re-jetting 660 carbs

[robocop900]

i have a bigger main jet that i got from a friend that used to race a baghira, he reckons,it should give me at least an extra 5BHP can anyone tell me if it goes in the left or right carb, cheers, fabby site by the way.

[Anders]

There is no way that simply changing one jet will add 5bhp... but there is definatley room for improvement from the stock jetting.

The jet only fits one of the sides i.e. proper (left) or CV (right) carb as they are not interchangeable you just have to check where it fits.

See also viewtopic.php?f=3&t=4134&start=0 and viewtopic.php?f=3&t=1157& for jetting related info.

[basser23]

Hi Anders,
I know you've tweaked your carbs jetting(before you swapped for Mikuni's) do you recall what you ended up with for jetting?
I thnk stock they are 30 main on left carb and 160 right side...did you swap or change the pilot jet?
Also I understand Keihin jets fit these carbs..
Thanks
Chip

[Anders]

After numerous dyno runs, drilling jets etc over 10 years ago I no longer have the specifics of what we came up with and also there are no jet sizes to go by as we used drills. The tuning was made to suit an engine with open airbox using a modified K&N insert, ported and flowbenched head, high lift cam, 672cc high comp piston, removed rev-limiter on a stock CDI and a fully open exhaust.

No change of pilot jet as I recall though. I dont think Keihin jets fit, haven tried it so I can be mistaken.

I have read that Egli recommends to go down from a #140 main jet to #102,5 in the left carb and up from #165 to #175 in the CV half for stock engines, mixture 2,5 turns out, needle position according to what works best for your bike. This is for stock engines with K&N type filer, slip-on and a Tunebike venturi mod. The above mentioned Jet sizes should be avaliable from your Yamaha dealer.

Klicking: viewtopic.php?f=3&t=1157& will give you specific info in the various stock jet sizes for diffrent incarnations of the 660cc 5-valve engine.

If you are having problems with the set up make sure that you cleaned the carb thoroughly including the little mesh filter in the carb housing on top of the float valve AND check that the diphragm in the CV carb is seated properly.

[basser23]

Thanks Anders,
Geez has it been ten years now? Whew...I've had mine for 8 ...it seems like yesterday though..
I checked that link and what is supposed to be in there is 130/165...next time they are apart I'll doulbe check.
When I purchased the bike,it had been raced in our Skorpion Cup series which ended in 2003 I think.
Supposedly it had a "jet kit" who knows...hasn't run badly even now,I just want it to run a bit better(dont we all)
It came with a K&N filter modified to fit the standard filter area,no snorkel,Holeshot (US) can and link pipe.
I have a set of carbs I got off Wonky(remember him?) at Slipstream a few years back as spares..these will be the
ones I fool with....wouldn't know where to get a bowl gasket would ya?
I dont remeber wether the arrow on the float pin faces the install direction or removal direction...I think it is install..
Eh?
Thanks for the help though!!!
Cheers

[Anders]

A rebuild kit for any old XT600 carb contains all the gaskets and a float valve, happy spares hunting.

If it has a jet kit it is most likely that the CV carb jet is drilled as this is how the Dynojet kit is set-up... new jet for left carb, needles, spring and a couple of drills for the CV side.

[basser23]

Anders,
Thanks for the heads up..found some at webmoto in Uk...
Took my spare set and checked the jets,130/165 ,cleaned the tiny filter in the fuel inlet,set float level and so forth.
question: if you are going to change the needle position in the left carb,how in the world do you access it?
Remove all the actuating gear from the carb top? Geez its a bugger,all that to lift a slide....CV carb no sweat
chip