The Stovebolt Site Forums The Shop Area Engine Shop Loping

My 55-2 series, 235-cu-in has a loping problem at idle. I have new points, new condenser, new rotor, new spark plug wires and have rebuilt the Rochester carb twice. It will idle w/o dieing but lopes and sometimes the loping will go away for 5 to 10 sec but then come back. Doesn't matter if the engine is hot or cold. The plugs have about 8000 mi on them. I'm not sure when the loping started cause it is so suttle. Any idea's? Thanks.

I would think that it is a small pc. of crud in the carb on the idle section or could be the float is not set right, even a spec of crud on the idle screw or the seat will not let the fuel flow evenly because there is no presure pushing the fuel , when I rebuild a carb I use toothpicks to clean all the jets and a good carb cleaner I make sure that all the ports are polished up and same with the mixture screws and jets some 4/0 steel wool and toothpicks will get everthing polished up and get You a good running carb.Check the ht. on the float to.


Pete

I'm going out to the garage now and re-check the float. But I'm almost 100 % sure it's right. And I'm pretty meticulous about carb cleaning. I'd like to think I've done everything right but I'll re-check it again. I'll let you know how it works out. Thanks.
Carl

Before you take it all apart again, it sounds like the idle fuel adjustment is too rich. Try turning the idle mixture screw in a little (leaner) to see if the loping condition improves. If you have a vacuum gauge, set the mixture screw to obtain the highest and most steady vacuum level. You might also raise the idle speed slightly. If the idle speed is much too slow, the fuel metering can get upset and the loping will start. You should get a pretty stable idle condition at 500 RPM or a little higher. Much slower will get you a poor idle condition, although I have seen the Chev 6-cyl engines go down to around 400 RPM, but they get unstable at that level.

If you adjust the idle speed, you may need to reset the mixture screw.

Harvester

Harvester

Well I found the problem to be a bad ignition wire (#4 wire in the firing order). Because two wks ago, I put a nylon braid covering on each wire,it came to me a couple of nights ago that's when the problem started. So I checked each wire with an ohm meter and found the bad wire. When I pulled the boot off to put on the braided covering, I pulled the center conductor loose from the crimp w/o knowing it. Replaced the wire and loping problem stopped.

Bought me a vacuum guage and set the idle mixture best I could. But I could see that my throttle plate shaft is a little worn. Truck now runs fine for now.

I would like to replace my Rochester carb with a Carter YF series. Any thoughts where I could buy one?
Carl