Hitting on Two Cylinders ?

[GTman]

I had an odd thing happen today when driving my speedster. Background is 1600 dp, dual Kadron 40s, Pertronix SVDA distributor and coil, and TrilMil dual tip exhaust.

After driving the car about 35 miles from home on the freeway to grab lunch. I finished lunch, started the car and headed to a friends about 5 miles away. About 3 minutes into my drive I noticed that the engine seemed to be stumbling at low RPMs as I was shifting, and then the idle was off down around 500 rpms (when its typically at 1,000 rpms), and it sounded like it was hitting on only a couple cylinders. I got the car to my fiends and while the engine was running I pulled some plug wires (one at a time) and with two of them (while getting spark at the distributor) it made no difference in the idle. I want to say it was cylinders 3 and 4.

Before I stopped for lunch (once I got off of the freeway) I filled the tank up with gas as it was very low.

My thought was that it might be the carb on the 3 and 4 cylinder side, and that I maybe I sucked something into it from the gas fill up.

I turned the car off at my friends. About 3 hours later hopped in it for my 35 mile freeway drive back home, going about 70mph. When I started the car up it sounded better than before (and I hadn't done anything). While driving on the freeway it felt great like before. When I got off the freeway and came to an idle, the engine idled smoothly but it was idling at about 800 rpms (fully warmed up) and not 1,000 rpms where it did before.

I checked the idle mixture screws on both carbs and the settings were good. I then went ahead and adjusted the idle screw on the carbs to get the idle back up to 1,000 rpm that I am used to.

This seems odd to me that after having things dialed in on the car for the last 6 to 8 months, that this little episode occurred and I had to bump the idle up.

Has this happened to anyone else ?

Any thoughts on what might be the cause, e.g., a clogged jet maybe in the carb ? Any possibly fixes.


I didn't have time this evening to pull the plugs, but now when I pull a plug wire at the distributor with the engine running, all cylinders appears to be running (any wire pulled causes the idle to drop off).

Any thoughts and/or input would be appreciated.

Thanks, Grant

[modok]

It is common with kadrons to idle only on cylinders 2/4

This question seems to come up once a week but is hard to search. Maybe try "kadron miss"

[bugguy076]

Is there a balance tube between the manafolds? Is it open and working?
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Grubby Fingers Racing
1976 Drag Bug
1967 Street Bug

[Bruce]

This is a design flaw with the intake manifolds. The plenum volume is too small.

Take the manifolds off (aluminum ones) and get your die grinder out. Remove the wall separating the two runners almost to the very bottom. Leave a short bit at the bottom to hold the gasket in place.

After you install them, they will idle on all 4.
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[APPLEGREENVW]

[GTman]

Fixed the problem.

Ended up pulling the idle jets from both carbs, spraying carb cleaner in the throttle body openings, and cleaning out both idle jets.

Popped idle jets in the carbs and engine is purring. It seems like the engine is idling even smoother than before.

There may have been an accumulation of stuff in the idle jets before some small particle cause a shutdown.

Also, when I bought the carbs new about a year or so ago, I never blew them out before installing. So who knows the amount of crap in the carb from manufacturing when shipped.

Anyway, all good now.

Thanks, Grant

[Bruce]

[Bruce]

[APPLEGREENVW]

[APPLEGREENVW]

[Bruce]

[Casting Timmy]

Nice trick. Looking forward to pics