Topic: Intake backfire, wht does it mean and how to fix?

[GroovieGhoulie]

I recall it means it's running lean, correct?

I am rebuilding a CT-70 and the engine is showing all the classic signs of leanness:

flat acceleration
little change in engine behavior in response to throttle opening
Way slower top speed (should be 45 MPH, but it won't go much over 25, only seeing 30 downhill in a hurricane with a bag of lead shot tied to the forks)
won't rev above a certain point well below the redline
won't idle for #$%*
etc.

The weird part is putting on the choke will quickly flood it out and it runs like ass and pulling out the air filer has no effect. I also moved the jet needle to the richest notch and adjusted the airscrew to spec and then in a little to richen it up all to no avail.

However, sometimes, when the throttle is cracked open, it backfires through the intake. 

The engine needs a tune-up and I think the timing is all out of whack, which might explain the backfires and poor get-up and go.  I need to figure out how to adjust the timing and when I do, I'm on it.  Any ideas of where to begin?

[dusterdude]

an actual backfire could be timing,a fuel related issue or an ignition issue.if the "backfire" is a spit,that indicates a lean condition,whatever may be causing it could be a few different things.

[Bill Vaughan]

These motors actually have quite a bit of punch when they're running right, so it's worth taking the time to go through all of the routine maintenance adjustments.  The owner's manual or clymers manual each detail the steps involved and the order in which they should be performed (best way to do it).  If you don't have either manual on hand, the link below may be of some help:

http://www.hondaheaven.org/index.php?name=Sections&req=viewarticle&artid=32&page=1

[Jay B]

What the other guys said, also it sounds like you might have an intake leak.