Roto36
XS650 Enthusiast
Trying to dial in carbs using dead cylinder method. For some reason the right carb seems to not cooperate.
Background: this is a rebuilt engine with Mikuni VM34-168 carbs (using remote fuel bottle)
When I started tuning carbs the bike idled good, but was smoky appeared super rich. Checked the jets found a 40 pilot, 250 main and 6f5 jet needle. Plugs were wet and sooty. As a precaution I rechecked the typical stuff, timing, timing chain, then the valves. The valves were noisy to start with but when I checked them they were quite a bit off. I reset the intake to .003 and exhaust to .006, a lot smoother sounding now.
Figured the jet setup was to rich to start with. So I put in a 27.5 pilot, 240 main and 6DH4 jet needle, clip at mid position, reset the carb slide heights using 7/32 drill bit, air screw at 1.5 turns out, set the floats to 22mm and put in new plugs. For good measure I used compressed air on the jet openings before installing new ones.
No problem starting up and idles pretty good. Smoke is way reduced. So I let it warm up for about 2 minutes then start the dead cylinder test. Ground the right side plug to the head and unplugged the vacuum hose. Dialed the left carb down to 900rpm any lower and would stall.
Air screw had noticeable effect at 3/4 turn out and at 2 1/4 turns out so I figure 1.5 turns is my sweet spot. I figure this is my starting point for a good idle.
The right carb is where I'm having issues, will run smooth around 1000 - 1200 any lower and it'll putter out. So at this idle it runs smooth for about 10 -20 seconds then the idle starts to drop and finally stalls out. I get a little "Pfh-tt" spit back out the carb, not a backfire but more like it's spitting back a puff of air. I have clear inline fuel filters on each side so I can see the fuel. The right filter seems to run out just sitting there not running. I can pull the hose off and fuel flows fine, but I just don't see a fuel level like in the left side filter. But the bike will still start just fine. As it runs I can see fuel come back in the filter and maintain a level.
So am I running out of fuel in the right carb because it won't run continuously? Or do I need to pull the carb and check floats again and re-clean the carb?
Thanks
Background: this is a rebuilt engine with Mikuni VM34-168 carbs (using remote fuel bottle)
When I started tuning carbs the bike idled good, but was smoky appeared super rich. Checked the jets found a 40 pilot, 250 main and 6f5 jet needle. Plugs were wet and sooty. As a precaution I rechecked the typical stuff, timing, timing chain, then the valves. The valves were noisy to start with but when I checked them they were quite a bit off. I reset the intake to .003 and exhaust to .006, a lot smoother sounding now.
Figured the jet setup was to rich to start with. So I put in a 27.5 pilot, 240 main and 6DH4 jet needle, clip at mid position, reset the carb slide heights using 7/32 drill bit, air screw at 1.5 turns out, set the floats to 22mm and put in new plugs. For good measure I used compressed air on the jet openings before installing new ones.
No problem starting up and idles pretty good. Smoke is way reduced. So I let it warm up for about 2 minutes then start the dead cylinder test. Ground the right side plug to the head and unplugged the vacuum hose. Dialed the left carb down to 900rpm any lower and would stall.
Air screw had noticeable effect at 3/4 turn out and at 2 1/4 turns out so I figure 1.5 turns is my sweet spot. I figure this is my starting point for a good idle.
The right carb is where I'm having issues, will run smooth around 1000 - 1200 any lower and it'll putter out. So at this idle it runs smooth for about 10 -20 seconds then the idle starts to drop and finally stalls out. I get a little "Pfh-tt" spit back out the carb, not a backfire but more like it's spitting back a puff of air. I have clear inline fuel filters on each side so I can see the fuel. The right filter seems to run out just sitting there not running. I can pull the hose off and fuel flows fine, but I just don't see a fuel level like in the left side filter. But the bike will still start just fine. As it runs I can see fuel come back in the filter and maintain a level.
So am I running out of fuel in the right carb because it won't run continuously? Or do I need to pull the carb and check floats again and re-clean the carb?
Thanks
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