Belt slack for key on idle

[68chevy2nova]

I got my 18amp 420 mounted in my 1989 marathon. It's going to be key on start, so I will be idling. I measure for a belt and came out to 38". I think I remember 2" is the right slack for an idle set up. Found a 40.3" belt cheap, is it the right one? Thanks

[68chevy2nova]

Bump for thoughts

[Shepard]

I run mine at about 1.25-1.5" of play.

[68chevy2nova]

Do you have a pedal start or do you key start and let it idle?

[Shepard]

Key start - idles 1250 rpm

[68chevy2nova]

Ok. Thanks

[sho305]

Sometimes it has to do with the primary clutch you have, stock yamaha for example have no spring and unless you idle really slow they will engage even with a loose belt. Too large a belt will hurt performance. 780 seem to idle fine. Also note a new belt is usually sticky and will drag until it gets some dust and miles on it.

You can also idle them slower, but you may have to drill the idle mix plug out and get at the screw, or buy a VC carb with one. You usually have to adjust the mixture to get a slow idle. My clone idles at 800 or something it will idle down until the comp release comes on. Not sure how it will idle with the new VC cam however, we will see. But I only idle it with the pedal anyway I still have stock gen starter on it and it quits if I let off.

[68chevy2nova]

I'll be running a comet 780. The one I have is junk but lets me mock it up. I had a belt come today in the mail and it fits great. As far as bc I wrote them off, I'll buy anywhere else tho. Thanks for the input sho305, keep us updated with your project!

[sho305]

780 should work great! Working on the motor today actually, about time.