The Stovebolt Site Forums The Shop Area Engine Shop 216 problems.

Hello. I have a 1951 chevy 3100 panel that has been sitting for 30 years.
I got the engine to fire up But it pops trough carb. If i give it a little gas and hold it steady it runs very Good, But if i give more gas or try to drop it to idle it pops and eventuelt dies. Any tips? I think all the valves closes AS they should. Then im left with timing issues or could it be that the carb needs rebuild? Im thankful for any tips:) My first Chevrolet👍😁

Stovebolt engines that sit idle for a long time are really bad about getting sticky valves. That's particularly true if gasoline is added to a fuel tank that has been sitting empty for years. Gum, varnish, and other byproducts of fuel that has evaporated are suddenly dissolved and ends up causing valves to stick in their guides. Be sure you're using fresh gas from a clean temporary tank for the initial startup and run-in, and clean or replace the vehicle's fuel tank before trying to use it. Soaking the valve guides from the top with a penetrating oil such as KROIL, PB Blaster, spray carburetor cleaner, or whatever similar product might be available to you is a good idea, but the only sure fix for sticky valves is a cylinder head rebuild- - - -that consists of regrinding the valves and seats, and cleaning out any sticky deposits in the valve guides.
Jerry

Thanks for your answer. I was also thinking it could be a sticky valve. But i removed the valvecover and inspected the head when running and it looks like all the valves move as they should. I have done the mistake by filling the gas tank with fresh gas but using a filter between pump and carb, maybe that helps?. I ran fresh fuel out of a can the very first time i started it and it was the same. Can it act like this if the carb needs cleaning or is it only valve sticking or ignition timing it could be?

Since a sticky valve only needs to stay open about the thickness of a strand of hair to cause a backfire, just watching them move doesn't accomplish much. At normal idle speed of 500 RPM or so, each valve is opening and closing approximately four times a second. The chances of catching one actually failing to close all the way and causing rough running or backfiring is pretty slim. Gummed-up valve guides caused by a dirty fuel tank usually happen after the engine has warmed up and then cooled down, and a filter between the tank and the engine doesn't seen to help much. I'd suggest using a clean auxiliary fuel tank and adding a healthy dose of lacquer thinner or some other type of strong solvent to the fuel for your next run, and be sure the valves are adjusted slightly loose, then run the engine for several minutes at a fast idle if possible (750-1000 RPM) . A little valve noise is better than getting valves stuck and possibly bending them. The intake valves and pistons are a close fit, and a seriously stuck valve can come into contact with the top of a piston. It's impossible for pistons and exhaust valves to meet because of the shape of the combustion chamber and the angle of the valve.
Jerry

Could have a burnt valve. Perhaps that was one reason it hasn't been run. Would also suggest checking the valve lash, or clearance between the valve and rocker arm in case one might be too tight.

Also, possibly a pair of crossed spark plug wires or bad distributor cap.

But it runs good when i hold steady gas. But when i release the gaspedal or press it it starts to pop. I made a crappy video so you guys can hear it yourself. Hope you can hear it. Its made with a old phone



I think it runs a bit better today but it can just be my imagination. Under the carb on the intakemanifold there is a vacuum port i guess? where should it go? It is just open on my car..

The vacuum port is just open? That's an issue... and will certainly foul up the idle mixture. From what you describe, I understand it's the port on the outboard side of the intake manifold, below the carb? That port should have a rubber tube that routes to the vacuum wipers, if the truck has them, or simply have a rubber cap closing off the port, if no vacuum wipers.

To see if that's at least part of the issue, close off the vacuum port (you will probably need to adjust the idle speed screw to keep the engine running), and double check the ignition timing. If you have an issue keeping the engine running, check the adjustment of the idle mixture screw by gently closing it (not too tight, so that you don't damage the needle) and back the screw out to its nominal setting, which should be about 1-3/4 turns out from the closed position. It is certainly possible that it was misadjusted to compensate for the vacuum leak at the open port. If so far, so good, run the engine until hot, adjust the carb idle mixture screw for best idle at about 500 rpm, and readjust the idle speed if needed.

The misfire that occurs on acceleration captured on the video and the fact that at higher RPM, the engine seems to run fairly steadily suggests the vacuum advance on the distributor may not be working correctly. If the vacuum advance mechanism is working, you should see it rotate the distributor slightly when you open the throttle from idle.

Still having issues? I suggest pulling the valve cover, inspecting the pushrods and rockers, and adjusting the valves to spec as a next step. Initial setting of the valves can be done cold (add at least 0.002" to Intake spec and 0.003" to Exhaust spec), but final setting to spec is done with the engine fully hot (intake 0.008" and exhaust 0.015").

BTW, if you haven't found the "vehicle information kits" on the GM Heritage website, they have a wealth of information on the original configurations of these vehicles. Here's the link for the '51 Chevy trucks: '51 Chevy Truck . Engine information starts on page 135.

Hope this helps!

Hello again. I have now blocked of the vacuum port under the carb and the engine is now idling but still a problem when i try to rev it. How much is the distributor supposed to move when i rev it? i can move it with my hands but when im revving it it sometimes moves just a tiny bit and other times nothing at all.
I took the vacuum pipe of the carb and tried to suck on it and it did not have a vacuum leak from the carb to distributor. i was not able to move it with vacuum from my mouth either. Could it be a carb problem or is it the vacuum advance? I will make a video to you can see how much it moves

At any steady engine speed much above idle, the distributor housing should move several degrees counterclockwise, and stay there until the speed drops again. It sounds like you have a leaky advance diaphragm. The old school method of checking a vacuum advance was to try to blow cigarette smoke into the tube and see if it came out of the housing, but trying to find a smoker to assist with the test is getting difficult these days. Try removing the tube at the distributor and attaching a vacuum gauge to it. There should be no vacuum reading at idle, and almost the same vacuum reading as can be measured at the port you plugged with the engine speed at a steady fast idle (1,000 RPM or more).

Plenty on Vapers out there. Find one of those guys.When they exhale, it looks like their Honda Civic is on fire. Be prepared to start with the rudimentary basics as most of them do not think like people do.

here you can see how much it moves. i will try the smoke test

Yep, it looks like you've got a leaky advance diaphragm There should be a little more movement, it should start moving sooner, and it should stay turned as long as the RPM is steady.
Jerry

Hello again. I have now testdriven the car a little bit. It drives Good when i slowly give gas. But when i step hard on the gas or rev it hard, it pops and coughs. Do you still guess its faulty vacuum advance? Or Does the carb needs rebuild.

Sounds like the accelerator pump is disconnected or worn out/needs adjusted. Rebuild kit should have a new pump in it:)

I think it is a carb problem to😁 so a rebuild kit is ordered. But can the acc pump be disconnected? How do i see that?

How old is your gasoline? You might be surprised at the improvement if you’ll run fresh gas in it.

The gas is new. Drove it 16km today. Run like crap when cold, much better when its wa.