How to prime the M38A1 carb to help start?

JeepdaddyRC · Post by **JeepdaddyRC** » Tue Jan 19, 2021 8:57 am

Is it correct that the Carter YS 950S accelerator pump is different and does not give a shot of fuel in the carb throat by depressing accelerator?

In the MB and CJ's a simple shot of gas poured in carb throat would help start a vehicle that had been idle.

If this M38A1 sits a week it is hard to start. Other than using the fuel pump lever to refill the carb bowl (this has no dash priming pump), how do you get an extra shot of fuel into the Carter YS 950S throat to ease starting?

Post by **wesk** » Tue Jan 19, 2021 9:13 am

The civvy carbs use a manually operated accelerator pump that will squirt gas into the carb anytime you pump the pedal. The Military carbs YS637S (M38) and YS950S (M38A1/M170) have a vacuum operated accelerator pump which must have engine vacuum available to operate.

This is why you often see the dash primer pumps which were actually necessary for severe cold weather starting.

The secret to starting the Military carbs is to use full choke which supplies a wee bit of engine vacuum while cranking then pump the pedal a few times. Don't try this for too long cause she'll flood very easily.

JeepdaddyRC · Post by **JeepdaddyRC** » Tue Jan 19, 2021 9:24 am

Thanks for the quick reply. I am also in WI. So you don't ever pour a shot of gas in the carb throat to make it easier on the battery and starter?

I'm not even sure how you would get a shot of gas around the 90 degree bend in carb unless you use a turkey baster or something similar.

Newbie to the M38A1. Thanks for your patience as I learn.

Why did the M38 and M38A1 use a vacuum operated accelerator pump compared to the MB, GPW and CJ that used a simple manually operated accelerator pump?

4x4M38 · Post by **4x4M38** » Tue Jan 19, 2021 4:30 pm

Remember the M38 was the first factory fully waterproof jeep.

I suspect the carb design was to support that.