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Leaky fuel tap causing bike to run on one cyclinder?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by thecptn, Jul 31, 2008.

  1. Just came back from the garage, the problem is this, my fuel tap, which is vacuum operated, has been on the leaky side, before, I would come in the garage and find a nice strong odor of fuel, and flooded carbs, problem was solved by disconnecting the fuel line and adding a makeshift fuel line to a container so I would not flood the carbs, this worked well.

    But today it just did not want to run on one of the cylinders, I was reading in a 650 forum, that these taps are re noun for doing this, and replacing them with a gravity one would solve it, well one costs 40 or dollars, now I have already had this problem in the past, in which it mysteriously vanished, and since I have already had the motor serviced, and most importantly, had my ignition tightened up and fixed, I am starting to think it could be the tap that is causing it, could that be the cause?

  2. Vacuum fuel taps can cause several problems.
    Firstly though, your carburettor needles and seats should not leak, even if the fuel tap fails open, so you should perhaps look at new needles and seats there. A cheap investment against hydrolock.
    Vacuum fuel taps can fail to shut off when teh engine stops, the diaphragm can rupture, which allows one cylinder to suck in additional fuel from teh tap, and they can spring vacuum leaks which can cause a lean cylinder.
    Running on one cylinder is probably a failed shut needle and seat, but make sure it's not a flooding carb causing amixture so rich it won't ignite.
    Rebuild kits for vacuum taps are around $20-30 max. I am not a huge fan of manual taps, there is a safety issue(riding off with it off), reliability issue (leaving it on and having carbs leak) and often a lack of reserve position issue.
    Consider that a typical vacuum fuel taps last 20 years or more before causing issues, and I think a rebuild is the way to go.

    Regards, Andrew.
  3. What he said..... :)
  4. I would ignore the problem - you've already got one cylinder too many on that young bike of yours!

    Nothing but trouble, those extra cylinders...
  5. haha, and what if the other cylinder konks out? cool, I have a 200kg bicycle with no pedals :grin: I had a chance to take the plugs out, and it turns out they are fouled, which is odd, I checked them last time 2 weeks ago and they where fine, I put some new ones in, and it fired up normaly, even did a compresion test, 150 psi on both cylinders which is healthy, I dont know, could be my carbs who knows, ill be having the engine rebuilt in the not too distant future I hope, and some new Keihin carbs :grin:

    I am starting to think it has been my rather, too relaxed riding style which is causing my plugs too foul up...hmmm
  6. Absolutely; take it out there and give it the berries.....
  7. +1 everyone else. consider fitting a new diaphragm and seat in the tap, new float needle, polish the seat, and check the float for any leaking. Also consider fitting a fuel filter inline. I'll bet your airbox has a nice bit of fuel floating down the bottom of it too.
    Worst case scenario for your problem is hydrolock from fuel. Best case scenario, contaminated oil and a locked engine. worst case - bent conrod and cracked block/head.

    As a stop-gap, if it's easy to get to your plugs, leave the bike overnight, and remove the spark-plugs and crank it a few times before starting the bike.
  8. Yeah, it has new diaphragms and slides, it also has an inline fuel filter, my pod filters did have fuel in them, it seemed it drained out through the filters, rather then in the motor, ill still change the oil any way, these carbies are giving me too much grief.
  9. Well I have found out why my plugs are fouling out, ever since I got it, it leaks oil both in and out on the left cyclinder, it seeps oil into the header pipe over night, which inturn fouls the plug, and to boot, my carbs are jetted on the rich side as they are rather sooty, so I went on a hotter plug and hopefully it should be better until rebuild time.
  10. ?? If someone can't remember to turn the fuel tap on and off, I'd have to wonder whether they'd remember to put their helmet on!
    I know I'm an OLD fart, but my current (since 2 months ago) bike is the first one I've owned with a vacuum tap. At the first sign of trouble its getting manualised! Never seen a bike with an original manual tap that didn't have reserve position.