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235 Plugs and distributor (very long)
#1341001 Wed Jan 08 2020 03:29 AM
Joined: Jan 2020
Posts: 6
jstoob Offline OP
New Guy
Hello all, longtime lurker, first time poster. I humbly post to Stovebolt where I hope someone can help me out. I have taken my truck to two mechanic shops which have failed to fix the problem permanently.

About the truck: 1950 Chevy 3100. It had sat for 20 years outside, been stolen once, and restored sometime in the 70's or 80's. Based on the valve cover, and the serial number stampings on the side of the block and head, I believe I have a late model 235, sometime between 58-62 is my best guess.

About me: Aircraft mechanic for the Air National Guard, but not a vehicle mechanic per se, unless you count the Youtube Academy and forum lurking. I've tried to do as much as I can on my own to learn and save some $$$.

Here we go:

I bought the truck sitting in a storage yard where it had been sitting for at least eight years. It had the aforementioned inline six, with a stock single barrel carb and a newer, unidentified alternator on it, and had what we thought was a Buick ignition coil (going of serial #'s) on it. After getting it on tires to get it rolling, myself, with the help of others did the following: brand new fuel tank, purged fuel lines, new points, new condenser, new plugs, new wires, new rotor cap, and oil change. At this time we attempted to start the vehicle, it was turning freely, and after finally getting everything in the right place, it fired up. It ran like a top, the best way to describe it was it sounded like a sewing machine--quiet, low RPMS, very smooth and pleasant sounding. After some brake work, we drove it around town and it ran very nice. After a little more work on the brakes (front disc conversion) I took it to a mechanic in town to have them bleed the brakes better than I, and look everything over for safety's sake. I picked it up on a Friday afternoon the weekend I was moving out of state. Almost immediately I noticed it was running extremely rough and would only run if it was taking on a lot of fuel, and even then it sounded terrible. Instead of leaving it behind for the mechanic to go over again, I took it with on the move. I called the shop up, told them the issue, and they said they hadn't messed with any throttle settings but recommended I check the accelerator pump in the carb. I then rebuilt the carb with a Mike's Carburetor kit and instructions and still had the same issue--real rough running, not holding idle, only running with a ton of fuel. Around this time I upgraded the unknown alternator with one from a '79 Chevy pickup.

Now in Denver, I tried to think of what could be causing it. I replaced the Rochester single barrel with a Weber 32/36 from Langdon's. (I briefly tried to explain the issue to Tom, but the more I talked the more flummoxed he got) Still having the issue after the new carb, I put on a new fuel pump that had the recommended flow, per Weber/Landon's specs. I checked vacuum advance, looked for vacuum leaks, valves not opening or closing. Nothing appeared off. I then took it to a mechanic here in Denver. After a few days they called back and said the truck was ready. I went in and they said they checked compression and timing, both were good. There was a loose bolt here and there, but nothing funky. They changed contacts, coil, and spark plugs. We went out to the shop and it was running just like it had when we brought it back to life--like a sewing machine, nice and quiet, and very healthy sounding. I asked if that was really all it took, swapping coil, plugs, and contacts and they said yes. I didn't understand but thought maybe I overlooked something.

I was ecstatic regardless, I drove it around all night, then the next day we took it to lunch in Morrison (20 minutes from where I live). It made it to lunch fine, still running smoothly, but on the drive back it started feeling funny again. By the time we had made it home, and since then, it has gone back to rough running. Will not hold idle without gas, and generally doesnt sound right. (Still dealing with that shop on a refund or a "fix") I pulled the spark plugs and they were covered in black soot already. I cleaned what I could off the spark plugs thinking if I got them clean again it should run like a top again. Unfortunately, it still ran poorly. Not holding idle, not running like a sewing machine. I tried messing with idle speed on the Weber, but it really did nothing different.

