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Hitting on Two Cylinders ?

GTmanGTman

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, Vintage Speedster.

 

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  

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Gordon NicholsGordon NicholsMassachusetts 1993 CMC Supporting Member

Happens to all of us at one time or another.....

 

While something like Sea Foam is really good stuff and certainly wouldn't hurt it, since you just filled the tank I would run the Sea Foam double strength to the tankful (just guestimate how much gas is in there), do not add any more gas to the tank and just run the tank out as low as reasonable, then refill with gas from someplace local that you trust.

 

Kadrons respond well to sucking crud through the jets by blipping the engine to about 3500-4000 rpm and letting it go and as soon as you let the throttle go, slap the palm of your hand onto the top of the carb throat, thereby blocking it off and creating a huge vacuum both below and above the throttle butterfly.

 

Sometimes this sucks the crud out of the blocked passage, sometimes not but it's an easy try and won't hurt anything.

 

Good luck. 

Last edited by Gordon Nichols
GTmanGTman

Thanks all for the input.  The idle jets on Kadrons are pretty easy to get at without removing the carb.  So hopefully its just unscrew from the throttle body, remove, blow out and see if there is a change.

 

Also, is there a preferred type of fuel filter for running between the gas tank and my electric fuel pump mounted near the tank?  I have one of the cheap transparent plastic ones there now.

 

Thanks, Grant

GTmanGTman

Fixed the problem.  Took the idle jets out of each carb, blew them out with carb cleaner, and blew out empty idle jet openings in the throttle housing with carb cleaner.

 

Didn't notice anything obvious with the jets, but when reinstalled the idle was up where it used to be.

 

Took the car for a 20 minute drive to let the engine warm up, and after a couple of "pull over idle speed adjustments" the engine is purring at 1,000 rpm.  And actually feels like it is idling better than before, smoother.

 

Thanks all for the helpful input.  Back on the road.

 

Grant

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