Idle & carburetor issues CN250 Helix Clone ZNEN TITAN
by: scooterfan86 - Apr 1, 2017 23:02:18 GMT -6
Post by scooterfan86 on Apr 1, 2017 23:02:18 GMT -6
Hi there. I'm rebuilding a Cn250cc clone thats been sitting for the last year. New valves, lapped and compressing well, new gas, head gasket, and more. Things seem to be working again for the most part, except I'm so far I can't get the bike to idle below 2000 rpm. It has also been taking a bit to start up the bike cold. I'll need to try several times to start it, then hold the throttle open until the engine is warm to keep the bike from dying. Easy start with the bike hot, a little easier warm but still may take a try or two.
I've replaced the rubber intake manifold thinking a vacuum leak was leading to more air, higher RPM to compensate and a hot engine, and got a new carburetor today that I'm trying out to see if that solves any of the issues. So far neither of these have worked. I'm in california so there is an extra vacuum line going to the EVAP from the intake manifold. The old manifold had 2 ports, and the new only has one so I tee'd off the vacuum lines going into it. The bike started up fine with this so it looks like there's enough vacuum through the tee.
I haven't tried opening the EVAP things up; could they be causing a vacuum leak I haven't tracked down yet? I'm running the engine with the air box and snorkel on, and have tried adjusting the valves with the engine running to be sure they're not too quiet. I remember that its better to have them a little tappy rather than too tight, but so far this hasn't affected the high idle RPM.
The new carb has an extra brass port running diagonally from the lower left, I've attached a picture. The new one's on the right. Does anyone know what this port would go to? Can I just cap it off? It did run without anything attached to it. I'm assuming this could be at least part of why the new carb seems to be running at higher RPM, with the extra air coming in.
The new carb also has a mixture screw that can be adjusted, while the older one is factory set, so its another thing to mess with but I'd need advice on what to try. It can only be turned around 300 degrees until it hits the edge of the carb.
I've thought about gutting the new carb and putting fresh parts into the older one to see if that helps. It did seem to be running smoother with the new one in, but too low on the throttle idle screw and the engine dies with both carbs. The old carb is japanese, and the new one doesn't say made in japan anywhere. Only around 2000 miles on the bike.
Anyone have any ideas or thoughts?
I've replaced the rubber intake manifold thinking a vacuum leak was leading to more air, higher RPM to compensate and a hot engine, and got a new carburetor today that I'm trying out to see if that solves any of the issues. So far neither of these have worked. I'm in california so there is an extra vacuum line going to the EVAP from the intake manifold. The old manifold had 2 ports, and the new only has one so I tee'd off the vacuum lines going into it. The bike started up fine with this so it looks like there's enough vacuum through the tee.
I haven't tried opening the EVAP things up; could they be causing a vacuum leak I haven't tracked down yet? I'm running the engine with the air box and snorkel on, and have tried adjusting the valves with the engine running to be sure they're not too quiet. I remember that its better to have them a little tappy rather than too tight, but so far this hasn't affected the high idle RPM.
The new carb has an extra brass port running diagonally from the lower left, I've attached a picture. The new one's on the right. Does anyone know what this port would go to? Can I just cap it off? It did run without anything attached to it. I'm assuming this could be at least part of why the new carb seems to be running at higher RPM, with the extra air coming in.
The new carb also has a mixture screw that can be adjusted, while the older one is factory set, so its another thing to mess with but I'd need advice on what to try. It can only be turned around 300 degrees until it hits the edge of the carb.
I've thought about gutting the new carb and putting fresh parts into the older one to see if that helps. It did seem to be running smoother with the new one in, but too low on the throttle idle screw and the engine dies with both carbs. The old carb is japanese, and the new one doesn't say made in japan anywhere. Only around 2000 miles on the bike.
Anyone have any ideas or thoughts?
