carb sychronizing

**Lamin Sambou** · #1 6th April 2009

Hi All,

when I bought my 34L it was in a bit of a sorry state. an original UK bike and it certainly looked like it had been used through quite a few salty winters. plus it looks like its been used on a big trip at some point, even got a spare ally tank, as if the original isn't big enough?

anyway one thing it did do was - open throttle and it pulled, then it seemed to get a second breath and pulled harder. basically a big flatspot in the low to midrange.

according to the manual the butterfly in the second carb should start to open after the slide in the first carb is 5mm open.

I have adjusted the mechanism to get it closer to this and it now pulls much better. however at wide open throttle the butterfly is actually closing a bit.

this bit was worn

so I filled the depression and made it flat again.

but it is still not possible to make the butterfly open early enough without it starting to close at wide open throttle

the wheel is a bit worn

has anyone else come across this problem?

seems easy enough to pick up a set of later carbs, but I'm told the 34L frame is a bit narrow for the later CV carb?

any help or suggestions greatly appreciated

thanks
Andy

oh.. and aren't the carbs a pain in the arse to get in and out.. if only they had designed it so the airbox could move back

**aukeboss** · #2 6th April 2009

The original is large enough of course, but size matters as we all know

As to 'synchronising', there has been a modification (official!) from Yamaha,second should start opening @ 6 mm opening of the first. However, same problem with the butterfly. How do you define full opening of the first - slide to the stop or slide flush with upperside of the venturi? This last one should be correct. I guess (and always do) the second carb should be set so that at full opening of the first carb the butterfly is parrallel to the second carbs' float.

Auke

**Lamin Sambou** · #3 7th April 2009

Quote:

Originally Posted by aukeboss

The original is large enough of course, but size matters as we all know

As to 'synchronising', there has been a modification (official!) from Yamaha,second should start opening @ 6 mm opening of the first. However, same problem with the butterfly. How do you define full opening of the first - slide to the stop or slide flush with upperside of the venturi? This last one should be correct. I guess (and always do) the second carb should be set so that at full opening of the first carb the butterfly is parrallel to the second carbs' float.

Auke

Hi Auke,

thanks for the reply , yes when i was messing with it I looked to see where the slide was when the mechanism hit the stop and it was flush.

if i set the butterfly horizontal to coincide with this then it doesn't start opening till about 1/3 throttle or more. I then get the big step in the power, it feels like it revs, gets out of breath and then wakes up and takes off.

the piston/slide in the CV carb runs nice and smooth,doesn't seem to stick.

I've set it so it opens early enough for smooth pull up to about 8/10 throttle and don't ride above this. if you do it surges up and down and then you get a forward surge after you let off.

or maybe the surging is caused by something else????

other than the adjuster screw I can't figure out anything else to move to change the relationship of the mechanism turning the butterfly.

maybe i'm looking at the wrong thing....I've got a supertrapp end can, maybe the main jet in the first carb needs to be a touch bigger????

cheers
Andy