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old school microns jetting advice

Started by Gil Gallad, September 24, 2020, 05:26:28 PM

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Gil Gallad

as some of you know, i converted a ramair gt250 to reed valve. after an awful long time trying to get it running again on both pots, i found the pick-up on my electronic ignition had a piece of plastic missing off the face, which put the timing all over the place. anyway, now sorted. so i saw a pair of micron power exhausts for a nice price and bought them. engine sounds lovely with them fitted, but i'm only blipping the throttle to about 4000 revs. when i was doing all the messing about i put the carbs back to standard, and i'm obviously going to have to change them, once the main jets come in they're going to be a tad small. any ideas on the jetting? atm i'm on 28mm mikunis, #30 pilot jets and 112.5 main jets. needle is on the middle notch. any advice would be greatly appreciated  ;D
cheers, gil.
p.s. looking at the plugs after a 5 minute warm up they look fine.

m in sc

well what matters is under full throttle & midrange. Id start about 4-5 sizes over stock.

Dvsrd

Hex or round main jets? That really matters, as hex are flow/area rated, while round are diameter.
So #100 to #150 round jet will increase fuel 100% or more. While the same increase with hex Jets Will give 50% increase.
Also, 5 sizes depend a lot on the increments available.
As always, start rich and jet down....
To make sure that the needle jet is large enough for wfo, some advise to test with a way too big MJ. If the engine four strokes above 1/2 to 3/4 throttle, the NJ is big enough.

Gil Gallad

thanks for the replies. i was going to start on a 130 main jet and go from there. main jets are round, slotted. i'll have to check, but i think i changed the pilots for #25 at some time. atm the frame doesn't even have forks or wheels on it, it's just on an engine stand on a low bench. now i'm getting somewhere close it might be time to get some wheels on it and get it mobile  ;D
cheers, gil.
p.s. i've also got some 28mm flatslide pwk's that might be worth trying  :whoop: