Jetting for my bike?

[RMX250MB]

i have a 89 suzuki rmx250 and cannot get it to run how it should. Right now the air-pilot screw is almost all the way in (specs call for 2 out) and the idle screw all the way in to make it idle coreectly while still hitting the powerband. When i adjust the air pilot out 2 turns it falls on its face in the higher rpms but idles good. Adjust it way in and it runs good in the high rpms but idles poorly.

The mods are:

pro circuit platinum full exhaust
performance reed valves (not sure of the brand or level)
aftermarket piston (pretty sure its a wiesco (SP) )
32:1 lucas semi senthetic with 93 octane premium
230 main jet (specs call for 270)


tried 20:1 and had unburnt oil coming out of the mid pipe where it conects to the silencer.

any ideas?

[RMX250MB]

no ideas i guess>?

[369DuneBunny]

if your compression is fine and everything else is too... you're gonna have to play with your carb other than the air screw.... when my bike idled fine but fell on it's face at 3/4 throttle to WOT it was rich....

i'm not sure what kind of power your pipe makes... bottom mid top, whatev...

but i do know with aftermarket performance reeds you're supposed to jet down... i already read that you did that... having a 230 main...

maybe try playing with the needle clip setting.

[dajogejr]

First thing I would do is completely dissasemble the carb, and clean the bejezus out of every single orfice in it.

Next, are you using a new spark plug, fresh gas and oil?

Third...leave the mixture of gas to oil alone....correct the jetting, don't adjust your mixture. 32:1 is just fine.

More oil in the gas actually leans the fuel to air ratio, not good on a two stroke.

Then, work on one jetting circuit at a time. Go back to stock jetting...get the main close first. If at 3/4 to WOT it feels zingy but it's not going anywhere, it's lean.
If it feels blubbery....it's rich. Go up or down 2 sizes at a time, that will help dial it in quicker...

Then adjust the needle. Same principle, 1/4 to 3/4 throttle. Move the clip towards the blunt end to lean it out, towards the pointy end to richen it up.

Then....adjust the pilot/air screw.

Warm the bike up.

Start with the air screw 1/2 turn out. Go for a ride. Come back, turn it out another 1/2 turn...wait 20 seconds for the new setting to take effect, go for a ride. Keep doing this until you get the highest idle...then your air screw is set. 1/2 turn or less out....your pilot is too small. More than 2.0 to 2.5 turns out, your pilot is too big.

Hope this helps.

[RMX250MB]

it sounds like it will help. I thought that when the air pilot screw was in that it was leaning it out, not making it richer. the origianl mix calls for 20:1 and the pipe seems to be a high rpm performer. I bought this bike modded so i might not find out till i go to rebuild it. I will go stock up on jets and see what i can find. Thanks

[MX86]

what's the plug look like?

[dajogejr]

If the adjustment screw is on the airbox side of the slide, it's an air screw. Out means more air, in means more fuel. (Lean/Rich)
If the screw is on the intake side of the slide, it's called a fuel screw, and it's backwards...out is more fuel, in less fuel. (Rich/Lean)

Just about all manufacturers recommend 20:1. Too much oil for my taste...I don't even run that much oil in my methanol bike. 32:1 is just fine for gas engines.

[RMX250MB]

plug looks nice and tan like it should. Its burning good the way i have it set right now, but its still not right. Mine only has 2 external adjustments...air-pilot and idle. i guess thats why i am being confused. Its a mikuni if that helps.

[RMX250MB]

let me look at the book and give a better decription of all the specs and all that.

[dajogejr]

Originally Posted by RMX250MB

plug looks nice and tan like it should. Its burning good the way i have it set right now, but its still not right. Mine only has 2 external adjustments...air-pilot and idle. i guess thats why i am being confused. Its a mikuni if that helps.

I'm sorry....I wasn't more clear.

A carb either has an air screw OR a fuel screw.
Not both...

And most have idle adjustments, PJ series use the choke for idle adjustments, most have screw that raises the slide for idle.....which it sounds like your Mikuni does.