Arty
Well-Known Member
Enclosed are a few pictures of the mods I did to adapt the JN Motors Stage 3 Walbro Carb kit to my 66cc China Girl engine.
The engine has 40mm stud spacing, not the 32mm provided with the stage 3 kit.
I also wanted to incorporate a thermal isolation spacer I fabricated from 1/2inch thick UHMW (ultra high molecular weight) material. Since I couldn't find long enough metric allen head bolts to reach all the way through the velocity stack, carb, thermal isolation spacer etc., and finally into the 40mm RSE Reed Valve, I built a reed block adapter incorporating a throttle cable mount, threaded to accept the velocity stack/carb mounting bolts provided with the kit, The adapter mounts between the carb, and the isolation spacer using the bolts provided in the kit. Thus, you bolt the stack/carb assembly to the adapter, then bolt the adapter to the reed block, with the isolation spacer sandwiched in between, using easily available longer allen head bolts.
I then modified the carb throttle shaft eccentric to incorporate a swivelling throttle cable clamp, with the new adapter plate built with the throttle cable mount positioned in such a way as to provide wide open throttle, since the cable adapter supplied with the kit was oriented in such a way as to provide only about 3/4 full throttle. The adapter plate also incorporates a stand off for mounting an additional throttle return spring, since I didn't trust the little helical spring provided on the carb.
I also drilled and tapped the carb diaphram cover plate to accept a hose barb for the vacuum impulse provided from my crankcase vacuum line (also drilled and tapped for a hose barb), since I noticed that the little vacuum hole provided on the back mounting face of the carb would be blocked when the carb was installed.
You might also note that I port matched the thermal isolation spacer such that its back opening is machined with a rectangular shape to match the inlet of the reed valve, and the front face is round, to match the carb.
I have to say, that after about two days of tuning, I am really happy with the set-up. It seems to have enhanced all aspects of the performance. It has good punch off the line, really good mid-range, and better top end.
The only thing I am struggling with now, is that I can't seem to get it to idle down as it should. - - Any suggestions?
The engine has 40mm stud spacing, not the 32mm provided with the stage 3 kit.
I also wanted to incorporate a thermal isolation spacer I fabricated from 1/2inch thick UHMW (ultra high molecular weight) material. Since I couldn't find long enough metric allen head bolts to reach all the way through the velocity stack, carb, thermal isolation spacer etc., and finally into the 40mm RSE Reed Valve, I built a reed block adapter incorporating a throttle cable mount, threaded to accept the velocity stack/carb mounting bolts provided with the kit, The adapter mounts between the carb, and the isolation spacer using the bolts provided in the kit. Thus, you bolt the stack/carb assembly to the adapter, then bolt the adapter to the reed block, with the isolation spacer sandwiched in between, using easily available longer allen head bolts.
I then modified the carb throttle shaft eccentric to incorporate a swivelling throttle cable clamp, with the new adapter plate built with the throttle cable mount positioned in such a way as to provide wide open throttle, since the cable adapter supplied with the kit was oriented in such a way as to provide only about 3/4 full throttle. The adapter plate also incorporates a stand off for mounting an additional throttle return spring, since I didn't trust the little helical spring provided on the carb.
I also drilled and tapped the carb diaphram cover plate to accept a hose barb for the vacuum impulse provided from my crankcase vacuum line (also drilled and tapped for a hose barb), since I noticed that the little vacuum hole provided on the back mounting face of the carb would be blocked when the carb was installed.
You might also note that I port matched the thermal isolation spacer such that its back opening is machined with a rectangular shape to match the inlet of the reed valve, and the front face is round, to match the carb.
I have to say, that after about two days of tuning, I am really happy with the set-up. It seems to have enhanced all aspects of the performance. It has good punch off the line, really good mid-range, and better top end.
The only thing I am struggling with now, is that I can't seem to get it to idle down as it should. - - Any suggestions?
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