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Carburetor Idles Rough; Carter throws fuel at idle!
Topic Started: Jul 24 2013, 01:44 PM (2,316 Views)
muddobber
Member
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Ok, while the 4002s is not the correct carb, it will work with some careful tuning.
Here's what I did, YF 4002s carburetor on 1963 CJ3B F head.
Went through all tune up procedures checking timing, plug gap and condition, point gap, all that stuff. Everything like it was the first time taking nothing for granted.

Check your fuel pressure at no more than 5psi, this one runs at 2 1/2 psi using NAPA AFP 572 fuel pump and the spacer on the old pump. Check the condition of your fuel inlet needle if it floods
Plug that carb vent with a vacuum line cap
Carefully set the float to the proper setting of 5/16 using a drill bit and check the fuel well level at 1 1/8"
I did have to replace the inlet needle with a kit from vietnam, inlet orifice sized around .081 with a spring loaded valve. I also added a vented fuel cap.
That solved my flooding problems and it runs good now.
My throttle body needle adjustment is 1 1/2 turns, yours may vary if you have a flat spot.
You might check engine vacuum, this F head runs at 19"@ 2200 ft elevation, add 1" hg per 1000 ft above sea level. It won't affect fuel well level though, just to give an idea of valve condition. Its checked at the port under the carburetor where the PCV line is connected.

If it is a 4002s it is stamped somewhere. I remember seeing it but I don't remember where on the carb its located.

ETA: My trials and tribulations with the YF 4002s
http://z4.invisionfree.com/CJ3B_Bulletin_B...?showtopic=4848
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oldtime
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muddobber, is correct so I must agree..

If you plug the vented fuel well opening and rebuild the YF 4002 S to YF 938 SD specifications there is no known reason why it should not function.

Basically you need to follow my instruction on "How to Rebuild a Carter YF".
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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spm1us
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The 4002s will work fine as long as you follow the previous recommendations. I wouldn't bother with the Solex as it's more hassle than it's worth. You can buy a NOS Carter YF on ebay from NOS4Jeeps in Turkey - ebay #310287781879. I have never purchased anything from him, but I'm sure somebody on this site has. He has the NOS YF listed at $349.00 + $65 shipping. I'm sure you can find a good rebuilt here in the USA for considerably less. Good Luck with your project, Sam Michael Jr Jax, FL
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muddobber
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The inlet needle valve kit from Vietnam is
http://www.ebay.com/itm/Original-Jeep-Will...358b5f4&vxp=mtr

I bought the kit just for the valve, and even it is slightly oversized at .081.
The correct stock size is .076
If you do get it, it does take a while to arrive.
Rebuild kits from auto parts stores will likely be for a Ford 300 c.i.d engine with a larger inlet valve around .090 and a soft inlet valve, the rubber tipped kind.

The F134 engine was the smallest displacement engine the 938 was used on, based on my research, so its hard to find the correct kits. Its one reason I question rebuilt carbs. I don't know what parts were used.

Its not a set and forget type thing. Once you get it running correctly, you'll have to check the fuel well level a couple times and maybe tweak on the throttle body needle valve based on plug condition. Small changes if the plugs are getting sooty, to the leaner side. Its a dynamic system, everything has to work together.

You can't change the metering rod and rod jet between different carb models without adding grief. Oldtime would know more about that.
His knowledge is encyclopedic, so trust him.
The 4002s metering rod number is 75-1714, I don't know the jet number. Aftermarket metering rods don't have the stamped number and would need to have the steps measured to verify they are correct. NOS carter metering rods for the jeep yf models are hard to find. Very hard.

The inlet needle can be changed and the pump discharge check, either ball and weight or needle check can be used. The fuel well level of 1 1/8 is the important number along with pump discharge pressure.

Almost forgot, the fuel pump I mentioned is non vacuum, and I had to rotate the upper diaphragm body 90 to make it work. It has electric wiper motors.

To agree with spm1us, while the solex may work for some, I have heard nothing much good about them, or Omix Ada in general regarding jeep stuff.

Please do follow up and let us know your results and what you did.
Its a help to everyone here.
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muddobber
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OK, here is a 1965 YF 4002s from approximately the same angle as your carburetor
The carbs look different to me as compared to the first page picture.
Seems like the first thing to do is correctly identify the carb on the jeep.
Posted Image
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oldtime
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Yes that's been my position from the beginning.
One must always identify component assemblies before correct repairs can be made.
In this case it seems that this YF may or may not be a 4002S.
I'm guessing that it is 4002S but cannot verify that without detailed input.

The only way to identify it is via checking all individual components such as throttle body bore, metering rod, main metering jet, calibrated orifes, ect.

