F-head wont run...

After about 4-5 yrs, im finally ready to crank the old f-head up. It wont do it though. First of all, i discovered that i had the wrong carb. Got that changed but now im unsure of whether the rebuild parts i used are correct. I want to make the YF work but the Carb shop repair kit is half the price of a Solex, and at this point those guys are the only place i really beleive will give me all the right parts for the F-head application. Opinions are greatly appreciated. Next, the -3b radiatior (Omix repro) is on backorder everywhere. So if anyone has a -3b rad that could be re-cored please let me know. Last, i dont know if my vacuum system is exactly right. I cannot find a PCV valve like the original one (threaded on both ends) and the one i have rigged in may not even be a suitable replacement. If anyone has a source and/or part number for the right pcv valve please let me know. Thanks in advance to anyone who took the time to read this.
Steffy

 

Kinda forgot to mention the symptoms: WAY to much fuel. Floats are set to 5/16 as manual says. Also, the fuel that is coming in doesnt appear to be atomizing correctly, but this could be just cause theres to much of it. #2+3 cyls are flooding horribly, and #1 cyl, judging by the look of the plug, appears to be firing, or at least burning, but very rich. The#1 plug is always dry but very carboned up. Timing is correct.

 

Inspect the needle and seat for the float. Sounds like some foreign material may have gotten lodged in there and allowing too much fuel into the float bowl. Might do a fuel pressure check and see if there is too much pressure, although I doubt that's the problem if it ran before. Sorry I can't help on the PCV part but maybe Walck's, Krage, etc. can help with that. Nickmil.

 

Very common problem. Very easy fix. First, get a carb kit from Jon at

www.thecarburetorshop.com

It'll set you back around 50 bucks, however it will have all the correct parts for the carburetor that you have, not the 'generic' rebuild kit that can cause flooding.

You'll need to know your carb number. It is on the webbing on the carb body.

It'll be 938sa or 938sc or 938sd most likely.

Adjust the carb per jon's instructions or the jeep service manual. Any other directions are for the YF used on other vehicles and won't provide optimum
performance. This is especially true of float level settings.

There are a lot of reasons why the carb wants to flood, but the most common is that the float valve was replaced with the generic float valve in a carb kit at
some time in the past. The opening on the 'generic' float valve is 30% larger than the opening on the Jeep correct float valve. Correct float valve is part of the kit you will get from Jon.

The easiest way to measure whether or not you have the correct float valve is "Kamel's 'ol quick and dirty method".

With the carb apart and the float valve removed, take the small pin that holds the float on and put it in the valve seat. If it fits through the aperture in the float valve seat then the float valve is the wrong size. If it will not fit through the float valve seat then the float valve seat is OK.

9,988 times out of 10,000 the carb will have the wrong float valve whenever there is flooding in the YF carb.

Oh, and by the way, if you have several YF's, never try to mix and match parts. They will interchange physically, but may or may not work properly.

 

WWW.DEBELLAJEEPPARTS.COM He has your pcv valves might even have an old radiator laying around ..

 

IF I recall correctly, from my past errors...

There is a ball type check valve in the standard F-head carb. It is very easy to lose this and/or overlook it when rebuilding. It drops right out when the carb is turned upside down, and may not be noticed. About a 1/8 inch diameter ball bearing, drops into a vertical passage in the bowl assembly.

If it's not there you will have the rich running, plus very likely fuel will be leaking from under the center of the float bowl onto the manifold, down around the accelerator pump linkage.

I recall a long thread on this forum a couple of years back where this was discussed.

Good luck

Pete

 

The thread I'm thinking of was "carb rebuild" posted on 02-08-2003

Pete

 

Good point on the ball check valve.

However, in the carb kit from Jon you delete that ball and its retaining spring (if it has a spring - sometimes it was never put in or is missing).

Instead, the carb kit has the latest modification which is a small needle valve ~ 1/4 inch long and really skinny that goes in the hole where the ball valve was.

It is a one piece unit and you won't get it confused with any other part in the kit. It is tough to describe, but obvious when you see it.

This was an improvement in the carb and a field change.

 

Had a retainer weight in the ones I've seen... didn't know about springs. Interesting info on the upgrade...

Pete

 

Cant thank you enough for all the info guys. After all the horror stories ive heard about the YF i was about to throw in the towel, but i think im gonna get the kit from The Carb Shop and we'll see what happens.

 

Years ago I tried the generic kit for my YF, has the symtoms you guys describe, got tried of it and installed Solex, wish I'd known about the Carb Shop then, but then the Solex was only $99.

 

I have had to repair half a dozen or so YF carbs - all for the flooding problem and I have had 100% success with the carburetor shops kit.

The flooding problem can be really wierd -- all the way from massive flooding to minor flooding (if there is such a thing) and even to what appeared to be intermittant flooding.

good luck

 

Okay, got the PCV from Debellas, thanks for the info, also, got the carb shop rebuilt kit for my 938sd (the one i was fighting before was something like a 1002 or something...doh!...fortunately had a spare. gonna try to get the carb rebuilt tomorrow and install the new pcv and we'll see what happens. one more lil question, though. I dont yet have a radiator, so how long can i let the engine run without damaging anything? obviously i know not very long but i was hoping to be able to run it long enough to at least get my idle set good. anyway ill let you know what happens.

 

I wouldn't even attempt it until the cooling system is repaired
otherwise, asking for trouble, in my opinion

 

I wouldn't try it. To set the idle, the motor ought to be at a "normal" warmed up temp. Without coolant, you'll fry something.

Pete

 

Yea, i stopped and thought about it and realized, duh, that i really cant do anything til i get a rad. Guess i was just getting so excited to get her runnin i wasnt thinkin. Thanks for gettin me back on track! Just ordered my welder today so thatll give me something to do til i get my rad.
Steffy