resizing main jets?

TThornhill

Cadet
Joined
Feb 19, 2011
Messages
28
1998 merc 150hp 2 stroke carb.
read a few places that after performing my rebuild i should retard the timing about 2 degrees and increase the main jet by .002, which would take it from .074 to .076. (i guess to further prevent a lean mixture and to aid break in) and was wondering if this jet swap would be a good idea to do, and if so, where could you find that particual jet?. mercurys next size available is a .078 and thats for the 175 models.
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: resizing main jets?

Generally factory jetting is sufficiently fat as to allow a .030 overbore during rebuild without the need to rejet the carbs.

Fuel pump rebuild is highly recommended as is a new water pump kit, poppet valve diaphram, T-stats, and fuel hoses.
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: resizing main jets?

Usually it's fuel delivery, float adjustment, or dirty carbs that cause a lean burn condition, not jet size except.........If someone has played musical carburetors with another motor, the jet size (base or start) goes with the carb model, not the motor size. Then you have to read piston tops and spark plugs to tune from there.

hope it helps
john
 
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