pilot jet and fuel screw

1 reply to this topic
  • humpness

Posted February 01, 2011 - 08:32 PM


So i added a new exhaust system and I am getting alot of back fire popping(with new gas). I thought it might be a leak so I listened in and couldnt hear any thing with a rag over the exhaust. I then took the pilot jet out to give it a look over since it had been sitting with a carb full of gas for six months. I boogered it up a bit removing the jet so I threw a size smaller(48 down to 45) back in.

Can you make two different size jets behave the same with different levels of adjustment from the fuel screw? For example; a 48 with 2 1/2 turns will compare to a 45 and 1 3/4 turns?

I dont know why I was getting bog and backfire at the same time. I know its cold out(25f) but I dont know what to expect. The only other thing I will mention is has some Marvel Mystery Oil in the tank.<---?? Any suggestions would be a great help!

thanks jake

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  • grayracer513

Posted February 02, 2011 - 11:29 AM


If you have a small jet that wants to be adjusted at, say 2.5 turns out, and the next size larger wants 1.5 turns on the same engine, you can sometimes run either one, yes. But that's not usually the norm.

Still, you can try the 45 and see how it goes.

As to bog and backfire concurrently, that's not odd, either. In a YZF, the ideal pilot setting will backfire a little, some of the time. As you go leaner, the backfire gets worse, and the engine will start to stumble off idle as the throttle is cracked. The leaner you go, the worse it gets. A pilot jet with a layer of varnish in it can act like it's several sizes too small even when you can see light through it.

Either try the 45, or just go get another 48.

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