No idle

[Staci Newsom]

I have a 78 GMC c15 with a 350 c.i. engine. I recently installed new head gaskets because I thought I blew out one side and re-assembly went mostly okay. I also installed a new hei distributor. I was having some trouble getting it to line up and so I took it to a shop because I needed another set of eyes on it. Presumably they got the distributor lined up now.

I should also mention that it has a Holley 4 bbl carburetor.

I have been told two different things. Originally I had a mobile mechanic do the disassembly and he decided he didn't want to complete the job so he backed off. He did suggest that it had been running lean. The shop I just took it to suggested that the valve adjustment may be too tight.

Running lean is a strong possibility but it was running well before disassembly. The valves may be a little loose because I haven't completed the final adjustment. I could see lean maybe being an issue but not the valve adjustment. Either way I can't get it to idle ad I know very little about Holley carbs. If it were an original Rochester carberator I could maybe make some adjustments and get it to idle. bottom line is I don't know what is going on.

What should I be looking at now?

 

[Bextreme04]

I have a 78 GMC c15 with a 350 c.i. engine. I recently installed new head gaskets because I thought I blew out one side and re-assembly went mostly okay. I also installed a new hei distributor. I was having some trouble getting it to line up and so I took it to a shop because I needed another set of eyes on it. Presumably they got the distributor lined up now.

I should also mention that it has a Holley 4 bbl carburetor.

I have been told two different things. Originally I had a mobile mechanic do the disassembly and he decided he didn't want to complete the job so he backed off. He did suggest that it had been running lean. The shop I just took it to suggested that the valve adjustment may be too tight.

Running lean is a strong possibility but it was running well before disassembly. The valves may be a little loose because I haven't completed the final adjustment. I could see lean maybe being an issue but not the valve adjustment. Either way I can't get it to idle ad I know very little about Holley carbs. If it were an original Rochester carberator I could maybe make some adjustments and get it to idle. bottom line is I don't know what is going on.

What should I be looking at now?

I've read this a few times and am still confused... what is the question here? What is the problem you are trying to solve? What do you mean "it won't idle? Is it too high, too low, rough??

 

[85K304SPD]

Adjusting the valves is pretty critical. If they are too tight it will make it hard to run, and might be bending pushrods. It doesnt take much. You should be able to idle it up until it stays running. Turn the mixture screws out about 1-2 turns, put a timing light on it and fire it up.

 

[Staci Newsom]

That's the thing, It starts fairly smoothly and I can hold the accelerator and get to an idle speed but if I let go then it stalls. I will run all the valve adjustments again but I had believed that they might be too loose (too much lash).

Bottom line is that I can get it to start when I add a lot of extra fuel but it won't stay running at an idle. Since this is the second time I heard valves then I will definitely run that again.

 

[Bextreme04]

That's the thing, It starts fairly smoothly and I can hold the accelerator and get to an idle speed but if I let go then it stalls. I will run all the valve adjustments again but I had believed that they might be too loose (too much lash).

Bottom line is that I can get it to start when I add a lot of extra fuel but it won't stay running at an idle. Since this is the second time I heard valves then I will definitely run that again.

Its sounds like maybe you are just throwing a bunch of stuff at this? Before you go to far down a rabbit hole, its probably best to set some baselines. If you have to hold the throttle a bit to keep a smooth(but still low idle), you might just need to adjust your idle screw(or high idle screw if you are on the choke when this is happening).

Make sure with it just sitting there cold, before you start it, that the throttle shaft is at least resting against the idle screw. If it isn't, then screw in the idle screw a bit until it is just pushing on the throttle blade a bit to open it.

Once you can get it to start up and idle a bit(under 1000rpm), then make sure the timing is set properly. Vacuum advance needs to be disconnected and plugged on the carb side before adjusting it. Make sure it is set between 4-12 degrees BTDC at idle(below 1000rpm).

Adjust the idle mixture screws. Here's a video from holley on how to do that.

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I suggest using this method when setting your valve lash.

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[Staci Newsom]

Thanks all, because I too have been confused. Nothing that is going on made sense and I just needed a direction.