Texthey all. been following the site for awhile but this is my first post. i need some help with jetting. i've got a p650 with stock jetting and recently did nyroc's exhaust mod. i got some advice that said i shouldnt have to rejett at my altitude(6000ft) as the stock jetting was propably rich, so i left it alone. today as i was riding it backfired pretty good. so, should i rejett and if so any ideas on what size jetts to use?

 

A single backfire isn't always a sign of a problem. If it's consitentely backfiring under the same conditions it would probably be worth looking into. Running lean will usually backfire through the carb instead of the exhaust. I think running rich will backfire through the exhaust.

Before you decide to rejet, you need to know which jets you have. Many dealers do altitude adjustments before they sell their bikes. This means jetting and changing weights in the transmission. Check with your dealer and see what kind of prep is done to your bike, then you'll know which direction to go. Kawi's recommended jetting tends to run a little lean, unless you're at the bottom end of the chart. If the bike has no altitude adjustment and is set for sea level, your bike should have been running rich. You need to do a plug read or use an analyzer to be sure. The exhaust mod will help lean out the mixture, bringing it closer to where it should be. Getting some extra air into the engine will also lean your mixture. So if you're still rich with the exhaust mod, try extra air and you might end up being about right without having to play with the carbs.

 

aj650, thanks for the reply! i'll have to check with the dealer i bought it from, but i dont remember them ever mentioning it being rejetted for alltidude or anything done to the clutch weights.

 

got an update on my jetting. talked with the dealer i bought the machine from and they said that they dont do anything with the carb or clutch unless someone asks then they charge extra for the service. they never mentioned this when i bought mine so it looks like i've got the stock jetts.[img]i/expressions/face-icon-small-disgusted.gif[/img]

 

At 6000' and stock jetting you should have been rich. How did it work before the mod? If you want to go up on the jetting try a #145 in the rear carb and put the rear #142 in the front carb.

 

always ran fine before the mod and to be fair it only backfired out the exhaust once since the mod. 1 other thing i could never figure out was how everyone is getting 65mph or so when all i've ever been able to get was 58 on pavement going downhill after i adjusted the belt! go figure.

 

I run 62 with only the altitude adjustments, which have got to be done to your bike if you want higher speed. The adjustment is 2 separate things.

1 is they put in smaller jets to compensate for the lower oxygen content in the air at elevation. They use the kawi recommended
settings, which maintains the slightly lean factory condition.

2 is the clutch weights. The CVT transmission uses a series of weights to change gear ratios. Since you are at a higher altitude, your engine is not going to make the same amount of power as a bike at sea level, and it's that power that moves the weights to change gears. As such with the stock weights your engine will never achieve it's final gear ratio. So you're basically doing full speed runs in 3rd gear instead of 4th. You will RPM limit before you can top out.

Both were done to my bike at the dealer for $100, so I can't tell you how to do it.

Since you have sea level jetting (138/142), even with the exhaust mod, you're probably a little rich. But since every bike is different it's impossible for me to tell you how rich you are. At your level with no other mods, don't go 142/145. That's the popular performance jetting for a sea level bike and will make yours quite a bit richer than it is now. Kawi recommends 132/138 for your elevation. The perfomance step would be about 136/140 or 138/140. I've got a set of 140 and 142 sitting on a shelf until I get a chance to play with the jetting. I'm planning 138/140 for the moment.

 

I agree with aj650, you must still be rich. Maybe try a plug check to see where your at before diving into the carbs. The one backfire might have just be a fluke.

 

Hey deck357 if your running at 6,000 feet with stock jets your running way to rich! When i bought mine they rejetted it from the shop @ 132 front and a 138 rear thats for 6,000 to 9,000 feet. I did nyroc's exaust mod on my bike to and it made me to lean so i rejeted to a 135 front and a 140 rear. Runs like a raped ape from 4200 feet to 7800 feet (so far). I also have a twin air filter though.

I would do as scotia650 suggested and do a plug check or to or three or four... get the idea.
I checked and cleaned my plugs for a while before i got mine dialed in. Now i can hit 70 mph on a down hill (not a ski slope just in case anyone was wondering.) and i can hit 67 on a flat dirt road.

Just keep checking those plugs and keep them clean with a wire brush. before you know it you will be going as fast as we do... if not faster [img]i/expressions/face-icon-small-wink.gif[/img][img]i/expressions/face-icon-small-smile.gif[/img]