Chevy 235 never ran right

I have a rebuilt with less the 10,000 miles 57 235 thats in my 37 chevy p/u thats never been what I call right from day one,its always had a little pop out the exhaust that never went away even with all ignition parts changed over the last 10 years. It had some weak valve springs so they all got changed and still the same so I was thinking that maybe a weak spring caused a valve to burn but 150 PSI in all cylinders so I am about at my wits end on what is causing the pop out the exhaust,reman distributor a few years ago along with new wires,cap and rotor along with the usual points and plugs. Never cared much for the Rochester carb and thinking about a carter YF and one of GMC Bubbas electronic distributors real soon but I need some ideas on something I might have missed.

 

valve sticking?

 

Would a sticking valve show up in a compression test,it had 150 on each cylinder.

 

Did u try the sheet of paper thing at the exhaust to see if a valve is sticking or burned? If the paper gets ****ed in intermittently then start pulling plug wires one at a time till paper is not being ****ed into pipe.

 

This is when it's idleing?

Small vacuumn leak where the intake meets the head is my guess. You know how to check for that with carb cleaner or propane, right?

 

Its doing it while idling so I will check for va***n leaks,being its a 57 motor the carb is leaning towards the front some since the intake was designed for the motor to sit lower in the rear and its not in the 37 ch***is and looking to find a 37-9 intake so I can level the carb. It almost goes away when the motor is warmed up and the intake is not heated so is that something that should be corrected before doing anything else.

 

I think you just found it: carb heat. what do you have for intake and exhaust?

 

maybe a warn cam lobe?

 

If you don't own a vacuum gauge, it's time to buy one.

 

I've worked on lots of the 235's and from what you are saying my diagnosis without any further information is a valve tick. Have the rocker arms been adjusted correctly? Engine idling at operating temperature? Unless I hear more I think that may be what you are hearing.
Normbc9

 

It has fenton headers with a full dual exhaust and a stock intake and carb,I filed the tips of the rocker arms and adjusted the valves while it was running and after I changed the valve springs checked them again and they were ok. I am planning on changing the intake to a 37-9 to get the carb to sit level and will get a heat kit and the more I think about it I dont remember it running like this with the stock exhaust manifold,it was never driven on the street with the stock exhaust manifold and it got the fentons right before I started driving it.

 

if you dont have a heat plate get one. check this out from inliners:

The most frequent complaint I have is from members who complain that since they’ve installed their multiple carbs, the engine hesitates and stumbles at low speed on initial normal acceleration even after warm-up. The most blamed culprit is the darn Rochester Carburetor. Usually it is falsely accused!
Usually when installing dual exhaust manifolds or headers, the production exhaust heat supply to the inlet manifold is eliminated because (except Edmunds and most recently Clifford) there’s no provision or instructions to provide heat…Why?? I don’t know and could only guess. In any event heat will be required to achieve good driving response and reasonable fuel economy. Here’s why:
As liquid fuel enters the manifold from the carburetor, the vacuum vaporizes the fuel and causes a chilling effect on the walls of the manifold much like the chilling effect of spraying an aerosol on your skin. Now you have a cold manifold. If you do not supply a continuous supply of heat the manifold will remain cold and even build frost in some conditions. At this point, if acceleration is attempted, the vacuum will drop, fuel will no longer vaporize, and will condense on the cold manifold walls until they are fully saturated with wet fuel – this takes about three seconds, during which time no fuel is going into the engine ( and thus no power or a "sag") After the walls are fully saturated with fuel the air flow finally picks up and floods some of the cylinders but not all of them because liquid fuel is notoriously bad for equal distribution.
More fuel (bigger jets) will only slightly help this problem and actually worsens the over-rich condition and spark plug fouling and fuel economy.
The solution: Moderate, and continuous heat supply to keep the walls of the inlet manifold warm and fuel in vapor form. Exhaust heat is fast but requires a ****erfly valve in one manifold to force the exhaust flow. Water heat is slower but very clean and not corrosive to aluminum manifolds. This method utilizes the water pump to continously supply warm water to a p***age underneath the manifold. It is sometimes necessary to weld a tube to the manifold but be sure to obtain intimate contact between the coolant and the manifold wall and floor. Simply tack welding a closed wall pipe to the bottom of the manifold will not result in sufficient heat transfer.

 

Don't recall V-8 intake manifolds having a heat source to keep carb warm, can you explain why they don't have this issue? Olds rockets, Pontiacs have an intake that is above the valley and would only get heat from the heads, so why don't they have this issue?

 

Lots of intake manifolds have heat crossover p***ages. It was common on high mileage engines for the crossover to completely plug up with carbon and cause cold stumble problems.

 

I don't think the carb on an angle is your issue. I still think vac leak. A couple of clamps needed to be modified when I put Fenton's on mine with the stock manifold. They were sitting at crazy angles and did not look like the clamp action was right.

A vac leak can get a little better when the engine warms up and things expand.

I have run the stock intake with no heat and also the Offy 2 X 1 with no heat. I've been driving this 235 for 20 years, I don't miss carb heat and we have high humidity and low temps. Perfect conditions for icing. I do have a Jeep that ices and also had a 300 six in a bronco that was really bad for icing and I need to run a manifold stove on both of them to get hot air to the carb. I just don't have a problem with the Chevy.

