stuartsn
Junior Member
Posts: 7 
First Name: Stuart
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Post by stuartsn on Nov 27, 2019 0:16:34 GMT -5
I need help with my 938SD on my F134 CJ3B. It leaves a pool of fuel in the manifold after running which makes hot starts a rich smoky ordeal. Fuel also leaks out of the bottom when I shut down. I'm unable to get the float setting anywhere near 5/16 or 9/32 with out flooding. It is currently at 13/32. The float valve is all metal and silver in color and is not Viton tipped. The last two rebuild kits I have done came from the Carb Shop in Missouri.
My fuel pump is from NAPA. It has no glass bowl or vacuum stuff on it so I will need to verify the fuel pressure for you. I don't have the gauge for that so I'll get one and do that and get back on that.
Also the vacum is a paltry but steady 14. I've had this carb for a long time and it has served me well. I have suspected it may be due for shaft and bushing work although I'm not experienced enough to tell that physically. The idle speed tends to increase as it warms up. The jeep is running remarkably well for the issues the carb has but Im tired of washing my cylinders down with fuel . Thank you for any advice and I hope your Thanksgiving will be great. We are expecting rain here in the desert.
Thanks, Stuart
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Post by Scoutpilot on Nov 27, 2019 6:24:55 GMT -5
What is your altitude? Vacuum diminishes by one inch per 1,000 feet increase above Mean Sea Level.
Is the float leaking and filling?
Inspect the tang that presses on the needle for a gouge or deep scratches. These deformities can cause the needle to become cocked in the seat and fail to seal.
Post some pics, if you please.
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stuartsn
Junior Member
Posts: 7
First Name: Stuart
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Post by stuartsn on Nov 28, 2019 10:49:30 GMT -5
Happy Thanksgiving!, My float is not leaking and appears to be in good shape. I did find that my pump diaphragm has a small crack forming which was not visible until the fuel dried on it. I took a picture which is visible at 12 o'clock. I can see light thru this so hopefully that will explain the fuel puddling in my manifold. I have a new kit coming from Mikes to address that problem. I measured 4 pounds of fuel pressure just running the starter only. When I get this back together I'll readdress that and see what i measure when its running.   |
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Post by Scoutpilot on Nov 28, 2019 12:43:33 GMT -5
Before you install Mike's kit look at the needle and seat components, then look to the instruction sheet for the proper float settings based on each.
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stuartsn
Junior Member
Posts: 7
First Name: Stuart
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Post by stuartsn on Nov 29, 2019 19:46:56 GMT -5
Will do, I also forgot to mention I'm at 1100 feet here.
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Post by Scoutpilot on Nov 30, 2019 4:51:32 GMT -5
OK. So altitude is not an issue here. Keep me posted.
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stuartsn
Junior Member
Posts: 7
First Name: Stuart
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Post by stuartsn on Dec 13, 2019 10:57:55 GMT -5
I finally had time to get the kit put in. It cleared my hot starting problem up and it fires instantly when I hit the starter after hot starts. This kit came with two different float needles and seats. The shorter seat which fits my float pin height came with a solid needle. The longer seat which does not fit my float pin height came with the spring loaded needle which doesn't fit in the shorter seat. I need to do some more road testing as I think I detect slight stumble or surge at cruise. My float is set per my instruction sheet for kit K1111 which say to use setting #2 (15/32) for resilient tipped needle. I assume this is viton tipped. Both needles in the kit are viton tipped.
The jeep is running good other wise but vacuum is still a steady 14. I can get the idle down to 500 rpm cold but when hot I struggle to reach 750 Rpm.
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Post by Scoutpilot on Dec 13, 2019 11:59:26 GMT -5
Have you performed a compression test?
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stuartsn
Junior Member
Posts: 7
First Name: Stuart
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Post by stuartsn on Dec 14, 2019 12:22:23 GMT -5
No but that is easily done so I'll report back with my numbers.
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stuartsn
Junior Member
Posts: 7
First Name: Stuart
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Post by stuartsn on Jan 1, 2020 11:25:53 GMT -5
I finally had time to check compression. When cranking I'm getting 130 on all cylinders. This is suing a cheap press on type gauge. I have a nice aircraft differential compression tester but its not setup for auto plugs.
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Post by Scoutpilot on Jan 1, 2020 12:11:01 GMT -5
All sounds good except for the vacuum reading. It may be time for bushings and a shaft.
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stuartsn
Junior Member
Posts: 7
First Name: Stuart
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Post by stuartsn on Jan 3, 2020 21:40:19 GMT -5
Yes, Maybe a good time to take it off line and fix some oil leaks as well. I will review your procedure for sending in carb work and make a decision. This engine got all carboned up since I drove it so long with the leaking pump diaphragm. I noticed now that my plugs have cleaned up to a nice tan color and my exhaust valves are now very light in color since I've been driving it with the corrected pump diaphragm. Cold and hot starts are better now than they have been in years but I'm still fooling with the stumbling problem at cruise. I checked my points and they were a little worn. I think I will replace them and the condenser. I put the dwell meter on and it and the needle goes crazy and unreadable. I'm not sure if that means my distributor is worn. The dwell meter is a low budget one so not too sure about it. What should I expect to see for a dwell reading?
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Post by Scoutpilot on Jan 4, 2020 5:22:59 GMT -5
You're making good progress. With the points set to .020", the Dwell reading should be a consistent 42º, +/- 1º. The points assembly should have a copper strap for the electrical connection and a steel spring strap to keep the arm stable across the power curve.
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Post by brucew on Jan 4, 2020 17:42:15 GMT -5
I've never had much luck with digital meters when measuring dwell or idle speed. They are too persnickity and jump around a lot. A good ol' analog meter works much better. B-dubya
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Post by Scoutpilot on Jan 4, 2020 19:13:46 GMT -5
My colleague is right. It's an analog motor and needs analog diagnostics.
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