Wierd idle!

[sjarrett71]

When my truck is cold it idles fine, between 700-800 rpm's. After the truck is warm and driven, the idle speeds up to about 1000-1100 rpms. The key is it has to be driven for the rpm's to kick up. If I just let it idle to warm up the rpm's stay fine. It's a 350/4 speed with a Holley 650 mechanic choke, nothing but the fuel line, choke cable, and linkage are attached to the carb. I don't use the choke when it's cold, I just feather it until it runs. Does it soulnd like a carb issue or a timing issue?

[Six862m6]

I no "Expert", but I think you've got a timing advance problem there man. I'd check out the springs on your advance in the distributor, or possibly a vacuum issue in the canister?

[geezer#99]

It's a carb and fuel puddling issue. When it's cold the way you run it without any choke or increased RPM the fuel puddles in the intake. After you drive it and induce some air flow and more rpm's the puddled fuel is used up. And the rpm increases. All you need to do is increase the rpm when it's cold. The fuel stays vaporized and it will warm up faster too.

[sjarrett71]

@ Geezer, it does it EVERY time. In 80 degree weather and 20 degree weather. And it doesn't stop even after driving it, no matter the distance or time.

[sjarrett71]

@ Six862m6, I was kinda thinking the same thing. My advance springs are worn a little. If that would make a difference I don't know either.

[Six862m6]

Originally Posted by sjarrett71

@ Geezer, it does it EVERY time. In 80 degree weather and 20 degree weather. And it doesn't stop even after driving it, no matter the distance or time.

Don't discredit what Geezer is saying either, it could be that as well. When he's talking about cold vs. hot, he's talking about the temperature of the engine, not the outside climate. Though if what he's saying is true and it runs at 1000RPM AFTER the puddled fuel is used up (which means it would be running very rich before, rich enough that its seriously affecting the A/F ratio) then the idle is also set too high as the truck shouldn't run that high of RPM at idle at ideal levels. Also, I think an easy way to check for the puddle/rich mixture would be to let it run like that for a decent amount of time then shut it down and check a few plugs. See if they look like they've been running rich. If so, I'd say he's right. If not, I'd say it has more to do with something in the timing mechanism (springs, canister, something) sticking.

[sjarrett71]

I'm definately not discrediting Geezer's analysis. I would just think the puddling issue wouldn't be the problem after the truck is driven and the fuel no longer has a chance to puddle.

[geezer#99]

So. You might be flooding just a little. Have you checked your float level. Should be a plug on the side of the float bowl. If you take it out and you get fuel coming out your float level is too high.
The rule of thumb is the level should be just below the opening. If it's set right when you lean on the fender a little fuel should trickle out.

[sjarrett71]

Thanks geezer, I'll check that.

[prostreetC-10]

I was asked to look at this thread and I'm going to take an educated guess here......

Of course it's usually the other way around. "she's a booger until I get some temp in the motor. Then she runs good". When you say it idles good when cold, do you mean that it will stay running? If you look at the motor running when it's cold, does it shake a little or a lot? Maybe sound like it has a little bit of a cam before the temp goes up and rpms go up? Here is what MIGHT be happening and would make perfect sense. Whether a motor is cold due to -10 degrees or 50 degrees, it still needs a slightly richer mix to run or idle well when cold. If the motor shakes at all when cold, and you need to "stay with it", that is a lean condition. There is a chance that the choke you are not using is has the set screw turned in too far and is catching the fast idle cam just a bit which affects and changes your primary throttle position. It will also expose more of your transition slot and allow more fuel to be pulled in. If it's just enough, it will actually act as a choke by giving you just enough throttle advance and fuel to run okay when cold. Problem is that as soon as the motor gets up to operating temp, it now loves the leaner mix and picks up easy in rpms. That would also be why it won't idle down. The fast idle cam wont allow the throttle to close a bit.

Anytime I build a Holley for someone local and get to set it up on their car, I always have that period where I get it to run/idle but can't set the a/f needles until she is up to temp. When idle fuel gets optomized, it will always bring the rpms up and shouldn't change as long as there is temp in the motor.

It's late and I hope I'm making sense. Bottom line it you have something going on that is allowing the motor to survive and idle when cold. When the temp gets up and A/F ratios are at correct values, the rpms go up and stay up. check that set screw on the bottom of the choke and make sure it doesn't touch the fast idle cam when the choke is fully off.

[Jacfourteen]

I think ProstreetC-10 is on the right track, especially since he's the carb guru on here . You said you don't run the choke right? To me it sounds like the idle was set high enough to idle when cold with out the choke, so now when it warms up it is idling too high. I don't have a choke on my truck so when cold it idles real low, I have to step on the gas for a minute or two then it will idle at 500 RPM or so because its still cold and running leaner than it would like. As soon as it warms up then it idles at around 800 RPM because the warm engine likes the leaner mix. So what I'm saying is that the mix doesn't change, its the engine's preference that changes as it warms up. I would say the best way to fix it is wait for it to fully warm up, then set the idle air mixture and the idle speed according to your carb's instructions (not sure what carb you are running). After this is set the truck prolly won't run or will idle real low when started cold like mine does, this is okay though because that is what the choke is for. So then you use the choke to richen it up and make it run right when cold. Then when it warms up shut off the choke and all will be good. I hope this helps you out. Let us know how it turns out.

[sjarrett71]

I sure will guys! Thanks for the advice adn I will get too it here in the next couple days hopefully.

I did notice that when I try to use the choke, it really wouldn't help the truck stay running and would actually kill it. So I just wouldn't use it and have to play with the gas pedal to keep it running.

[prostreetC-10]

A lot of times that's because the choke flap is not set correctly with the fast idle cam. In most cases, the flap will close too much before the fast idle engages and it creates too rich of a cold mix. This is due to the fast idle set screw backed too far off. I only use manual chokes and always have to modify them to my liking by bending the choke flap rod or bending the choke flap itself up to allow a little more air in/leaner mix to the idle speed I prefer when cold.

[geezer#99]

I've done the same by reshaping the fast idle cam on so I have less choke closing with a bit more idle rpm.
I still don't think it's a choke problem as it continues to run bad even after warming it up.
When you get it running get a chunk of old garden hose and use it as a stethoscope and listen inside the carb. If it's crackling a bit you could be flooding just a touch. Raw fuel dripping off the boosters will crackle or sputter as it passes the throttle plate.
I had a carb do that to me once even though the float was set right.
Just a thought!!!

[sjarrett71]

I'm going to try everything everyone suggests until the problem is fixed. I appreciate the input everyone!