Exhause backfires when releasing the throtle

Discussion in '1st & 2nd Generation 1983-1989' started by Nony Pestejo, Apr 23, 2007.

  1. Nony Pestejo

    Nony Pestejo New Member

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    Anyone know the reason why my VF750F backfires, sounds like an exploded baloon when releasing the throtle at high gear? I'm thinking that the air-fuel mixture is not proportion. Am I right? appreciate your feedback. Thanks.
     
  2. tbones86

    tbones86 New Member

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    That would be where I would start, could also be timing related.
     
  3. Jaymz

    Jaymz New Member

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    could be a leak in the exhaust.
     
  4. masonv45

    masonv45 New Member

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    I'm guessing you mean it is popping through the air box.

    On the first Gen's - means it's too lean. Try adjusting your pilot screws.
     
  5. Nony Pestejo

    Nony Pestejo New Member

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    I don't get what you meant by too lean and adjusting the pilot screws. Where can I find these? thanks.
     
  6. Gatekeeper

    Gatekeeper New Member

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    Yep, lean misfire. Caused by too lean mixture or air leak in the exhaust system usually. Dwell angle on point ign and horribly off timing can also do it.
     
  7. masonv45

    masonv45 New Member

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    Get a manual - although Clymer I think has incorrect pictures concerning the location of the pilot screw.

    The pilot screw is on the side of the carbs and has a thin cap you have to remove to access the screw. Per the EPA, you're not supposed to mess with it. But it needs to be adjusted to get the best performance from your bike.

    http://img.inkfrog.com/pix/billyc/pilot_hole.jpg

    If your cap has never been removed, CAREFULLY drill a hole into the thin cap, CAREFULLY thread a screw into the hole and pull - this should remove the cap.

    The pilot screw is sorta like a jet with a pointed end. It is soft brass so don't mess up the head. Behind the screw is a spring, tiny washer and tiny o-ring. Make sure you get them all out. Usually the washer and o-ring will be left in bore. I take a long thin deck screw and insert it into the bore and then GENTLY screw it in until it bottoms out. Unscrew 1/8 turn and GENTLY pull out. The washer and o-ring should be on the threads of the deck screw. A dentist's pick could probably get them out too.

    Many forget to remove the pilot screw when they are cleaning the carbs. This causes two things - the tiny passageways are not cleaned, and the carb cleaner causes the rubber o-ring to distort.

    The manual should have the factory pilot screw settings for your bike. I would stick with the factory settings until everything else has been fixed.

    For optimum performance, the carbs need to be synced and then the pilot screws need to be optimized. Search on Idle Drop method.

    Also mentioned was an air leak. Spray WD-40 or an unlit propane torch around your carb boots. If the RPMs change, you have an air leak.
     
  8. Jaymz

    Jaymz New Member

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    Sounds like good advice. thanks for posting the Pic. I'm gonna save it in my bike folder. Also I like your Ronald Reagan Stamps
     
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