Hello again! I had some leak issues with my carb, so I left it to a mechanic to clear and fix it. Since then it works great, much more smoother and powerful, but it has a big problem. It causes my bike a lot of popping at deceleration. It was popping a bit before clean&fix too, but now it does it every time I close the throttle above 3k rpm, which is extremely annoying and a bit dangerous in long time (I heard). So my first thought is that he changed the needle position and it is too lean. Well, it seems it's not, I tried every position in needle, it just keeps farting even with the bottom (rich) position, in which it gets drunk and doesn't work cool anyway. An air leak is not possible, since it wasn't popping before the carb clean. Any other thoughts on this? Plz, don't tell me to buy an FCR, I'd love to, but I can't afford it atm...
i would try richening the idle/pilot circuit some...thats all that is used on decel. im not familiar with your carb however
does your bike have anything that circulates exhaust gas back into the engine? some streetbikes have this and blocking it off decreases or eliminates this. i went thru this on my zrx...however, i was only told by experts with zrx bikes that the decel popping was harmless, only annoying. i know its a way different bike but thats my experience with it. richening the pilots on those did help a bit along with a full exhaust, i blocked off the exhaust recirculation and the popping is gone. it sounded like a popcorn machine stock and frightened people sometimes, i think!
No, never heard about exhaust circulation before. I'm pretty sure that carb causes the problem, many KTM LC4 with the same Mikuni fart like Terence & Philip too, I just don't know how to reduce it to the "before carb cleaning" state, which was happening occasionally at hard deceleration. If it's caused by lean mixture, it means higher temps, in long terms can possibly cause damage I guess.
^It is, also, if there was an air leak there, it should have popping at the same rate before the carb job, and it wasn't.
After all, I decided to buy an FCR. Does anyone know what i should check before I buy it? I need a 41mm right?
Make sure the 2 halves of the carb have not been split. They have yellow tamper seal, and I'm pretty sure the bolts are safety heads. Make sure the slide plate isn't worn out, and installed the correct way. Check the choke and or hot start knob where is screws into the carb body for cracks. Take the mixture screw out, and check the tip under a magnifying glass... if it's damaged, don't buy the carb, it'll never run right if the fuel screw was dropped and damaged the inside of the carb body. Will have horrible idle issues. I would personally not buy a used FCR, but get a Lectron carb instead, they're about the same price as a used FCR, and lightyears easier to tune.
FCR39 should be plenty. I ran a TM40 on my DR650 and richening up the pilot reduced the decel popping quite a bit. Go with a Lectron. BST40 is a hunk of crap IMHO. Way too much surging at low speeds.
Just finished FCR installation and tuning. It is 41mm, it was working on a Duke. One word: WOW. 3 words: O.M.G I have a totally different bike! Still can't believe how much power I was losing till now cause of crappy Mikuni. No pops at all also. Thnx all for the advices!
