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Re: 235 Plugs and distributor (very long)
jstoob #1341074 Wed Jan 08 2020 05:09 PM
Joined: Sep 2001
Posts: 30,326
ace skiver
"Dump the Weber off a bridge with a deep river underneath, . . . " nono (the EPA might be watching, Jerry)

It is hard/useless to argue with your unfortunately-factual point of view (based on many observations/experiences).

The 261 in my Suburban has an AA1 GMC truck carburetor.
The old/original Rochester was a "tearful weeper". I needed a "larger" carburetor, anyway.

However, I have non-weeping dual Rochesters on another 261 in a 1954 Chevrolet pickup that I traded to a friend. It has run nicely for almost 20 years.

I am going to take a gamble on the non-leaking original Rochester on my 1954 235 Hydra-Matic. That carburetor was rebuild/inspected by a pro. It did not leak, and it worked nicely, on the rebuilt original 235 during break-in after a professional engine-rebuild.

I am hoping to keep that Rochester - for historical purposes. I think is is the first year a Rochester with an automatic choke ("stove pipe style") was standard equipment on a light Chevrolet truck? If I have to use a different carburetor I will not be surprised, and, it will not surprise me.

Tim []
1954 3106 Carryall Suburban [] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. []
Re: 235 Plugs and distributor (very long)
SimS #1341082 Wed Jan 08 2020 06:28 PM
Joined: Mar 2000
Posts: 1,371
Red dot, center of chest ...
Originally Posted by SimS

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.


You raise a very good point, which got me to thinking of something else. These old engines sometimes had problems with vapor lock due to the fuel lines being too close to the engine. It wouldn't hurt to check the fuel line to make sure it's not too close. The fuel lines were usually run through standoffs that bolted to something so that they couldn't get bent too close to the head. The problem was often at the front of the head where the line wraps around the motor to lead back to the carb.

Another possibility is that the carb is slightly warped, and as it heats up, the distortion of the metal causes it to begin sucking air in at the base.

The odd thing about his symptoms is that he initially describes what sounds like a classic vacuum leak, but then when he gets to Denver, he's obviously running over-rich. Two descriptions that are at complete odds with each other. That's why I suggested he may have more than one problem.

Jerry's suggestion is a good one. If Ed is available, he can probably sort it out pretty quickly.

The key to situations like this is to eliminate things one at a time. Once you have verified that something is not the problem, don't keep going back to it again. That will drive you nuts.

68ironhead points to a little-thought of issue. Sometimes there are vacuum connections in places you'd least expect them, like the wiper motor, and people seldom even think of those or else they assume it's OK. Never assume anything is OK until you've checked it out and verified that it is.

Some of the advice he got from professional? mechanics is nuts. What does the accelerator pump have to do with a rough idle? Again, mechanics are just guessing. They clearly don't even know that an accelerator pump is only used during - wait-for-it - acceleration. Sheesh.

Here's some things to think about. The problem occurred before he changed the carburetor. "would only run if it was taking on a lot of fuel" After he changed the carb, he had the exact same symptoms - "Will not hold idle without gas"

So, changing the carb changed nothing. Therefore, it's not the carb, although changing the carb could have introduced a second problem. He doesn't know if the plugs were fouled in his original location, because he never checked them until Denver. So, what sort of condition could cause the engine to need additional fuel to keep running yet fouls the plugs from too much fuel and is not related to the carb? Any time a motor needs additional fuel just to keep running, it's getting too much air. But, how does that foul the plugs?

If it were me, the first thing I would do is change the plugs. If it runs fine, then you know the poor running is caused by fouled plugs. Then you just need to figure out what's fouling the plugs. Obviously, it's too much fuel in the compression chambers. There are several things that can cause that; maladjusted carb, too high a pressure fuel pump, blocked air passages screwing up the fuel/air mixture, carb adjusted to overcompensate for a vacuum leak, a weak spark that prevents all the fuel/air mixture from being consumed.

Of course, all of this assumes that he's buying the right parts to begin with.

