Post by marinervella on Jan 5, 2016 19:01:40 GMT -5
Happy New Year! I'm sharing a problem/solution that I just experienced in hopes that it might help someone else solve a similar pesky problem.
I have a Benjhou Road Queen (gotta love that name) -- it's almost identical to a Roketa MC-54B with the horizontal Linhai 257 engine. For some time now, I've been having problems consistent with a vacuum leak or fuel delivery problem -- really hard cold-starting, wandering idle speed, dying of fuel starvation during high-speed runs... So my holiday project was to install a Mikuni DF44 fuel pump and replace all my vacuum lines; also checked the valve adjustment, carb jets, and float level, while I had the plastics off.
Much to my dismay, the engine didn't run any better after all that work. I pulled the carb again, and I'm not sure why, but I hooked up a hose to the ACV vacuum port and sucked on it. I found that I could suck or blow air almost unrestricted. I pulled the top cover off the ACV and saw that the rubber diaphragm was apparently in good condition, but the tiny O-ring that is supposed to seal the gap between the ACV base and top cover didn't look so good, and was apparently the source of the vacuum leak. On deceleration, high vacuum is supposed to go from the hose/port on the base of the ACV, up through a small hole in the middle of the tiny O-ring, to a passage in the ACV cover, where it pulls up on the diaphragm causing the tiny air valve below it to close. But the O-ring was letting large amounts of air in instead. Check the photos of 250cc carbs posted by alleyoop elsewhere on the board to help visualize this part of the carb.
Not having a spare O-ring (and they are not usually included in carb rebuild kits), I carefully applied some Permatex gasket material with a small screwdriver to the top and bottom of the O-ring (kind of like icing a tiny doughnut while trying not to get any gasket stuff in the center hole/air passage). After reassembling and letting the sealant dry, I was able to pull a good vacuum with minimal air leakage. And when I reassembled everything, the scooter ran MUCH better. It starts immediately first thing in the (cold) morning, gets to a stable idle speed quickly, holds its idle setting better, and so far, hasn't died of fuel starvation.
I hope this tale helps someone else with a similar problem in the future -- I think it's probably a pretty rare problem, but that's what made it so hard to identify. My only question for the experts is -- do you have any idea what size O-ring or seal could be used to replace that little part?
I have a Benjhou Road Queen (gotta love that name) -- it's almost identical to a Roketa MC-54B with the horizontal Linhai 257 engine. For some time now, I've been having problems consistent with a vacuum leak or fuel delivery problem -- really hard cold-starting, wandering idle speed, dying of fuel starvation during high-speed runs... So my holiday project was to install a Mikuni DF44 fuel pump and replace all my vacuum lines; also checked the valve adjustment, carb jets, and float level, while I had the plastics off.
Much to my dismay, the engine didn't run any better after all that work. I pulled the carb again, and I'm not sure why, but I hooked up a hose to the ACV vacuum port and sucked on it. I found that I could suck or blow air almost unrestricted. I pulled the top cover off the ACV and saw that the rubber diaphragm was apparently in good condition, but the tiny O-ring that is supposed to seal the gap between the ACV base and top cover didn't look so good, and was apparently the source of the vacuum leak. On deceleration, high vacuum is supposed to go from the hose/port on the base of the ACV, up through a small hole in the middle of the tiny O-ring, to a passage in the ACV cover, where it pulls up on the diaphragm causing the tiny air valve below it to close. But the O-ring was letting large amounts of air in instead. Check the photos of 250cc carbs posted by alleyoop elsewhere on the board to help visualize this part of the carb.
Not having a spare O-ring (and they are not usually included in carb rebuild kits), I carefully applied some Permatex gasket material with a small screwdriver to the top and bottom of the O-ring (kind of like icing a tiny doughnut while trying not to get any gasket stuff in the center hole/air passage). After reassembling and letting the sealant dry, I was able to pull a good vacuum with minimal air leakage. And when I reassembled everything, the scooter ran MUCH better. It starts immediately first thing in the (cold) morning, gets to a stable idle speed quickly, holds its idle setting better, and so far, hasn't died of fuel starvation.
I hope this tale helps someone else with a similar problem in the future -- I think it's probably a pretty rare problem, but that's what made it so hard to identify. My only question for the experts is -- do you have any idea what size O-ring or seal could be used to replace that little part?
