running poorly - F-head

Correct me if I am wrong, but I believe the L-heads would do that also.

 

Ok, I have 100 psi compression on the front 2 cylinders, and only 60 psi on the rear 2. Looks like the head gasket theory may be correct......
I don't wanna do a head gasket...

 

No.
It does idle well,but falls on it's face after that.

 

So, I think I'm going to have to replace the head gasket - any shortcuts or tricks out there?
Meanwhile, my plan is to start gathering parts to complete a 4.3 swap - I already have the motor mounts, radiator and dual exhaust for it. The 4.3 is complete and running (fuel injected too) from a full size chevy van. So all I should need is the adapter plate from chev to t-90, a flywheel and clutch - and a bunch of time to swap over the wiring harness and computer.

 

O.K. so I removed the cylinder head - man is it filled with gravity!
removed the head gasket and cleaned up the surfaces.... it appeared to be a bit damp between #3 & 4.
Installed a new head gasket and rocker cover gasket, installed the pertronix unit (again). Now all that is left is to install the upper rad hose and heater hose, put on 2 new belts, and see how she runs (after refilling the coolant of course...).
It was way easier to tighten the carb with the valve cover removed - I am pretty sure it was not tight enough before...

 

Don't forget that there's a hidden head bolt under the carb, inside the intake manifold!

 

No Joy here.
It starts and idles, but is not running properly - ran it up to temperature and found it is surging when the throttle is held at anything over 1300 rpm or so - it will rev up, but will not hold a steady rpm. Kinda touchy about the initial acceleration too - it will stall out unless you really rev it. Haven't done a compression test again at this point, but I do now have a very noisy tappng from under the rocker cover that wasn't there before. I give up.

 

Beware of overtightening the carb - it can bend the flange ears down and then the base is not flat. If a previous owner did this, it coud be causing an air leak. Quite a common problem. You might want to check the base for flatness. It can be filed flat if necessary.

Pete

 

sounds like you need some new rings atleast-- the 'running but with no power' is exactly what mine was doing-- it'd idle pretty well, and sort of rev-up, but it had NO power-- not to mention going through a quart of oil every time I filled the 10 gallon gas tank. : P

 

ok i was gonna put my 2 cents worth in yesterday and the last thing i saw was you were gonna pull the head,noise more than likley a valve out of adjustment,as far as the lack of power no one has mentioned fuel pressure ,new fuelpump? i cannot rember even so you may have worn fuelpump lobe on the camshaft,rare but it happens,check your fuel psi either by a gauge or an electrical fuelpump and a gallon of gas in a can ,this will eliminate the entire fuel system,i still say this thing is starving for fuel,sorry to be so long winded but after reading 11 pages,like i said my 2 cents worth,hope this helps

 

WHOOOOOOHOOOOOOOO!

IT LIVES!!!!!

After replacing the cylinder head gasket and making a coolant leak in the process. I set the intake valves tonight and it made it a touch quieter, but still not running right - went back thru EVERYTHING. I figured since swapping the carb didn't make a difference, I would swap my old carb back on.
I'll be damned if it doesn't run like a champ again.
Even had to take it out in the snow to really see - with another Jeep (just in case)
yeeee-haaaa!
(by the way, the Rubicon really is a big grader, and my little F-head did just fine pulling him out of my way)

 

congrads

 

WOW. Never say die!

Very happy for you!

Since it was apparently the carb, I went back over your posts and see it was a YS. Just for yuks, check the acceleration pump diaphragm - it is under the cap on the side of the body, that has four screws in it. A leaky diapragm there causes weird problems. Just wondering...

Congrats on your stick-with-it-ness.

Pete