Hi all, Been chasing a bad misfire and power loss and had a general question. 235 chevy, 1954. Stock distributor, dual carbs from langdon and dual exh. Bad miss and resulting loss of power. Doesnt seem to be a certain cyl and often more than one. Backfires in exhaust. New coil, cap, points, rotor, condenser, wires and plugs. New fuel filter also. Timed to the ball on flywheel. Usually i time with a tach and vacuum gauge but doing it that way made no difference. Set points with a feeler and checked with a dwell meter. When i shoot the bb on flywheel it moved around probably 10 degrees somewhat randomly but it coincided with the miss. Pulled the dist tonight and want to know of a way to test whether its good or causing this issue. Backfires in exhaust too when running. Btw, also did compression test got from 115 to 122 on all cyl and I did a valve adjustment. They were a little tight bit now I have the 'normal' light clatter when cold. Thanks, Scott
I timed my 54 235 by getting up on TDC to the ball. Once running I adjusted both carbs with a vacuum gauge. Then used my ear to get then in snyc. Finally, I fine tuned my timing by driving it till I had the best response and no pinging. I also got rid of the points and went with Langdons mini HEI. It's been fine for years.
Thanks for the reply! I think the mini hei is in my future. I did set up the carbs using vacuum. They werent difficult to set up and for the last year and a half have been a great set up. Usually time using vacuum and tach to get the highest vacuum and then readjust rpm if it goes too high and then do the timing again looking for highest vacuum. Worked great for years. The distributor is a little loose in the hole even when everything is locked down. That bb jumping around has got me suspecting the dist but wanted to find a way to confirm before buying electronic ignition.
The wire from the distributor to coil sometimes breaks down. Three million years ago my 54 stopped on the highway. Couldn't find the problem. The town kid mechanic came to the stopped car. Used his knife to fix the problem. He was there and gone in five minutes.
I remember this issue from years ago. It seemed like every Chevy did it. Like a traveling skip that moved around to each cylinder at different times. V8 and 6, and the common factor I guess is brass bushings in the distributer worn and letting the dwell time vary as the shaft wobbles around. Also the timing changes as the dwell changes. Also years ago we all used crappy used 7mm rubber wires from the junkyard which didn't help either.
Before you lay out $ for HEI check for wear in the cam timing gear. It could be a fiber gear signaling you it is getting ready to give up. Rotate the crank back & forth and watch the rockers to see if they move at the same time. There should be very little or no play between them. Glen P might try the same thing.
What carbs are you running? I had similar issues running a pair of Rochester B's and found that there was some very fine dirt in the idle circuit causing the fuel to drip. Also,the mini HEI is from an '83-'85 2.8L S-10 V6. If you have access to a lathe, they are easy to machine down....I've done quite a few. The Langdon's stick up too high, I prefer to machine them so the sit near the stock height. You will not believe the difference that distributor will make.
Thanks for the suggestions. I should mention that this started as an intermittent problem. First time it happened I was driving and pulled over and looked for loose wires, fuel supply etc and started back up and drove fine the couple miles home. Had a couple other times where it started running good and went bad after a couple miles. Now it seems to be bad all the time.
I believe that's because the entire upper part of the distributor housing rotates when the vacuum advance is doing its thing. As a result, the wire to the coil gets a lot of flexing even with normal use as mentioned above. This may help you with your troubleshooting. http://www.jalopyjournal.com/forum/threads/hot-rod-technical-library-basic-ignition-systems.983424/
Because the movement of the distributor they are hard on the primary wire from the coil do to flexing and they need a good ground.
The wire from coil to distributor is good. I replaced it about 2 years ago and its still nice and pliable with good connections. I put the meter on it and bent, moved flexed it all over and it remained at about .3 ohms so it seems good. It's a good thing to remember though. So would the timing moving around be caused by a very loose advance mechanism? I pulled the distributor and initial inspection shows the linkage mechanism to be very loose. The octane selector plate is no where near tight around the shaft. I know it cant be 1:1 fit but i can push the plate down about 1/2" below the clamp.