So, as the title says, I guess I'm back to plugs and the distributor; perhaps the coil as well. Could it be I'm frying spark plugs somehow? Is the distributor not functioning properly? Is the coil too hot? Is the condenser incorrect? Is the alternator incompatible? Do I just have the wrong darn spark plugs? At this point I'm thinking about swapping over to HEI or something to eliminate one more thing, but I don't want to continue throwing parts at it (even if that would be an upgrade).

Would appreciate any help or suggestions you fine folks have. At this point I don't know what to do otherwise.

Many thanks,
Jared in Denver

1950 Chevy 3100
1985 Mitsubishi Mighty Max
2003 Mitsubishi Montero Sport
Re: 235 Plugs and distributor (very long)
jstoob #1341024 Wed Jan 08 2020 06:31 AM
Joined: Mar 2000
Posts: 1,393
Red dot, center of chest ...
Alright. Now think about what you wrote.
Originally Posted by jstoob
would only run if it was taking on a lot of fuel,
. Engines run on a mixture of fuel and air that is ignited by a spark to create an explosion. Too little fuel, or too much air, and the engine won't run well at all. You statement is screaming "vacuum leak". There's air getting into the fuel system somewhere that's screwing up the fuel/air ratio causing the engine to run bad.

Now, think about the sequence of events. You sent the truck to a mechanic to work on the brakes. That has nothing to do with the fuel system. However, if he was working in the engine compartment, he could have easily caused a vacuum line to slip off and cause your problem.

When you got to Denver, you got snookered by mechanics who either don't know what they're doing or are deliberately cheating you. You stated
Originally Posted by jstoob
new points, new condenser, new plugs, new wires, new rotor cap
, yet they replaced the points, coil, and spark plugs. They were already new. How would changing them fix anything?

Next, you state that the spark plugs are covered with black soot. This is an indication of too rich of a fuel/air mixture, which is the exact opposite of a vacuum leak.

Nothing irks me more than people replacing brand new parts simply because they don't understand how to troubleshoot. You don't need another coil, points, or anything else, although you may have to replace the plugs depending upon how badly they were fouled.

Based on your symptoms, you may have a combination of problems, but they are all fuel/air related. There's nothing wrong with your ignition system (coil, condenser, plugs, wires, distributor.)

Here's what you need to do.
  • Look for vacuum leaks while the engine is running (you do this by spraying carb cleaner around every vacuum nipple, at the base of the carb where it mounts to the manifold, and anywhere else that air can get into the engine other than the air horn of the carb, where it's supposed to come in. If the engine speeds up, you've found a leak. Do not stop looking if you've found one. There may be more.
  • Look at the spark plugs. Are they wet? You have unburned fuel. Are they covered in black charcoal (dry)? You're running too rich. They should be a light chalky brown after many miles of service.
  • Look at the choke plate. Is it closed almost all the way? What happens when you open it with your finger? Does the idle smooth out? How about if you push it closed? Does the idle smooth out? Adjust the choke. Make sure the choke mechanism moves freely throughout the length of its travel and is not hanging up at any position.
  • Check every rubber hose that feeds vacuum to something (like the advance on the distributor) for cracks by spraying it with carb spray. If the engine speeds up, you've found a leak. Replace the hose.

If none of that helps, replace the plugs, do nothing else, and see if that solves the problem. If it does, yet it reoccurs, go back to the list until you find the problem.

Whatever you do, do NOT replace or rebuild the carb. It's brand new. If you find a vacuum leak at the base of the carb, take if off and inspect the gasket. Place if over the manifold opening. Does it cover the intake holes at all? Does it sit flush with the manifold mount? Next, place it on the base of the carb. Does it restrict the area where the fuel dumps into the manifold? Is it missing a hole that allows fuel to enter through the accelerator pump? Does it sit flat against the base of the carb sealing it?

All of these things could be issues. Once you have verified something, you do not need to verify it again. One of the biggest things that drive people nuts is going over the same ground over and over again. Do each check carefully and then, once you've verified that it's not causing the problem, do not revisit it. The problem is elsewhere. Persistence is your friend.

