Slight stumble when in gear

[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!

[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!

[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

[tmea]

Excellent! I'm glad it has worked itself out. A new fuel filter and you are good. Sometimes the strainer inside the gas tank can become clogged too. The symptoms can disappear after a fill up by mixing the sediment around.  I cleared mine by taking the sending unit off the top of the tank and starting a siphon thru it. Using a flashlight I sucked all the debris off the strainer and bottom of the tank with the siphon hose.

[bhartwell59]

Thought I had the in-gear at idle stumble licked... of course not! Hadn't had an issue for 5-6 weeks though.

Any other ideas? I'll check the in-tank filter sock next.

Is it possible this could be an electrical problem?

[bhartwell59]

FWIW... as mentioned earlier, I have a Petronix Flamethrower 3.0 ohm coil.

Will also try swapping the condenser out and see what happens.

[bhartwell59]

Cleaned the inside of gas tank and the in-tank sock. Plugged in new condenser... no change.

Runs really well and idles just as well.

Starts the intermittent in-gear stumbling (to the point of almost stalling) after warm.

Could I be back at a coil issue?

[bhartwell59]

I saw that sb001 (on The Samba) had a similar issue:

"wanting to stall' after engine is completely warmed up when stopped at a light in gear.

I was hoping he would chime in and enlighten me on what he did.

BTW - I apologize for droning about this problem.

[bhartwell59]

Well, after all the things I tried/checked on, it turned out to be the spark plug wires. Nothing to do with the autostick components.

Although, I probably needed to change: dizzy cap, rotor, plugs, condenser, points, check servo, check valves, add Petronix coil, clean out manifold heat risers, check for vac leaks, clean fuel tank, clean original 34 pict 3, re-time... ANYWAY.

Next time I'll start with the wires!

[Wunderbug]

I had the hesitation just off idle and changed the idle jet to a larger one and that took care of the problem. My engine is a 1776 and I went from the standard 55 idle jet to a 60, still had a slight hesitation and went to a 65 and that solved the issue. It's a 2 minute job to swap out the idle jet. Worth a shot.