Externally we obseve 3 main components.
1) It has the ventilated "Air Horn Assembly".
The ventilated air horn assembly was used on YF 4002S and on other post 1965 YF carburetors.
2) Apparently this particular "Fuel Well Section" is not externally identafiable.
3) What did you say is the number on the Throttle Body ?
(AKA body flange assembly)
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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garyc1955
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As regarding the fuel coming out the accel pump check the integrity of the check valve,if it does not seal ,fuel will be vacuumed out much like the venturi.
1964 cj3b ,extremely rust free seems mostly unmolested and starting a restore in southern New Mexico
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RMinPA
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Rebuilt YF 938SD. www.carburetorshop.com wants $995 plus shipping. Does that seem overpriced?
Rich Meyer
1962 CJ-3B Ser#57348 88612. Restoration finished 9/6/2013 to stock with factory optional wheels/tires and heater. Engine#807895
2007 JKU Rubicon on 37's, 4 1/2" Lift, 5.13s, etc.
Now in Rockford IL
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oldtime
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It's probably a rebuild of the same junk 938 I sold him for $25 two years ago.
Cost a lot to rebuild junk !
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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muddobber
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RMinPA,Jul 29 2013
11:31 AM
Rebuilt YF 938SD.  www.carburetorshop.com wants $995 plus shipping.  Does that seem overpriced?

Surely that must be a typo?
$995??
$995????
Yes, it seems prohibitively high unless it has gold jets and platinum plated.
Most of the "new" rebuilds I have seen run $250-300, but provide no details of parts used. The highest I've seen is from Turkey at around $379 plus shipping.
People speak highly of Walcks rebuilds, though I have no experience with them. Core required for sale I think.

I'd be hitting every junkyard around to find a decent 938SD core or even a 938S to modify. And learning up on them hard.
A good 938SD core plus a rebuild kit containing the metering rod from Mr Hardgrove would be the way I would go. The kit is approx $90 which may seem high, but it has the unobtanium metering rod and jet. It probably has the inlet valve also, but I didn't ask about that.
Then again, I'm cheap and prefer to do stuff myself.

If you are confident in your ability to rebuild one and a little patient in acquiring the correct parts, you might find a decent 938 core on ebay and acquire the right kit.
It depends on whether you want it now now now or if you want it more cheaply.
Its not hard, it just requires some attention to detail and a little patience.
People here can help.
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RMinPA
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Update:
A rebuilt 938SD is on its way to my restorer. There are still unknowns since it has been on a shelf for a while. Worst case it needs to be rebuilt again and I'll get the parts from thecarburetorshop.com since everyone recommends them. They, were, however the carb scalpers who wanted almost a thousand for one. Their rebuild kit would only be $82. Of course they ONLY take orders on Monday and Tuesday and only by phone.

Thanks for your help, everyone.

I will update this string when it runs.
Rich Meyer
1962 CJ-3B Ser#57348 88612. Restoration finished 9/6/2013 to stock with factory optional wheels/tires and heater. Engine#807895
2007 JKU Rubicon on 37's, 4 1/2" Lift, 5.13s, etc.
Now in Rockford IL
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oldtime
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These are excellent OEM kits but do not contain metering rods nor the main jet.

eBay item number: 261243844084
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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RMinPA
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Quick update. It's running!
Rebuilt carb via Ebay ($100 plus shipping) bolted on and the Willys is idling happily.
Thanks for your help!
Rich Meyer
1962 CJ-3B Ser#57348 88612. Restoration finished 9/6/2013 to stock with factory optional wheels/tires and heater. Engine#807895
2007 JKU Rubicon on 37's, 4 1/2" Lift, 5.13s, etc.
Now in Rockford IL
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muddobber
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Glad you found one.
I'd be curious to know as a follow up, if you have any flat spots or additional carb related problems. You know, stuff like backfires or fouling plugs, idle rpm, that sort of thing. And if so, what the resolution was. Any fine tuning needed.
The reason I ask this is because of rebuild kits seeming kind of iffy and varying in quality from place to place.

Its always to great to hear it run like its supposed to.
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RMinPA
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Not quite done.

Idles well with the "new" carb but on-the-road my mechanic tells me it hesitates. He has ordered a rebuild kit. The carb seller had purchased the inventory of a auto parts place and while the metering rod looks new, he did not guaranty that it had been rebuilt or, if so, how long it had gathered dust.

The adventure continues.
Rich Meyer
1962 CJ-3B Ser#57348 88612. Restoration finished 9/6/2013 to stock with factory optional wheels/tires and heater. Engine#807895
2007 JKU Rubicon on 37's, 4 1/2" Lift, 5.13s, etc.
Now in Rockford IL
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