Engine wont idle

[4eyedblonde]

I have a 69 440 that I just put new heads (906) on. when it warms up it will idle in neutral or park. Put it in gear and it dies off quick. at this point I have the idle at 1000-1100 rpm to hold in park/neutral when hot. Put it in gear...done. Is this a carb problem that has come up? Any thoughts??

 

[hashmaker]

It could be many things at this point. A vacum leak, timing off, carb too rich/lean. Something wrong with the heads that is affected by the temperature going from cool to hot. Low compression. It would help to know how it ran before the head swap and more details about the parts in the engine.

 

[WP29440SE]

more info would go a long way

 

[Kerplunk]

My first guess would be a vacuum leak at the intake, since you would have reinstalled when you did the heads.

Where abouts are you in Oakville?

 

[4eyedblonde]

It could be many things at this point. A vacum leak, timing off, carb too rich/lean. Something wrong with the heads that is affected by the temperature going from cool to hot. Low compression. It would help to know how it ran before the head swap and more details about the parts in the engine.

With the old heads it would cold start relatively fine (couple of pulls to get it to run) and it would idle up fine. Albeit blowing smoke from the driver's side head initially. Now, I have to play the throttle to get it to warm and idle, choke just kills it off. I set the idle high but have since dropped it back to around 900 rpm. Still when in gear you need to feather the throttle to get it to idle. I spoke to a tuning shop and he mentioned that it sounds like carb issues. It is an old Holley 750, but I did nothing to it but blow some carb cleaner through it on the bench. I packed the breather tubes with steel wool (not tightly) to trap the oil that blows out and oddly that seems to effect the idle (orso it appears to me). When I removed the wool, it seemed better, put it back in, idle was sketchy again. I mistakenly added Lucas octane boost to the old gas that was in there but have since run new 91 octane through it. Check plugs 1 & 7 and both were clean and dry. Every thing is torqued to spec and I can't hear any vacuum leaks, no oil seepage from intake bolts etc. Since driving it on the highway (had a complete 3" exhaust system installed last week) it seemed to be better. An old school Mopar racer said put some miles on it before jumping the gun with expensive tune/dyno work. I'm thinking the smaller valves in the new ported 906 heads is playing with the carb settings? (it Had ported 516's) When it's hot, it will sometimes "run on" a little when shut down.(timing?) Only once in awhile this happens.
Old girl's a mistery...she needs a diaper too!

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My first guess would be a vacuum leak at the intake, since you would have reinstalled when you did the heads.

Where abouts are you in Oakville?

I'm south of Dundas between 6th line and Trafalgar Rd. If you drive a black mercedes and like to phone the police, you know exactly where I am LOL!

 

[boltupal]

Can't be a vacuum leak if the choke kills it.

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Put a vacuum gauge on it.Check the vacuum at the lowest steady idle you can get. Be sure to check above and below the throttle blades. What were the old and news heads combustion chamber size? The run on is just the idle being so high when it dies.

 

[4eyedblonde]

Can't be a vacuum leak if the choke kills it.

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Put a vacuum gauge on it.Check the vacuum at the lowest steady idle you can get. Be sure to check above and below the throttle blades. What were the old and news heads combustion chamber size? The run on is just the idle being so high when it dies.

I'll try that. Need the gauge yet. What vacuum am i looking for? Or am I just looking for vacuum? I was wondering if the Vac advance timing was non existant. As for combustion chamber size..?? I think these 906's are 82-85cc but that's out of my knowledege area. The old heads were worked over pretty good but as I understand, the 516's are open chamber and the 906 are closed? Plus the 516 had .214 or .218 valves. These heads are smaller. I went this route as it was going to be a street car and the 2500 for the Edelbrock Perf RPM's was rediculous. These were 950. The car cruises fine, just the idle at a stop, in gear drops to 500

 

[mopar505]

if it back fired recently you could have taken out the power valve in the carb ? had one do that to me and that was the fix. new power valve. run on sounds like timing adjustment fix.

 

[Dodge 330]

if it back fired recently you could have taken out the power valve in the carb ? had one do that to me and that was the fix. new power valve. run on sounds like timing adjustment fix.

That was the first thing I thought of. If it's a Holley it sounds like bad power valve.

 

[bandit]

Not sure how old the Holley carb is but new ones have built in protection to save the power valve if a backfire happens. Best way to test if blown is to turn in your idle screws while engine running. If engine does not start to stumble, the power valve is probably gone. When the valve goes it lets gas in at idle and the screws make no difference.

Engine sputtering on after turned off sounds like timing too advanced and/or bad gas.

