hot pipe

[rmooney21]

im trying to jet my bike, it dont lean pop but the pipe glows orange. its a full yoshi system does that mean its too lean, i have a 158 main jet in it the needle is one clip down it dont feel to bad it has a slight stutter at high rpm

[400eXr1d3rZ]

That sounds way too lean. Go up to about a 165 keihin. And work your way down. Get a 50 pilot. and mess with the air/fuel screw try 2.5 - 3 spins out.

[rmooney21]

if i go with a higher main the top end stutter gets worse i have a 50 pilot in it so ill try a higher main and mess with the air fuel screw, thanks again

[400eXr1d3rZ]

No problem ;)

[firefighterjosh]

I would keep going up on the main until the bike stutters then back off one jet size. That should get ya were you need to go:)

[GPracer2500]

Originally posted by firefighterjosh
I would keep going up on the main until the bike stutters then back off one jet size. That should get ya were you need to go:)

That'll put ya way too rich IMO.

[firefighterjosh]

Originally posted by GPracer2500
That'll put ya way too rich IMO.

Thats how I have done all my quads. My dad did it in his drag bikes to.

Just keep stepping up Jet size until the bike stutters then back off one jet and the stuttering stop bike runs smooth. I don't see the problem? Then mess around with the pilot and needel.

[GPracer2500]

Originally posted by firefighterjosh
Thats how I have done all my quads. My dad did it in his drag bikes to.

Just keep stepping up Jet size until the bike stutters then back off one jet and the stuttering stop bike runs smooth. I don't see the problem? Then mess around with the pilot and needel.

With all do respect, just because that's how you and some others have always done it doesn't make it the best way.

Most engines will run without misfiring even though the air/fuel mixture is way too rich. This is especially true with a modern and effecient combustion chamber like that found on a 450r and most other quads. If you keep going richer until the engine misfires and then back down one size you are leaving a lot of HP on the table.

Lets say a hypothetical engine has a range of main jet sizes from 170 to 190 in which it will run without misfiring. The "best power" air/fuel mixture will be much closer to 170 than 190.

The engine will generate a corresponding increase in heat along with that HP. For that reason it's often reasonable not to jet on the edge of lean even though that's where the highest HP will be found. But that's a much bigger consideration with an air-cooled engine. Liquid cooling is much more forgiving at allowing for best power jetting because it's so much better at getting heat out of the head/cylinder/piston/etc. Jetting closer to a 190 in this hypothetical engine will run somewhat cooler but won't perform nearly as well. A good part of why it's running cooler is because the engine isn't producing as much power.

Your method of evaluating main jet size is "safe" but far from ideal. Jetting right at a best power mixture leaves no room for error as weather or riding conditions change, if the fuel used is of a marginal octane rating, and under very hard running could even overwhelm the engine's cooling capacity. That last point gets back to the differences between air and liquid cooling. On the other hand, jetting way too rich can cause problems with carbon deposites building up inside the engine.

From what I've observed most people have a tendency to run richer jetting than necessary. The old saying that lean is mean is grounded in truth.

The "problem" with jetting up until a misfire occurs and then backing down one size is that you're creating an unecessarily large cushion for protecting yourself from running too lean. Getting back to my hypothetical engine example, if best power is realized with a 170 then running a 190 is overkill. Running--lets say--a 175 or 178 should provide adequate "cushion" against accidentally running too lean. Running the 190 does nothing but hurt performance.

[firefighterjosh]

^^^I see what your saying, and understand it.^^^

I guess the way I have done it has always worked. I should have made myself more clear by saying, "Up your main till the bike sputter then drop 1 jet, that should get you in the BALL PARK" I guess that gets you close to were you need to go.

A little rich never hurt ether. Like myself and most ppl don't have the money to rebuild there engines. I race XC and like to have my machines a little rich. Not a smoking black smoke rich, but Just a tad over.

[Architects]

whats your plug look like?

[rmooney21]

im going to pull the plug today, i was testing at 10:00 pm last night and the neighbors were coming outside with flashlights so i decided to stop before they call the cops. but i will post when i check after work.

thanks again everyone for the great help!!!