Fhead Tuning Issues

i have been messing with this fhead for a while now, it runs ok i guess. But still seems a little rough, and i cant get a real good reading with the vacuum gauge, it fluctuates around 15-16, i have always used the vacuum gauge as a indication of how good the engine is running.

In the past i swapped out the points to petronix ignition, and had Rick rebuild me a fresh carb, been playing with it like this since last year. Spent a lot of time messing with the timing too,

The background on the engine is it was rebuilt by these guys right before i got it.
Engines - MDR Engines

Today i started to do a little more digging, i did a compression test, and cylinder leak test.

Below are the results, and pics of the plugs. Plugs look good, comp looks good, and leak down reading are within speck, but there something odd when doing the leak down test.

On cyl, 1, 3 and 4 as i turn up the leak down pressure, the leak gauge rises steadily with the input pressure gauge, it lags slightly behind until i hit the test pressure, which was 100psi, then it settles in at its resting pressure, indicated by the leak % on the chart. They look good

On Cyl 2, ( also the cyl with the highest leak reading). The pressure lags way behind, even gets stuck for a better word then pops up to the resting pressure. Almost like something leaks until some pressure is built up to seal it.

The only place any leakage is showing up is in the dipstick, which would indicate rings i think, but compression is fine

 

Is your timing stable? If not look at the distributor bushings and the advance mechanism.

You're not detecting any leakage in the intake or exhaust? Even while the leak down gauge is lagging behind (before it "pops up") in #2?

 

I adjusted the valves, timing, And carb, found a vacuum leak, it’s running pretty good now, still can’t get better vacuum. Going to run some mystery oil through the fuel and oil, think it just might be gummed up a bit

The engin has about 1500 miles since rebuild. It pretty much has sat for the lasted couple years.

 

Put new plugs in today too

 

Looks a tad rich on the plugs, but I'd be very happy to have your readings. Is there really a problem?

 

the reading are good, the inital problem was it just was not running right, could have been any of ten reasons. i did what i usually do in this case, and hook up a vacuum gauge, the readings were bad, not only low, but fluctuating bad, bouncing from 14-17. So i started the work last year, fresh carb rebuild from ScoutPilot, petronix inginion, and some tuning. It got better, just not great. i hopped back on it now and i figured id do the compression and leak-down test just to see if the engine was fresh like i was told, and i agree, the reading look good, so i went back to the basics this weekend, replaced the plugs, adjusted the valves, timing and carb again and found a vacuum leak and fixed it. its running pretty good now, better than it has vacuum reading are still lower than i like, dont really know what the cause of that is. This CJ sat for a long time, so im going to put some miles on it and see how it goes

 

Restricted exhaust? I once had squirrels completely pack my exhaust system with acorns.

 

interesting, have not looked at exhaust, i could just disconnect at the manifold to rule that out, thats easy

 

I suppose.
But my wise old Dad always told me about old vehicles, "if it ain't broke, don't fix it."

 

Still no luck, I have rechecked the compression, because the first time I did it, it was kind of quick with an beat up gauge.

New readings are even better

Warm engine. Dry test
1 - 130
2 - 135
3 - 135
4 - 130

It’s still too rich. If I lean it out it runs terrible, almost not at all. If I adjust timing to a place where it will run the leaner setting, it runs terrible. Rough missing etc.

Back where it runs pretty good, is a almost acceptable, but I know it’s not right. Vacuum is only at 15, and it’s fouling the plugs

 

no, pulls pretty good and runs overall pretty good now, just bad Vac reading, and seems a little rich
Was sitting before i got it, since then i:
replaces solex carb with fresh carter from Rick,
new points, cond, then tried petronix, and new wires
adjusted valves,

 

Sure your vacuum gauge is accurate?

If so, the symptoms could be restricted exhaust.

 

I vote for fuel pump excess pressure.

 

On a Carter YF flooding usually would show up as leakage from under the bowl.

As for timing - set it and forget it. It is a specification, not an adjustment.