Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Carbie? Maybe...

Discussion in 'Technical and Troubleshooting Torque' started by shakey, May 27, 2005.

  1. Hi All,
    I've got a CBR2500RR that I've just finished rebuilding after a uninsured twat T-boned me 12 months ago.

    When I started it, it idled fine for about 20mins, i took it for a gentle run and after about 10 mins it sounded like it was being fuel starved, then I realised fuel was pouring out the top of the carbie.

    It's not the fuel as i drained the tank after the accident and flushed the tank before putting it back together.

    I checked all hoses, lines, fuel tap, etc...... I don't think it's the float either.

    The only thing i can think of would be the butterfly sticking.

    any ideas? because riding for ten minutes at a time sucks.

    Any help would be greatly appreciated.
  2. My, that's a big bike :shock:

    It sounds like either the float set too high, or more likely the float needle had gone hard or has some gunk. The float needle is moved up and down by the float and regulates the flow of fuel to the carby bowl.
  3. Sorry 250, yes I know, i thought a 2500 was more impresive.....

    Would it be able to idle ok if the float or needle were buggered?
  4. Well if it is the needle or float whats the best & or easiest way to rectify? Once again......if it was the needle or float, would the bike idle for 20 minutes without a cough or splutter?
  5. As far as I know, only a dodgy float or a dodgy or clogged float needle will cause a carby to overflow.

    I did have a wet foot once as a result of a float that was *just* touching the inside of the float bowl, and got stuck once or twice. A bit of bending fixed it.

    If the float needle is worn, and it is free to rotate, then it might be fine for a while then jiggle into a position where it lets too much fuel through. On idle, it spend most of its time closed, and wouldn't move much, but at higher speeds, letting more fuel through, it might move around a bit.

    I'm not familiar with the layout of your carbs, but it shouldn't take long to pop the bowl, drop the float and inspect the needle. If float needles are as cheap for your bike as they are for mine, and it's more than a couple of years old, I'd get a new one anyway and replace it.

    It could be that sitting around unused for 12 months has let the rubber bit of the needle go hard. You might even consider getting a gasket and O-ring kit for the carbie and doing it properly as long as you're taking it off.

    But first, check for debris under the needle. It doesn't take much, and it's suprising what can happen to an empty tank or a can of fuel.
  6. Thanks a million champ, I'll give it a shot, I've been scratching my head for a couple of days on this one, almost wore a hole through.

  7. Ok, I stripped the carbies, cleaned them out, very little gunk in them, still, cleaned them thoroughly, replaced all gaskets and rubbers, check the heads on the needles for wear, the floats are non adjustable and they all move freely and all sit perfectly even.........put it back together still getting fuel overflowing

    Had a mate strip them down same thing.

    Paid a bike shop to do it and they couldn't find anything wrong at all, they gave it another clean regardless, balanced the carbs, and when they gave it back to me they said that it was spotless to start with and had no idea why it would overflow, Put back on the bike, still same problem.

    Went to a wrecker and borrowed a set of carbs cleaned them out put them on the bike "BINGO" it all works.
    Have now bought the set of carbs.

    Obviously problem solved now but what the Hell would have caused this? Any ideas????
  8. Just because you "cleaned" and checked the needles/seats with the naked eye doesn't mean that one or both aren't faulty. Swapping the carbs and it's now working... Well that proves its the in the original carbies.

    The only things in a carbie that controls fuel level is needle, seat, float, and in most cases the pressure of the fuel pump.

    They're most likely plastic floats, take em out of the original carbs and hold them under a container of fuel, do bubbles come out??? do they eventually sink? if so then there's the problem, the float(s) gradually sink and the needle will never close.

    Intermittantly sticking needle/seats will give almost the same results.

    But hey.. It works now :D

  9. Thanks for that Iffracem, I actually checked the floats that exact way and they where fine.

    I acually swapped the needles between the carbs and the problem didn't follow.

    The only thing i can think is that the seats are worn, a little odd but the only explanation i can come up with.

    Oh well as you said it now works!!!
  10. Now I *could* be wrong about this (it's been known to happen) but I've never seen a non-adjustable carbie float. In most cases, the adjustment is done by bending the little metal tab that pushes on the float needle. It takes a careful bit of controlled force.

    It would be very difficult to manufacture a float that is spot on from the start, so there is usually some room for adjustment.

    Now that you have a working set of carbs you could compare them for float level...When they're right, put them on ebay.

  11. what brand are the carbies?
  12. I do agree that non adjustable floats are unlikely to be manufactured perfectly but it shouldn't be a matter of adjusting the tabs (I wouldn't have thought) because i did swap the needles & floats between the carbies to see if the problem followed or made a pattern, which it didn't

    I think the carbies are 'VP' ?? maybe not sure, will check tonight.
  13. OK, I didn't know you'd swapped the floats as well.

    When it comes down to it, the only thing that will make the carbies flood is if the fuel supply isn't cut off when the bowl is full. That can only be the float, the needle or the surface the needle works against.

    If the original floats and needles worked in the 'new' carbies that narrows it down to the surface the needle works on. (although a float that is correctly adjusted for one carbie body might not be right for another...)

    Are you getting exactly the same problem from both carbies? (or all of them? I don't know how many there are in your bike, being an old fart who never had to deal with modern 250s)
  14. how many carbs are leaking fuel? where is it coming out of?

    might be worth measuring the fuel level, if its good then it could be the needle getting stuck
  15. The leak or overflow, happens or happened after riding the bike for about 10-15 mins, bearing in mind it could be left to idle for as long as you like without the problem happening.

    The overflow was hard to monitor because to get it to overflow you had to ride it.

    There are 4 carbies

    When it did overflow i stripped it down on the street and the fuel that was coming out was sitting in the plastic surround around the carbie trumpets and (starting from the left) carbie#1 was full to the top, carbie# 2 also had fuel in it but wasn't as full, i think this was because it splashed out when i put the bike on it's side stand.

    I tried to monitor this by pulling the tank off and hooking up an 'IV' of fuel and let the bike idle, tried revving it and caring on but couldn't replicate the problem.

    As soon as i put the tank back on and went for a ride it would get the problem. (bastard!!! you have no idea how many times i have taken off the tank and air box!!)

    This made me think the problem was related to being under load or motion.

    With the needles and floats I swapped them around completely so that no needles or floats matched the carbie they came from......as the needles are rubber tipped i would have thought that the rubber would have made a tight seal and not actually worn it's seat....?????
  16. what were the results of measuring the fuel level?
  17. Never actually measured the fuel level, to be completly honest didn't know the best way to test...... any suggestion?
  18. I think it should say in your service manual, but you basically connect a clear tube to the drain thing at the back of the carb, hold the tube vertically and open the screw. then you will measure the fuel height against some reference point on the carb.
  19. Yeah i was hoping for something a little less fiddly... oh well I'll just have to stop being a lazy SOB.... Won't be able to straight away but will give it a shot purely out of interest sake.

    The only thing is i don't like the chances of it showing any variation as the bike runs fine when stationary.

    Will definitely try though thanks mate......will keep you posted.
  20. yeh I agree about the idling, but I figure this way you could rule it out as a possible cause :)

    you could always bring it to dyno day on sunday and see if u can reproduce the problem on the dyno :LOL: