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Need advice for rough running 235 #1291944 Fri Dec 21 2018 11:30 PM
Joined: Dec 2018
Posts: 10
C
ChevyTrace57 Offline OP
New Guy
I have a 1957 Chevy 3600 with the 235 engine, and it's been running very poorly. It will start up fine and revs good in neutral but when I try to drive it is when it runs very rough. It won't go above about 1500-2000 RPM and eventually stalls out, but will start up again just fine. I've also noticed from the plugs that's it's running a bit rich even with the carb mixture set very lean.

Some things I've already did to try and fix it:
Checked timing
Checked compression (All around 130-140)
Adjusted valves
Adjusted points gap (points are just a year old)
New vacuum advance which works fine
New fuel pump and fuel filter
New spark plugs and plug wires
Replaced intake manifold gaskets

I've also taken apart and cleaned the carburetor. I also tried using a second carburetor that I had which made no difference, so I would say my carb checks out, but with either carb on it still runs rich (both carbs have been rebuilt before) I also made sure the hole on the bottom of the carb lined up with the cutout on the insulator which it did

I don't have much experience with these engines so I'm pretty stumped on what to do now. Any advice would be great, thanks!

Re: Need advice for rough running 235 [Re: ChevyTrace57] #1291952 Sat Dec 22 2018 12:31 AM
Joined: Mar 2000
Posts: 1,286
baldeagle Offline
Server Fixer
Good performance depends on several things; fuel, air, ignition, and compression. It sounds like you've already verified the fuel, compression, and ignition. The only thing left is air. Getting too much or too little will affect performance. Since you've already leaned out the carb as much as you can, it sounds like you're not getting enough air. The fuel/air mixture has to be right for the engine to perform well. What you're describing is poor performance under load.

Are you using the original oil bath air cleaner? If so, try running (briefly) without it. Those things can get gunked up pretty good and really restrict air flow. If running without it solves the problem, then you can try soaking the oil bath cleaner in solvent overnight to clean it out. Or, replace it with a paper filter, which would require buying a filter assembly (or scrounging for one that fits.)

Do not run without an air filter for very long, because it can ruin your engine. The air filter protects your engine by keeping particulates out of the engine, where they can scratch the cylinder walls and the piston rings, reducing compression. They can also get into the oil where they could damage bearings.

Note that if this works, you may have to richen the carb some to get it to work well without the air filter. If so, that would be a clear sign that the air filter is the problem.


Paul Schmehl CI 12
geek@stovebolt.com
Stovebolt Staff: Geek
1948 Chevy 3100 Five Window
Re: Need advice for rough running 235 [Re: ChevyTrace57] #1291955 Sat Dec 22 2018 12:57 AM
Joined: Feb 2004
Posts: 19,687
H
Hotrod Lincoln Offline
Boltergeist
Loosen the exhaust pipe at the manifold flange. Air has to get out of the engine as well as getting in. I've seen deteriorated mufflers collapse inside, and some exhaust pipes were also made from one pipe nested inside another and the inner pipe can collapse and restrict the exhaust flow.
Jerry


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: Need advice for rough running 235 [Re: ChevyTrace57] #1291957 Sat Dec 22 2018 01:06 AM
Joined: Apr 2005
Posts: 8,140
Justhorsenround Offline
Grease Monkey, Moderator General Truck Talk & Greasy Spoon
Regarding the points. Just because they are only a year old does not mean they are good. Today’s points and condensers are a hit and miss crap shoot. Did you adjust using a dwell meter? I had a Corvair powered dune buggy many years ago that I lost a drag race with just because the points were not properly adjusted. Wouldn’t rev over 2000rpm. Readjusted the points and won the next race easily. Clean them with a point file and try adjusting them again. If you decide to replace the points/condenser try to find NOS Delco, they pop up on evilbay every so often.🛠


Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne 4dr 230 I-6 one owner (I’m #2)
‘39 Dodge Businessmans Coupe


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Re: Need advice for rough running 235 [Re: ChevyTrace57] #1291964 Sat Dec 22 2018 01:34 AM
Joined: Mar 2014
Posts: 1,185
J
Jon G Offline
Shop Shark
Assuming you have a Rochester, did you pay attention to the power system (ie power piston, etc). Right there is a large culprit in the rich running situation...


