Yamaha XJ750 MidMax 1983 Carburetor problem

Allright so... I'm literally out of ideas. I'm from Saint-Jean-Sur-Richelieu Quebec, Canada.

I had a problem with a float and some fuel inside the engine. took off the carburetors and only checked all my float adjustments and did the adjustment on a single one (#3) . I guessed it was the culprit since now everything is okay but of course. Another problem emerged when i installed back the carburetors. I now got a misfire on cylinder number 4 or maybe a rich detonation since at high RPM around 4K it pops loudly (Seems there's too much fuel going) I changed 4 sparkplugs with the correct resistance and also changed my plug cap with no resistance on those ones since the sparkplugs are already at 5k OHM. thought those ones were the culprit but no.

cant stand in idle and dies within a few seconds. I look at every carb boots and they are holes free. no air leaks on every boots. RPM also takes a good time to get back into idle before it dies. I also changed the carb bowl gaskets and found they are different than the OEM one (they are made of rubber. Bought them on amazon like a dumdum) I'm really out of ideas. Is there someone that had the same issues ? Also, When playing with the idle screw ( The big one in the middle) even if its all the way off the bike still stays at around 1500 RPM and dies a couple seconds after. When i adjust it further. at around 4K RPM now it stays at idle but pops loudly. Oh also. i just realised i didnt put back the clamps on the boots on each side ( Airbox and engine) Could this be the problem ?

 

Certainly could be, as they would let more air into the carbs than is intended, thus cause a lean mixture and a hanging idle.

Also-----very important-----have you performed an engine synch? An out-of-synch engine will exhibit all sorts of odd problems that seem to be caused by other causes, but is really due to the lack of engine synch.

 

Before my little surgery the bike ran super fine on four cylinders. after my float adjustment my problem appeared. Dont know if it got out of sync because of my adjustment ?

Thank you for your reply by the way. much appreciated

 

Yes, anything that might change the power output of any individual cylinder (fuel level/float height adjustment), mixture screw adjustment, valve shim adjustment, etc.) can (will) throw off the engine synch......in this case, synch means "each cylinder is outputting the same amount of power". Out-of-synch engines can (will) display all kinds of issues that can (will) seem to be due to other causes, and hence the tail-chasing commences. Synch is easy to check, so recommend that you do that first. and confirm that is (or is not) the problem.