QuestionMy friends Yam. 600 surges. Usually not hard, but you can feel it more than you can hear it. It has a new plug as of last fall because it was doing it then also. I pulled the carbs (2) and checked the jets, which looked clean. Fuel supply seems adequate. It starts good and idles fine, but between 4k and 5k rpm it surges and will often quit until the rpms come down, where it usually recovers and runs again. I am stumped. This is a single cylinder thumper that has had little done to it in 20 yrs. Could this be a valve adjustment problem?
AnswerJohn, I have a couple of friends who have had these bikes and the good news is that you can do a few mods to make them run very well.
The bad news is that they are VERY frustrating to work on, especially the carburetors when the air box is still in place. Based on your note, I guess you already know that.
Dynojet used to make kits for them, but I don't know if they are still available now.
Surging conditions exist when the carburetion is too lean. If you ride the bike, get it into the surging range and then apply a little choke, it will probably smooth out again verifying the lean condition. Mid range leaness is generally due to factory settings because of emission control requirements. Raising the needles in the slides will richen it up and eliminate the stumble.
For more info..
http://www.srx600.net/
http://www.micapeak.com/reg/bikes/SRX600/
http://www.geocities.com/srx34/index.html
http://www.yamaha-motor.co.jp/global/product-history/mc/1980/srx600/index.html
http://www.thumperpage.com/articles/srx6faq.html
If it hasn't had a valve adjustment, it is a good idea after 20 years, but I doubt it has anything to do with the problem. The last page link has a revealing story about the side stand switch affecting power output at high rpms, though!
Bill MrHonda Silver
