Jetting issues 70cc DR, VM18, Boyesen Reeds

I got my new carb, a VM18, and reeds last week and i decided to bolt everything onto my NC50 (with a recently bored intake, stock exhaust) today. I've tried every jet I have (70, 75, 80, 85, 90, 95, 100) and no matter which one I have in the silly thing fourstrokes like mad. What jets do you guys run on your carbs to get the stupid thing to run right? What can I do to make it run right?

Re: Jetting issues 70cc DR, VM18, Boyesen Reeds

Matt Mahloch -- MBM Customs /

Puch 70 treat kit 80 I think I had.

Re: Jetting issues 70cc DR, VM18, Boyesen Reeds

I basically have the same configuration as yours, except for a Vm16.

I had the same problems. (Nc50 1981)

At this point, you have a exhaust issue: you must increase your outward flow.

Gut your stock exhaust or change it.

In 2 cycle engines, exhausts must match engine size. (very important)

At least get your stock exhaust clean as a whistle. (inside of course)

Then, a jet in the 85 range should fit....that's what I have.

If you're four-stroking, you're running way to rich: reduce your jet size.

Check your spark plug, it might be fairly black...which is not good.

It should be light chocolate brown.

Your four-stroking might also be the result of unburned gas back flowing from the exhaust...again caused by your to large jet.

Took me 2 weeks to figure this out.

Keep it up, you're almost there.

Re: Jetting issues 70cc DR, VM18, Boyesen Reeds

Rem Bullis /

I'm cutting my exhaust open and gutting it this afternoon. You think that some pipe solder would be enough to close it up? I'll let you guys know how that goes.

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