Surging idle and stalling Update 7/21/16 Fixed

[thegreatjustino]

Some of you have followed my thread about buying my '67 from the original owner in my neighborhood a couple of years ago. It has been giving me issues for the past couple of months.

After taking it on a 300 mile road trip over Christmas, it sat on my driveway for a couple of weeks before I started it up to move into the garage. There it sat for three months until I started it at the beginning of April to take to the Wildhorses roundup.

It started right up in the garage and idled fine. I moved it to the driveway and continued to let it idle and warm up. When it reached operating temperature, I shut it off and it dieseled a bit. About an hour later when I went back out to leave for the roundup, it wouldn't stay running unless I kept giving it gas. Driving it, it will die every time I come to a stop but starts right back up and will run if I keep giving it gas.

Idling, it has a bad surge and will die unless I keep the idle speed up.

So far I've adjusted the timing, cleaned out the carb idle circuits, re-set the float level, and even tried swapping the carb with the one on my Mustang. Nothing has really had much effect.

This is a completely stock engine with the exception of an electric fuel pump. Bronco ran fine on the 300 mile road trip back in December and started acting up after sitting in the garage for three months. I'm not sure what to try next, but I can't drive it at all.

 

[Viperwolf1]

It has a vacuum leak. Maybe base of the carb, maybe intake gaskets.

 

[thegreatjustino]

That's what I was thinking too. A mechanic friend came over with his smoke machine and we couldn't see any leaks when pumping the smoke in.

However, the idle does smooth out a bit when you spray carb cleaner toward the back of the manifold.

I took out the vacuum tree and put in a plug - no change. The only other thing I can think of is a small leak in the back intake gasket or a leak in the emissions valve at the back. Although, with the vacuum plug in place of the tree and the line to the emissions valve plugged, wouldn't that remove it from the equation?

 

[surfer-b]

Get the engine up to operating temp then smoke it, I bet you will find it. I would guess when the gasket heats up it expands enough to allow a leak.

 

[DirtDonk]

If the idle changes at all when spraying, you need to fine-tune your spray down to a narrow area to find out exactly where it effects it. That's your leak.
About the only places allowed to do that and not be a problem are directly into the carb and, well, nowhere else. Even around the PCV grommet, while "common" is not correct.

The side of the carb means the shafts are worn.
The base of the carb means the gasket or a vacuum hose or a vacuum cap are the culprits.
The back of the intake might be the vacuum fittings, or it might be a gasket, but you need to narrow it down.

Anywhere it changes the idle, it is sucking in where it should not be.

Paul

 

[blubuckaroo]

I've had an intake gasket vacuum leak inside the valley. I doubt the smoke test would find it.

You referred to a plugged emissions valve. Is than an EGR valve? It had a vacuum diaphragm nipple as well as a port to the intake. Could be a leaky gasket between the EGR valve and the PVC/EGR spacer.

 

[cldonley]

What Paul said about the shafts is one of the easiest to miss. Old carbs are prone to have it. But since you said you swapped carbs and it still happened, either you have the same problem on the Mustang or that's not the issue.

 

[thegreatjustino]

I think it's the back of the manifold. Time to pinpoint

 

[Viperwolf1]

I've had an intake gasket vacuum leak inside the valley. I doubt the smoke test would find it.

I've had the same leak. Impossible to find but it acts exactly like a vac leak. When in doubt swap them gaskets out.

 

[thegreatjustino]

Well 1,000 thanks to the geniuses on this board. New intake gasket fixed her right up. Purring like a kitten upon start up this evening. Must have been a small leak somewhere in the back. Whoever put the old gasket in used the cork ends. I used a thick bead of silicone instead of them on the new gasket. Hopefully I'll be good for the foreseeable future.