"So would the timing moving around be caused by a very loose advance mechanism? " Yeah, but I would check the dwell with a dwell meter. If the dwell varies much, it is likely worn internal distributor parts, and will change the timing along with it. Note this reference to ported vacuum advance for 1949 to 1951 Chebbies. http://chevy.oldcarmanualproject.com/shop/1949_51/4951csm1226.html
Distributor shaft to housing isnt loose with the clamp tightened and shaft to hole has maybe .050 - .070" play side to side and front to back. Theres probably quarter inch of play up and down of the shaft within the housing.
The terminal on the dist for the coil wire isnt shorted. I can put the ohm meter on it and on the plate inside the dist and when the points are closed there is continuity. When the points open there is no continuity.
I'd guess that to be on the loose side of the specs and it may not be helping matters any. I think that distributor also has a grease cup on the side of the housing. It was to be packed with grease as necessary and the threaded cup was to be given a half or maybe a full turn with every oil change to lube the distributor shaft and bushings. Have you ever taken the grease cup off to see if there's even any grease in it? I don't think these engines provided any splash lubrication to the distributor except to the drive gear. I suspect that after several years and a few owners nobody bothered so give the grease cup a twist every now and then, or refill it when it was empty. Also check the advance weights to make sure they're lubed and moving freely, and that the advance return springs aren't broken or disconnected.
The terminal on the dist for the coil wire isnt shorted. I can put the ohm meter on it and on the plate inside the dist and it i
Thanks Clay. The grease cup has some grease in it and it was fairly close to the shaft (meaning it was screwed down nearly tight. I will regrease that. I took a short video of how sloppy the vacuum advance unit is. Hoping i can post it.
I had a similar problem years ago, and it ended up being a faulty condenser. It took a long time to narrow it down. If you just installed the points and condenser, you may have gotten a bad one, throw the old one in if you still have it, see what happens. Jim
I have tried three different condensers. I bought two new ones thinking that i coulda gotten a bad one out of the box.
Never been inside a distributor below the breaker plate but things seem to be good there. Springs intact and functioning. I can move those weights with my fingers and they move back on their own. They feel smooth and dont bind.
So this octane selector plate mounts the whole works to the block. It should sit flat to the bottom of that clamp above it. It being this loose a problem? I want to throw down for the hei but want to make sure that the distributor is the problem. Thanks to those who have replied. It's appreciated.
So I thought I would update this thread and thank everyone for chiming in. I installed the Langdon mini hei tonight with the little square coil, new plugs and new wires. I set it up according to directions and fired it up. It ran great but idled high. I had forgot to reconnect electric chokes. So I did that and idled it til the chokes warmed up and tapped the throttle and she settled right down into that familiar 500-550 rpm idle. Stabbed the go pedal and the little sixer barked nicely through the fentons and smithys. Now, during my troubleshooting I had checked the valve adjustment and even when not up to operating temp the valves were tight. I backed them off too far. I will readjust soon and also tweak the timing but so far I am very impressed with the upgrade! Once I tune it I expect even a bit more from it since I feel like I am using a decent amount of the cam just taking up the slack that I adjusted into the valve train! Even the exhaust sounds a little different. Almost snappier somehow. Anyhow, worn distributor and vacuum advance mechanism seems to have been the issue.
Glad you got it sorted out and thanks for the updates. It really is amazing how well those mini S-10 distributors work. I actually have the same situation going on in a '53 truck that's in the shop right now. I've been messing with the original one but it is so badly worn that it's not really worth messing with.
Well hopefully someone will still read this... Aaargghhh! Car is back to doing the same thing. It ran a few miles good and then it started again. Same symptoms. It is intermittent. Last night I drove about 5 miles to the store and in my 4th mile on the way home it started running very rough. Backfiring through exhaust. Tonight it did it immediately after start up. Then it idled smooth in driveway snd indrove a couple blocks ok and then it started acting up again. I had fixed the timing before i drove it yesterday. Its maybe 5 degrees before the bb. Wondering about the carbs now
csn i bypass the ignition switch ? How do i do that? Does a switch sometimes go bad that way? Intermittent?
Sorry, gotta do it. Resurrecting. Was there any fix? Same issue with my 1962 235, dual Carter Webers. Intermittent low power with mild backfire.
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