popping and farting out of my carbs

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
drumyn39
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popping and farting out of my carbs

Post by drumyn39 » Sat Sep 01, 2018 9:24 pm

Out of the blue lately, my Ute has been popping and farting out of the carbs and I can't seem to figure it out yet.

I've changed the battery, new battery positive wire, cleaned all surfaces of distributer and ground straps and tore a part both carbs thrice as well as Ohm tested coil and Pertronix.
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drumyn39
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Re: popping and farting out of my carbs

Post by drumyn39 » Sat Sep 01, 2018 9:49 pm

I wonder if I just found my problem.

Should I take a plug out and spray a little oil on the valves?
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pajeff02
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Re: popping and farting out of my carbs

Post by pajeff02 » Sun Sep 02, 2018 3:30 am

I am not certain as to the popping, but as far as adding anything to the fuel I do run TC-W3 two stroke oil in the fuel tanks of our collection. The ethanol in today's fuels does not play well with old school carbs and fuel system components. Adding 1 ounce of TC-W3 to 5 gallons of fuel seems to work in that I have had zero issues with the fuel systems on any of our cars during the 10 years I have been doing this. I presume that the MMO recommendation is for similar reasons.

GI.
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Re: popping and farting out of my carbs

Post by GI. » Sun Sep 02, 2018 3:43 am

Possible fuel starvation, maybe add two more carbs. :roll:
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Wolfman
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Re: popping and farting out of my carbs

Post by Wolfman » Sun Sep 02, 2018 6:36 am

Cracked distributor cap. Carbon track between two terminals in the distributor cap. Bad plug wire. The electronic ignition puts out a considerable hotter spark. If you have a bad plug wire, the spark can jump to another terminal instead of following the path through the bad wire as it should. Electricity is lazy and will always follow the easiest path.
Tight or burned intake valve. Possibly a broken valve spring.
Lean mixture. Vacuum leak ? Seems you have the carbs covered.
Low fuel delivery pressure. Fuel pump. Filter. Fuel line drawing air. Plugged fuel tank pick up.
Intermittent electrical connection.
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drumyn39
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Re: popping and farting out of my carbs

Post by drumyn39 » Sun Sep 02, 2018 3:29 pm

I shut down each carb separately and they both still popped when I gave them gas. I specifically bought solid core wires and they seem to be getting a great spark.

I'll check cap now hopefully inspect valves as well.

drumyn39
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Re: popping and farting out of my carbs

Post by drumyn39 » Sun Sep 02, 2018 9:38 pm

Compression is 100 pounds on #1 and 125 pounds on 2,3,4.

All valves are opening perfectly so I guess it's time to take the intake and header off and inspect the cam.

fernando mendes
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Re: popping and farting out of my carbs

Post by fernando mendes » Mon Sep 03, 2018 5:00 am

drumyn39 wrote:
Sun Sep 02, 2018 9:38 pm
Compression is 100 pounds on #1 and 125 pounds on 2,3,4.

All valves are opening perfectly so I guess it's time to take the intake and header off and inspect the cam.
Ratio....6.5.......Pressure....110.
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Wolfman
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Re: popping and farting out of my carbs

Post by Wolfman » Mon Sep 03, 2018 7:01 am

The 100# reading on #1 while the rest are 125# looks suspect.
You familiar with a " leak down test" ??
Each cylinder is placed on TDC of the compression stroke and pressure is applied to the that cylinder.
If something is leaking, Like an intake valve ! , you can here air coming out the carb. ( Carbs). Same for exhaust and out the oil filler for bad rings.
A second look shows the two carbs and manifold sections, front and rear, are connected by an equalizer tube, so a back fire from the front could still pop out the rear.
Still trying to figure this out "before" you tear the engine apart !!
Mike Wolford
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Comm./Inst. SEL
AOPA ( 44 yrs)
EAA ( 44 yrs)
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drumyn39
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Re: popping and farting out of my carbs

Post by drumyn39 » Mon Sep 03, 2018 12:34 pm

I did a leak down and not a peep out of any of the carbs or oil filler tube.

Wolfman
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Re: popping and farting out of my carbs

Post by Wolfman » Tue Sep 04, 2018 5:20 am

Another one off the list.
Well, How about a broken valve spring ??
Just because the valves are closed and sealed during a leak down test does not mean they are keeping up to the task at running speed. This sort of problem appears at a set RPM. Engine may start and run OK at idle but at the exact same RPM, as you slowly increase the throttle, it starts to run poorly and may backfire. Gets worse if you try to increase RPM. ???
Also a problem that is only related to multi. carb. engines. Carburetor synchronization. One carb. is open more than the other. This can cause throttle response problems. Even though you have an equalized manifold, one carb could be opening late causing a lean mixture in two cylinders. I see a shaft between the two carbs. but not sure how you adjust synchronization. Maybe something slipped ???
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 44 yrs)
EAA ( 44 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

drumyn39
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Re: popping and farting out of my carbs

Post by drumyn39 » Tue Sep 04, 2018 5:58 am

You may be on to something with the dual carbs, I'll take a look at the linkage today.

drumyn39
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Re: popping and farting out of my carbs

Post by drumyn39 » Fri Sep 14, 2018 7:26 am

Well, I think the carbs have been the issue. I noticed that one of the small screws holding the throttle on one of the carbs was stripped and it was opening slower than the second carb.

I replaced the screw with a stainless steel screw and it still pops slightly but no where near as bas as before.

THANK YOU WOLFMAN!!

Does anyone know which is the most accurate synchronizer tool? I'm currently using the silver one but I heard that the black one is best
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GI.
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Re: popping and farting out of my carbs

Post by GI. » Fri Sep 14, 2018 9:22 am

Why don't you put the old single intake manifold on with one carb. and see how that works, I doubt if that little four banger need's two carb's, sometimes their more trouble then their worth.
You can always go back with the two carb's for a car show. :wink:
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Re: popping and farting out of my carbs

Post by Ben Dover » Fri Sep 14, 2018 9:47 am

We had a USAF Colonel customer that had a new late 50's Morgan with twin S.U. Carburetors, I used to synchronize the carburetors by ear listening thru a tube inserted into the throats of of the carburetors.
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