Rot Box
Diesel and Dust
- Location
- Smithfield Utah
I think there are enough Yamaha/Keihin FCR guys here now that maybe I could pick your brain on a little problem I'm having
Long story short: A friend bought a YZ426 recently and he said it rarely starts and runs like crap when it does start I offered to help tune it in for him and man I've been busy fixing little things that just weren't right. After installing new wheel bearings (it helps if they have balls in them ), cables, levers--and fixing a lot of other neglect now I'm sorta scratching my head with the carb.... It has the power now intake mod, boyesen quick shot, and an aftermarket fuel screw to make tuning easier. A slip on spark arrested muffler and NO air box lid seems to be the only other modifications.
After starting it I found the ilde to be erratic and what seemed to be too much fuel on bottom. Not responding well to the fuel screw I pulled the carb down and found a 48 pilot which I swapped out for a 42 (stock jet btw). The bike starts decent now but it has a nasty bog when the throttle is wicked. A slight bog seems acceptable to me but this is flat out fall on your face bog while riding with a warm motor. Here's what I'm thinking please let me know if I'm on the right track here
1. Too much fuel or too quick of a shot from the accelerator pump? Is the timing on the pump adjustable? If so how do I go about doing this?
2. Pilot jet? Seems to run and idle fine on bottom as long as I have the idle set fairly high.
3. Needle too high? Mid to top seems great though....
I'm convinced there isn't a 2T out there that I don't feel comfortable tuning, but since I've been living under a rock for half my life this new 4T stuff is a little out of my league. Anyway we're sitting right on 4500ft. here in Cache Valley. Thanks for any tips or advice!
Andrew
Long story short: A friend bought a YZ426 recently and he said it rarely starts and runs like crap when it does start I offered to help tune it in for him and man I've been busy fixing little things that just weren't right. After installing new wheel bearings (it helps if they have balls in them ), cables, levers--and fixing a lot of other neglect now I'm sorta scratching my head with the carb.... It has the power now intake mod, boyesen quick shot, and an aftermarket fuel screw to make tuning easier. A slip on spark arrested muffler and NO air box lid seems to be the only other modifications.
After starting it I found the ilde to be erratic and what seemed to be too much fuel on bottom. Not responding well to the fuel screw I pulled the carb down and found a 48 pilot which I swapped out for a 42 (stock jet btw). The bike starts decent now but it has a nasty bog when the throttle is wicked. A slight bog seems acceptable to me but this is flat out fall on your face bog while riding with a warm motor. Here's what I'm thinking please let me know if I'm on the right track here
1. Too much fuel or too quick of a shot from the accelerator pump? Is the timing on the pump adjustable? If so how do I go about doing this?
2. Pilot jet? Seems to run and idle fine on bottom as long as I have the idle set fairly high.
3. Needle too high? Mid to top seems great though....
I'm convinced there isn't a 2T out there that I don't feel comfortable tuning, but since I've been living under a rock for half my life this new 4T stuff is a little out of my league. Anyway we're sitting right on 4500ft. here in Cache Valley. Thanks for any tips or advice!
Andrew