Working on my brother in law's 28 Chevy. New valves, seats, carb rebuilt, new plugs, wires. Timing is set with rotor point to number one. Starts right up and runs good for about a minute and then starts to misfire. Pulled the plugs and they are fouled with carbon. Cleaned the plugs, adjusted the carb to run lean and still have the same problem. Any suggestions would be a big help..
I would doubt new plugs would carbon up so quickly.I would suspect they are oil fouled. Do the plugs clean up with varsol? Have you done a dry and wet compression test?
New coil or the old one?
Are you advancing the timing after the engine starts?
Plugs clean up real well with varsol. Have done a compression test on all cylinders with 50 lbs in each. Coil is three years old but has good spark to the plugs. I advance the timing on the steering column once it starts. The later really doesn't help..
If advancing the timing doesn't seem to make much of a change perhaps the timing is not set correctly. It should fire the #1 plug just after tdc with the timing fully retarded, just like a Model T or any other old car. Have you checked the timing to see when it actually fires? Way retarded timing will foul plugs.
Thanks Royce. Will do. Probably not until tomorrow because it so hot...
If the engine runs long enough a sure sign of late timing is overheating.
Does it smoke or does the exhaust smell right?
It could also be as simple as a bad condenser.
Craig. gets hot and boils quickly. Smells a little like gasoline...
Oh boy.......lot's of different scenarios there.
I'd start with the timing. It must be VERY late.
Does the engine sound right? Like it's not laboring?
Just for the heck of it are the spark plug wires WIRE wire?
Who rebuilt the carburetor? Sounds to me like it's loading up and flooding.
Engine sounds good. New plug wires correct for the era. Carb was rebuilt professionally in the northwest. Carb isn't flooding.
Depends on the carb. Is this the carb that was on it before?? If not, and it has a Zenith S04 on it, they were used on a lot of cars of that vintage and the jets can be way off for the necessary application. This should be a 28 4 cylinder. Some of them also used a Carter Carb. Which one is it?
If it's the Carter RXO, it has a small well jet that is easily forgotten. It could be the wrong size or left out. Your diagnosis indicates a fuel problem--Too much. Backfire can be caused by too much fuel as well as timing. You said it runs good then dies with the plugs blackened. Take the advice or not.
This is so simple I maybe shouldn't even bring it up, but............have you checked the choke to make sure it isn't sucking closed when it is running. That can happen pretty easily on some of the Zenith's that don't have a spring to hold them open or that aren't attached to the choke wire. They will close due to the vacuum and then after the engine stops pop back open so you don't notice what caused it to run rich and then stop. Might be something to check. I dunno.
I recently rebuilt a Zenith S04 for somebody for a 20's Chevy. I test run them all on a Ford 134 cubic inch engine and if it is this one it should be OK but if there is a problem with it, send it back. I dunno if this is the one or not, I've done a bunch of them in the last two or three years. They are a pretty simple carb, the main problem with them is usually the needle and seat - which I replace with a modern set. There is only one adjustment on them, plus the idle speed screw.
Thanks everyone for the suggestions and help. Checked the jet and is ok, checked the choke and is ok. Here's my question, on a model T I always set the rotor so that the it it coming up on number one at TDC. I tried this with the Chevy this morning and still got a misfire. It is a royal pain in setting this distributor as it meshes with the cam. It is either too bit too advanced or a bit too retarted. Do I need to set the rotor so that it is pointing directly at number one when number one is at TDC?
Are you retarding the ignition exactly the same way as you will do on a Model T???
Because then it is obvious that the timing is the problem since with a Ford - fully retarded is at the top - BUT FOR CHEVROLET IT IS EXACTLY OPPOSITE!!!
So when you adjust the timing - set the ignition lever at the LOWEST position, turn the engine to be at TDC at cylinder one, loosen the distributor and turn it back and forth until it just opens the contacts and the arm points to cyl #1 in the head of the distributor.
Now start the engine and once it fires, advance the ignition by pulling the lever UPWARDS!
Charles, get the front piston up on the compression stroke. Then, using a piece of wire down a spark plug hole, watch for when the piston JUST starts going down and stop.
Loosen the distributor, turn on the ignition switch and gradually turn it until the points JUST open. You might see a small spark at the points when they open. That's when the spark occurs.
It's possible the distributor gear is a tooth off at the cam as well.
You'll get it!......
Thanks again to everyone. I am thinking I may be a tooth off. will keep you posted..