1. Husqvarna Motorcycles Made In Sweden - About 1988 and older

1973 CR250 carburetor hesitation

Discussion in 'Vintage/Left Kickers' started by Gord, May 5, 2015.

  1. Gord Husqvarna
    AA Class

    Location:
    New England
    I have a stock 36mm Bing on my 73 Husky. Bike runs great, as I have rebuilt it. The only issue is the pilot jet. At 0 to 1/8 throttle, there is some hesitation. All I have to do is open the throttle and it will catch up. This only happens when it's warmed up and in a tight woods type Hare Scrambles situation. Not on an MX track as much, as I'm not at that point in the throttle that often. I can't remember what I have in there for a pilot jet, but thought I would ask, with this situation, should I go up a size or down a size. I can never remember.
    Thanks.
  2. Crashaholic Husqvarna
    Pro Class

    Location:
    Antelope Valley, CA.
    Husqvarna Motorcycle:
    73 450WR 6spd motor in a 75 MK frame
    First thought is how long has it been doing this. Has it done it since you acquired the bike or did it begin after the rebuild or since the last ride?

    Its possible you may have a piece of debris in the pilot or in the tiny hole beyond the pilot. Another possibility is an air leak. Vacuum is necessary to pull fuel through all jetting circuits when cracking the throttle and if the engine is pulling air in somewhere other than through the carbs venturi then its possible for a brief lag in engine speed to exist. Once the engine rpm has increased theres enough vacuum to make things work well enough to ride.

    First check for debris and if that's okay then, if you have the next size up pilot, go ahead and throw in the next bigger pilot. I can't emphasize enough the problems an air leak can cause even when the motor doesn't have a lag problem. Most folks don't notice air leaks because they don't ride hard enough to do any engine damage or to really notice performance and minor starting problems. But for those who are on the throttle constantly and in some cases for long periods of time it can result a seized piston.

    Let us know what you find out.
    SteveJ likes this.
  3. Bigbill Husqvarna
    Pro Class

    Husqvarna Motorcycle:
    '83 250wr
    Other Motorcycles:
    0 right now
    If you checked everything in the above post.

    Did you try to adjust the balance screw? On the Bing carb the balance screw adjusts the flow of gas. The screw is on the engine side of the carb. Turning it out is more fuel turning it out is less fuel. Your looking for a smooth idle best rpm. You may have to adjust it, lower the idle and adjust it, till you have the best idle mixture. The balance screw shouldn't be opened more than two turns. If it's ok your done if not I'd move the needle up first.
  4. Gord Husqvarna
    AA Class

    Location:
    New England
    I think I know what you meant. I think turning it out gives it more air. Will try that tonight. Haven't had time to play with it yet this week.
  5. Bigbill Husqvarna
    Pro Class

    Husqvarna Motorcycle:
    '83 250wr
    Other Motorcycles:
    0 right now
    Turning it out gives it more fuel, in is less fuel. The screw when it's on the engine side of the carb controls the gas balance like a delorto. When the screw is on the air cleaner side it balances the air.
  6. Gord Husqvarna
    AA Class

    Location:
    New England
    There is only one screw on the Bings of my era bike, and it's on the air cleaner side of the carb. That's why I said turning it out gives it more air. There is no fuel mixture screw.
  7. Bigbill Husqvarna
    Pro Class

    Husqvarna Motorcycle:
    '83 250wr
    Other Motorcycles:
    0 right now
    Your right I have brain fade my old age is "winning" as sheen would say.
  8. Gord Husqvarna
    AA Class

    Location:
    New England
    Moved the needle up one slot, as Bill suggested, and got good results, while riding on trails behind my house. Still has some hesitation when stopped. Just sitting there idling in neutral, it runs and idles fine. When I blip the throttle, it hesitates and then goes. But while riding, it doesn't do it anymore. Tomorrow will be a better test day.
    Thanks Bill
  9. Gord Husqvarna
    AA Class

    Location:
    New England
    Raced my first Hare Scrambles of the year, with the new Vintage NETRA series today. Bike ran great!. Thanks again Bill. Raising the needle worked out well!

    Off topic, but I'm looking for a set of 14" shocks for my Can Am MX1-125, set up for a 150 pound rider, for HS and MX.
  10. Bigbill Husqvarna
    Pro Class

    Husqvarna Motorcycle:
    '83 250wr
    Other Motorcycles:
    0 right now
    Glad it worked out. Awesome you raced it. Congrats.

    Did you try to adjust the balance screw? Once the carb jetting and needle setting has been gone thru a tweeking of the balance screw could clean up the response a tad. Try turning it in 1/4 turn.