Mudcat, your right the higher the elevation the "thinner" the air which requires a richer mixture ie: larger jet size. K@N jet numbers are reverse. (I think K@N wants to purposely confuse the backyard mechanic to prevent us from catching on.)The larger the number the smaller the hole in the jet.

I went to my dealer and he tells me replacement Keihin jets are bigger by number. I have to be sure before I lean out my machine. I usually check the jet holes by running a tapered sewing needle in the jet. The farther the needle enters the hole the bigger the jet. I also check my pipe and plug at full throttle blasts looking for a gray ash deposit rather than the black soot deposit.

 

Thanks, I thaught that was right, but the #s had me confused. I can't believe that they want $60 for $10 worth of parts. There are a lot of the K&N jet kits sold though.
Thanks for setting me straight, at 600 feet we don't have to deal with a lot of elevation issues around here. But it is good to know.

 

Well ,I had the opportunity to take some plug checks which confirmed my theory. The bike is running lean at 1500 ft. The plug reads dark tan with a carbon ring and grey and black ash at the tail pipe. I think with a 148 main being stock a 150 should be perfect. Anyone around 750 ft to sea level should use a 152. I also notice a very slight hesitation when gunning it. If I find an adjustable needle I will lower that a notch. The plug should read very light tan with no carbon ring and grey ash at the pipe. Always, take a plug reading at full throttle (riding) and cut the engine.

My dealer was wrong about the sizes always ask a partman.

 

duplicate post

 

You have it backwards. The higher you go the smaller the jet needed. If you have less air with altitude you need less fuel. The optimum fuel air ratio is 15:1. Anything higher, such as 13:1 or such, is too rich. Over 17:1 is too lean.

Dark tan is not too lean. That is actually what you want.

 

Listen to minehunter he is 100% right!

 

I agree with you on the elevation part but not the plug color. Pull your plug on a computer controled fuel injected car. It runs the same fuel with perfect 15:1 air/fuel. Compare. The plug will be very very light tan with the insulator very clean not dark tan with a carbon ring. I might be confused as to the corresponding number for the jet. If the plug was showing a white insulator with no color than this would indicate a lean condition. Poor throttle response, hesitation, all symptoms of rich carb condition.

 

The 400 & 500 have the same engine block so both use the same filters, at least that is the case for the year 2000 models. I've used the NAPA & STP filters with no problems. But prefer the STP because the NAPA doesn't have the bypass valve built in should the filter become clogged. But I guess changing the oil so often makes clogging unlikely. I've also been using Mobil 1 10w30 since the first two oil changes. The cat just rolled over 2000 miles last week. No problems except the plastic housing around the gear indicator lights cracked where the brake cable and wire bundle from the LH handleber had it in a bind.

 

I have a 2002 500 and was wondering if anyone was having problems running full synthetic oil. I ran it in a motorcycle with a wet clutch and they began to slip after a short time. I am a firm believer in syn. oils but I don't want my wet clutch to begin slipping. Any success's or failures out there?[img]i/expressions/face-icon-small-confused.gif[/img]

 

Its all my 375 has had since 50 miles. It has had no problems. It is an automatic, but it does have a clutch system. It now has 600 miles with much hill and mountain climbing.