If, after all this, you still have problems, come back and describe precisely what the symptoms are at idle and at speed. Does it just run rough? Does it stall at idle? When you step on the gas, does it bog down? Does it shudder? Does it die? Be precise. It matters.

Paul Schmehl CI 12
Stovebolt Staff: Geek
1948 Chevy 3100 Five Window []
Re: 235 Plugs and distributor (very long)
jstoob #1341040 Wed Jan 08 2020 12:51 PM
Joined: Jul 2008
Posts: 358
Shop Shark

I can go along with your diagnosis, but why does it run "like a sewing machine" for a period of time before it runs like crap? If it is a vacuum leak I would think the leak would be present at all times. The thing that I can't figure out is that it has had two carburetors {one old and rebuilt and one brand new) and the symptoms turn out the same. Almost sounds like some sort of heat related vacuum leak not associated with the carburetor itself. Let's see what the OP finds after going through your checklist.


Re: 235 Plugs and distributor (very long)
jstoob #1341054 Wed Jan 08 2020 02:51 PM
Joined: Dec 2017
Posts: 866
Shop Shark
There is a little low hanging fruit you can mess with here. On the carb issue, I myself am not a fan of the single weber. Pairs yes, but a single in place of the stock one bbl no.But you are stuck with what you have I guess. Also, I have generally found that the ported vacuum advance port on the weber is not sufficient to actually allow the stock 235 vacuum advance to work properly. So just asking, how many turns out on your mixture screw are you on the weber and how may turns out on your idle screw. The webers are very sensitive in that regard and may require an idle air jet change.

Plugs, which are you using? The 235s use an extended tip type. I have always run champions (43 years). J12YC, J14YC or the resistor versions RJ12YC and RJ14YC.

Is the clamp on the distributor tight? Is the bolt on the octane selector plate tight and is the hash mark on the octane selector set to zero with the hash mark on the distributor pad? Really what you are checking is whether the distributor is moving (it should move when the advance moves it) but not because its loose. Also, can you confirm that the diaphragm in the vacuum advance canister is holding and not ruptured?

Spark plug wires, take a look and make sure they are not laying across one another and cross firing.

Is the firewall ignition resistor in place and wired correctly to the coil?

Just a couple of things to check and get out of the way. Now if you don't know how to do some of this your self, now is a great time to buy a few basic tools, roll your sleeves up and dive in. Lots of help here.

Last edited by Dragsix; Wed Jan 08 2020 02:57 PM.

Re: 235 Plugs and distributor (very long)
jstoob #1341055 Wed Jan 08 2020 02:53 PM
Joined: Mar 2019
Posts: 1,148
Shop Shark
You mentioned loose bolts here and there? Double check around the intake gasket area with carb cleaner when its running bad. Are the bolts tight there? Gasket damaged? It might take specific circumstances to get the veh to run like crap. Heat changes things.

Re: 235 Plugs and distributor (very long)
jstoob #1341058 Wed Jan 08 2020 03:25 PM
Joined: Jun 2004
Posts: 8,254
Master Gabster
You are building up carbon on the plugs causing the engine to miss fire. It is obvious your mixture is too rich. You need to fix a carb. that will run the correct mixture. I would mess with the original model B. They are simple & easy to work on. The usual problem with them is the power valve staying on all the time. There is a lot of posts on this in this website. Do a search. It would pay you to get a cheapy spark plug sand blaster & clean those plugs up instead of buying new ones every time they get carbon on them. You need compressed air to use it.
HEI would help as it fires a dirty plug better then conventional ign. That would not solve the problem though.

