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Mikuni jetting for methanol

Posted: Sun Feb 24, 2013 12:41 am
by ChrisACT

I'm looking at running a Mikuni TM32 on my M/F 100cc bike.

Can anyone suggest some jet sizes to start with for running methanol?

Main jet, idle jet, needle jet etc.

The carby ships with the following gasoline setup:

250 Main Jet
45 Pilot Jet
389 Q-2 Needle Jet
5FP17 Jet Needle
831-39012 4.0 Throttle Valve

I presume the main and pilot jets are going to have to flow at least twice the fuel of the standard jet.

I guess I need to work out the gap between the jet needle and the needle jet and calculate a needle jet which will flow at least twice as much fuel with that jet needle.

I have no idea whether or not I'd need a different throttle valve.


Re: Mikuni jetting for methanol

Posted: Sun Feb 24, 2013 8:22 am
by gennyshovel
Firstly, jet it for gas, test run, then increase ALL your jet sizes by 2.2, than go up a couple of sizes with the mains, test again,,if it feels right flog it for a mile, do a plug chop, then look at the heat discoloring of the plug threads,,safe is 1 1/2 to 2 threads,,3 threads is the danger zone.(make sure the plug(s) are new before doing this.)
Main jets are easy, as they are numbered according to their flow rate
Pilot jets need a little more effort, accurately work out the orifice size, then the area of the hole,,then measure the parallel section of the needle,,work out its area also, subtract one from the other which will give you the area the fuel has to flow thru,,then also increase this by 2.2
Flog the engine for 2 miles,,or 3 minutes,if it hasn't burnt the piston by then,,you should be right , but what would I know,,having just melted a piston, after spending 3 months getting the mixture "right" in the manner just mentioned,,lol

Re: Mikuni jetting for methanol

Posted: Sun Feb 24, 2013 9:11 am
by ChrisACT
Thanks for that.

Sorry to hear you melted one. You gotta watch them 4 strokes, mate. They eat pistons they do ... <cough>. :wink: