1983 VF750f start but die immediately

Discussion in '1st & 2nd Generation 1983-1989' started by BruceTee, Aug 21, 2019.

  1. BruceTee

    BruceTee New Member

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    Hello all,

    I recently purchased a 83 vf750f. Bike been stored for 9 years. I removed the carb and cleaned it with ultra sonic. Was able to get it running and idle however, it takes a while to return to idle so suspected airleak; I removed the carb and did more cleanning . however, the bike now can barely start and just die immediately.

    I check the idle jet and can push guitar string through it without problem. What could cause the bike to start but die immediately? I adjust the mixture screw 2 1/5 turn out. I can see the fuel push through carb from fuel pump. And since I have glass gas filter I can see the gas being sucked in carb. I do have spark from sparkplug...not sure why it doesn't stay running. I did a compression test, front cylinder about 170 both, and rear not remember exactly but at least 160 psi

    Could weak spark not keep it running? I'm stumped as already remove/install carb 5 times now.
     
  2. Boomtank

    Boomtank New Member

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    Could be a number of things. Idle screw set too low, bad carb boots, carbs too far out of synch, choke issue. Just to list the main things to look over.


    Sent from my Moto Z (2) using Tapatalk
     
  3. Spriggan

    Spriggan New Member

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    Add float bowls need adjustment to the list.
    From limited experience, handing them off to a professional is the most cost effective.

    Your ignition pickups on the clutch side might be faulty as well
     
  4. BruceTee

    BruceTee New Member

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    Hello,

    Thanks for chiming in, guys! I have some update. After fiddling with carb for awhile and couldn't see anything out of ordinary. I proceed to check the valve and they were pretty tight, couldn't slide 0.006 feeler gauge in. After adjustment, the bike is able to start and idle; However, the idle hand after rev still an issue. The bike rev response is great, but it just stay hanging around 2-3 k , either that or slow return to idle. I spray some wd40 around carb boot, but see nothing change. Not sure where the air leak come from.
     
  5. squirrelman

    squirrelman Member

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    try synching the carbs if you find no air leaks.
     
  6. BruceTee

    BruceTee New Member

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    Thanks squirrelman#1. I just found out the air leak, it seemed to come from the boots between carb and engine. It seemed wd40 didn't do anything, but when I spray starter fluid, rmp reacts right away. I ordered new boots and looked like it fixed the crazy idle hang. Going to use starter fluid from now on to check for air leak. Drove around the neighbor hood a bit today for the very 1st time :) It seemed the bike crashed at some point as the steering out of alignment. Fork leaked and neck bearing screeching when move around. Did the oil change and filter, so i'm very happy at this point. At least I know the engine is good to go. Going to focus on steering and forkseal next. Have never done a forkseal job yet
     
  7. Diving Pete

    Diving Pete Member

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    After V4 carbs - forks are easy....

    Don't forget to synch the carbs.
     
    Boomtank likes this.
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