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Need advice for rough running 235 [Re: ChevyTrace57] #1291988 Sat Dec 22 2018 03:14 PM
Joined: Dec 2018
Posts: 10
C
ChevyTrace57 Offline OP
New Guy
Thanks for all the info!

In regards to the air filter I did forget to mention it's a brand new paper filter, but I'll try running without it just to see if theirs any noticeable difference.

I'll definitely try loosening the pipe off the flange and see if that makes a difference. It does need a new muffler so I'll probably just remove it all together and see if it runs better.

I only adjusted the points to the new gap size according to the shop manual. I don't have a dwell meter but I'm sure I could find one to borrow.

I do have a Rochester 1B, the power piston seems to be alright, but I'm not all too familiar with this so I'm not sure if I may have missed something.

Also if this info helps, it was running fine over the summer before this all happened. I'll try what all you recommend and I'll be sure to get back with results soon

Re: Need advice for rough running 235 [Re: ChevyTrace57] #1292022 Sat Dec 22 2018 10:24 PM
Joined: Mar 2010
Posts: 8,870
5
52Carl Offline
Master Gabster
You have covered all of the basics.
Spark plugs are telling you that you have a rich condition. An engine can run pretty good even if it is running a little rich.
I am guessing that you are having more than one issue at the same time. This makes troubleshooting difficult.
My bet is that you have an ignition problem, such as dirty/pitted points and/or weak condenser. The points are a year old. Change them and the condenser. They are cheap. Make sure to burnish the new points with a credit card to clean the crap commonly found on new points these days.
Once you are done with that, it will be easier to track down the cause of the slightly rich condition.

Re: Need advice for rough running 235 [Re: ChevyTrace57] #1292192 Mon Dec 24 2018 09:07 PM
Joined: Jun 2011
Posts: 27
G
GeneBrink Offline
Wrench Fetcher
Just one other possibility - a worn distributor bushing that allows the shaft to move when it is under some torque pressure. About lost my mind on an old Volvo that acted exactly like your problem - replaced the distributor and the car was running years later just fine. Good luck!

Re: Need advice for rough running 235 [Re: ChevyTrace57] #1292195 Mon Dec 24 2018 09:40 PM
Joined: Dec 2018
Posts: 10
C
ChevyTrace57 Offline OP
New Guy
I was able to do some more troubleshooting with the engine yesterday. I tried to run it with the air filter and exhaust pipe disconnected, but did not change anything once it went in gear. I also had my carburetor looked over carefully by my uncle who's rebuilt them before, and he said that it all looks good. We went through and cleaned everything while we had it open, but again it made no difference once the truck went into gear.

I also did a vacuum test and the needle on the gauge was sitting fairly steady around the 20 mark at idle and while revving the engine.

Im thinking this is most likely an ignition issue, so I'll be getting into the distributor next. I also will get new points and a condenser to see if it helps. Is their any way I can test for a worn bushing? I am able to rotate the distributor a bit, but I'm pretty sure it's just for the vacuum advance since it snaps back into its original position.

Re: Need advice for rough running 235 [Re: ChevyTrace57] #1292243 Tue Dec 25 2018 06:20 AM
Joined: Mar 2000
Posts: 1,286
baldeagle Offline
Server Fixer
Vacuum should change when revving the engine. When you open the throttle, the vacuum should jump initially and then come back down as the engine settles.

To check the vacuum advance, remove the distributor cap, connect a rubber line to the advance and suck on it. the plate should move when you suck (which is the same as applying vacuum.) If the advance isn't working, that could definitely be your problem.


Paul Schmehl CI 12
geek@stovebolt.com
Stovebolt Staff: Geek
1948 Chevy 3100 Five Window
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