Curvy running poorly.

[craig dow]

hi iv an sv650s 1999 , when i open up the throttle the bike chuggs as if its going to stop , then all a sudden its off runs great at speed , when i stop the revs some times goes up and down , from 1000 to 2000 revs , iv had new plugs in it a month ago , any help please will be greatful
thanks

[craig dow]

sure i have water in carbs , can someone tell me where the drain screws are on a sv650s 1999 , read few posts , one says there faceing each other by the fixing bracket on the rear brake side , and one thread said you can get it via the two flaps inside the carb right down at bottom , and you need a ball allen key , which is right ?are they ball allen key if so what size will i need or is it a diamond head screw on out side of carb ? if so where , . i just dont know where they are , thanks realy need this bike sorted ,

[Sid Squid]

If you reckon you've got water in the carbs, then start there. Drain screws are 5mm Allen head screws almost facing each other on the float bowl. Awkward to reach, remove airbox, and you'll see them, ball ended driver makes access much easier.

If there's water in the carbs, there's quite probably water in the tank too, this possibly the consequence of blocked or damaged filler well drain, search for that - lots of info on here.

Written for someone else with a similar problem:
This is quite possibly Mav's problem, but it isn't caused by the fuel cap leaking, what's happening is the filler well drain hole/pipe/hose is blocked.
If you lift the fuel cap and look into the well around the filler hole you'll see a small hole, (~3-4mm dia), toward the left. If it's blocked, rainwater sits in the recess on the top of the tank, when you open the cap to fill up it drops into the tank.
It's not unusual to find a significant amount of water in the fuel, but another problem is that if blocked, the metal pipe that leads from the hole to the underside of the tank can rust through from water sitting in it, if it does the tank is scrap as the pipe is inside the tank and not practical to repair. Most commonly the problem is the rubber hose that leads from the stub on the bottom of the tank, right at the rear by the hinge, is kinked. Carefully arrange the hose so that it's not kinked when you drop the tank.
But it's not unusual to find the pipe full of crud too, blow it out with an airline or foot pump, every so often check it's clear and squirt WD40 or a dab of light oil down it every so often to ensure it doesn't go rusty.

If you're going to do this you'll be dealing with fuel, so bloody well be careful OK.

And don't get fuel all over the floor, even if you don't barbecue the garage petrol is a bit slippy and you'll easily end up your backside, so be more careful.

To drain the carbs, lift the tank and take the airbox off, the drain screws are 5mm headed Allen bolts roughly pointing at each other between the carbs as they are mounted almost base to base, open them a few turns and let them drain. Good practice says that you should allow them to drain into a receptacle and then carefully dispose of the fuel, however if you can get anything in there to drain it into you're doing better than me. When whatever was in there isn't anymore, lightly tighten the drain screws, careful with this the carb bodies are made of a light zinc alloy and are very soft, it'd be only too easy to make a nasty mistake here so go easy, they just need nipping into place.

Draining the tank: Take it off and turn it upside down with the cap open, (preferably removed), shake it about to get as much out as possible, then remove the fuel tap to get the rest out, get a half pint of new, clean fuel and swill that around the tank, to make sure there's no water or other contaminants in there, reassemble it all making sure that any disturbed gaskets or seals are in good condition, preferably replace them.

[craig dow]

thanks for that sid , will see if thats my problem , bike just revs up but not going any where , then its shoots off , when at high revs bike runs fine , i some times get a back fire befor it takes off , and only does this in low gears or revs , so think its something todo with carbs so thought id see if its water first , thanks again

[embee]

...and check the choke plungers are returning properly. If the idle speed is rising occasionally about the only thing which could do that is if one or other choke plunger is slightly cracked open, it only needs to be a fraction to cause all sorts of bad behaviour at or near closed throttle/idle.

[m1tch_1987]

It might be the case that the jets could be blocked as there are different jets in use depending on how much throttle used.

[craig dow]

thanks for that . but came out of work at 4 tonight started bike up back fireing real bad , revs up and down , got bike two mile up road , backfireing all the way stoped in car park , phoned rac they came by 5-30 lad real good , checked plugs , not a problem , told him about poss water in carb , so he , drained carb , great now i know where the screws are , loads of fluid came out both , he tightened them up , ran bike , wee bit better , said think see if any more comes out , did it again bit more came out , then he went and did other carb again , looked and first carb had stoped dripping , said great didnt thik it would stop , so waited till other stoped then got bike together and started it ran , better , but soon we reved it it just would not go passed 300 revs then die out , any way couldnt think what eles apart from blocked jet , bike just not getting the juice , so an hour had passed , so called out brake down truck , to take bike home , so i was waiteing , try reving hell out of bike , just wouldnt go above 4000revs now , looked and thick pipe from air box comeing down to engine was off at the bottom , put it on , reved well but still wee back fire around 5000revs , kept reving hell out of it , and pop , then bike ran great , phoned rac to cancel tow truck , said be with you in ten mins , waited an hour gave up rode bike home , ran great , 36 miles , still wee bit rough , but no back fireing , but sitting at 2000 revs idel then going down to 1500 revs , flickering , had bike up to 70 and ran well , so still not sure if its sorted or not , and now its 22.00pm and iv just had a call that the tow truck will be with me in ten mins from brake down call out service , brill night

[m1tch_1987]

Hmm might just mean the carbs need cleaning or there might be some muck on the float needles meaning that the bowls don't fill correctly, at least you have got the water drained out!