302 Idle Speed?

[jdbronco]

So when I google search 302 idle speed I see numbers all over the place. What is the best idle rpm for a carb'ed 302 with an automatic trans? I am running at 800 in neutral which seems high and might be the cause of my random dieseling issue.

 

[blubuckaroo]

The valve cover sticker on my '77 said 600 RPM while in gear.
Some came with an anti-dieseling solenoid that would allow the throttle to completely close when you shut off the ignition. Those are still available if you have that problem.
Flag #4 is the solenoid.

 

[jdbronco]

Thanks. I'm running a 600 holley so that won't work for me. I'm thinking the too high idle is probably the main cause. I'll adjust it down and see if that sorts it out.

 

[Broncobowsher]

Generally in the 600s is a good idle speed for a good running stock V8.

Before you go and unwind the idle screw there are a few more things to check.
Is the fast idle cam clear? It might be hanging up and holding the throttle open a little.
Vacuum advance. You mention running a Holley, so things are not stock. The vacuum advance should be on the ported vacuum, not manifold vacuum. And make sure you don't have excessive base timing. Too much timing (base and/or vacuum at idle) will increase idle speed and sacrifice idle speed performance.

 

[Rustytruck]

700 rpm in drive with your foot on the brake. Check your float level and make sure your fuel level isn't too high. Check for any vacuum leaks and correct those issues and reset the carb idle screws if necessary. If you adjust a carb while there is a vacuum leak your covering up a problem with more fuel which is something you don't want when you shut your engine off.

 

[Lawndart]

800 in neutral seems about right.
I have seen the fast idle cam screw hang-up on the carb base gasket that protrudes a bit at the base. Quick trim takes care of that.

Generally in the 600s is a good idle speed for a good running stock V8.

Before you go and unwind the idle screw there are a few more things to check.
Is the fast idle cam clear? It might be hanging up and holding the throttle open a little.
Vacuum advance. You mention running a Holley, so things are not stock. The vacuum advance should be on the ported vacuum, not manifold vacuum. And make sure you don't have excessive base timing. Too much timing (base and/or vacuum at idle) will increase idle speed and sacrifice idle speed performance.

 

[jckkys]

You have to put EB idle specs in perspective. The C4 wasn't available in Broncos until '73, and by then idle speed and timing were determined by emissions requirements, not what a good running engine needs. Other Ford cars and trucks had 289-302s and C4s years before emissions laws were the primary determination of tune up specs. 1968 specs, when the 2bbl 302s were introduced in cars are; 625 RPM for a standard trans and 550 in drive for automatics. The only problem with these specs is the fact that Ford started retarding the crank sprocket 4 degrees I think in 1972. This hurts low RPM somewhat. The early or roller timing sets give you a more crisp running engine, and always a good idea with nylon sprockets.
The same idle solenoid you have does work on Holleys. The bracket is a little hard to find, but I do have one. It's Holley Part#20-29. Using the '68 specs will eliminate any need for a solenoid in preventing dieseling.

 

[blubuckaroo]

It'll fit your Holley too.

 

[Rustytruck]

Too low an idle speed wont turn the water pump fast enough to cool the engine at idle especially when out side air gets over 90 degrees.

 

[jckkys]

What's too low an idle? 550 in drive is how most stock non-performance engines were set up, for before the emissions crap was mandated. It didn't result in overheating unless there was something else causing it. I put it in neutral when stuck in traffic on a hot day. With no torque converter to fight the idle goes up to about 650 RPM. No reason to load the engine when you can't move anyway, but I've seen no reason to believe it runs cooler.

 

[Broncobowsher]

Automatics, notably early ones without lockup convertors and low stall speeds like the C4 are quick to build heat with a fast idle. Going up 100 RPM to help cool the engine can make things run hotter as the transmission puts extra load on the engine since the engine is now fighting the convertor more. And in stock form the C4 is cooled with engine coolant, so you are dumping heat into the cooling system. A faster idle can cool better, providing there is no load. Which means shifting out of drive when you come to a stop. That activity should be saved for limping home with a problem, not a normal daily driving practice.

 

[jckkys]

Are you saying, that to put it into neutral in a traffic jamb on a hot day is a bad idea?

 

[jdbronco]

Thanks guys, turns out my idle had creeped up quite a bit on top of what I had it set at and the timing wasn't quite right either. Got everything adjusted and set it to about 625-650 in gear and that seems much better. Should solve the random dieseling too I hope, but since it's random it'll take a few days of driving to know for sure.

 

[Broncobowsher]

Are you saying, that to put it into neutral in a traffic jamb on a hot day is a bad idea?

Opposite. If running hot while stopped in traffic it is a good way to take load and heat off the engine. But you should not need to. It is a way to overcome a problem that you should not be experiencing. A way to make it home and find out what is wrong. Not a way to get through life day to day.

 

[jckkys]

Should means that's what you want. I shouldn't have to sit in a traffic jamb on I10 in Phx when it's 115. I don't want that either, but it happens. I'll do anything I can that MAY help me get to get through that kid of scenario.

 

[SC74]

What oil pressure are ya'll getting at an idle while in gear (500-600 RPM)? Should I be concerned with 10 psi at 500 RPM, but good 30-50 psi range with 1,500-2,500 RPM range?

 

[jckkys]

Nothing to worry about there.

 

[Broncobowsher]

It just means your engine is well broke in. Nothing to worry about until it drops to half of what you have now.

 

[Rustytruck]

What oil pressure are ya'll getting at an idle while in gear (500-600 RPM)? Should I be concerned with 10 psi at 500 RPM, but good 30-50 psi range with 1,500-2,500 RPM range?

change to a wix or motorcraft oil filter and see if that helps.

 

[SC74]

Thanks for the re-assurance! I do run a Wix filter already. We will keep on rolling!;D