running poorly - F-head

Like Sparky says, a minor leak may not show until the engine is put under load, and then it stumbles.

I could easily be wrong about this idea of a leak, but the symptoms you describe could fit pretty well.

Pete

 

Pertronix does recommend a ballast for non-race apps less than 8 cylinders. You might try bypassing the resistor just to see. I swapped an engine out of my 3B because of a bad one (LONG time ago)

 

Well, the next step is the distributor - no ballast resistor on the coil wire presently - I double checked that when I installed the Flamethrower coil - it apparently needs 12 volts all the time.
I'll check timing etc. first, then if I have to, I'm gonna swap back to points and see how she runs.

Is there any ported vacuum source on the F-head intake at all? With the military carb, there are no vacuum lines going to the carb at all, and no change in vacuum or engine rpm when I sprayed carb cleaner ummm....everywhere........(carb,cylinder head,brake booster, and anywhere else I could think of...)

BUT.....
It is currently -29 degrees celcius outside (-21F) and I have no heat in my garage, so she'll have to wait a bit....wind chill is -37C (-36F).

 

Hmm.

If it idles ok, but falls down coming off-idle, that sounds like you are opening up a large vacuum port. But then, I'm old and blind and can't hear very good either. I am probably wrong.

 

I had a problen with a poor ground to the distribulator. (sp) I had to clean the rust and scale off the adjusment plate on the bottom of the dist' and clean the bolt and when tightened down, then I could get a reliable spark. I rigged a jumper to the dist body and loosened the bolt to time it. You might check the other grounds too.
I usually figure on the fuel that if I can see fuel from the accel pump in the carb throat when I pump the throtle linkage the fuel is there and the problem is somewhere else. The bad ground in the ignition circuit was a real bugger to find, I was considering re-engining at the time.
good luck

 

Unfortunately, with the Carter YS carb, I cannot look down the carb throat to see if it is getting fuel...
http://www.farmersservice.com/images/carter4s.jpg
It has a 90 degree bend in the upper body - and there is no
"traditional" accelerator pump or linkage that I can find.
Gonna go thru the distributor the next chance I have - I'll clean up the ground surfaces and check the timing, etc.

When the Jeep was running really well, I used a vacuum gauge to set the timing - basically set the idle speed and mixture, then advanced the timing to get the highest vacuum reading - 17" was as good as it ever got, and it ran AWESOME. At that point I was running 36x12.50R15 super swamper TSL's and it pulled them decently enough......

 

Gonna drop in a complete points style distributor (used one I found up here) instead of messing around with swapping out the pertronix unit - if that fixes it, GREAT! but, I'm not holding my breath.

 

Well, didn't get the distributor yet, but swapped out the pertronix unit with the old points. I took a look at the advance weights and springs while I was in there - they appear intact and not siezed. the upper piece that the rotor clips onto has 2 slots where the advance weights engage -they seem to be worn a bit at the edges - maybe allowing too much travel??
Jeep starts and idles o.k. stumbles a bit at part throttle, but sorta cleared out after revving the snot out of it in the garage (got a little hazy in there...)
Went for a drive to the gas station - put $20 of 87 octane in it- Stalled twice on the way there - about 6 city blocks - had to pull the choke part way to get it to start again - drove home, and at just off idle, it was stumbling a lot, but seemed to pull fairly hard when the gas pedal was floored.
?????????????????

 

Man, you are setting records here for the most posts ever, I'll bet! Maybe we should start taking bets, have a pool on what the fix turns out to be! We are rooting for you.

I gotta say it again - the pulling of the choke, and running when 'floored' are classic signs of vacuum leak. The stumbling and stalling seem to remain at 'high vacuum' situations, e.g. part throttle under load. But I have been wrong before...

You already know this I'm sure, but in your position I would be ruthlessly methodical at this point. Do one thing at a time, follow it all the way through, and very carefully and thoroughly make sure it is totally correct, by the book, before moving to the next item. Doing more than one thing at a time increases the unknown variables. You need to isolate and pin down the systems, making absolutely sure each item is correct, one by one.

Trap that gremlin into a corner and pin it down!

I feel for you! But the laws of physics will eventually prevail... gas/air/spark in the right proportions, and it HAS to run. And will!

Good Luck,

Pete

 

As Churchill said, I think it was, don't argue with a man who buys printer's ink by the barrel. Or in this case, runs a forum! ;-)

No one can challenge you on a 51 page thread, I don't believe. Wow.

Pete

 

Been a while since I proved my ignorance; might as well jump in. Any chance in all this that we've solved one problem and substituted another? Sparky's carb change involved an incorrect base gasket, as I recall. Simple, yet hard to see, until (seemingly) everything else was elimanated.

Doesn't seem likely that a major problem just shows up one day without a corresponding event to promote it. Wear and tear sorta stuff "should be" more gradual in it's appearance. I'm betting some "fix" here has merely masked another root problem. It's there, somewhere. Time to go back to basics. Really basic. I'd start with a vacuum gauge and a long hose to connect it. See what happens under different circumstances other than just in an ice cold garage at idle and no load. And so on.

Well there now, see? I'm as ignorant as ever. Good luck; it will be interesting. Sparky's problem certainly was!!

 

not sure if I read it or not, probably dreamed the whole thing.

Did you say you rebuilt the carb? Any possibility of a screw missing in th inards somewhere that could be causing your off-idle stumble? Or maybe the bushings have started to go away where the throttle shaft rubs causing a leak there? Although if that were the case I would think it would lean out your mixture at idle too.:?

Had an old ford 223 6-cylinder that sucked in part of the base gasket once, on the back side closer to the valve cover where you couldn't see it 'til you pulled the carb and looked. but that would cause the over-all lean mixture situation, too.

 

195 degree high flow thermostat - temp was up to 195 when I took it to the gas station last night.
The engine seemed to smooth out a bit at mid to higher rpm with no load when I sprayed carb cleaner near the 'T' fitting on the cylinder head just below the carb. As I have found, this fitting is for the pcv valve vaccuum source (which is not connected on mine, I have the pcv tube just routed up by the firewall for now) - I have the vacuum booster for the power brakes running off of this fitting, and the other side is plugged off.
As for the carb, I installed a N.O.S. military surplus unit - throttle shaft and fittings were all good.