why do some people put different size jets on the front and back carbs on a 650 ?

 

So you mean that one carb has one size, and the other carb is a different size? That is odd. [img]i/expressions/face-icon-small-shocked.gif[/img]

 

YUP
FOR EXAMPLE 132 FRONT AND 138 REAR OR SOMETHING LIKE THAT.I'VE SEEN IT MORE ON THE KAWASAKI THREADS, BUT THE MOTORS ARE THE SAME, OR DO I STAND STUPID.............[img]i/expressions/face-icon-small-blush.gif[/img]

 

What you will find when you start custom tuning is that in reality the V-twin is 2 one cylinder motors tied together. Each cylinder will have different requirements due to it's physical location to the direction of travel, the variations that exist within production tolerances and the difference in the exhaust pipes. Back when I as racing cars, there would be different jets in each of the throttles bores of the carb because of the way each throttle bore saw the engine. The firing order, the intake runner lengths and the physical location to the direction of travel all effectted the flow to individual cylinders requiring a different mixture to balance everything out.

 

SO IS THERE A FORMULA FOR THIS KUZZ THE LAST THING A WONT TO DO IS LEAN MY MACHINE TO THE POINT OF "DAM THAT SUCKS ".

 

There isn't a formula that works for jetting. You need to be able to read your spark plugs or combustion chamber/piston top to know what is happening in your engine.

 

My question would be exactly how much more performance would you expect if you spent the time and "tweaked" the jets?

 

If you had an engine that has really badly jetted to start with and you spent 16 hours doing all the test runs and checking plugs and adjusting again and again and again.............................You might get 5%, but usually more like 1 to 2 percent increase in performance. For the average guy he will never tell the difference.

 

That's what I was thinking. More of a perceived increase in performance but not too much actual increase.

I am not too sure I could detect it. Then again I have, on occasian, had diffuclty finding my rear end with both hands.

 

If you are racing and need every last little bit there is to get, then yes it's worth it. For the average guy that changes to a K&N filter and puts a pipe on, following the recommendations of the aftermarket part's manufacture is good enough. I once spent 5 days straight, 8 to 10 hours a day, rejetting a 6 cylinder race motor with 6 carbs, one for each cylinder. A major pain and it netted a whole 2.75 mph on the big end of a 95 mph boat. Worth it? Well, I did take the National High point Championship the next 2 years and set a couple of records, but for the regular guy, Don't bother. As to finding rear ends? I have found a flashlight, a map and a guide helps.[img]i/expressions/face-icon-small-shocked.gif[/img][img]i/expressions/face-icon-small-happy.gif[/img][img]i/expressions/face-icon-small-wink.gif[/img]