carter YS m38a1 problem

gianjeep · Post by **gianjeep** » Wed Mar 25, 2009 5:00 am

hi guis
need help for ys carburetor on my m38a1
when accelerating it sounds like it`s got a hole...
the diaphrams are all new and also the inner jet is new
there is no dirt or water inside it
i ve noticed that when i pull the choke half way it runs perfectly...
many thanks gian

GPA · Post by **GPA** » Wed Mar 25, 2009 7:51 am

Hi,
Sounds like you have a lean condition, check the springs at membranes if they were mixed up. Weaker one goes at the metering rod. Should recheck the float level, fuel pump delivery volume and pressure. While you are typing why not type in your location so we would now were you and your Jeep are.

MODIFIED · Post by **MODIFIED** » Wed Mar 25, 2009 10:28 am

I'M HAVING THE SAME PROB.... I'VE TAKEN THE CARB APART AND REBUILT USING JOHN'S REBUILD KIT FROM MWM. SOAKED HE CARB IN MIN SPIRITS FOR A WEEK AND BLOWN CLEAN BEFORE REASSEMBLY.
I'M USING AN ELECTRIC 24V FACET FUEL PUMP.

-DOUBLE CHECKED THE LOCATION OF SPRINGS AND FLOAT CLEARANCE (9/64", NOT 1/4").
-HAVE GOOD FUEL FLOW AND PRESSURE.
-BACKED OUT IDLE SCREW 1-1/2 COUNTERCLOCKWISE FOR SMOOTH IDLE AFTER ENGINE REACHING 180 DEG.
-CHECKED FOR VACUUM LEAKS WITH PROPANE GAS...(HAVE YET TO CHECK VACUUM W/ GUAGE) NON FROM WHAT I CAN ASSESS.

STILL WANTS CHOKE. - RUNS WELL THOUGH AND NO BACKFIRE OR INAKE BLOWBACK.

GPA · Post by **GPA** » Wed Mar 25, 2009 11:14 am

Running problems are difficult to diagnose from long distance, sometimes even if the vehicle is right in your shop. All of the Facet 24V pumps should have enough fuel volume for this application, but not the pressure. For example part #477003 is too high, #477974 is too low. May have to fit a fuel pressure regulator in case of too high pressure. Plunger(weight) and ball in acc. circuit is in place? Check ign. advance mechanism as well.

MODIFIED · Post by **MODIFIED** » Wed Mar 25, 2009 11:18 am

plunger,ball weight in place. will check the pressure on the facet. timing as well.
thanks for the heads up.

Post by **wesk** » Wed Mar 25, 2009 12:50 pm

Having to apply choke to keep the engine running can mean one of two things:

1-Too much air.

This means you are sucking in extra air somewhere. Could be the carb base gasket, the PCV valve, the manifold plugs and fittings or the cast in the head intake may be cracked. This is troubleshot by using a propane cylinder and discharging it at a low flow rate and aiming the raw gas at the typical leak locations leaving the choke as far open as you can and still keep it running for the test. Any improvement in running and that area has an air leak. The PVC valve is tested by blocking it off. One very common source of excess air on a M38A1 is that distributor vent line that runs from the distributor around the back of the engine to the wiper "T" breaking or rusting through. So to continue your trouble shooting you can actually disconnect these vacuum systems and plug them and if your running improves you found your leak.

2-Not enough fuel.

This means that fuel available for burning in the engine is inadequate. This could also be several different problems. The best way to approach this issue is in clear cut system increments. Start with fuel supply. Check for unrestricted flow from the tank. This can be checked by disconnecting the tank line from the fuel pump with the shutoff closed. Point the line in a can and open the shutoff. Fuel should flow freely and it should be clean. Now remove the gas cap from the filler pipe. If the flow suddenly increases a lot you have a restricted fuel tank vent system. Next check fuel delivery pressure at the carb inlet fitting. It should be 4.5 to 5.0 PSI. Finally check float level and float operation. Next move to the carb internal systems or circuits. The low speed first and then the high speed. Restrictions in either can be the source of your symptoms. As previously mentioned leaky accelerator and metering system diaphrams can cause this as can the wrong placement of the diaphram springs.

The key to success here is patience and organized effort.

You'll note one should not automatically assume the described symptom is low fuel until he troubleshoots the problem properly. As you can see checking for air leaks first covers the easier things to check. This is how an organized approach to troubleshooting saves time and money in the long run.

gianjeep · Post by **gianjeep** » Thu Mar 26, 2009 2:43 am

ok thanks
today i will try to check the float level..
i've fitted all the original parts as a brand new AC pump,membranes etc
i've also got doubts about the spring tension on the pump side of the carburetor...
see ya
thanks for giving me tips...
giancarlo nord west italy
md17452

gianjeep · Post by **gianjeep** » Thu Mar 26, 2009 3:05 am

need conversion in millimiters 9/64''
tanks a lot

TomM · Post by **TomM** » Thu Mar 26, 2009 5:51 am

3.6mm