I have been trying to get a 1978 CT70 running and have had little success. Last summer the bike would run but only on full choke. So, over the winter I took the carb apart to clean it and replace gaskets that I am sure have not been replaced in a long time...I reinstalled the carb and tried to start the bike up. One question i have is what are the factory settings for the idle and air screws on the exterior of the carb. I screwed the air screw in until it was very lightly seated and then backed it out 2 full turns, and I would get the bike to start but would not continue to run unless I was giving it throttle. Is there a "factory" setting for the idle screw or do I just need to keep messing with it until i get the bike to stay running? Any advice would be greatly appreciated. Thanks!
CT70 Idle and Air screw settings
- Thread starter P.Lew
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- 1978 carb carb tuning ct70 idle idle screw
I hope that what you're calling the "air screw" (which it actually is) is the pilot airbleed adjusting screw. Typically, you'd start with 1.5 turns out from seated, as the initial adjustment. Counterclockwise (out) allows more air to enter the idle (pilot) circuit, which results in a leaner mixture. Clockwise (in) does the opposite. The optimal setting may end up closer to 1 turn out; that can only be established when the engine is fully up-to-temp. For now, I'd try 1/2 turn out...very close to the practical limit. If the idle mixture goes too rich (which it should) then it's just a matter of finding the sweet spot. OTOH, if it still won't idle properly (i.e. choke open) then you probably have a clogged pilot jet. Pilot jet orifices are minuscule and can be difficult to clean.
FYI, the only way to verify that the jet orifice is 100% clean & unobstructed is by running a thin wire through it. The same also applies to the emulsion tube, which doubles as the main jet holder. Jets, both mains & pilot can be sourced new. Emulsion tubes, however, are hard to find as new parts...they are fairly easy to clean.
FYI, the only way to verify that the jet orifice is 100% clean & unobstructed is by running a thin wire through it. The same also applies to the emulsion tube, which doubles as the main jet holder. Jets, both mains & pilot can be sourced new. Emulsion tubes, however, are hard to find as new parts...they are fairly easy to clean.
I have tried turning it out anywhere between 0.5 and 2 turns from the seated position and will occasionally get the bike to run (only with throttle) and if I let it go back to idle it dies. When I cleaned the carb I poked a wire through all the jets on the inside to make sure they were clean. Does the idle screw position not matter for the bike idling? Does it just effect the bike to run lean or rich?
