I just took the bottom off of the carb. The # on the main jet is 126. If I order a new jet through my dealer-137.5? will I have to replace the needle jet also? I am attempting to contact the previous owner to see what it is that was done. If I replace the jet with an original what adjustments will I have to make? This whole thing is starting to p*ss me off. When I took the carb off I noticed that the air cleaner boot was torn and had been repaired with silicone calk. So I have to order one of those too. I should have just bought a new bike.

 

Steve - I can tell you how to determine if it is a Dynojet or a Mikuni - the Mikuni jets have a groove around the head, and both ends of the hole will be chamfered. Dynojets have no groove, they are smooth on the side of the head, and both ends of the hole have no chamfer, its just drilled straight through with no chamfering. If the main jet is Mikuni, you can assume the needle is too.
I just read on another thread that the cats have a screen inside the air duct that may be clogged. I've never looked inside the duct, take a look inside yours. Any blockage of air flow will cause a rich condition, causnig the plug to blacken.

Since your plug is black, this indicates rich, so you won't want to go up on the jet size.

 

I saw the screen inside the air box, but didn't really check it. I will pull the carb apart and try to see what the jet is. I looked on brownsleisureworld.com, they have every part listed out. The main jet is listed as 137.5. Why in the heck would mine have a smaller one in it? I will go look at it right now. Thanks for the help!

 

I looked at the jet. I don't see any groove on the side of the jet, but it does look like the hole is chamfered. Before the #126 there is some sort of symbol, but I can't tell what it is. Also, which hole are you talking about. The hole on each end of the jet is bigger before it goes down in and then there is a smaller hole. It is not chamfered on the very ends, but is where the smaller hole is. Does that make sense at all?

 

I also just looked on the dynojet site. For the stage one kit it lists the main jet as 126, so I guess that I can assume that it is a dynojet in it. I am going to put the foam filter in it no matter what. Can I leave the existing jet in, or do I need to change it back? What if I get the new filter and try adjusting the mixture to lean it out a little bit? Which way do I turn the screw?

 

Sounds like you just about got it figured out. With a stock filter and untorn boot, you can pretty well count on the dynojet istructions, so if the carb has a dynojet kit in it then it should be tuned right, as long as the filter is clean and that screen isn't blocked.
One other thing I guess you should check now is the needle clip position. Look at those instruction again, then take the top of your carb off and see if the needle clip is on the right groove. This too can fowl a plug.

Here's how the fuel circuit works, it may shed some light:
Air/fuel screw controls mixture at IDLE ONLY
Pilot jet controls mixture from idle to 1/4 throttle
Needle controls mixture from 1/4 to 3/4 throttle
Main jet controls full throttle

After checking the needle postion, adjust the idle screw per the instructions too.
Also, pay attention to the altitude recomendations on the instructions - it makes a difference.

 

Yes, Hightower is correct about how the fuel circuit works. If you are not running quad full throttle, you should not even be looking at the main jet. To adjust your air screw, have a buddy turn throttle 1/4 while you turn air screw until your engine runs smoothest. If no one is there to help, you can idle bike all the way up with idle screw & do it.

 

I looked at where the clip was set and it was in the wrong position. I put that to the third ring. The only problem now is that the main jet that is in it is the wrong one for my altitude. The one that is in it is for 3000-6000ft. I am not even close to 1000ft., but if the main jet is for full throttle only I guess I don't have to worry about it?

2fat4moto, you said to turn the air screw? Is that the idle mixture screw? I hate to sound ignorant, but I am. Can you tell me exactly which screw it is? I am now going to put it back in the garage and wait for my air filter and the air box boot to come in before I screw something up by sucking crap into the carb.

Again, Thanks for the help!!

 

Air screw, idle mixture screw, same thing, there is only one adjustable screw on the carb. Set it where the kit instructions say to +/- a 1/4 turn for a little fine tuning if need be.
Run the way it is for a while after you get the stuff you're waiting for, with a fresh new white plug. if the plug doesn't get a nice tan color after your first good ride then call Dynojet and get the right jet - $2.00 each. The fuel has to pass through the main jet before the needle can meter it, so even though the main jet is mainly for the full throttle mixture, it can have some effect on the entire thottle travel if it is lean. Lean causes more heat in the combustion chamber and exhaust gas, at a faster rate than the cooling system can dissipate it, but being one jet lean isn' going to do any damage for just a couple rides.

 

Thanks everyone. I will post after I get it back together.