Carb Headache

[Roger Friedrich]

I have a 1963 M37 that had the carb rebuilt by a guy who was a mechanic in the Army and the rebuild is great but...... When the M37 sets for anytime it need to use ether which gets it running and when you start it after that it will start without ether. The mechanic purchased the rebuild kit and cooked the carb before he put the kit in and he's also baffled. He has worked on several military truck as a civilian and a mechanic all his life and has many of the gages that are used to set the float and other things

So this is my request to see if anyone has any ideas what be the problem.

A few other things is I purchase gas that has no alcohol - I use Seafoam to help keep the gas from going bad - the tank has been Red Coated which I had to dump the first tank due to the Red Coat - I have checked the fuel pump and it does work but not sure of the pressure to the carb - it does have a glass bowl with the screen fuel pump


Any thought on other areas to check would be appreciated

 

[rtk]

My fix for my M37 was to put in a electric fuel pump back by the tank . I used a momentary on toggle switch , only use the pump when I need it . Usually after the truck sits for some time . A 24 volt pump is available from most of the MV vendors or Flea Bay .

 

[61sleepercab]

Some times fuel systems will drain back towards the tank and you have to crank the engine a lot to get new fuel to the carb. Have you tried a cold start after you have filled the carb with a squirt gun or bottle into the carb vent tube or put some fuel into the carb throat and then start. If this runs truck you are losing fuel to the carb over time. The primer pump idea would solve the problem. I have a 85 Chevy v8 with carb and if it sets for a while it takes forever for the mechanical pump to prime the carb and the engine catch. The other mystery unit was a MB Jeep who would start ok run 5 minutes and stop no matter what it was doing. The carb needle and seat would let in one bowl of gas and the Jeep would go till it ran out and then the pressure would change and it would fill up again. What fun...... Try figuring out if a full carb will run and if you are losing prime, start truck more often or change to electric pump and fuel pressure regulator as low pressure pumps can over power the pressure that a needle and seat can hold without flooding the carb........ that is another story. Mark

 

[M543A2]

I will bet the fuel is evaporating out of the carb as it does with mine. The fuel cannot go back to the tank out of the carb because the needle/seat assembly is above the fuel in the bowl; it cannot suck up fuel out of the bowl. If you have the correct fuel pump on the engine it has a primer lever on it. Several pulls on the lever and you will hear fuel going up into the carb. The lever will no longer go full stroke when the carb is full and the needle valve stopping flow. If you do not have a fuel pump with the lever, I would recommend going to an electric pump completely, bypassing the engine pump. The suggestion of a momentary electric is good given when running the manual engine pump can draw adequate fuel through it. I do not like to feed a manual pump continuously with an electric because if the manual gets a hole in the diaphragm in the right place you can fill your crankcase with fuel.
REgards Martin Sacks

 

[Roger Friedrich]

Thanks everyone for the suggestions and I will install a electric fuel pump near the fuel tank. The current fuel pump is a civilian pump so it doesn't have all the extra things on it the military pump does.

Again thanks

 

[rtk]

Make sure you keep the pressure down on the electric fuel pump 3-5 PSI is plenty of fuel . Also remember electric fuel pumps are better at pushing than pulling fuel , which is why you install the fuel pump on the LS frame rail close to the tank , there actually is a fitting in the fuel line just in front of the tank that makes it easier .

 

[misupratwin]

I run a Carter mil spec 24v pump . Bought it at my local Napa dealer. They offer two styles, solenoid and vane, I run the vane style .

 

[Bill W]

I made this up for my 37
There it a fuel line coupling on the frame near the drivers side rear shock that you can route your ( elec ) fuel pump hose to and not have to cut the line.

 

[GUNNY 155]

Did the problem exist before the carb was rebuilt? How long is your vehicle sitting before starting? Mine is all GI and if I do not take it out for a ride I start it every few weeks and it starts right up. Point being if it started ok before the rebuild I would look at the carb again. Also check the fuel pump pressure.

 

[Roger Friedrich]

Thanks to all who have posted about my carb problem and I plan to put a 12v electric pump with a circuit breaker and switch. One problem I have is the weather is getting colder and my garage is full of parts. HA HA I'll need to restack everything to get the M37 inside to put the pump on. The truck has always been hard to start and if I could afford it I would put a NOS fuel pump and new carb on it, but what I've seen both of those would cost more than what I paid for the truck.


Again thanks for the great information and if I get the pump on before the thread disappears I'll let everyone know if the pump helped