Slowing Top Speed

Discussion in 'Heads and Cylinders' started by StevenMain, Aug 10, 2016.

  1. StevenMain

    StevenMain New Member

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    So, I took the bike out ALL night with my friend and we raced all over town. Im worried though, I started out topping at 41, I made a new cylinder as my old one had scratches in the plating around 300 miles. The new one I ported "better" and only managed 40.25 (44 tooth)
    as the night went on my top speed kept dropping lower and lower and lower and I ended up topping out around 36.5... Is the cylinder wearing out THAT fast? I don't know what else it could be.

    Also 41mph was the BEST recorded top speed on 44 tooth to date. Anyone ever logged any faster on GPS? I have done EVERYTHING you can do to this motor.
     
  2. allen standley

    allen standley New Member

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    So, I took the bike out ALL night with my friend and we raced all over town.

    Keep trying... You seem determined to blow it up.
     
  3. StevenMain

    StevenMain New Member

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    Thanks for the sarcastic as **** answer... if you want to behave like a child go elsewhere.
     
  4. Tyler6357

    Tyler6357 Member

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    If you just put a new cylinder on it the piston rings need to set, you should follow break in procedures again any time you replace the rings, cylinder, or head gasket. It's possible that when the rings get set you will have more consistent performance.
     
  5. crassius

    crassius Active Member

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    while it usually take only a mile or so to get these warmed up enough to run well, it takes 8 to 10 miles to get these motors to stable temps - mixture may be diff once it warms up to that point
     
  6. codyj528

    codyj528 New Member

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    I wouldn't call it new, it had a proper break in then was pulled and gifted to him. 16:1 ratio break-in.

    And if $50 is to much to throw away in 1 night, consider a night out for dinner/movies with a chick.... .duh.
     
  7. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    Whenever you install a new cylinder, you should also install new rings...
    (so the new rings can easily break in to match the new cylinder).
     
  8. maniac57

    maniac57 Old, Fat, and still faster than you

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    Using so much oil basically triples (or more!) break-in time due to rings being overlubricated and unable to properly seal to cylinder wall.
    Break-in means rings seating and too much oil can easily prevent it EVER happening.
    Poor compression, poor manners and reduced power are usual results of too much oil.
    I'd bet $50 your jug was basically new inside regardless of prior use, so it ran like a new top end: poorly.
     
  9. StevenMain

    StevenMain New Member

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    Thanks for the reply, I took the cylinder off today and did more port work to try to hit the magic 10k rpm... plating had definite scores. Not terribly deep but obvious. I've hit 9,733 rpm at 41mph before and the motor is well balanced to with the lightened piston.
     
  10. StevenMain

    StevenMain New Member

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    39.75 mph tonight which is within my range of acceptable. If it wasn't 84 degrees and 78% humidity it would probably be a little faster. (This is at 3am!)

    My new question is at top speed the bike surges hard and slow. Once it hits a certain speed it litterally falls on its face entirely for about a whole second, then pulls again for 1/2 a second, then dies for a full second.

    There must be a float height issue, fuel sloshing from the slight vibration, or maybe the bowl is running dry due to a filter restriction idk. Any thoughts ?
     
  11. codyj528

    codyj528 New Member

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    Meh. I couldn't remember the spec sheet but it was more like 20 or 25. Whatever the Chinese called for. And it had about 3 tanks of fuel ran thru it so I'd consider it a ok broken in. Besides. This isn't a gt500 break in.... but you know we drove that thing like a stolen car the first 5 miles off the lot on a 4 hour road trip home. Let's just say my Datsun couldn't keep up. :(
     
  12. codyj528

    codyj528 New Member

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  13. Kioshk

    Kioshk Active Member

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    BINGO.

    I've had the same "problem", but I think it's a good thing. It's either that the carb-bowl's fuel is aerated from sloshing (doubtful), or there's not enough fuel getting in at high-revs (probable). Hold down the tickler with your left-hand when it starts happening again and report your findings. Better yet...for safety purposes...bring along a small child for the ride and have them do it.
     
  14. StevenMain

    StevenMain New Member

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    Hold down the tickler ? What? Lol
     
  15. Kioshk

    Kioshk Active Member

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    The goldy thing!

    [​IMG]
     
  16. StevenMain

    StevenMain New Member

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    I have a keihin 20mm there is no primer.
     

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