78 -- 120 -- 120 -- 120

Just the other day, while running my Jeep, I noticed that when I got the engine speed up to around 2500 rpm, it would start running funny and backfiring through the carb. Up to that point it had been solid up to 4000 rpm, which was the highest I took it under load. Since there are many things that can cause this, I thought that since I hadn't done a compression check on it, I would do that and see, if per chance, I had a problem with an intake valve. The numbers in the title of this thread represent those readings.

So I added some oil to the #1 cylinder and the first number jumped up to 115.

When I first got the Jeep, the engine would not turn over by hand. I didn't want to force it, so I pulled the plugs, let some Marvel Mystery Oil soak in and eventually it finally broke loose.

The engine was overhauled, not long before I got it, mileage-wise, but the Jeep did sit under a tarp for several years without being started, so the questions in my mind are as follows:

1 -- Could I have broken a ring getting the engine to finally turn by hand? There was no noise and I didn't have to use a lot of force, so I am thinking this may not be the case, but out on the end of a breaker bar, maybe there was more than I thought.

2 -- Could the backfiring and this issue be related? I don't see how, but if in fact, somehow this is due to an intake valve issue, then maybe it would be. However, the oil test seems to prove otherwise.

3 -- Is the oil test fairly effective, or could this still be a valve issue?

4 -- Should I let it run the way it is and see if it improves after some miles are on it?

5 -- Am I even asking the right questions?? (LOL)

I know the braintrust in here will have some good ideas. Pass them along. Thanks...

 

To be an objective comparison, how much did the other cylinders "jump" with oil in them?

I have had a number of F-heads over the years, and busted rings have seemed (to me) to be a common problem in them.
Like yours, they often tended to have been "seasonal" vehicles, left idle for long periods, and I wonder if that is a factor.

Just my personal intuition, but curious if anyone else has the same opinion.

 

It sounds like it is time for a leakdown test so you will at least know if it is the valves or rings.

 

Im going to be an optimist and say its probrobly stuck rings. Id run marvel mystery oil in it and let it go for a while. Maybe a few cycles getting it good and hot will loosten them up. Try other stuff too I think they recomend diesel or atf/acetone im not sure look it up

 

I didn't put oil in them, as they were even.

 

Unca, what is the best way to perform this? The compression gauge has a release button on it, so it will hold the reading until I let it go. I have heard of these, but have not done one. Can you describe it, or give me a link? Thanks...

 

I am hoping you are correct. I really don't want to have to pull the head, but it isn't really that tough, compared to some of the heads I have pulled in more modern vehicles.

Thanks for the input...

 

I would check the valve adjustment or a possible broken valve spring as well. The backfire suggests something going on in the intake tract and not a ring issue.

 

I have a compression guage that can be used for this. You hook it up to a compressor while it is screwed in and basicly listen for where the air is escaping, intake, exhaust or from the crankcase. It certainly wouldnt hurt to try the Mystery oil or others have had luck with ATF to free up rings and others have used diesel. It could just be a chunk of carbon stuck in an exhaust valve or a stickey valve.

 

Right.

But it would be interesting if they improved a proportionately equal amount as #1 did. If so, it would suggest the specific problem in #1 is something else.

Putting oil in any cylinder will "improve" the compression.

 

I believe he put in electronic ignition/distributor. Just me, but I always suspect the newest thing first.

 

low on one cylinder and popping back through the carb says chunk a crap between the seat and the head of the valve. Try running a can of SeaFoam or carb cleaner through your running at high idle engine.

 

A couple more things I have thought of, if it's a chunk of carbon, just go out and run it. My mother used to have me go to Denver to take a trip down to Co Springs just to blow the carbon out out of her Chevy. Really, she just wanted a ride down to the outlet mall and didn't complain if I got it over 80. The other thought is to have a spray bottle of water that you can spray down the carb, Not a whole lot at a time but the steam from the water breaks up the carbon if it is the issue. I think people do similar things with Seafoam.

 

Ah, water injection. Fighter planes during the Battle of Britain had a bottle of water mixed with alcohol that had a line running to the carbs. One for each carb. The water was injected into the airstream either above or below the throttle plate in a spray not a stream and the heat of the engine would cause steam to be introduced into the fuel mixture and would both clean the combustion chamber and raise the power output by adding more oxygen and hydrogen into the fuel mix.

 

I belive in the late '50s, some of the Fords used to run a water injection system. I hope the water was injected below the throttle plate. When a carb feeezes up on you it isn't too fun. Yeah, a BTDT time. I've had carbs freeze up on VWs and Volvos. In some of the old planes, they knew how to get them to backfire so they could clear the ice out of the carbs.

 

Your opening statement "backfire through the carb" can only happen with a valve (intake) problem. You may have other issues as well but I would begin by eliminating the valve issue.