Pump gas jet size?

P

Phenom20

Member
What size jet do I need to run pump gas? I currently have a 52. I haven't ran the flathead since 2008 and can't remember If I had it set up for alcohol or gas anymore
 
There's a 5% difference between a .036" and a .037", a .037" and a .038" etc. etc. The difference gets smaller as the jets get bigger. Don't forget the low-speed jet, it needs to change too.

Too small and that could harm the engine. If it was me, I would start out a little bigger.
 
alvin l nunley said:
There's a 5% difference between a .036" and a .037", a .037" and a .038" etc. etc. The difference gets smaller as the jets get bigger. Don't forget the low-speed jet, it needs to change too.

Too small and that could harm the engine. If it was me, I would start out a little bigger.
Click to expand...
AL What size jet did you run in your flathead engine?

Most people usually start with 36 and adjust from there depending on build, altitude, air density and carb differences.
 
alvin l nunley said:
There's a 5% difference between a .036" and a .037", a .037" and a .038" etc. etc. The difference gets smaller as the jets get bigger. Don't forget the low-speed jet, it needs to change too.

Too small and that could harm the engine. If it was me, I would start out a little bigger.
Click to expand...
Where is that mysterious low speed jet, again? Just teasing you, Al.
 
Complete Flathead newbie here.... I removed the jets in our "donor engines" for the laydown kart. They are hand marked not stamped for ID, one has a 555/999 on either side of the screwdriver slot, the other just has a 9 marked on it. They both measure about .057 thru. Are these Alky or gas jets?

Also, how much oil should be added to the CC????
 
^ .048" would still be an alcohol jet - simply for an unrestricted carb (ie no restrictor plate.) The .057" that was in it was probably accompanied by a turquoise (blue) restrictor plate in my "guesstimation."
You could be anywhere from a .036" to .038" for gas depending on bore size and air flow through the carb(s).


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