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Thread: VT250 carb issues

  1. #1
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    18th May 2012 - 22:03
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    VT250 carb issues

    My VT250 carbs are being a complete whore, one cylinder after the other keeps dropping out. I got it good then it had a tantrum and the front cylinder is totally dead again. Spark is strong, tried several modules and coils as well as leads, new plugs. It's the carbs, it's fuel.

    So before it went totally dead at around 6000rpm it'd flatspot bad, this got worse till the cylinder dropped out totally. Some things to note here is for one the carb boots are a little shitty looking and may not be totally sealing, are new ones available? Are they something generic or more specialist? Also given the age and problems present I'd like to give the carbs a tickle up, so can you get kits easily enough for them? There are some jets on trademe but what about new floats or whatever, can they be had?


    Or maybe I'm totally missing something and there is somewhere else I should start. But I used carb cleaner and a compressor on everything. Still seems to get worse, I even did the filter and lines to get rid of any residue but it's still not working. Maybe I need to overnight soak the things in something.

    Suggestions?

  2. #2
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    17th April 2011 - 14:39
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    Have you given the intake boots a spray of something while the bike is running, or a bit of light oil?? That should tell you weather or not your intake is leaking.
    For a man is a slave to whatever has mastered him. Keep an open mind, just dont let your brains fall out.

  3. #3
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    Quote Originally Posted by unstuck View Post
    Have you given the intake boots a spray of something while the bike is running, or a bit of light oil?? That should tell you weather or not your intake is leaking.
    I did, didn't seem to make much of a difference but then again I'm still unsure half the time if the cylinder is even getting fuel. It won't hold an idle so I have to crank it open a bit to keep it running so it's not pulling a full vacuum which makes that test of somewhat small worth. If I can get it to pull a good vacuum then it would be more helpful.

    Basically it's running like a true sack of shit XD

  4. #4
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    17th April 2011 - 14:39
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    Is the plug dry on the cylinder you suspect? If so no fuel. Time to look at the carbies again.
    For a man is a slave to whatever has mastered him. Keep an open mind, just dont let your brains fall out.

  5. #5
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    Bone dry. But every now and then it fires into life. I'm just looking for something I've missed. I've had these carbs apart a good 5 times and been quite careful in putting them back together. Fuel tap works, fuel lines and filter are new, everything seems clean but it delves into running like a sack of shit when it feels like it.

    Bike is going to land up in the waikato river off the back of a ute at this rate /problem.

  6. #6
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    6th May 2012 - 10:41
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    when tuning carbs i believe it's correct to start at the top and work your way down.
    ie, go hero on some nice straight roads, tweak your jet/needle
    then your midrange, then your idle.

    air pilot circuit ok?
    slides sliding?
    diagphrams in tact?
    throttle linkage working?
    fuel in bowl for affected cylinder?

    good luck...

    -edit-
    and did you bench sync your carbs before putting them back on?

  7. #7
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    Quote Originally Posted by 328FTW View Post
    Bone dry. But every now and then it fires into life. I'm just looking for something I've missed. I've had these carbs apart a good 5 times and been quite careful in putting them back together. Fuel tap works, fuel lines and filter are new, everything seems clean but it delves into running like a sack of shit when it feels like it.

    Bike is going to land up in the waikato river off the back of a ute at this rate /problem.

    Undo the drain screws on the carb bowls. Suck on the vacuum line on the fuel tap, and see if petrol comes out of the drains.

    Sounds to me liked blocked float needles.

  8. #8
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    Balance your carbs, V twins are very picky about carb balance to the point that they will drop a cylinder. As this looks like the only carb issue that you haven't checked out or cleaned it is worth doing. also have you checked the compression on the cylinder that's not running, a low compression cylinder will not draw fuel out of the carb. balancing carbs on a v twin is easy to do as there is only one adjustment screw, either borrow a set of vacuum gages or book it in as should be a quick and cheep job for a shop to do.

  9. #9
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    Quote Originally Posted by spanner spinner View Post
    Balance your carbs, V twins are very picky about carb balance to the point that they will drop a cylinder. As this looks like the only carb issue that you haven't checked out or cleaned it is worth doing. also have you checked the compression on the cylinder that's not running, a low compression cylinder will not draw fuel out of the carb. balancing carbs on a v twin is easy to do as there is only one adjustment screw, either borrow a set of vacuum gages or book it in as should be a quick and cheep job for a shop to do.
    I did balance them :\ Compression is good on the dead cylinder, I did A LOT of checking which is why I'm starting to get frustrated. At one point I had jambed slides but I fixed that, the diaphragms look perfect. It really acts like a blocked needle but I've checked that so many times it makes my head spin.

    And yes bowl is full, I mad sure it had a supply. I might drain the tank and clean it out. I'll have to start at the start and go right through again.

  10. #10
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    If the needle valve was blocked/not working you would have no fuel in the bowl. I would be looking at the delivery system between the bowl and cylinder.
    For a man is a slave to whatever has mastered him. Keep an open mind, just dont let your brains fall out.

  11. #11
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    They're known for shitting fuel taps, sometimes you'll have a fuel leak through the diaphragm in to #1 cyl. Sometimes you don't...
    If it has spark, it may not be the kill switch, or cdi.

    Some have little filters above the float needles
    The fuel filter in teh tank may be fucked too
    The fuel line between the carbs may be fugged too etc etc


    What I would do is:
    Clean carbs in pinesol or something similar, or even thinners (if you don't have an ultrasonic cleaner)
    Check fuel tap and filter
    Check tank vent
    Set carbs up to fact specs
    Duct tape/silicone the intake boots if they're cracked
    BIG FUCKING HAMMER

    If they don't work, you probably don't have a carb issue
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
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  12. #12
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    what filter and lines did you clean out

  13. #13
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    Info from the boys at factorypro. Refered to this many a time...
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  14. #14
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    18th May 2012 - 22:03
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    Ok so here is what I did, went back to basics. Got a spare set of VTR carbs, took them to bits. Cleaned EVERYTHING. New seals and whatnot. I bench set them, and put it all together back on the bike. Also put in fresh fuel, then fine tuned the balance to finish.

    Runs on both cylinders most of the time and seems healthy till you get up in the revs then it splutters and is way down on power. But I do note there is a lot of backfiring and some of it sounds like it might be coming from the carb area and it wouldn't surprise me if that's the cam being on the wrong tooth on the front cylinder because it's been a real problem child. It got it going well enough to ride it to the shop where I'll be replacing the motor. Then I can check my crank pickup gap and all that stuff, I think there are some cumulative other issues. All these little things are amounting to making it one big problem.

    I'll set the old carbs right as rain and put them on the new motor, the main filter was the one I cleaned. The ones in the carbs were clear as well. There didn't seem to be anything specifically wrong, I'm just starting to shift my thinking to that the carbs aren't the single root of problems. I miss my old motor, the one that half the piston is on my desk and the other half is scattered along some south auckland road.

  15. #15
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    What a fucking troublesome little bastard this thing is!
    Have you done a comp or leak down test? I've had issues with bikes getting hot and trying to seize but it wouldn't be highly likely on a VT motor.

    Is it fine when cold? If so, I'd warm the leads up with a hair dryer and the coil and start checking for cracks/splits and resistance.
    Bench sync on carbs won't do sweet f.a unless you have even compression and valve clearances.

    I'd be really trying to find if it's lean/rich when the issue happens and then go from there.
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
    Bling your bike out!
    PM me

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