How to tell if your quad has been jetted?

[RobG]

Here's the deal... I bought my '00 400EX used a few weeks ago. The previous owner said it was jetted with a 155 main jet. He gave me a stack of receipts with it too, as the shop did all the work on it.

There is mention on two receipts about them selling him some various carb jets, but nowhere is there talk of a needle, or a full jet kit (from Dynojet or K&N or anywhere else).

So I'm wondering... how would a 400EX run with just a 155 main jet and a full Big Gun exhaust (header and muffler)? Also, how would I tell if the needle in it now is a new one? I'm tempted to open it up to see.

Rob

[BornOnFire]

Opening it up would be the only way to find out. The Jet will have the size stamped right on the outside. As far as the needle goes, It may be more difficult to ID.

[ExVillin400]

well if its not jetted you will be running lean, to find that out you hit the gas, cruz or open it up it don't matter, then let of the gas WITHOUT using the clutch and listen to see if it back fires, if so your running lean. hope that helps a little.

[Lorduss]

actually, you can be running to learn without backfireing, a better way is to check your sparkplug, somewhere on this website is a photolink showing what color means what your running. but other people do know so someone well come along, but if your backfiring dont run your way to learn, being a little learn well burn your piston rings faster. and cause other problems over time.