I am going off of another thread where Jed and Ron were explaining a main jet tuning issue. So as to not steal his, I figured start this one....A couple of questions then...

1. The main jet controls WOT in any gear right?
2. It is possible to be off only enough for it to effect WOT 5th?
3. Could there be that much difference in bikes, that one will not run worth a crap only being off one size, and another can be off 2 and still run ok?

What do you all think?

 

No one???

 

1. main jets does control WOT any time.
2. wrong main jetting would probally be most apparent at WOT in the 5th gear because that would be the greatest load on the engine.
3. i guess it could be possible that one engine is more sensitive to wrong jetting than another. i would think that a high performance engine would be more sensitive and the lesser would be more forgiving.

 

Thanks for the responce eRo.

As for #3 I really need more peoples input. I do not need Crash thinking he has a more high performance engine then me ;P

 

It is hard to comprehend all the variables in "like" motors. They look the same and should theoretically be the same but small casting differences, tolerances, nuances seem to make noticable differences in tuning and output.

 

my quad ran great with dynojets 128 main but better with a 130....with the same settings other than that

 

What are your symptoms?

What carb?


You could possibly be putting more load in 5th WOT opposed to 3rd and loading up in 5ht.. You may be too lean or rich on the main. Need more info.



Depending on the fuel, Some motors like different jetting. IE- I left my carb the same and dropped the stage 3 in and it went lean ALL over. What combo are you running?

 

They are both on the stock carb right now, and these were more of just generic questions. And now it makes since. The higher output needed to go full speed in 5th with my fat butt and resistence in wind and sand would be larger in 5th and not as harsh in 3rd. So if you were off just a tad on your main, it would suffer greater in 5th due to the higher demands of the engin.

As for the comparrison between the two bikes, it just seemed that my brothers without a K&N filter was more hurt by being off, then mine with one. It seems the air filter can help reduce some of that. Could also just be a difference in manufacturing....

 

If you take a 70 hp race engine and leave the airbox lid on, it will cost the motor more hp than the air box lid will effect a 40 hp stock motor. That indicates that the higher the air demand the motor has, if a restriction on a stock motor is left unchanged it will percentage-wise be a bigger bottle neck.

Lets say you gain 2 hp at 6000 rpm by removing the lid and installing a K&N (of course rejetting to optimal mix) on a stock bike. The more air you start sucking into that motor by carburator, porting, displacement, cams, less exhaust restriction, etc. the more the lid will cost you. On the 70 hp motor it might cost you 10 hp. On a 150 hp motor it might cost you 35 hp or more.........who knows. Those numbers are for illustration only.

My point is, whatever is the restricting, hedging or curbing a motor from breathing and/or operating to its full potential (jetting could be that hinderance) it will effect a built motor more if left unchanged from a stock motor.

That's my understanding anyway.[img]i/expressions/face-icon-small-wink.gif[/img]

 

Get it going in 5th gear at WOT. Quickly back the throttle off by about 1/3. If you feel the bike surge or speed up before slowing, you are too lean. If it really falls flat, or pops, you are probably too rich. The reasoning behind this tuning method is that when the venturi of the carb is closed a little when running at full throttle, it allways richens the fuel for a brief time. Knowing this you can use the info to tune.