Yamaha XJR 1300 carb balancing help

[snowwolf]

A mates XJR1300 was a bit temperamental when started from cold, and tick over was not very stable, I stuck the vacuum gauges on it to check balancing, they were out so balanced 1&2 carbs but when trying to balance 3&4 number 3 was fluctuating badly on the guage needle, I swapped 3&4 hoses over to eliminate the gauge but 3 was still fluctuating badly, I can only think it may be the mixture or there is a problem with the inlet valve seating, the down pipe on number 3 is blue, compared to the other downpipes which are nice and clean, could an air leak cause this aswell?


The bike runs ok on throttle but slow engine revs and little throttle is not stable, on tick over if you give it a slight increase on the throttle from 1000 to 2000 rpm its sounds like the carbs are out of balance and from 2000 rpm it sounds fine.


Any suggestions please on what could be the problem.

[N Dentressangle]

Would a blue exhaust normally mean it was running hot? Lean mixture on that cylinder?

[Hooli]

From what you say about it working at higher revs I'd be suspecting a blocked idle jet on Num3.

[snowwolf]

N Dentressangle said:

Would a blue exhaust normally mean it was running hot? Lean mixture on that cylinder?

I would be thinking that too

[snowwolf]

Hooli said:

From what you say about it working at higher revs I'd be suspecting a blocked idle jet on Num3.

Cheers for the info, I will have a look see where that is