No announcement yet.

Help needed with engine stubbling

  • Time
  • Show
Clear All
new posts

  • Help needed with engine stubbling

    Can opening up the hole in the rear valve cover that is connected to the air cleaner cause a bad engine stumble? Following is just some history. Had a perfectly running Hawk, better than it had ever ran because of carb work by a factory trained mechanic, in the fall of 2021 when I stored the bike. Did all of the prober storage procedures as verified by Squirrel Man. Because of oil getting into the air filter housing by the hose to the crank case ventilation from the rear valve cover, I opened up the hole on the valve cover thinking that would help. In the spring of 2022 when I brought the bike out of storage it was hard to start and stubbled so bad that it was undriveable. Had the mechanic come back to work his magic to no avail. Worked with Squirrel Man on possibilities and decided I needed to rebuild the carbs. Took the carbs off today and remembered that I had increased the hole size for the crankcase breathing and now am wondering if that was my problem all along. I don't just want a bunch of opinions but want someone to explain why this could be the cause of the engine stumble. It feels and sounds like a lean stumble but the plugs are very dark as if it is running rich. Don't want to go to the hassle of putting the carbs back on unless I have some confidence that the larger breather hole is my problem. Thanks in advance for your help.
    Last edited by OldGold; 02-08-2023, 06:56 PM.

  • #2
    no, hole very unlikely to be responsible for stumble, but plug the hole in the airbox if you run without the hose.

    very dark plugs might be your problem, so u need to correct that. maybe incorrect float setting or main jets too large, dirty air filter, etc. its usually best to try NEW properly-gapped plugs, fixes many problems.

    the hole on the valve cover must remain open.
    Last edited by squirrelman; 02-09-2023, 07:53 PM.
    "It's only getting worse."

    MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

    Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.


    • #3
      Slides sliding ok?

      Im with Jerry, id start with fresh plugs. Worth a shot if they are dark, but more that that, new plugs are far better for reading than old.

      Also, while you have them off id take a look at the intake boots and see if they may be hard/cracked.
      Don't spend money and buy, spend time and learn.