Fixing lean-running bike w/out pulling the carb

[EBOD]

I just put the FMF Rev Pipe on my otherwise stock (including air box cover--for now). The bike now seems to be running a bit lean at smaller throttle openings (1/8 - 1/4).

I'm not too good with a wrench, so I'd like to address this without having to pull the carburetor/change my jetting. To that end, how will the following affect (help??) my issues:

1) Pre-Mix Ratio: If I change from 32:1 to 40:1 will that make my bike run a little richer?

2) Altitude: I live at about sea level, but I ride at about 2500 to 3000 feet. It seems that the thinner (less dense) air would make my bike run a little richer. Is this true (or, as so ofter is the case for me on carb issues, did I get confused along the way)?

3) Air Screw: I've read articles/posts saying that air screw adjustments can help with low-throttle lean/rich issues. Have any of you had success with such adjustments? Also, where exactly is the air screw (sorry for the stupid question)? My owners manual lables only the idle adjustor and the choke and I don't want to mess with the wrong thing.

4) Air Box: When I remove/drill my air box lid, will this problem get better or worse? It seems better air flow would lead to the bike running a bit leaner. As stated above, however, carburation issues tend to be a little counter-intuitive to me. Thus, I may have this backwards.

Thanks in advance for any advice you may have.

 

[dirt bike dave]

1) Yes, but in my experience the difference will be minor. Adjusting jetting by varying the oil mix is no substitute.

2) You are correct. If you jet your bike for sea level, it will run rich at altitude. The easy way to think of this is any time there is less oxegyn, you will want less fuel for optimum jetting.

3) The air-screw is a small brass screw at on the lower left side of the carb, just above the float bowl. You will need a small screw driver to adjust. Many riders ignore this or don't know about it, but it can make a profound difference in low speed running. The way to keep track of the adjustment is how many turns out. Turned in is richer - turning out leans the mixture. As a general rule, if you are more than 2 turns out and the bike is still too rich, you should get a smaller pilot (low speed) jet.

4) You are correct. Anything that reduces restriction in the airbox will cause the bike to run slightly leaner, but again the differences might be very minor. Going the other direction, if your airfilter is very dirty, the bike will run too rich.

The proper pilot/low speed jet and fine tuning with the air screw are really important to get the bike running right! You will be rewared with better throttle response and low end power - well worth the time!

 

[freydog]

You are on the right track.

1) Changing the oil ratio will probably not help you that much. If you try it, I wouldn't go any leaner than 50:1 with a synthetic oil.

3) With the airbox lid on, you should be able to improve the situation by turning the airscrew clockwise, thereby richening things up. Try moving it 1/4 turn at a time. This will also increase your idle RPM, so you will have to readjust it. No big deal.

4) Removing the airbox lid will make your problem worse. In my experience, you will probably need to change jetts or jet needle position to make it run right. This is not that hard to do either.

 

[Nevada Sixx]

Could a colder spark plug make it run any richer? may use a ngk br9es instead of br8es?

 

[flyinfish]

Where in Cali are you

Hey Ebod where in California do you live I'm in the Central Valley but spend a lot of time in San Diego. I'd be glad to help you change out the pilot jet if your local to either of these places.

T.J.

 

[David Trustrum]

ARRgh Spark plug to make it richer???

No. Just no.

Dude you should become familiar with pulling the carb as residue can block up jets so you should clean it out every so often. Really, with guidance your grandmother could do it. Don’t be afraid, you’ll have fun.

 

[EBOD]

Thanks and

As usual, this forum really helped answer my questions. Thanks again for all of your replies. I can't wait until I learn enough to answer people's questions (so I can return the favors) instead of just asking them.

Also

Flyinfish,

I live in LA. I have family in Newport Beach, so I spend some time down there as well. I've been riding at Gorman (mainly because I haven't discovered any other cool places to ride yet). If you ever ride at Gorman or a place not too far from Newport, let me know. It'd be cool to meet/ride with DRN/Just KDX forum members. SD and Central Valley are probably too far for me to go to learn how to change jets, but when it's time for me to try the wrench, I'll post again and see if your offer still stands.