This is my first time trying this, so I hope I do this right... My dad has been having trouble diagnosing a problem with his 235 in his '54 Chevy 2 door. When you start the motor, it idles perfectly, no pops or misses. After it idles for a bit, it just slows down and dies. When you give it any throttle under load, it pops, backfires and misses so bad, it sounds like the thing is coming apart. You can re-start it after a bit, but it is hard to start, and does the same thing. When it is not under a load, it will rev up, and sounds fine. We have tried a tune-up, carb cleaning, accelarator pump, timing adjust, valve adjust, wiring check, ignition switch check, etc., and nothing seems to take it away. He found problems that needed addressing, and all of that stuff is fixed (and all helped a little), but it still does it. He's owned this car for over 20 years, and it has NEVER done anything like this before. Could it be possible that it has jumped timing on the timing gears themselves? We're stuck, and need some help. The worst part is that it just up and happened all of a sudden, no warning whatsoever. What do you guys think?
Mechanical pump? Sounds like it's sucking the fuel supply dry. Try running it out of a gas can with a line to the suction side of the pump. (disconect the car's fuel line back to the tank)
bad condenser? i also found one time on mine the manifold slipped down just enough to reveal the top of one of the intake ports. light a cigarette and see if the smoke gets pulled into the head
Blockage in the gas tank or fuel filter clogged? Crap in the carb? Gas cap not venting for some reason?
I would agree with the above, sounds like fuel starvation. Try the gas can trick first, and if it still does it then check fuel pump pressure.
Check to see that the fuel pump is pumping too, also could be a bad rubber fuel line that has a big hunk of loose rubber floating around in there. Watch out on the gas can trick...my 235 will flood like it's got a stuck float if it's running off a can up front. I tried for DAYS to diagnose the flooding on mine before finally running it from the back (the gas tank needed drain/clean, so I ran off a temp can up front.)
dont these things crack heads alot or is that the 292 or something. but dont account for all the problems i guess
I think this is likely ignition related. What you've described is that this car is running erratic after it heats up. When it cools down it's fine. Something is failing when it heats up. Fuel delivery is usually not effected by heat outside of vapor lock or carb warping. If you haven't changed anything mechanical, (i.e. fuel line rerouting ect.) these things should not have happened spontaneously. When electrical components fail, they rarely show physical signs. I agree with the condenser theory. If you've got the cash, put a petronics kit in the distributor. You can install them without removing the distributor. If not, try a condenser and a known good coil. Insidently I've experienced coil problems on my 235 after heat up. Good luck.
How old is the exhaust system? My 57 Ford did the same thing and after trying all the above mention fixes, it turn out that the inside of the muffler had came apart.
Thanks for all of the input on this. I think we're going to try the gas can trick first, because everything else seems to check out fine. Weirdest damn thing I've dealt with in a while. The coolest part about being involved in this hobby is the fact that we are all constantly learning, even if you've been doing this forever (like some of us have). I'm also glad to see that I'm not alone with this problem, as it sounds like some of you have experienced a similar issue. Keep the suggestions coming!
I agree with taking a look at the vacuum advance. My wifes 52 chevy started fouling plugs and missing badly, we went through evrything fuel and ignition related and finally found vacuum advance was not advancing fully.
Sounds familiar to me..mine did that a year ago. It was electrical stuff but it was doing the same thing. backfiring, missing, etc..sounds like it is a gas problem though..I'm anxious to hear what you find.
I would try the fuel stuff first, and then go to the ignition, primarily the condenser. Just because the condenser has been changed doesn't necessarily mean it is any good. One last thing, does it have a heat riser valve on the exhaust, if so it may be stuck.
Look at it objectively, if you flush the fuel system, put a clear filter before the pump and put in new points, condenser and fresh ground wires, the worst thing you can have happen is nothing different. The dizzy could be sloppy and cause erretic spark once it warms and the clearance tightens. You eliminate the easy and work towards the expensive, its a very easy car to work on with not many variables.
i had the exact same problem with my '53. ill say it is the distributor needing replacing... i took the old distributor in for the core, got a new (rebuilt) one and the problem just plain went away. i believe it was because the dizzy was loose in its seat. it wobbled a lot, 1/16 of an inch or so...the new one doesnt and it runs like a top.
This doesn't quite fit the symtoms but check carefully the primary wire from the coil to the dist. When I was a young'n one broke ,only thing holding it on was a bit of insulation. Made for weird running.
My distributor wobbled around like a hula dancer. Damn thing seemed snug and everything else was in good shape. Replaced it with a reman also and all of "my" erratic" symptoms went away. I would look into the same for your cars issues as well as the fuel system. Sounds like you have crap clogging the fuel system but you need to eliminate that possibility as well as the ignition.
points look good? the coil could be throwing a weak spark under a load,good enough spark to keep it idleing smooth, but as demand increased the spark is too weak to keep up with the gas intake causeing it to flood out, hence the poping and the letting it set a while before it starts again, any fuel smell after it dies? points and condenser will lead to the same type of problems also . when changeing always change them in pairs dont just change one or the other. thats my guess
Sounds like you have tried all of the usual stuff. You can't jump teeth, but the cam can slide back out of the gear. If the timing is correct, then I wouldn't think this has happened, but if you pull the dizzy and find that the drive gear on the cam is not centered in the hole for the dizzy, then its likely. When you have a timing light on it, does the mark bounce around erratically or is it pretty steady? It may be possible to trash some of the teeth if it has a fiber gear on it. Looking down inside the carb, when you pull the throttle (engine not running), do you see a pump shot of gas? What carb is it? if its a Rochester, there is a hole on the bottom of the carb for a vac signal to the power valve. If you blocked this off when you rebuilt it (wrong or no gasket), then its not going to behave right. Test your fuel pressure as suggested. Should be around 3-4 1/2 psi. Crud is also possible, but if the car has been in regular use for some time before, I would think its less likely, but it is still possible. Disconnect the fuel line at the pump, and put a hose on it so it can drain into a pan, then pressurize the tank for a little bit, and see if there's any crud in the pan. You allready did the points and condenser right? did you check it with a dwell meter or just a feeler gauge? Is the car 12 volts? if so, make sure you are using a resistor or a coil with a built in resistor. If you haven't tried a different coil yet, try that. Perhaps a different dizzy if you have one. I wouldn't go spending money on it until you've exhausted everything else, though. firing order is 1-5-3-6-2-4 clockwise. Double check all of the connections and don't assume that just because you did something allready, that it can't be the reason. Sometimes you have to step away from it for a while. Don't get in a hurry...
do a compression check. I had a 235 in a 52 truck and it would idle all day just fine. it would even run good in first gear, then when I went to second it would pop and buck like crazy. did all the usual tests and just decided to give a compression check. one cylinder was dead. ended up selling it before I had a chance to fix it or diagnose the low cylinder. my symptoms were a bit different than what you describe but you never know.
I'll post how this turns out when we can get to it. Lots of good suggetions, seems like a few of us have had similar problems. Thanks again for the input!
O.K., if anyone is still interested in what happened with this, it turns out that after changing and checking everything that we could think of, and using some of the suggestions posted here, we accidentally found the problem: a bad coil wire was the culprit! Dad said he changed all the plug wires, but he FORGOT to change to the new coil wire! Damn thing runs like a watch...amazing how something so small and insignificant can cause so many problems! Thanks for all of the suggestions!
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