98 RX650L main Jet size?

**BDF** · #1 13 Jun 2005

Can anyone tell me the factory main jet size? I have a miss / backfire. Currently it has a 160 in it, but the plug is a bit white on the tip indicating lean. Air pilot screw seems to be happy around 3 turns, that is about 1/2 a turn farther an any other of my bikes.
Through my scope on the CDI and it looks good, stable, constant.
Any other thoughts or suggestions would be great!
Thanks.

**RichLees** · #2 13 Jun 2005

you previously said this misfire was off idle - main jet only really affects 3/4 to full throttle so, while 160-165 would be right for many exhausts, that's unlikely to be the problem. is it misfiring under load or when revving it at the side of the road? is it when opening or closing the throttle.

the number of turns on the airscrew is only indicative. are you clear on how to set it properly? thoroughly warm the engine and then, with it still running, wind the screw in until the revs fall, then wind it out as the revs rise and then fall again. the right setting is halfway between the positions at which revs fall when winding in and out. if this is 3 turns, fine. remember to set the idle speed once the mixture is set rather than to use idle speed to compensate for bad mixture.

despite all that, I'm not clear that it'll help you much because I'm not really clear what the symptoms are. one XR400 I had came with a high float so the fuel level was high. this caused an intermittent hiccough under load which pointed to a large main jet, but was actually resolvced by adjusting the float height

good luck and try describing the symptoms more fully

**BDF** · #3 13 Jun 2005

Thanks Rich,
Yes I have dialed the air idel all the way out, till the revs drop, and back in till they drop. 3 was in the middle. The issue had been at idel as well, the air idel was at 2.5 when I bought it, (cranked it in and counted before removing) by correctly setting the air idel, the miss has cleared up at idel. I will PU a 165 Main and see what that does through my mids. How do you adjust the float level in these, it seemes to be set in plastic?
The miss seems to be in the mids, not even really under load. When I crack it while at mid RPM it seems to accelerate fine. Any further thoughs or suggestions would be great!
Thanks.

[This message has been edited by BDF (edited 13 June 2005).]

[This message has been edited by BDF (edited 13 June 2005).]

**RichLees** · #4 14 Jun 2005

well, it sounds like you've been doing all the right things with the carb.

to adjust the float level, you can usually bend the tag that pushes on the valve seat, but I'm not clear that's going to be the issue.

**BDF** · #5 14 Jun 2005

I am going to try a bit richer on the main & the pilot, also check the valves. What does the diaphragm on the side of the carb do? It appears to be some sort of a switch, one end of it connects down to the oil pump, and the other "Y" goes to in front of the butterfly. What does this control / accomplish? Also if you happened to know the valve clearances that would be great.
I have had many bikes, but this is my first true thumper, Currently also have an 85DR200, but I get up into the foothills and 7000 feet, and the little DR doesn't have much left up there. I had a 92 ZX11 but was doing more and more riding on the DR, so I got a straight across trade for the 98 XR650L but with the miss. The carb had some residue in it, but the problem is still there, the air idle cleaned up the miss on low end, so I figured richen up the main & pilot, see what happens, for the cost of a couple of jets. The bike "appears" to be in good shape, but after close examination, a few heli coils here and there, some one had welded on the frame, making me question the CDI (Quickest way to nuke a Ho2 sensor on a car), but I scoped that and it looks good.

**BCK_973** · #6 14 Jun 2005

From factory it came with a 152 jet.
KH

**BDF** · #7 14 Jun 2005

Thanks BCK_973, so I guess a 160 is already a bit richer. My intake valves have 0 clerance, that is probably and issue as well, and certainly needs to be addressed.