Carter YF Stumble Off-Idle

[Kowpie]

Hello
I've been picking away at the major issues on the '73 J4000, 258, manual trans. Got it running decent enough to take it to town this past weekend for errands, even asked the wife to go! Very cool having a bench seat so my lady can sit next to me. Gosh it took forever, everyone and their brother was asking about it, giving thumbs up, or telling me their J truck stories... we loved it! I've never had that kind of attention, even in the CJ7. These FSJ's are popular!
Now for the drivability stuff. Under acceleration, there is a medium stumble off-idle. I know it's coming so I feather the throttle through it but it is annoying. I'll give the details, I'll try to be comprehensive but I might miss something: full tune-up, plugs, wires, cap, rotor, it has a Pertronix trigger, fuel filter, air filter, PCV valve, checked timing chain stretch, set timing (vacuum disconnected and plugged, should I use manifold or ported vacuum? Just kidding, those kinds of questions can start a fracas!) fuel pressure at 4 psi, carb disassembled and cleaned all passages, set float drop and level, checked accelerator diaphragm, check ball and weight, throttle plate shafts don't have excessive wear, checked for vacuum leaks and none found. What am I missing?
Bear pepper stick and adult beverage for the one that fixes it!!! Cheers.

[Dorien]

Is the accelerator pump working well?

[tgreese]

When you say "disassembled and cleaned," did you replace all the soft parts? Any new-old car with a carburetor will need a kit, IME. The only Jeep I've owned with a YF ran flawlessly, so I don't have much experience with YF problems. Looking at the book, to get the needed pump shot, you need good check ball seals (inlet check ball, and discharge ball and weight) in addition to a properly sealing diaphragm. The TSM has a thorough discussion of YF carburetor function.

The CJ guys have a lot of cumulative experience with these carbs. From my exposure to the CJ world, I understand the check ball can get stuck in the carb body. I assume that's the discharge ball. Supposedly the you need the right kit for the YF to work right ... supposedly the kit from "The Carburetor Shop" is good. http://thecarburetorshop.com/ RockAuto shows the HyGrade kit, which is more likely ok than other parts-store kits: https://www.rockauto.com/en/moreinfo.ph ... 19&jsn=388

There's lots more on this site if you search: http://www.earlycj5.com/xf_cj5/index.ph ... es.139131/

https://www.bing.com/search?q=site%3Aea ... ebuild+kit

[Kowpie]

Is the accelerator pump working well?

It squirts fuel upon throttle manipulation. Now is it enough or timed right??? Not sure.

[tgreese]

There's got to be a way to measure the strength and timing of the shot, but new parts are less complicated.

[Kowpie]

When you say "disassembled and cleaned," did you replace all the soft parts? Any new-old car with a carburetor will need a kit, IME. The only Jeep I've owned with a YF ran flawlessly, so I don't have much experience with YF problems. Looking at the book, to get the needed pump shot, you need good check ball seals (inlet check ball, and discharge ball and weight) in addition to a properly sealing diaphragm. The TSM has a thorough discussion of YF carburetor function.

The CJ guys have a lot of cumulative experience with these carbs. From my exposure to the CJ world, I understand the check ball can get stuck in the carb body. I assume that's the discharge ball. Supposedly the you need the right kit for the YF to work right ... supposedly the kit from "The Carburetor Shop" is good. http://thecarburetorshop.com/ RockAuto shows the HyGrade kit, which is more likely ok than other parts-store kits: https://www.rockauto.com/en/moreinfo.ph ... 19&jsn=388

There's lots more on this site if you search: http://www.earlycj5.com/xf_cj5/index.ph ... es.139131/

https://www.bing.com/search?q=site%3Aea ... ebuild+kit

1) No soft parts replacement yet. I disassembled to inspect, clean, and verify adjustable settings.
2) Most work that I've done so far has been at the direction of the TSM.
3) The check ball and weight are there and in good condition. The seat for the check ball is in good condition.
4) Kit has been ordered from RockAuto, should be here in a few days.
5) I scoured the earlycj5 site last weekend and reviewed several discussions. Presently, what I have tried have come from the earlycj5 site and the TSM.

I will install the proper kit items and keep tinkering. Report to follow. Thank you.

[Dorien]

It may work when you pump it...try just a gentle throttle movement ( same as when you are driving) and you should get a dribble. Not guaranteeing this is the problem, but by elimination we may get there.

[Stuka]

Dorien brings up a good point. Quickly moving the throttle by hand may work fine. But moving it slowly may not because it allows fuel past the plunger.

[Kowpie]

It may work when you pump it...try just a gentle throttle movement ( same as when you are driving) and you should get a dribble. Not guaranteeing this is the problem, but by elimination we may get there.

Barely a dribble... tough to get my old carcass up into the engine bay, holding a light in my teeth, playing twister to work the throttle, and resting a hand on a hot 258 valve cover!