2strokerfun
Member
- May 19, 2006
- 1,500
- 1
Have a 1976 Honda MR250 currently running a CR cylinder, which effectively makes it a CR engine with wider gearing and one heck of a heavier flywheel (CR cylinder different in that exhaust port 1mm lower). Gave up on on worn-out 34mm Keihin about a year ago and bought 36 Mikuni. Had to start sorting jets and needles from scratch, but I finally thought I got it jetted perfectly.
However, the last few times I rode I noticed a problem: Once the bike is good and warmed up, if I really really romp on it at high rpms under a heavy load (and about the only time I ever get in that situation is on a long straight section of track) I'm getting detonation-like clatter. Back off the throttle it disappears. If I'm already going really fast with throttle open, it doesn't exist. Only does it under heavy load at high rpm. Only does it after the bike has been running 10 minutes or so--really warmed up. Throttle has to be close to 3/4 open or more for this to happen. In other words, I'm really running the heck out of it when it does this.
I did plug chops forever when trying to jet this carb from scratch. Finally got what I thought was the correct main, needle, needle jet and pilot jet. Plug chop still looks correct. Took the head off to inspect the piston. No signs of damage from detonation or bearing coming apart yet, but I have no doubt I will soon see some soon if I don't address this.
Bike is still running great when I experience this. No signs of anything wrong other than the noise. Now I am extremely sensitive to the sounds of my engines. It isn't a loud clatter at all, but it is definitely there. I think that most riders wouldn't even notice it. (for instance I don't think even I would hear it if I were riding in flat desert. The weeds and trees along the track seem to echo the sound back to me).
I'm thinking I'm completely or almost completely off the needle when this happens, but I'm not sure. My bike is extremely sensitive to the needle size/settings with this carb. In other words, if I raise the needle, I'm definitely too rich at points.
Even though my plug chop looked perfect, I increased the main one size. It might have helped a pinch, but it might also be my wishful thinking.
Probably going to try going up another main size this weekend and test it, but I'm wondering if anyone has any other ideas. Have new main bearings, but crank rod bearing is getting long in the tooth. Still no up and down play.
I'm probably overly paranoid but I hate exploding engines.
Thanks
However, the last few times I rode I noticed a problem: Once the bike is good and warmed up, if I really really romp on it at high rpms under a heavy load (and about the only time I ever get in that situation is on a long straight section of track) I'm getting detonation-like clatter. Back off the throttle it disappears. If I'm already going really fast with throttle open, it doesn't exist. Only does it under heavy load at high rpm. Only does it after the bike has been running 10 minutes or so--really warmed up. Throttle has to be close to 3/4 open or more for this to happen. In other words, I'm really running the heck out of it when it does this.
I did plug chops forever when trying to jet this carb from scratch. Finally got what I thought was the correct main, needle, needle jet and pilot jet. Plug chop still looks correct. Took the head off to inspect the piston. No signs of damage from detonation or bearing coming apart yet, but I have no doubt I will soon see some soon if I don't address this.
Bike is still running great when I experience this. No signs of anything wrong other than the noise. Now I am extremely sensitive to the sounds of my engines. It isn't a loud clatter at all, but it is definitely there. I think that most riders wouldn't even notice it. (for instance I don't think even I would hear it if I were riding in flat desert. The weeds and trees along the track seem to echo the sound back to me).
I'm thinking I'm completely or almost completely off the needle when this happens, but I'm not sure. My bike is extremely sensitive to the needle size/settings with this carb. In other words, if I raise the needle, I'm definitely too rich at points.
Even though my plug chop looked perfect, I increased the main one size. It might have helped a pinch, but it might also be my wishful thinking.
Probably going to try going up another main size this weekend and test it, but I'm wondering if anyone has any other ideas. Have new main bearings, but crank rod bearing is getting long in the tooth. Still no up and down play.
I'm probably overly paranoid but I hate exploding engines.
Thanks