 

[Kerplunk]

I'm south of Dundas between 6th line and Trafalgar Rd. If you drive a black mercedes and like to phone the police, you know exactly where I am LOL!

Nope not a big Mercedes fan LOL. I'm 10 minutes up 6th line in Milton, if you need a hand let me know, Id be happy swing by and help, a few years ago we were on the west side of 6th line, in River Oaks.

 

[69Bee]

I'll try that. Need the gauge yet. What vacuum am i looking for? Or am I just looking for vacuum? I was wondering if the Vac advance timing was non existant. As for combustion chamber size..?? I think these 906's are 82-85cc but that's out of my knowledege area. The old heads were worked over pretty good but as I understand, the 516's are open chamber and the 906 are closed? Plus the 516 had .214 or .218 valves. These heads are smaller. I went this route as it was going to be a street car and the 2500 for the Edelbrock Perf RPM's was rediculous. These were 950. The car cruises fine, just the idle at a stop, in gear drops to 500

A couple of things concern me:

1) You put steel wool where? I wouldn't introduce steel wool particles anywhere on a running engine, you are just asking for trouble.

2) 516 heads are the early closed chamber small valve heads, and 906 heads are open chamber large valve heads.

3) Did you re-use the intake valley pan?

4) Did you re-use the carb base gasket?

5) Is the large vacuum port on the carb base disconnected?

6) Did you possibly over tighten the carb base bolts/nuts?

What is the possibility you changed the distributor weight springs for the lighter Mr. Gasket set? I did that, it at would die at idle, and had to set the timing and curb idle to about 1200 RPM just so it would idle.

 

[4eyedblonde]

A couple of things concern me:

1) You put steel wool where? I wouldn't introduce steel wool particles anywhere on a running engine, you are just asking for trouble.
It's very coarse wool, notthe type that sheds. I used it as a sort of coalescer to trap the oil so it doesn't leak out the breather. These are Cal custom rocker covers with the rectangular breather vents on hte side of the cover.

2) 516 heads are the early closed chamber small valve heads, and 906 heads are open chamber large valve heads.
Thats strange because the heads that came off had larger valves (516's)

3) Did you re-use the intake valley pan?
New valley pan

4) Did you re-use the carb base gasket?
New gasket

5) Is the large vacuum port on the carb base disconnected?
Yes, vacuum cap and clamp

6) Did you possibly over tighten the carb base bolts/nuts
I'd have to say no to that one but I didn't use a torque value on them.

What is the possibility you changed the distributor weight springs for the lighter Mr. Gasket set? I did that, it at would die at idle, and had to set the timing and curb idle to about 1200 RPM just so it would idle.

I didn't touch the distributor at all other than a new cap and rotor. But that is what is happening. Idle is set to 1200. I've since turned it down around 900, but the engine will drop to 500 or lower when in gear.

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Not sure how old the Holley carb is but new ones have built in protection to save the power valve if a backfire happens. Best way to test if blown is to turn in your idle screws while engine running. If engine does not start to stumble, the power valve is probably gone. When the valve goes it lets gas in at idle and the screws make no difference.

Engine sputtering on after turned off sounds like timing too advanced and/or bad gas.

I have no idea how old the carb is but it's old. It did backfire through the carb on inittial start up attemps after the heads were installed. Nothing violent though but just the same..it did. I'll look into that theory as well. Thanks for the tip.
Idle screws? I was turning the adjustment screw near the linkage to increase the idle rpm, I take it that's not the ones you are referring to? It wasn't stumbling adjusting that one.

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Nope not a big Mercedes fan LOL. I'm 10 minutes up 6th line in Milton, if you need a hand let me know, Id be happy swing by and help, a few years ago we were on the west side of 6th line, in River Oaks.

That would be great. I have to get a vacuum gauge yet. It sounds like a carb/timing issue so I'll rent a timing light as well.
pm me and I'll get you a # to call and we can set something up.
Charlie

 

[bandit]

"Idle screws? I was turning the adjustment screw near the linkage to increase the idle rpm, I take it that's not the ones you are referring to? It wasn't stumbling adjusting that one."

That is the idle speed screw. Just set that so you have the correct rpm setting for your car. My 383 says to set it at 650 rpm. The idle mixture screws(2 of them) are sticking out of the carb on both sides towards the front of the carb. Turn them in until they bottom out(do not turn in hard, just until you feel them bottom out) and the engine should die. To reset them, just back them out EQUALLY to a point where the engine runs the best or smoothest. FYI, I believe it is Holley carbs pre '92 that do not have the blowout protection but not positive on that date. Maybe someone else can weigh in on that date.