How do you know if your bikes too lean/rich?

[Blaise22]

Im trying to tune my pilot screw right now. I started with it running very rich and have leaned it out a lot. I could tell when it was running rich but how can you tell if its running too lean?

 

[cthowards]

I'm no expert but I adjust my pilot by turning up the idle screw to get the revs up, then turn in the fuel screw until it almost stalls. I then start backing out the screw slowly until she purrs (you can hear when it runs nice and smooth). I then go a little bit richer (1/8th - 1/4th or so) and that's it. Before doing this, the bike needs to be warmed up good (ride it for 10 minutes). Also, count the number of turns you back the screw out...if it's less than 1 or greater than 3 then you likely need a smaller or larger pilot jet.

Finally, I once had an instance where the bike was crackling on decel. I adjusted the pilot screw as described above and it went away.

Good luck.

 

[Blaise22]

Thanks for the advice Ill try that :nod: About how many turns do you turn the idle screw up?

 

[2strokerfun]

how can you tell if its running too lean?

Warm it up. Then stop and put a new spark plug in it, open it up with a load on it (like going up a hill), pull in the clutch and hit the kill switch. Now check the plug before running it again. If it's white or slightly off white, you are too lean. That's very basic test. It can get pretty complicated, so you might do a search for more information

 

[cthowards]

Thanks for the advice Ill try that :nod: About how many turns do you turn the idle screw up?

I have an hour meter with a tach on it so I just turn the idle screw enough to get the idle up to 2,000-2,200 rpms or so. I really don't turn it that much since I have the idle higher than stock anyways...maybe like a half a turn. It doesn't' have to be too precise...just try to get it at a fast idle and then play with the screw and see if you can hear the difference once you start backing it out from the ready to stall point.

Good luck.

 

[Rich Rohrich]

Warm it up. Then stop and put a new spark plug in it, open it up with a load on it (like going up a hill), pull in the clutch and hit the kill switch. Now check the plug before running it again. If it's white or slightly off white, you are too lean.

Four-stroke plugs are ALWAYS white when they are jetted correctly. There is no oil burning in the chamber so there are no oil deposits on the plug to color the insulator.

Unless you have a ton of experience, trying to jet a four-stroke by reading plugs is really difficult.

 

[Blaise22]

Four-stroke plugs are ALWAYS white when they are jetted correctly. There is no oil burning in the chamber so there are no oil deposits on the plug to color the insulator.

Unless you have a ton of experience, trying to jet a four-stroke by reading plugs is really difficult.

Do you have a special way of tuning a four stroke :) ?
Does the idle screw have an effect on the engines performance?
( Im not sure if its called the idle screw, its the big silver one on the bottom left of the carb. Ive been using it to increase/decrease my idle so I hope it is :ohmy: .)

 

[Rich Rohrich]

Do you have a special way of tuning a four stroke :) ?

If it feels right, then it is right. They aren't as sensitive as two-strokes, and you won't hurt the engine even if you are way too lean. The worst that will happen is the engine will bog. So work in small steps and ignore 80% of what you read on the internet. :)

Get familiar with the fuel screw at the bottom of the carb near the intake manifold. The fuel screw and the pilot circuit is all most people need to adjust to get good response. Once you get really comfortable with the bike's characteristics and how carb adjustments impact performance, then it might be worth looking into something like a JD Jetting kit for your bike to fine tune things.

It's also worth reading the FCR tuning guide that Patrick Burns wrote. It has a lot of really good info : http://www.factorypro.com/tech/carbkei.html

Does the idle screw have an effect on the engines performance?

It only changes the idle speed. Set the idle speed at the correct rpm as outlined in the service manual and then leave it alone.

 

[Blaise22]

Wow theres a lot of useful info in that link, thanks rich :nod:
Ive got it to where it needs to be but it backfires alot when I decellerate, any ideas?

 

[flynbryan]

Rich knows ALOT more than I'll ever think about, but in my experience backfiring on decel is generally a lean pilot jet.

 

[BigRedAF]

Rich's post are always good, check his history.

2Strokerfun, sorry but that just doesn't work on a thumper.

cthowards did a good job of describing the process.

You just need the idle a little higher than normal so the bike won't die when you go in/lean. Going out gets rich and sounds flat if you go to far. When your lean and you blip the throttle it will go BOWWA when its spot on it will rev cleanly. To rich and throttle response is slow.

flymbryan, backfiring is as you say most of the time. The fuel screw can solve that problem too if your within it's adjustment range. If not the pilot comes into play.

 

[Rich Rohrich]

Assuming you exhaust system isn't leaking anywhere and drawing in fresh air that causes a re-fire, when the low speed jetting is correct it should backfire a little bit when you decel hard from high rpm. If it bothers you, as was pointed out in one of the posts above, richening up the low jetting with the fuel screw or the pilot jet will eliminate the backfire, but usually at the expense of some throttle response.

It's been my experience that people run the low speed jetting too rich to eliminate the backfire, and then spend countless hours (and usually $$) jerking around with the accelerator pump trying to get the throttle response back.

It's a system, and making a change in one area will have usually consequences in others. So working carefully making one change at a time and documenting what the results are across the board will generally give you the best results as you are learning this stuff.

 

[Cman250]

"It's a system, and making a change in one area will have usually consequences in others. So working carefully making one change at a time and documenting what the results are across the board will generally give you the best results as you are learning this stuff."





Kind of like in algebra class when you try and solve for different unknowns but you have to use the order of operations solving each varible one at a time or else you just scew youself up later.

So this math stuff might be usefull after all.. :coocoo:

 

[Blaise22]

Assuming you exhaust system isn't leaking anywhere and drawing in fresh air that causes a re-fire, when the low speed jetting is correct it should backfire a little bit when you decel hard from high rpm. If it bothers you, as was pointed out in one of the posts above, richening up the low jetting with the fuel screw or the pilot jet will eliminate the backfire, but usually at the expense of some throttle response.

It's been my experience that people run the low speed jetting too rich to eliminate the backfire, and then spend countless hours (and usually $$) jerking around with the accelerator pump trying to get the throttle response back.

It's a system, and making a change in one area will have usually consequences in others. So working carefully making one change at a time and documenting what the results are across the board will generally give you the best results as you are learning this stuff.

The backfiring dosnt bother me at all and if its supposed to do it alittle then I think its perfect where it is . I just thought backfiring meant something was wrong but I guess not. Thanks for all the help guys :cool: .