View Full Version : jettin 3/4 wheeler or what ever you ride

11-13-2002, 12:42 AM
from what i understand when you jett trailprotrailpro bike all your doing is jetting it to your regional atmosphere. i dont see how this can be a mod. so what trailprotrailpro burning more fuel even wasting more fuel cause trailprotrailpro bike cant burn it fast enough due to the amounts that are drawn in. the way i see it it wears your motor out faster and cause your bike to flood more often. would you have to change the kind of gas you run in it or would that even come into play. you see it as a mod i see it as the gas companies and aftermarket companies finding new ways to increase gas sales and parts sales. when you throw an fmf pipe on your bike that lets out more exhaust right. so y do u have to jet your bike when putting a pipe on it. i hear an aftermarket pipe is useless unless you jett your bike. why cant you just adjust your air screw to tune your bike whats the main purpose of that. lets get this out since there r 2 different sides here.

11-13-2002, 01:24 AM
nice point :!: , but i have no idea :?:

11-19-2002, 10:56 AM
When you add on a new pipe or other engine flow modifier, it allows your engine to flow more freely. ie. Less restriction. The higher flow obviously means that more fuel is going to have to be utilized, otherwise the engine will run lean and that WILL make a parts shopper out of you. The idea is to get the correct jet for your carb that takes your air/fuel ratio back to what it should be. Since the air flow is higher, so must be the fuel flow.

Sometimes people will rejet their bikes because of riding in different elevations. They do this because the air changes pressure as you move from one elevation to another. Air at sea level is about 1 psi higher pressure than air at 1000 ft above sea level. The different pressure makes the air a differnt density. Air at a hig density will not need to flow as fast as air at a lower density to maintain the same air/fuel ratio. What this means is people in Miami need to use a larger jet than people in Denver, because the air in Miami is much denser.

Most of the time, rejetting a carb is pretty much useless without modifying some part of the air flow system also.

11-19-2002, 11:36 PM
well that about raps that up. I am in the middle of re-jetting an old YZ400 a 1978 actually. This thing is being a pain. I have learned more about jetting in the last couple days than I ever have. I am now trying to figure out needle sizes and tapers and junk. Pretty soon I will have this stuff down. I know that when you jet the objective is to get it to run as lean as possible without it blowing up, but there are alot of little circuts that need to be metered with different type jets. and I'm only working on mikuni carbs right now. The real test will be when I finally get the TM38 dialed on the Z when the port work finished. That thing is gonna friggin fly, swear to god.