Good luck, Frank

 

On the subject of heat on V-8 manifolds - I don't know of any older stock (pre-65) O'head V-8 without exhaust heat routed from the head under the carb with a heat riser valve incorporated to help it along.

Plus, on an I-6 the intake hangs off the side of the head keeping it away from most of the heat radiated off the top of the engine - most of heat from the exhaust manifold under the intake on a 6 is lost without a direct connection.

A heated manifold is necessary for normal street driving and it has to do with not only outside air temperature but also with relative humidity.

 

X2!! Everyone that comes on here with a running issue on an internal combustion engine should have one...know how to read it..Before throwing any parts at the problem....just saying

 

Reread the original post please......He is complaining of a "little pop out the exhaust" that never went away.....This could be from a number of things.....The valve springs have been replaced so the valves have been adjusted, sticking valves...will show up during a compression test as a slow rise in pressure compared to the other cylinders. Pooling of fuel in the intake will show up either on the plugs(two center ones will be fuel wet) or as a bog while driving. I vote for a vacuum leak (carb spacer?) OR an exhaust leak. I had a 250 that had a "tick" at times, turned out to be an exhaust leak at the #3 cylinder blowing towards #4. I only found it after taking off the intake.

 

Cant answer that.

Why did GM put the intake and exhaust together with a heat riser in the exhaust on the 216 and 235 and 261?

 

To carry this a step further.... If this is happening at idle, get some insulated pliers and with the engine running at operating temperature disconnect one spark plug wire at a time. You should notice a miss and hear the RPM drop. Do this for each cylinder and you may also notice that the popping stops when a specific cylinder has no spark. This may not pinpoint the exact problem but it will isolate one cylinder as far as searching for an ignition, compression or valvetrain problem or a vacuum leak.

 

To stay foucused on the derail side of this thread My 235 intake, now an alum Offy, gets so hot after a highway run, that you cannot touch it. The ambient heat in the engine compt overcomes the cooling effect of the gas vapors inside the manifold. This helps boil away the gas that leaks from the Rochesters, and helps prevent forest fires from gas dripping on the exhaust
To derail a little more, the B rochesters seem to leak where the accel pump rod goes in thru the top of the airhorn. Ya think they would have not designed that into it.

 

I vote for using the vacuum gauge. This should give you some info as to where the issue is. As far as carbs, has anyone called them ROTTENCHESTERS?

 

I am going to put a va***n gauge on it after I get off the computer and I backed off the timing some since I could never see the ball on the flywheel so its always been timed by ear,it was cutting out a little when revved up and backing off then timing fixed that. It does not idle like it has a va***n gauge and is somewhat smooth and tunring the mixture screw changes the motor but will get a reading,I have been putting up with the pop out the exhaust since it got back on the road and can live with it but somethings wrong and would like to fix it. The rochester has always leaked and thats why I want to try the carter.

 

What is the throttle position when it pops?

 

bad carb

 

I just got back in from tinkering with it,I put the va***n gauge on it and shortly after it started running very rough and popping out the exhaust even when I was giving it some gas so I pulled the plugs and reset the float and still the same. I looked in my parts stash and found a new Delco condensor in the box and installed it and now its running alot better,I set the timing with the va***n gauge and when its at the highest (21) it does not want to run the best so I set it at 18 inches of va***n and it likes it. I had the rattle I was chasing come back and now think it was spark knock and might have to run a better grade of gas even though its supposed to be a very low compression motor it dont like much advance with our ****py regular grade of gas,I bought what I thought was good ignition parts (napa) but they only lasted about 3000 miles so its time for one of Bubbas electronic distributors as the points and condensors are junk now. In a couple weeks I am going to send for a 37-9 intake and a heat kit plus rebuild the Carter YF and see how it does. I had to put points and condensors in my 65 custom 500 daily driver every year regardless of miles so tune up parts quality has gone down hill fast lately so no more points systems for me.

 

It blows my mind how ppl will just throw parts at a car hoping it will fix the problem....when they have no basic understanding of how the system works.....

 

I also pulled each plug wire off with the motor running and it made no difference as it still popped out the exhaust,I hope it was just a bad condensor and will fire it up again tomorrow and this time take it for a road trip instead of idling in the garage. I did not have any carb cleaner to check for a va***n leak at the intake but with a steady 18 inches of va***n I dont think there is a leak,what was strange is when I removed the last three plug wires it sounded funny as it seemed to make the sputter out the exhaust louder. Its strange that I cant get this motor to run right and just thought about checking the voltage to the coil and distributor which I will do as soon as I get off the computer.

 

Do you have the firing order correct?

 

Even the old low compression engines were designed to run on much higher octane than they sell today. Have you checked the dwell time on the points and set the timing where it's supposed to be using a light on the flywheel? Timing by ear or vacuum is a shot in the dark. While damper rings can move, the marks on the flywheel don't. Set it right to see if it helps. Dwell time allows the points to be closed long enough to build the electrical field in the coil. Too short and the coil won't build enough field strength resulting in weak spark. If that gets too long it can cause the coil to overheat and the points to burn resulting in poor spark. An electronic distributor removes those variables.Then try some higher octane fuel. Do the easy things first then move on to the more difficult.

You can try a carb, check intake manifold temperature, check the lift on the cam lobes, check cam timing etc.