They say money can't buy happiness. It can buy old Chevy trucks though. Same thing.
1972 Chevy c10 Cheyenne Super
Re: 235 Plugs and distributor (very long)
jstoob #1341059 Wed Jan 08 2020 03:43 PM
Joined: Jan 2020
Posts: 6
jstoob Offline OP
New Guy
At work now, reading through all these, thought I'd answer a few responses. Thank you for all of those by the way. I am planning on working on the truck tonight with your responses. I had read numerous posts regarding a vacuum leak around the carb on here and other places. I have had someone ever so slightly holding the gas pedal down to keep the engine running and sprayed carb cleaner around the carb base (both with the Rochester and the Weber) and did not hear any variation in the engine speed. I also tried to spray a little around the intake manifold, and a couple other places I might have a leak and I didn't notice anything there either. If memory serves correct, the new Weber came with a new gasket to go on the manifold. I will again attempt to see if I can stabilize the idle and spray again, just to see if my installations were correct. It would be a mild surprise that I had a vacuum leak considering of how well it ran for a day, then degraded, unless the shop had somehow plugged a leak without knowing and it rattled loose. The spark plugs were black and sooty after only 40 miles or so. I figured it was running rough, so I cleaned them up and put them back in, ever so slightly better sounding, but overall, still rough. At this point, I should change out every vacuum hose on the engine. I should have done that in my initial work but will track down some hose and just replace everything for peace of mine. I do have a manual choke, and will check the cable adjustment on that when I get home.

@SimS, I'm not sure if sewing machine is the right way to word it, but for the times its been running well, it sounds like a smooth and quiet sewing machine. The rest of the time when it's running poorly it sounds rough. It ran fine when I picked it up, and apparently slowly degraded.

@Dragsix I will check Weber's settings and try and reset the carb to their suggested settings. I can say that it ran very well twice throughout the high altitude with no changes on my part, From the Friday afternoon I picked it up it was humming just fine, and by late Saturday afternoon the performance had diminished without messing with anything. I will buy some Champions, which ones should I use, resisted or non-resisted? I would like to get a known working spark plug. If nothing changes, I'll have at least eliminated that. I have checked vacuum advance and it is not ruptured. I did find a replacement, swap it in, and had no change. Both felt to give about the same resistance. I will check the clamp on the distributor, but I believe the carb advance is working. I will also check wire arrangement... in fact, I'll take a picture for all to see if that helps. The ballast is new and should be wired correctly but I will check that as well tool.

@glennstowing The shop mentioned a loose bolt on the starter and a couple other places I cant remember now. Starter is touchy, but works. (Floor type still)

1950 Chevy 3100
1985 Mitsubishi Mighty Max
2003 Mitsubishi Montero Sport
Re: 235 Plugs and distributor (very long)
jstoob #1341064 Wed Jan 08 2020 04:27 PM
Joined: Jul 2007
Posts: 323
Shop Shark
Quick kills are :
1)check vacuum advance travel in distributor. Check for smooth unimpeded travel
And operation...make sure any other vacuum leaks have been remedied first..
2) condenser failure...... today’s junk fails often!
3) distributor hold down clamp and bolt....... stove bolts often loosen causing
Timing issues

Re: 235 Plugs and distributor (very long)
jstoob #1341069 Wed Jan 08 2020 04:45 PM
Joined: Feb 2004
Posts: 21,650
Shotgunning parts at a problem without adequate diagnosis just increases the chances for creating more difficulties, without solving the original problem. Unfortunately, the type of structured maintenance protocols that aircraft systems have do not exist in the automotive world. Back when I spent some time doing USAF electronic maintenance, once the degree of difficulty on anything aircraft-related got beyond swapping minor components and twisting safety wire, everything went back to a maintenance depot or the factory for repair. Very little actual diagnosis or rebuilding got done- - - -we were just parts changers. I doubt that things have changed much since I went back to fixing cars 40-something years ago.

Your sooty spark plugs are a symptom of a flooding carburetor. Dump the Weber off a bridge with a deep river underneath, and go back to the right carburetor. I'm partial to Carter, but a few people still use a Rochester for something other than a paperweight.

Edit: Ed Pruss is in your area. Once you make 2 or 3 more posts and have access to the private message system, drop Ed a PM- - - -he can probably solve your problem in a matter of minutes.

The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: 235 Plugs and distributor (very long)
jstoob #1341072 Wed Jan 08 2020 04:51 PM
Joined: Apr 2010
Posts: 232
Shop Shark
Vacuum leak under dash at wiper motor ?

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