Paul Schmehl CI 12
Stovebolt Staff: Geek
1948 Chevy 3100 Five Window []
Re: 235 Plugs and distributor (very long)
jstoob #1341090 Wed Jan 08 2020 08:01 PM
Joined: Feb 2004
Posts: 20,855
Carburetors calibrated for elevations close to sea level also run RICH at Denver's altitude, since a carb mixes fuel and air by weight, not volume and the air at 5K+ feet isn't as dense as it is at lower elevations. Running a main jet a step or two leaner is probably a good idea, but looking for different jets for the Weber is probably going to be like finding a chicken with lips.

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 #1341092 Wed Jan 08 2020 08:42 PM
Joined: Jan 2020
Posts: 6
jstoob Offline OP
New Guy
One more clarification post to help with the troubleshooting. When we brought the truck back from the dead (In Lincoln, prior to the move), it ran smooth when we first fired it up with the Rochester. After a while it just ran like crud and not smooth anymore. I remember pulling the original plugs, and saw nothing noteworthy, but we put new ones in anyways. I will circle back on the wiper motors for a leak. Is there a manual somewhere I can find ID/OD of hose sizes? I have listed the plug & wires I bought below to see if those were incompatable in the first place.

Overall, its mind boggling that I could drive it around a couple times in Lincoln without issue and it got worse the more I drove it. Then, when picking it up from the mechanic in Denver, it ran smoothly all Friday night, ran smooth Saturday morning, then degraded into rough running. If all they changed was plugs, wires, coil, and it ran smoothly for a while, it made me wonder if one of those was wrong. Heck, is one wire backwards somewhere screwing it up? I will post a picture when I get home, maybe a keener eye than I will spot a really easy fix.

First plugs and wires:

Wires: Belden BEL 700126
Plugs: ACDelco AC R43

1950 Chevy 3100
1985 Mitsubishi Mighty Max
2003 Mitsubishi Montero Sport
Re: 235 Plugs and distributor (very long)
jstoob #1341104 Wed Jan 08 2020 10:20 PM
Joined: Jun 2011
Posts: 3,608
Shop Shark
At our altitude we also lean out the idle jet, advance ignition, no pinging though.


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
Re: 235 Plugs and distributor (very long)
jstoob #1341115 Wed Jan 08 2020 11:29 PM
Joined: Dec 2017
Posts: 795
Shop Shark
Either the J12YC or the J14YC. Either will work fine, whichever is easier to get. Skip the resistor plugs. What I found with those webers is that the ported vacuum for the vacuum advance does not provide enough signal. Keep in mind that the original carb used ported vacuum for the advance, that is the port was to atmosphere (above the throttle blade). When the throttle blade began to open, vacuum built as the air passed the port, allowing the advance to start opening, reached max signal and max vacuum advance, and then tapered off as the throttle blade opened fully, eliminating the vacuum advance. So with a stock carb, when you gave the gas a rap at idle, the distributor would move quite a bit. Because the port is ported vacuum, you can set the timing at idle without disconnecting the advance line because there is no vacuum (or very little) to the advance unit at idle.

With the webers, the insufficient signal from the weber's vacuum port impedes proper advance. So generally you have to run the advance line to full manifold vacuum (where the wiper motor hose is). Thus, you set the timing with the vacuum hose disconnected and after reconnect the hose.

As for jetting, couple of places sell them, Redline, Sterling, same jets as the 32/36 and 38/38 weber. Keep in mind that for the Weber, there is an idle jet and an idle air jet. Both play a part in idle mixture. Also emulsion tubs but you dont even want to go messing with them unless absolutely necessary. The mixture screw only adjusts for volume. So if the idle jet is too large, and the idle air jet is too small, it will always run rich no matter how much you turn the mixture screw in. Worse, the main jetting plays a part on the off idle circuit with these webers, which in turn affects the quality of the idle fuel. They are very adjustable, but you need a good bit of patience to tinker with them. I am still learning with my dual 38/38s and I won't lie, the curve is steep and sometimes frustrating.

