Carburettor trouble? - Fixed

[mchaggis]

The engine revs fine with the clutch in and in neutral. However, put it in gear and accelerate and it splutters, misfires, hiccups and generally refuses to rev any higher. This comes complete with kangaroo hopping and much shuddering and shaking. This problem has only really started since I filled up with fuel last week. It is fine up to a distinct point, basically until you ask it to do anything, then it starts spluttering.

I cleaned out the carburettor, but couldn't see any problems. However, I am not convinced that the fine jet is completely clear, and without an air line, I can't see how I can be sure. Is the fine jet the one used for wide throttle openings with decent engine load?

I had thought that it was perhaps siezing a little, but it has plenty of oil and the fact that if you pull the clutch in while moving it revs fine would kind of negate that. It's just when you put load on it when it starts. My top speed is about 35mph just now, basically idling in top gear.

Try to clear the fine jet? Get a compressor? Buy a new jet altogether?
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I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[Trixie]

If it was fine up until you filled up with petrol last week, then I can't help thinking it may be something to do with that. Not sure what, though....I find that if I use the petrol from Total garages in my car, it pinks more than if I use petrol from anywhere else. Go figure?!??

How much petrol have you used? Can you get the bike somewhere else and fill it to the brim then go for a run? It may blow a possible blockage through.

How high do you rev it at standstill? Have you taken it to the redline? Do you rev it higher when it is under load, and have you checked the chain?

Does the bike generally run like crap, or does it actually cut out?

Sorry for all the questions, but it may help determine what's wrong!
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Dead nobodies in company cars...

[VFR400UK]

check that the back brake isnt binding on. If it is then it will be like driving a car witht he handbrake on and could explain alot!

You can blow out jets using your mouth and visually check if they are clear ot not (they really arn't that high tech!).

Get the back wheel off the ground and check it spins freely and that your chain and sprockets are in good order before stripping down looking for complex problems.

[mchaggis]

Chain and sprockets are fine, and the back brake isn't sticking. The rear wheel also spins freely.

I have managed to make it do it in neutral too now. As far as I can tell, it cuts out/ misfires with above a particular engine speed. What is confusing me is that the small jet I'm on about seems to be the pilot jet, and hence cannot be the problem, can it? I'll have to strip the carb again tomorrow and have another look I suppose.

Mr Haynes isn't much use for a Chinese bike, even though it is supposed to be based on the CG and CM125...
____________________
I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[Trixie]

I had a similar problem years ago with my old 400/4. As soon as I hit about 6,000 rpm it started spluttering.

I went through everything I could think of. As it was a fairly old bike, I ended up replacing the coils, HT leads, spark plugs, plug caps, etc, etc.

Turned out in the end that the engine was flooding and the carbs needed an overhaul. I bought 4 carb overhaul kits, replaced the gasket above the float bowl and the rubber O rings that went round the main jets in each jet.

Now this happened, I think because the bike had been stood for a long time prior to me buying it. With your bike it does seem quite strange that this is a sudden thing. Does this happen at a certain speed or a certain rpm? In any particular gear?

If it's fuel related you could try something I was advised to to. At the time that it starts losing power, pull your choke out (if you've got an automatic choke I guess this is irrelevant!). If it gains power then your engine needs more fuel. If it gets worse, then it's flooding.

Hope some of this helps!
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Dead nobodies in company cars...

[mchaggis]

Something else interesting I've noticed is that if you can get the bike to accelerate using a hill, it sometimes starts running again fine and revs away off towards the red line. Then you get to the traffic/ junction and let the engine speed drop, and it then starts spluttering and misfiring again. Seems definately a carburettor problem then?
____________________
I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[bish777]

Sounds like water in the fuel possibly.

Occasionally petrol stations can get water in the tanks, or water thats accumulated at the bottom of your tank has been chased down when you filled up-esp possible if your fuel level was very low.

As has been mentioned before give your plugs/caps/leads/coils a once over.

As for carb cleaning, I find in the absence of an air line, find a large bucket, some swarfega and a kettle. strip the carbs down to its larger bits and remove all rubber items. Fill the bucket with boiling water and swarfega and soak the carbs (minus the rubber bits). Once its cooled enough to touch scrub and swill them in the solution. Then rinse them off.
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GSXR1100J

[mchaggis]

I stripped and cleaned the carburettor today, using boiling water and swarfega. That part worked really well, but it didn't solve the problem. At least I have managed to eliminate that as the problem though.

What I was ignoring before was the sound of pinking accompanying the misfiring and general shocking performance.

The spark plug is a bit mucky and has sooty deposits etc. I didn't think it was running rich, but it's possible I was just misreading the plug. Perhaps I put too much oil in the air filter last time I cleaned it. Time for a decoke anyway methinks. Am I likely to need a valve spring compressor? (It's possible the valve clearances are too tight too... ) Edit: the answer is obviously the question as to whether I need to decoke the valves and ports too, which will presumably involve lapping the valves back in as well? Fun.

Thanks for the help so far, anyway.
____________________
I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[mchaggis]

The loss of power, misfiring, and latterly knocking was all the result of soot buildup, presumably preventing the inlet valve from closing properly, losing compression and creating hotspots, causing pre-ignition. The carburettor was not the cause at all, oil consumption several months ago was. Why it occurred so suddenly is beyond me.

The solution? Half a bottle of Redex split between the tank and straight into the carburettor (without the air filter) at a high idle. Redex in the fuel had an unnoticeable effect. Straight into the carburettor solved the problems instantly. It felt rather odd to have sort of power again.
____________________
I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.