm reading this right but if your getting random increases / decreases in idle speed that says you may have too weak of springs in the dist.

 

[Geoff 2]

M/car,
Idle timing is a most understood topic, even amongst seasoned mechanics. The lower the idle vacuum, the more timing that is a needed at idle. Unless you are using a programmable ign 'box' [ & you don't need one ], the best way to give the engine the timing it WANTS is to use a dist with adjustable vac adv. Very cheap from Summit, $140. Set the Allen Key fully CW. YOU DO THE INTERNAL CENTRI CURVE LAST, NOT FIRST. Connect the VA unit to manifold vacuum { MVA} [ ported is USELESS ]. See link below. My engine idles @ 48* BTDC. Yes, 48, not a misprint.
D. Vizard has authored 30+ auto books, forgotten more than most will ever know.
Below is from a carb book, not an ign book. Hmm....
'The optimum idle advance is typically about 35-40* for a short cammed street engine & though not commonly realised as much as 50* for a street/strip engine'.

And from PHR magazine', Nov 04, while reviewing a new Crane dist:

' At idle....the amount of advance to most effectively utilize the air & fuel entering the engine can be as much as 50-55*. This is handled by the vac adv....By taking the time to hook up the VA to a manifold source you can get that big cam to idle as it were 20* less than it really is'.
Cannot stress enough how important this is to getting optimum carb performance & idle. Mopar missed the boat on MVA, GM used it & got it right.

More on MVA, scroll down to post #6.
www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html

 

[Moparnocar]

I'm not sure that i'm reading this right but if your getting random increases / decreases in idle speed that says you may have too weak of springs in the dist.

That was the weirdest part, not sure which springs it has

 

[Moparnocar]

M/car,
Idle timing is a most understood topic, even amongst seasoned mechanics. The lower the idle vacuum, the more timing that is a needed at idle. Unless you are using a programmable ign 'box' [ & you don't need one ], the best way to give the engine the timing it WANTS is to use a dist with adjustable vac adv. Very cheap from Summit, $140. Set the Allen Key fully CW. YOU DO THE INTERNAL CENTRI CURVE LAST, NOT FIRST. Connect the VA unit to manifold vacuum { MVA} [ ported is USELESS ]. See link below. My engine idles @ 48* BTDC. Yes, 48, not a misprint.
D. Vizard has authored 30+ auto books, forgotten more than most will ever know.
Below is from a carb book, not an ign book. Hmm....
'The optimum idle advance is typically about 35-40* for a short cammed street engine & though not commonly realised as much as 50* for a street/strip engine'.

And from PHR magazine', Nov 04, while reviewing a new Crane dist:

' At idle....the amount of advance to most effectively utilize the air & fuel entering the engine can be as much as 50-55*. This is handled by the vac adv....By taking the time to hook up the VA to a manifold source you can get that big cam to idle as it were 20* less than it really is'.
Cannot stress enough how important this is to getting optimum carb performance & idle. Mopar missed the boat on MVA, GM used it & got it right.

More on MVA, scroll down to post #6.
www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html

Wow, that goes against everything I've read and done on Mopar. I always do 36-38 total. Interesting

 

[4406bbl]

With that cam you need 20 degrees or less in the distributor, 16 initial, and holes in the throttle blades to get them fully closed so it quits running on the transition circuit. I will bet if you remove the carb the idle stop screw is holding the throttle blades open. With that cam my 6bbl needed 6
.080 holes to fully shut the center carb at 900 rpm, it had 6.5" of
vacuum. Stock 1970 6bbls have 6 .070 holes in the blades stock so I would start with 1/8"holes. 2-1/8"holes is the equivalent of 6-.070 holes in area.
I got rid of that cam and now a 290/540 solid idles at 12" and runs way better. There was a bad run of those mp 284 cams, centerline was wrong or intake / exhaust not the same can't remember exactly, and they were miserable cams. I would change that cam if it is just a driver, about any choice would be better, even a 292/.509 mopar cam idled better in mine.

 

[Geoff 2]

Mçar,
Post # 29. You are confusing idle timing with total timing under full load. Please re-read ALL of my posts.
I just watched a Nick's garage 440 video, done two days ago on Mar 29. Nick has become a recent MVA convert, because this engine has the VA plugged into the rear of the carb, a manifold vacuum source. Reported smooth idle at 950 rpm & it would only be smooth with a LOT of initial timing, which will be provided by the VA unit connected to a manifold source.
16* init in the post above is nowhere near enough if you want the best idle quality & tip in response that the engine is capable of. If you do the simple test I outlined in post #5, you will see what a difference the extra timing makes.
GM cars used MVA as stock. GM was smart-er. Chevs idled at about 24*, Pontiacs 26*. More cam needs more idle timing.....which is why 30+ for a cammed engine is not that much.
If you keep listening to bad advice, you get a bad outcome...

