The Stovebolt Site Forums The Shop Area Engine Shop Need advice for rough running 235

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!

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.

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

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.🛠

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...

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

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.

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!

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.

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.

And when you suck on the rubber line as Paul says, stick your tongue on the end and leave it there. If the tube goes limp (even though it moved when you were sucking on it) your vac advance is failing. The plate should stay still as long as your tongue is on the tube.

Just checked the vacuum advance and it seems perfect. I sucked on the line and put my finger on the end of it and it held its position for 30 seconds until I took my finger off. I did notice that the distributor does have a little play. I'm able to shake it left and right just a tiny bit. Is that normal, or is something not right there?

The distributor housing can have a little play in the block without a problem. Watch out for play between the shaft and the distributor housing, however- - - -that changes the point gap and causes variations in spark timing between cylinders. There's a spring and a plastic disc under the grease cup that's supposed to keep the shaft pushed against the housing to minimize shaft wobble, but that's a band-aid fix. I modify distributors to put a Torrington needle bearing at the top of the shaft and eliminate all the slop, resulting in no timing changes between cylinders at all.
Jerry

Double check the plug wires and confirm that you have them in the correct firing order. I just had a friend of mine who was trying to get a newly rebuilt 283 running right. Was running rich, stumbling, cutting out, restarting. He swore up and down that he had the wires right. He ended up taking it to a mechanic who discovered . . . He had a plug wire crossed.

If the wires and carb are right, could be the mechanical advance. Easy to check as noted above.

The photo with the distributor body shows the cap, spring and Bakelite bushing arrangement. Finding some nos Bakelite spacers is near impossible, at least for me anyhow. I use delrin as a replacement. Best is to get a rod of delrin and have someone with a lathe cut it down and then cut you a few pieces, about 1/4. You can find delrin rods on eBay. No access to a lathe, chuck about 1 inch of the rod in a drill press and spin the rod, use a flat file to shape the diameter down, then cut 1/4 piece.

The photo with the grungy advance mechanism was a distributor I just recently rebuilt. I had it on the sun machine and it would not advance at all. Once I took it apart I discovered why. If you look closely, you will see that the spring for one of the two advance weights broke off its pin and jammed in between the advance weight and the plate. So no advance. Might be your problem also, or it could be a lot of rust or crud gumming the advance up. You might not have anything wrong but it is another place to check for a problem.

The next photo is an advance with the retaining plate installed, and one with the plate removed so you know what you are looking at when you take yours apart.

Thanks for the photos, they helped a lot for someone who has never been inside a distributor before. It looks like my weights are in good shape and are not stuck. I also confirmed that my plugs are in the correct order. I did notice when I removed the distributor that the condenser was barely attached. I'm hoping that's the issue.

I took a picture of the mechanical advance and the condenser that I'll post here. I'm going to replace the points and condenser and should have it back together later today, hopefully with good results!

How much wobble is there at the top of the shaft? Even a little movement can change the point gap, which definitely affects the spark timing.
Jerry

Actually, your points are barely connected. Remove the nut on the outside of the distributor where the wire to the coil attaches. Then remove the small little retainer/plate (if its still there). Right behind that is a ring slot nut. They make a tool for that kind of nut but in a pinch a small screwdriver may do the trick, Loosen the ring slot nut. New points and condenser, and tighten the ring slot nut up, install the retainer/plate over the stud, the coil wire and tighten the nut. Set your point gap and don't forget a little smear of of point grease on the distributor lobe (should be able to get it at parts store). Now, you have gone this far, go a little further and install a new distributor cap. Fingers crossed!

Thanks for the walk through on that, I got the connection in place nice and tight. However after new points, condenser, cap, and fixing that loose connection theirs still no difference. I checked timing again which was fine and I set the points gap to .018

The whole distributor housing has a tiny bit of wobble against the block but the shaft in the distributor doesn't wobble at all, it seems very good.

I think it's gotta be fuel related at this point, I think I've ruled out almost everything with ignition and timing. I also checked the spark plugs again, which are still running rich with the carb on lean mixture settings (just 1 full turn out on the mixture screw) I'll put a photo of how the plugs look, I'm pretty sure their very rich.

I’ll say. Running pretty rich.

The only thing tinkering with the mixture screw accomplishes is changing the air/fuel ratio at idle. Once you get above 1200 RPM or so, the mixture needle could be bottomed out entirely and it would have no effect on the mixture at all. You've either got a very high float level, or a power valve stuck in the full rich position, or both. You could also have a float that's partially filled with gasoline and unable to exert enough force on the fuel inlet needle valve to stop the fuel flow when necessary.
Jerry

Sounds like you've touched on about everything it could be. Are you using fresh fuel?

