Hi everyone, I got this old Honda VFR 750 from 1986.
It’s a 4 cylinders bike with Keihin VD carbs of 34, V shaped engine.

I’ve cleaned my carburetors, replaced all the 4 intake mainfolds, replaced my idle jet with a compatible one, replaced mixture screw and overflow screw and all their o-rings, replaced also o-rings around the pipes.
Is always the same story: initially, it starts wonderfully, then the rpms begin to decrease gradually and eventually shutting off completely and making it impossible to restart.

When the bike stalls, there are always at least 2 cylinders emitting a lot of white smoke while the other two do not, but I noticed that they changed last time I mounted the carbs (last time was cylinder #1 and #4, now #3 and 4#).

What could it be in your opinion?

I assured that fuel doesn’t come out from the needle while idling, so I don’t think it could be a overfilling problem (maybe?).
I set the float height at 7mm like service manual reports and replaced the needle valve.
Mixture screw set at 2 and 1/2 turns (always read it on the manual)

  • RudbeckiaIS@alien.topBEnglish
    1·
    1 year ago

    Were the vacuum slides sound when reinstalled? Carburetor circuits cleaned throughly? Were those tiny silly washers and o-rings on the pilot jets still sound? Are the carburetors themselves fully seated?

    Those Keihin carburetors are fantastic when everything is fine, but they are also far less forgiving than Bing and Mikuni.

    • Prestigious-River686@alien.topOPBEnglish
      1·
      1 year ago

      I didn’t pay attention to the vacuum slides actually, gonna listen carefully next time I’ll be able to restart the bike, it takes a bit of time after it stalls like this, maybe too much flooded, don’t know. What sound do I have to look for, precisely?

      Yes, carburetors cleaned with compressed air and wd-40 with every screws removed, and air comes out flawlessly.

      I don’t get what you mean by “still sound”, but yes, the pilot screws have all their components (spring, washers and oring in this order)

      About carbs fully seated I guess so, but could it be that cylinder #4 and #3 are not properly tightened and could this cause the white smoke issue?

      Thanks for the reply, by the way