Originally Posted by Luke
No wonder you were having trouble with jetting. Mikuni and Keihin jets sizes have nothing to do with each other. According to the manual, if your correct main jet at sea level was 162, you should run a 152 at 7000 feet. Not 122.
Here's the chart:
No Luke I wasn't running a 122, I was just making a point based on Mikuni as I have a MIkuni 34mm on my XR600. And I realize that I made a mistake in my advice just today. Another reason not to take everyone's advice blindly without doing your own homework.
I have the stock Keihin in my XR4 and I think I had a 168 at sea level but I still wasn't sure it was right. I didn't have the Trailtech hooked up till I got to CO so I really didn't have a baseline to go off of. When I got to CO the shop in Durango suggested a 142 and I even thought that was wrong but I went ahead and got it with a 148, 152, 158, 162 and a 166 cause they had them. I was wrong all the way around. I ended up putting in the 166 in Moab for the whole rest of the trip till Reno and it ran better but not perfect. I also pulled the top end in Reno and discovered the 10:1 piston and about 1.5mm of carbon build up on top of the piston. Those two factors raised the compression to around 11.5:1 and once I got it cleaned off the temps came way down and I jetted back to I think 152 above 4000 and 162 at sea level to 4K. The only damage I noticed from the high heat problems was a noisy cam bearing that cost me $12 at the Reno Honda dealer.
Owell she held up and my compression is still very good. I'll probably put a 440cc kit in it when it needs freshening and rejet all over again.
Thanks for the link about the Kehin. Later Travis