Can't get this thing running right...very frustrating!

F head starts great and will idle but will not take acceleration. When giving it throttle, it bogs, sputters, misses, and backfires through the carb. I've timed this thing many times now by ear and with a light. I've tried two distributors, the original (with new points/condenser) and a new electronic ignition one. No change.

I've tried two carburetors, the original (rebuilt twice with two different kits) and a brand new Solex, no change.

I've lashed the valves multiple times.

The fuel lines, fuel pump, and tank are all new. I am not (yet) running a filter and I have not tried a fuel regulator but I can pick one up if anything thinks that fuel pressure might be an issue.

Everything in this engine is brand spankin' new, all completely rebuilt and everything replaced new. I don't freakin get it and I'm losing my patience. Any advice? At this point I'm willing to try anything.

Thanks!

 

x2, also check the distributor bushings. Excess runout caused a similar issue from variable point gap due to the wobble.

 

I've tried a brand new distributor with electronic ignition and it makes absolutely no difference. One weird thing, though, is that the new distributor was keyed backward from my original. When I built the engine, I keyed the oil pump so that the distributor meshed with it having cylinder #1 around the 5 o'clock range. The new distributor puts my #1 cylinder at 11 o'clock. Don't think it matters I just found it odd. But the new distributor changed nothing in the way it runs.

 

Vacuum problem? Vac advance I suppose. Not mechanical advance, right? Maybe the vacuum line for the advance is hooked to the wrong place. Just guessing.

 

Could your cam timing be off?
Just a WAG as I know nothing about F heads-is it a chain or gear driven?

 

Not vacuum advance, mechanical. I'm hoping the cam timing is correct, I was VERY careful when I assembled this thing, followed directions from several sources. It is gear timing, not chain, and I was careful to ensure the markings on the cam and the crank lined up when I assembled. Not saying I didn't make a mistake but, again, I took extreme care to make sure it went back together correctly.

Another funny thing is that it ran this same way before I rebuilt it, although it smoked like a chimney because the rings were definitely shot. The cam is brand new as are the valves. In fact, everything is brand new except the crank, although it was turned and inspected at the machine shop.

Vacuum leak is possible but I went through all the vacuum lines (all hard steel lines like original.) New OEM PCV valve as well.

Frustrating.

 

OK, some more information to digest. I hooked a vacuum gauge into the port on the head below the carb (where the vacuum for PCV runs) and here's what I learned. At idle it reads normal range but flickers between 20 and 22. When I rev the engine, it drops fast to the 14 range. This usually indicates ignition timing is off but how? Like I said, I was careful to line up the markings on the cam and crank sprockets, should I pull the thing back apart and check?

I guess I can pull the grill and radiator and then remove the front timing cover to inspect that I have it right. Not looking forward to doing that, though.

 

I don't think that's a problem, as I recall, 20-22 inches of vacuum at idle is just fine, and it should drop when you throttle it up, dropping to 14 doesn't seem particularly excessive to me. I would note, I've never actually worked on an F-Head, but those numbers don't sound too off for a carbureted gas engine of any type.

 

Are you sure its running on all 4 cylinders? One time I had two ignition wires switched on the wrong cylinders. It would run exactly as you described. You would be surprised how well a F head will idle on only two cylinders.

 

Hmmm...here's something interesting. I put the new carburetor back on (Solex) but this time I put on a new carb gasket and it runs much better now. I can rev it and it doesn't sputter anymore, however it still skips a heartbeat every once in a while at high RPMs. Running VERY rich, though; it stinks of gas and smokes. I've twiddled with the carb adjustment but can't seem to find a sweet spot.

Weird because I've gone back and forth between both carbs multiple times, the only thing I did different was a new gasket even though the old one was still new.

I guess I'll search the forums now for how to properly adjust a Solex.

 

With the solex carb.,if I recall, you need around 1 3/4 lbs to 2 lbs pressure. You might need
a fuel pressure regulator.

 

Your initial post sounded to me exactly like a vacuum leak, and quite possibly at the carb base. You seem to be confirming that possibility, but it's hard to figure since you've changed carbs. But I'd continue to look for a vacuum leak.

Overtightening can bend the mounting ears - check that the carb base is perfectly flat... Also if you have mechanical vaccuum pump/fuel pump, I'd check the vacuum diaphragm and check valves.

 

Take a can of spray carb cleaner or starting fluid, and spray it around the base of the the carb when the engine is running. If you have a leak, the idle will change when you spray over the spot where the vacuum leak is.

Have some one turn the engine over with the cap off so you can observe which way the rotor turns. Hook up your vacuum gauge again, and adjust the distributer till you have the highest reading at idle, then turn the distributer very slightly in the direction the rotor turns which should retard the timing a little, and should be the optimum position to lock your distributer to.

I don't have a Solex, so someone else will have to tell you what the mixture screw should be set to. Probable 1 1/2 to 2 turns out from being gently seated.

 

I tried the old carb with the new gasket as well and it still ran like crap. So I was chasing two variables -- bad carburetor and bad gasket. Possibly three variables if the old distributor was malfunctioning. I don't think I have any leaks anywhere else, the vacuum gauge reads fairly steady now. I still flickers slightly but that may be the gauge, I noticed it is very sensitive to vibration. The elbow fitting that screws in to the head under the carburetor cracked when I tightened down the vacuum line so I'm wondering if it was already cracked and leaking -- possibly a 4th variable.

But it runs now. I probably need to tweak the timing some more and fiddle with the carb settings but at least I am down to a few knowns rather than a multitude of variables.

 

Apparently that little elbow fitting that comes off the head just beneath the carburetor is a 1/8" NPT male to 1/4" tube (7/16-24 thread) female. More apparently, it is the rarest item on the planet Earth! Nobody has one nor have they ever heard of one -- Napa, Advance Auto Parts, Autozone, etc. I even Googled it and can't find one. For those who have extra Jeep parts laying around, they are like gold and more valuable than an early CJ passenger side seat. For those who don't have extra parts laying around, DON'T BREAK IT!

 

The part number for your elbow is a Weatherhead 402x4. The NAPA number is WH 402x4.

 

Yeah Napa was the only place I went to who even knew what I was showing them (I had the old one in hand) but all of my local Napas were out of stock. The other auto parts stores didn't even know what I was showing them but they let me look through their sparse selection of fittings to no avail. I was just frustrated today as it seemed I was trying to find one stupid little part that doesn't seem to exist anywhere.

 

Are you talking about this one?


might try a hardware store brass fittings section. (Home Depot, Lowes, Ace)

 

Yeah that's the one. I haven't tried any of the hardware stores but that's a good idea. I ordered one from Napa, should have it by Christmas.