 

[4406bbl]

With 6" of vacuum he will never get to 30 degrees. 16-18 on the crank and 20 in the dizzy is correct advice. Pretty sure that gm did that because they were so smart the junk starter they had could not start a big block with 16 initial with there better smarter starter. I used to laugh at my buddies chevies in the 70s tryin to start hot. Mopar was always better and smarter

 

[4406bbl]

You and Nick may want to look at some charts before you give bad advice, check out these charts. He will be lucky to get 1 or 2 degrees at 6" of vacuum. Pretty much every vacuum can needs 11" of vacuum, unless there is some special aftermarket one I do not know of.

 

[toolmanmike]

Have you ever checked the fuel pressure? Changed the pump lately?

 

[Geoff 2]

6bbl,
All car makers made mistakes, agree about GM starters. C made a mistake not using MVA [ well actually they DID in the emission years ].
Most aftermarket adjustable VA units work with 5-7" of vac. When you start an engine, you give it some rpm; that will increase vacuum & pull in the plunger to give it more timing....& increase vacuum to stabilise the timing. I have been doing this for 30 yrs. I have seen idle rpm increase by 300 rpm, just by turning the dist with the engine idling; you cam imagine how much idle vac increased.

 

[4406bbl]

I get it, but he needs to get his initial and mechanical in line first, if he can't get his vacuum up to 10" at idle the vacuum advance trick will not work. I doubt that cam will see that kind of vacuum an idle of 800 -900 rpm, a bigger solid or roller will. Vizard is brilliant, but sometimes things are simplified and it is made out that just by moving a vacuum line and things will be fixed, then there is also the advance gain vacuum can give at high rpm under load, knocking the ring lands off of the pistons with a big cam and high compression, that is why a vacuum can has to start at 4-6". I will stand by the 16-18 on the crank, 20 in the dizzy, and drill the primary plates to get them fully closed, almost off the screw at idle. Then play with the vacuum advance.

 

[Dan64]

That was the weirdest part, not sure which springs it has[/QUOTThe springs have to be strong enough to hold the timing steady. You want your timing to stay steady for 400 or so rpm above idle before timing starts to move. The old theory used around here was throw in the two lightest silver springs ( MSD) and let the curve take off right from idle. That's all well and good IF those light springs are actually holding timing rock solid steady at idle, some times it doesn't quite hold it and allows the arms to swing out (but not always, that's why it's random) advancing timing too early which will give you random increases/ decreases in rpm. Warm the car up get it to idle best you can, put your timing light on it and watch very closely as you or someone else pours a little gas down the carb. Don't use the throttle linkage or accelerator because you want fuel only, no air, you are trying to get the motor to bog down not rev up. If the timing drops at all when the engine bogs the springs are too light. All this talk about idle quality is really about the tip-in change from idle to main circuits. This is what makes your car feel snappy off idle. BYW my post refer to a car that does not have vacuum secondary's or has it plugged off for now to get a base line on initial and total timing. If you have a vacuum secondary dist. ( good idea on a street car) you can mess with that part later.

 

[Moparnocar]

Yes brand new, Around 6, bounces a bit

Have you ever checked the fuel pressure? Changed the pump lately?[/QUOT

 

[Moparnocar]

Have you ever checked the fuel pressure? Changed the pump lately?

Yes, new, around 6, bounces a bit

 

[Moparnocar]

Mçar,
Post # 29. You are confusing idle timing with total timing under full load. Please re-read ALL of my posts.
I just watched a Nick's garage 440 video, done two days ago on Mar 29. Nick has become a recent MVA convert, because this engine has the VA plugged into the rear of the carb, a manifold vacuum source. Reported smooth idle at 950 rpm & it would only be smooth with a LOT of initial timing, which will be provided by the VA unit connected to a manifold source.
16* init in the post above is nowhere near enough if you want the best idle quality & tip in response that the engine is capable of. If you do the simple test I outlined in post #5, you will see what a difference the extra timing makes.
GM cars used MVA as stock. GM was smart-er. Chevs idled at about 24*, Pontiacs 26*. More cam needs more idle timing.....which is why 30+ for a cammed engine is not that much.
If you keep listening to bad advice, you get a bad outcome...

I had a engine w this cam 20 years ago, I did modify the weights, I just don't remember my initial timing, must of been 16-18