Mountain bike
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What size jetting should I use in a Yamaha yz 80 carb?



I have 2 YSR 80s one is air cooled and 1 is water cooled and I think both are jetted wrong. What did the mid 80s yz 80 dirt bike come stock (jetting) with? I started with a 310 jet in the air cooled (way to big) then a 280 now a 270 but its still not their yet? any thoughts?
(crappy low end and crappy top end)
thanks ahead!

air cooled yz's are in 180 ~200range

water cooled are 200~220 range for early 80's

240~280 range for mid 80's

.....................
Sounds like you're trying the water cooled #'s in the air cooled carb

The Last a/c YZ's used jets almost as big as the 1st W/C ones.
But all those would be 220~240 at biggest.

I'd try a 200 in an aircooled one,,,and work from there.

**Dont Fry it ,tryin' it.
Ya never know on bikes that old what's been modded etc.
Original Size jets "can" be way off.

If it goes flat & blah trying to rev up,,,don't push it just to get a plug check to see if it Really Is lean as it seems.

Stick to "feel" to get it narrowed down a bit to within a couple sizes.
A 200~210 should still be rich and have it blubbering a bit.

But ya never really know till you try it.

Good Luck with it
Contact a Yamaha Dealer and ask for their Repair shop. Someone there should be able to look up that information. If you can't get anywhere there, Contact the Yamaha Manufacturer. You could email them and they will get back to you. I understand your frustration when working with Carbs. The most important item to remember is there are several different types of Jets for different Carbs and they are not easily interchangable. So, that may be the problem. You know, right size, wrong Jet for that particular Carb. However, the ideals mentioned above will work best.

Good Luck
Tech
Stock jet sizes
http://www.bikebandit.com/partsbandit/oe...
Contact me for a carb trouble shooting guide.
It'll explain what to change to correct certain running problems.
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