Slight stumble when in gear

Started by bhartwell59, 11 June 2024, 15:30

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bhartwell59

That would be when I'm at a light, in L and the car is running.

The problem: there is a stumble (not so major that it stalls) that then catches itself and runs fine... to another slight stumble.

When dealing with this problem earlier this year (it was really bad then) I checked everything to no avail. Stumped, I finally replaced the coil to a Petronix which ALMOST fixed it.

So it sounds like an ignition/electrical issue. I'm 95% of the way there but I just can't figure out these stumble gremlins.

I've checked ALL the usual suspects (timing, valves, plugs, spark, swapped carb out for testing, etc). '74 Ghia, 34pict3

Hopefully, this makes sense... I'm open to any suggestions!

Thanks!

1974 zambezi green Ghia vert

tmea

It is a hard question to answer without knowing whether it is a stock engine etc..

Do you have the stock carburetor and distributor or something else.

Tom

bhartwell59

Everything is stock... properly mated dizzy to the carb.

There's no stumble when moving, just in gear at a stop light. The stumble is not consistent either.

Any suggestions would help!
1974 zambezi green Ghia vert

tmea

 I had this problem on my autostick several years ago. Assuming your engine is tuned and the vacuum advance is working.. The first thing I would check is for vacuum leaks. I did this by spraying some carburetor cleaner at all of the manifold joints where it bolts to the carburator and cylinder heads (with the engine idling) any change in idle speed indicates a leak that you will need to fix. Mine was very hard to find. The intake had a substantial crack underneath the lead sheath they mould around it and the heat riser. The crack carried out about 1" past the sheath so it was sucking in a substantial amount of air. I repaired it with some JB Weld until I could find a replacement. Don't forget to spray around your carburetor linkage for the throttle butterfly.

The next thing I would do is to do the same procedure around all of your clutch vacuum hose connections and actuating valve. Sometimes the valve can fail to cutoff properly and allow vacuum to leak leak back into the manifold. Usually you can take the valve apart and clean it up to fix that problem.

Hopefully this helps. Let me know how it goes. I'll try to give you more suggestions. The picture of my cracked manifold is in this forum somewhere. You can probably find it by searching by my user name.

V/r

Tom

 


bhartwell59

Hey Tom,

I followed your trials and tribulations re: the vac leak with great interest. Fine detective work!

After reading your post, I did test/check everything until I narrowed it down to the coil. The Petronix did solve a lot.

Since about early May, the slight idle stumble (in gear) is gone. I don't know why... I didn't do anything except fill up with gas. So now I'm thinking it WAS a gas issue all along (maybe summer formulation?).

So for the moment, thing's are good (until we shift to a winter gas formulation, who knows!).

I'll be keeping on eye on my past or future issue, and report back.

Thanks!

-B

1974 zambezi green Ghia vert