fastest way to check jetting (cheap & fast)

[therustyaxe]

I was asking my neighbor (state champion in 250cc dirt bike class) for help with my carb issue. He gave me this track side tip that really works! Kliff might know this one but I thought I would share anyway. ;D

He grabbed a plastic cup (red beer/party cup) and partially covered my UNI filter and zip tied tied it on.

The theory ...

If the bogging or stumbling gets worse at 3/4 to WOT, you are running to rich.

If it gets better, you are running to lean (getting to much air).

The reason why ...

If you restrict the air to equal out or increase the fuel to air ratio the performance should increase.

It is a track side trick they use in the pits for fast evaluation to steer them in the right direction during a race because they don't have time.

I found this useful to me and maybe you can to.


Paul

[oldchopperguy]

Cool tip! Gotta try it out! Should be a real time-saver for us Rebs who are changing jets, exhausts, etc. Probably more quick and "seat of the pants" effective than having to run "X" number of miles, then check the plug, then do over, and over, and over...

THANKS for passing it on!

Sincerely,

Leo in Texas

[Rebel]

I would have guessed just the opposite.

At 3/4 to WOT you would be letting more air in and if it starts to stumble I'd think it was too lean. Then putting the cup over it would restrict the intake making it like turning the throttle back. But I'm not expert.

[xs650]

Paul's friend had ir right because the cup acts like an old fashioned butterfly choke and the way he is using it only effects things at wide throttle openings.

Put the cup on (it's a partial choke) and it richens the mixture at high throttle openings.

Reduced choke effect is the main reason you need bigger main jets when you install a low restriction air cleaner.

[Rebel]

That makes sense to me.

[therustyaxe]

I'm a retard when explaining things lol,

Thx xs650, your explination is easer to understand.

It would also help if I could learn how to spell to, LOL!

Paul

[Rebel]

spel wot?