Engine stutter (after a good blast) - Curvey 2000 S

Hi Fellow SVers,

I am after a bit of advice on my SV. When I am on the way to work, on my own private motorway, I am usually averaging between 85 and 95 mph, for a steady seven or eight miles. I then pull onto a slip road to exit the motorway and then nip onto a roundabout. At this point, when my revs have obviously dropped to slow for the roundabout, often, when I pull onto roundabout, I ease the throttle out to accelerate, and the engine stutters, like as if it is going to cut out and then, thankfully, picks up, just in time .

It never happens at any other time. Always after a good blast. Once the stutter has gone, I then tootle around the town into work, and it doesnt ever seem to happen again. Any ideas will be gratefully received please.

Tony

How long since your last service?

Tony.

The following only applies to the carbbed curvy model.

Tools needed,
ball ended allen key to fit float bowl drain screw, 3 feet 6mm ID hose, receptacle for drained fuel.
My raptor 650 had similar symptoms, it was water in the fuel.
The carb float bowls have drain screws and wee drain pipe stubs, fit a length of hose 6mm ID to the stub and open the drain screw, a ball ended allen key helps for access.
You may have to remove the fuel pump fasteners and shift it out of the way for access no need to pull fuel pipes.
Drain through the hose into a jar, any water will be obvious.

if you find water , ditch the fuel in the tank. Simulate engine vacuum by sucking on the manifold connection to the fuel tap to open it then pinch it over to maintain the vac, petrol will now flow out . You need to disco the tank to fuel pipe line and run it into a jerry can, use the contaminated stuff for a bonfire!.

i found the drain / vent hose that allows water to drain around the filler area was blocked hence water getting into the tank.
Blow through this vent to clear, mine had insect and dust debris as a blockage.

if you dont drain and ditch the fuel the problem will reappear since there is probably a hefty slug of water lying in the low point of the fuel tank BTDISTFBTTS.
I spent a month draining just the float bowls before twigging this. Since I cleared the breather and dumped the fuel its been OK since.
Hpe thats all it is.

I think what happens is when you slow down after a blast a slug of water moves over the fuel passages in the carb , so when you next open the throttle it sucks water not fuel, hence the cutting out, usually happens more on one cylinder than the other, after a few revs it sucks clear untill the next time.
As you blast along at steady speed water fuel mix settles out in the float bowl but at fairly large throttle openings this doesnt block the larger main jet passages. All changes when you decellerate then open up again. hence the stumble.
Cheers
Pod

[embee]

Good advice from pod there.

Due to the known issue of rusting water drain pipes from the filler, it's a good idea to check regularly that it's not blocked, and give an occasional short squirt of WD40 or similar just to help. Don't overdo the WD because it will eventually get down to the drain outlet down under the right side of the engine and might drip near your rear tyre .

The other thing to check on a curvy is that the chokes are free and not sticking. Often a combination of cruddy cables and corrosion where the plungers go into the carb bodies. Your problem doesn't really sound like this, but worth bearing in mind.

It could be that the idle mixture is a bit off, which will tend to show up after a long overrun, any water will just make the effect worse.

Could your tank breather be partially blocked? More likely to show up after a blast when you're using lots of fuel, but restores itself after a bit of town riding as the air struggles to get back into the tank..just a thought...

Cheers pod, skidmarx et al. Does make sense what you are saying, I have a feeling the breather pipes need looking at, not sure about tackling your instructions pod (I might take to local bike shop for that) ...

Thanks, I will have a look this weekend.

Cheers

Tony

Just as an aside. I have recently drained my tank of fuel, as I had to replace the gasket underneath the tap, as it was leaking petrol. And it did the occasional stutter prior to me sorting that out. Can I therefore assume there isn't water in the tank therefore, and its a breather pipe problem.

I do have the Haynes manual, there are quite a few pipes I note, I checked one this morning thinking it had come off and noted that it had a bung in the end so therefore it's not that one!!

Again, any pointers appreciated.

Tony

Sounds like it might be carb icing to me

I'd check the carb heaters as well

Carb-icinng?! At this time of year? Am I missing something? You surely aren't saying that there is sufficient windchill to create an icing effect?

Tony

Id still do the draining of the float bowls check,
its a faff to get to the screws but the principal is easy , undo them a 1/2 to 1 whole turn , drain the crap out, shake the bike a bit to make sure its all out.
Nip them up not too tight and Bobs yer fathers brother.
Ill bet theres a gob of water in each bowl.

Its too warm for carb icing up here in Argyll so I doubt if thats your problem although the sypmtoms are similar.
Halfords sell stuff to add to your fuel that help prevent icing , forget the name , a wee purple bottle, the heaters do next to F all, mine work and I still get icing.
The icy thing happens in the choke venturi area miles from where the heaters are.
its all down to pressure drop and Daltons laws, same thing happens when you let air out of a tyre frost round the valve cap at over zero temps. Dont dwell on this though.
Drain your carbs, be happy.
Cheers
pod