If you really want to get this truck running well, at least in my opinion, I would get back to basics. Put the single bbl carb back on (confirming that the power piston is not sticking), or get a Carter replacement carb (I always had very good luck with the YF's) and start from that point as those carbs were designed and engineered for these motors. Then fresh plugs, and just for giggles and because they are cheap, replace the condenser. As a couple of the fellas here have noted, today's stuff can be junk right out of the box.

Then confirm your timing, adjust the carb, and start from that basic point. Like I said, I myself am not a fan of a single weber on a 235 single bbl manifold. I am not saying that is your problem, but too many rabbits going down too many holes, in my view anyhow.

Re: 235 Plugs and distributor (very long)
jstoob #1341118 Thu Jan 09 2020 12:10 AM
Joined: Mar 2010
Posts: 9,400
Master Gabster
I'm with HRL. You need a nearby Stovebolt guru to spend 32 minutes to find out what is going on with your poor running engine issue. (If its HRL, it will take an extra 23 minutes because he talks slower. smile )
It is my opinion that you have had more than one issue going on at the same time. This is the most challenging of situations to diagnose in person, let alone trying to do it via keyboard..
What you have had done in an attempt to fix it may have added one or more problems, complicating things further.
This is why "Test, don't guess." is brought up on this site so often. (Thanks to HRL.)
Mine is, "Its never the carburetor."
Carb King Jon once stated, and I paraphrase, "Apparently the updraft carburetors were much more reliable based on how many rebuild kits we sell." He went on to state that the reason why he didn't sell many updraft kits was because that carburetor was difficult to remove, therefor the mechanic instead, worked on the issue which was actually causing the problem.

Re: 235 Plugs and distributor (very long)
jstoob #1341126 Thu Jan 09 2020 12:53 AM
Joined: Jan 2020
Posts: 6
jstoob Offline OP
New Guy
Thank you for your responses. Here is what I did after work:

Test fire, would barely start, and only with the pedal applied to keep it running, will not idle by itself.

Installed six new J12YC plugs. The six I removed were heavily covered in soot, especially for only running 40-50 miles and for three hours. It's running rich, I see that.

Test fire, smoother, but still not holding idle, and still not running right.

Go to carb, return idle advance to just making contact, then 1 1/4 turns in. Then turn idle mixture all the way in, and back out two turns.

Test fire, no change.

Check distributor. Vac advance screw is slightly loose, and octane selector not at 0. New hardware for the screw to tighten, set octane selector to zero.

Test fire, no change.

Back out mixture screw 1/2, test fire, 1/2 again, test fire. No change.

Disconnected vacuum advance and sucked on it, I was able to turn the dizzy slightly.

If anyone sees a "hey dummy" in the picture below I'd be happy to feel stupid for a while if it meant it got fixed.

Again, thanks for all the help.


1950 Chevy 3100
1985 Mitsubishi Mighty Max
2003 Mitsubishi Montero Sport
Re: 235 Plugs and distributor (very long)
jstoob #1341135 Thu Jan 09 2020 01:17 AM
Joined: Mar 2019
Posts: 954
Shop Shark
Oh didnt realize loose bolt was a starter issue. Check em anyhow. Not to much mention on the timing. I would look there also. Different carbs with the exact same problem??? Very unlikely, but yet possible. Verify timing and advance functions as well. Wont cost nuttin but time. Test dont guess... No black smoke, indicating a rich condition? But yet, fouls plugs in 40 miles. Hmmm

Re: 235 Plugs and distributor (very long)
jstoob #1341157 Thu Jan 09 2020 02:52 AM
Joined: Feb 2004
Posts: 20,855
Did the shop that sold you the Weber explain that you'd probably need a fuel pressure regulator also? They're notorious for flooding with even a tiny bit too much fuel pressure. If you're going to stubbornly stick with that carburetor, you'll have to spend more money- - - -get the fuel pressure down to 2-3 PSI or it will never quit flooding. Also, install a VERY good quality fuel filter- - - -not one of those Mickey Mouse see through things- - - - -even microscopic bits of dirt or debris will make a Weber flood.

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!
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