I checked over the power valve and it moves freely. However I did find something that didn't look right, the end of the power valve that goes to the check ball is split open, and looks a bit mangled. I couldn't get a great picture but I think this one will give a good idea how it looks. I'm curious if this is how it's supposed to be.

There were two types of ends. One like you have (if I were you I'd take fine sandpaper or a fine tiny file and make the area where it has mangled at the very tip straight) and the other which resembled a solid brass rod. That tip goes down and pushes the power ball of its seat allowing more fuel to flow into the mast. Where yours is flanged out, it might hang up on the hole in the mast. But as rich as these are known to run, some might argue that is a good thing because it would keep yours from activating the power system if it is hanging up. From what I've seen, the solid rods were used in the later model carburetors and the ones like you have were used in the earlier models...but with all the stuff done by rebuilders through the years, you never know what mix of parts you may have.

The actual "power valve" is the spring-loaded check ball that piece contacts when there's low manifold vacuum and the spring above the piston pushes the ball off its seat. The V shape allows the plunger to center up on the ball. When the ball is pushed off its seat the main jet is bypassed and the mixture goes full rich. Sometimes the ball and spring gets gummed up and can't seal. Also check the carburetor base gasket to be sure there's a slot that aligns with the vacuum passage that connects to the power piston and overcomes the spring pressure.
Jerry

Jerry is right...the plunger is your power piston. He also made mention of a really important fact. The important gasket hole will be the one between your manifold spacer and the throttle body of your carb. The gasket provided in most rebuild kits doesn't have the proper hole punched and you don't get vacuum to the power piston as a result. Also...back late summer I did a lot of work on these carburetors and posted all of it. If the air horn is warped (and it probably is) you may have loss of vacuum which will cause the power system to not work correctly.

Here is an image of your vacuum passage hole. And here is an image of the gasket you'll get in most rebuild kits. You can see why it doesn't work. Your power piston will never get pulled up off the power valve ball and you will run as rich as possible all the time.

Thanks for the info, the engine is running incredibly rich all the time so I'll definitely check that vacuum passage next. I'll also file that side that's flanged out a bit to make sure it won't get hung up. I also looked up the float level and adjusted the float to 1 9/32" It was a bit higher before the adjustment so maybe that will help too.

When you say "a bit higher" do you mean it was sitting at more than 1 9/32"? If so, that would have lowered the amount of fuel in the float bowl and made the carb run slightly leaner. If it was sitting at less than 1 9/32" the opposite would be the case...since this measurement is made with the float sitting on top of the needle, gasket in place.

Ideally, the fuel level in the float chamber should be almost- - - -but not quite the height of the fuel nozzle in the venturi. That way, just a little vacuum developed by air flowing through the venturi above idle speed begins to draw gasoline into the airstream due to the vacuum developed by the airflow. If the fuel is at or above venturi height, it dribbles into the air stream all the time- - - -including at idle. If your truck has an altered stance, like the goofy-looking bumper draggers do, you might have to lower the float level slightly to compensate.
Jerry

There was mention of difficulty finding a new bushing for the points connection. You can buy new ones from Steiner tractor parts.

I had the same problem running pig rich that I chased for a while, took the truck to a carb shop they replaced the power valve reset the timing( I messed up chasing the problem) and it now runs like a champ.
good luck

I just put the carb back on today, also cleaned the whole thing while I had it apart. I checked for that vacuum passage and it is lined up. Took it out for a test drive, and I'm thrilled to say it's no longer running rough! It's running just fine, I was so excited I even drove around town for a bit. And more good news, the plugs look like the mixture is good as well. I guess it was that power valve that needed attention.

Thanks so much for your help guys. I think I know twice as much about this engine now then I did before this issue started!

Ford called that same system an "economizer" and it consisted of a screw-in device about the size of a quarter with a rubber diaphragm and a cone shaped valve in it. A spring held the valve in the open position and engine vacuum would overcome the spring and hold the cone plug closed. Anytime vacuum dropped below a preset point, the valve would open and bypass the main jet(s) to provide a rich mixture. Ford (and Holley) made several valves with different spring tension and different orfice sizes to control when and how much enrichment was available with the valve open. That feature made those carbs more tunable that Rochesters, where the power system was more of an on/off situation.
Jerry

I had a similar issue with 1949 3600, 216/235 back in 76'. A little sand got in the Rochechester. It slowed the gas flow then stalled. Ya wait and it fires right back up.