OK, here it goes. I have a friend (no really, its my friends bike, not mine) who has a freshly built 77' XS650. Frame off...powdercoated frame...the works. He did a really nice job. Also tore down and rebuilt the motor, and I trust his work. He also has the full Hughs PM/Charging and ignition set up. So (sparing no expense) he also buys brand new Mikuni VM34's for the bike. While he is a very good mechanic he does not excel at carburation. So, enter me...
Here are the current specs of the carbs:
MJ: 180
PJ: 25
Needle: 6F9 (middle clip)
AJ: removed
Red UNI filters
What looks to be stock exhaust (with baffles)
Here is my best description of the behavior. Starts very easily and idles well. On the stand will rev up to about 5K where it just falls on its face. If I try and drive it it has very little power under load. I have a driveway with a slight incline and it struggles to make it up the driveway unless I got 1/2-3/4 throttle. I have went up to 220 main jets and down to 170 with almost no difference. It does pop a little more with 170's (so I'm guessing that is lean), but other than that, the behavior is pretty consistent regardless of jets, which makes me think there could be something else going on. I also checked the float hight...22mm, I even made it slightly lower to raise the fuel level. Popped the fuel tank cap to be sure there is no pressure lock. No leaks at the boots.
I've built and tuned 3 or 4 xs650s over the years, but this is my first exposure to VM34's so don't assume anything. I did verify the slides are 2.5. I have read that there are two stroke versions of VM34's out there, is it possible I have those? If so, what should I check for. I'm in Asheville, NC so we'r at about 2k elevation re: jetting.
I am at a bit of a loss at this point. I did a compression check and ~145 on both cylinders. Spark is strong on both sides. Thought I would pull the covers and check the valve clearance just in case (though compression is good that shouldn't matter right?).
Any help, commentary or jeers appreciated. Oh, and yes, I have read THIS and the Super tuning manual.
Here are the current specs of the carbs:
MJ: 180
PJ: 25
Needle: 6F9 (middle clip)
AJ: removed
Red UNI filters
What looks to be stock exhaust (with baffles)
Here is my best description of the behavior. Starts very easily and idles well. On the stand will rev up to about 5K where it just falls on its face. If I try and drive it it has very little power under load. I have a driveway with a slight incline and it struggles to make it up the driveway unless I got 1/2-3/4 throttle. I have went up to 220 main jets and down to 170 with almost no difference. It does pop a little more with 170's (so I'm guessing that is lean), but other than that, the behavior is pretty consistent regardless of jets, which makes me think there could be something else going on. I also checked the float hight...22mm, I even made it slightly lower to raise the fuel level. Popped the fuel tank cap to be sure there is no pressure lock. No leaks at the boots.
I've built and tuned 3 or 4 xs650s over the years, but this is my first exposure to VM34's so don't assume anything. I did verify the slides are 2.5. I have read that there are two stroke versions of VM34's out there, is it possible I have those? If so, what should I check for. I'm in Asheville, NC so we'r at about 2k elevation re: jetting.
I am at a bit of a loss at this point. I did a compression check and ~145 on both cylinders. Spark is strong on both sides. Thought I would pull the covers and check the valve clearance just in case (though compression is good that shouldn't matter right?).
Any help, commentary or jeers appreciated. Oh, and yes, I have read THIS and the Super tuning manual.
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