Im building another 400ex. Stage 1 hotcam, je 12:1 piston, and so on. I took off the carbs to clean them. The needle jet with the needle jet holder was in the bottom of the bowl.

Running high compression, 110 octain gas and a 170 main jet, my question is how far do i screw the needle jet holder in to get the best performance. And should I go down a few on the main jet size? Maybe like a 150?

Also what is the purpose of this device? Device being the needle jet holder. Why cant you just screw the jet right on in.

ANY HELP WOULD BE GREAT!!

 

okkkk! Did sum research... From what I hear the more you screw it in, the less power and speed you have. You want to kinda bearly screw it in, then lock it in with the lock nut. Is this so??? And if so, what is the purpose of a "needle jet holder"? Its not just to hold the jet either!!!!! It does something else!

 

wow!!!!!!!! nobody knows. o well

 

The inside diameter of the jet holder has a profile, and a close tolerance, for the needle profile. I was unaware, the length made any difference, because it doesnt extend into the air flow, no matter where you screw it in to. The clip positions are on the end of the needle, to change midrange jetting...not the jet holder position. As long as the main jet is in the gasoline in the float bowl, nothing should change. If you screw it in too far (which isnt posible), and the main jet is not in gas, then the float level is too low.
Screw the jet holder, into the carb body, til it stops.., dont be superman, then snug down the locknut, then put the main jet in the holder, and again dont be superman, but snug it in there,. You should be able to remove and reinstall the main jet, without the jet holder moving, and thats what the lock nut is for.
The reason for the separate piece (jet holder) is economy. Its much cheaper to just make the short stubby jet,(for cheap jetting changes) and have a permanent holder, which never gets changed, than to make very long jets.(which require more brass, and adds to machining time)
I would go by the drivibility symptoms for whether or not the main needs changing. But 150 sounds too small, 148 is stock.

 

Well heres the scoop[img]i/expressions/face-icon-small-smile.gif[/img] If i screw the holder in all the way with a 170 main jet, it runs like trash!! If I run it all the way out with the 170 main jet, it runs about the same but in diffrent areas. Half way...with the 170 main runs great. Im drawing a blank here???

Hondabuster, Thanks. It runs well, but always room for improvement!!