1981 KZ650 throttle response

Hi guy it's me again.

Bike has been running great lately.. (Finally). For those who don't know, I went from a 4-2 to a 4-1 with an open cone muffler (basically no baffle inside). Had the carbs done before the switch, but even after the change bike seemed to ride pretty well. Only issue was that first 1/4 of the throttle there would be a little hesitation and than it would fly off perfectly so I was pretty happy. Couple of weeks passed and I wanted to give a cooler look to the bike and wrapped the exhaust. I had read it could affect a little bit the bike but in the first couple of km's everything seemed intact (400-500 kms). The other day, it was a colder day (15-20 degrees celsius) and that morning the bike didn't sound the same. I guessed it was because the air was denser so that carbs were reacting differently. I basically had more hesitation on the bike (1/2 throttle plus didn't sound as ear piercing as before at 80 + km/hr)and I had some backfiring. Didn't go crazy told myself everything would go back to normal the next day. The next day came (25-30 degrees celsius) the bike still sounded weird and didn't respond as well as before the cold day. Today, I bought some carb cleaner. Cleaned the outside of the carbs because they were a little bit dirty, cleaned the pods with some compressed air, went ahead and sprayed inside the carb as mentioned on the carb cleaner bottle (once the engine was hot), but nothing changed. Went ahead and sprayed the exterior of the carbs while the bike was running and on the two last carbs (left to right so I guess carb 3-4) the bike reved up a little when I sprayed the carbs. This could be an indication of an air leak. Ok fine, I'll order some new boots (looked online.. Holy shit 70$ for 4 boots.. Damn). Looked at the air screws on the carbs, played around a little (making sure to keep track of initial position, because I don't want to fuck up the timing) and the 3-4 seemed to react a lot more to the 1/4 twist of the needle than the two first ones (more backfiring and burping plus higher idle speed).


Now I'm pretty stuck. Never done a carb job (undo them check the jets, needles, etc), but I have a Stage 3 Dyno Jet Kit installed from my mechanic because he said it would be better because of the pods I have. Pretty new at all this stuff so I don't have such a good ear to know if I'm just panicking for nothing or I'm in on a problem..

What would you guys suggest I do next?

Only issue was that first 1/4 of the throttle there would be a little hesitation and than it would fly off perfectly

That is a big issue if I had just paid for a dyno jet fitting -most of you riding even on a 550 is 1/4 throtle.

i suspect it was not really set up right to start with and now the weather has changed, coupled with this induction leak problem.

Fix the boots, research carb tuning. IIRC the CV carbs have a rubber O ring under the pilot airscrews that can deteriorate causing tuning difficulties.

Tyrell Corp wrote: Only issue was that first 1/4 of the throttle there would be a little hesitation and than it would fly off perfectly

That is a big issue if I had just paid for a dyno jet fitting -most of you riding even on a 550 is 1/4 throtle.

i suspect it was not really set up right to start with and now the weather has changed, coupled with this induction leak problem.

Fix the boots, research carb tuning. IIRC the CV carbs have a rubber O ring under the pilot airscrews that can deteriorate causing tuning difficulties.

Yeah well the had played a lot with the carbs before they fitted the dyno jet (had stock jets with pods) and bike had been in the garage for a while so he told me you can adjust the 1/4 throttle issue back at home (didn't charge me a whole lot for the job because he felt bad for me (had had a lot of issues with the bike before)so can't complain...

My only worry is that I fuck up the synchronization of the carbs while playing around with the air screws. TBH I don't know where to start when it comes to adjusting it. I know what makes it leaner and what makes it richer, but I don't know if I have to adjust carbs in order or not or if there's a method on re adjusting the carbs without undoing the synch. I have Mikuni 24ss carbs...