The Stovebolt Site Forums The Shop Area Engine Shop maddening hiccup

I 've got a '54 3600 with the 235 engine. I've also got a a maddening hiccup in the engine when running at freeway speeds. This is a fairly new development occuring last month one day. I said to myself, "time for a tuneup". I checked the points first as it seemed the likely culprit. Sure enough they were worn, So new points, plugs, condensor, cap, rotor. It ran great!.... for a day. I started getting this hesitation in acceleration as I get to freeway speed. I quickly changed the inline fuel filter, no difference. I said to myself " probably fuel related" , so I rebuilt the Carb...still a hiccup on acceleration. I blew out the fuel line to the tank, replaced the fuel pump, new spark plug wires...same performance. This hiccup is not all the time but most under load. It acts like a condensor that is breaking down, but not all the time....Starving for fuel?, I have taken the Carb apart 3 times to clean and check for crud, nothing visable. I have a fairly new coil, (one year), So I am searching for ideas. I know that there are guys who can point me in the right direction...So please point! Thanks B_H

Check to see if your vacuum advance is working properly. When you rev it up slightly, the distributor should move. If not check the vacuum lines to see if you have vacuum to the advance mechanism. If you have vacuum and it still does not move you need a new advance. You can also check it with a vacuum pump.
Fred

ethanol? water?

Bill

It ran great!......for a day.

Typical of new points. The rubbing block wears rapidly at first and they need to be checked and rechecked until the rubbing block seats. SO - recheck your dwell, and good luck.

B_H,

It sounds like you are very sharp in this regard and have done everything possible to remedy the problem.

If you did everything right, what didn't you do? Do you think that you changed something and the problem really did go away for a day, or was it wishful thinking.

Your fix-it list truly covers everything possible short of a hanging valve. I would try to dial in on the problem more. Find out if you can recreate it at will, and note what conditions bring it on. This will take lots of things off your "what is it" list.

'Under load' means low vacuum, power valve, higher combustion pressure with resulting spark loss. Maybe try looking in these areas.

If nothing else, dump a can of Berryman Chemtool in your gas tank and see what happens. Good luck!

Stuart

If the ignition system is working properly and you have good pressure out of the fuel pump, I would lean toward the carb. When you disassembled it did you use an air compressor to blow out every little piece and part???

Jeff

Adjust the valves & check to make shure they are all opening. Yoy could have a bad camshaft.

Thanks for the replies fellas!...I checked for the vacuum advance working and, it does, it moves when the throttle is advanced. I thought that I might change out the new condensor with another to see if it could be faulty and still have the missing stumbling under load. Accelerating fully up a slight grade I experience the stumbling as I near the shift point, usually in 3rd and 4th gear. On the road when I am cruising at 60, 62 mph, no problem. When I need to pass I may get it as I get on it like it is about to starve for fuel. If I decelerate back to cruise....no problem , it doesn't miss a beat. I did recheck the dwell and made sure things were right. I usually always use Carb cleaner and blow things out well before I reassemble... I think I did 3 times to this point. The fuel may be an issue, I will get some Berrymans and try that.I am guessing that I will start over and check AGAIN!. Thanks again for your help guys. B_H

Hello!, Thought I'd up date you guys on this rabbit I'm chasing. I went back to square one , reset the timing, checked the dwell, removed and cleaned the fuel line from the tank pickup to the carb, checked the valves ( they were all opening), tore the Carb down again, checked the ignition wiring etc.....the stumble is still with me. I have a couple of choices left...the heat control spring on the exhaust manifold may be my culprit, I was looking at it and looks like it has been modified, broken and re-bent. I had some help one day so maybe?? anyway, I an going to replace the vacuum advance (what could it hurt) and the spring to the manifold. I'll let you know...anything else you guys can think of?.

I'll throw my 2c in here as well. I see in post 11 that this is happening at full throttle? My experience is that my 552nd w/235 does a similar act. at full throttle it sounds like it is just sucking air, and actually slows down from cruise speed. I hooked my air/fuel meter to it and watched what happened, it went way lean there. I have yet to tear into the carb to fix it, but I've narrowed mine down to that.

My meter is an LM-1 by InnovateMotorsports. An excellent tool I could justify buying due to having 4 carb'ed vehicles.

Devin

I thought I would end this thread with the hiccup fix for those that tried to help. By the way thanks!...after going back and checking everything again I found that the vacuum advance had a very slow leak. It would work under initial throttle advance but slowly leak down and be insufficient when I needed it. Thanks to rfs56trk for the lead on the vacuum advance. I replaced it and the thing is working great. I guess the lesson here is don't trust your eyes... I saw the advance working when I rev'd the engine and assumed it was fine, after all it was working just fine.... until it wasn't.

If it happens when accelerating, your gas flow increases, maybe your float level is too low.