Bike is running only on 3 cylinders

[j0nes]

So my bike started to pull badly on low rpm. I had to drive 400 kilometres because I was long away from home. Firstly it sound like its running on 3 but when it takes 6k rpm it sounds normal again. But now i think its running on 3 cylinders all time and cant go above 120 km/h. I have driven only 2k kilometres on my sparkplugs but i tested my old plugs and it works the same way. 1 cylinder exhaust pipe doesnt heat as much as others. When I emptied carburetors there was much less gasoline on 1 carburetor than others. So can a bad carb balance make that one cylinder isn't running or should I take carbs out and try to clean them? It also backfires on exhaust pipe if accelerate full throttle and then let it go.


 So what should i try first? TPS, sync carbutetors or take carbs out and clean.

[His Dudeness]

start with a set of ngk plug caps and trim the ends off the ht leads. that'll most likely fix it. if it doesn't clean the carbs and balance them if you have a balancing tool.

[Bretty]

If firing on 3 cylinders, the first thing to do is determine if the issue is with (A) Electrics/spark plug/cap/coil or (B) Fuel/Air/Carbs.

The thing to remember is spark plugs 1&4 and 2&3 spark at the same time. (although only one cylinder will fire on compression stroke as the other is on exhaust stroke)

So say for example your issue is with cylinder 1. You would swap the spark plug and HT lead over with Cylinder 4.

If the problem remains with Cylinder 1, the issue is Fuel/Air/Carbs related
If the problem moves to cylinder 4 the issue is Spark plug / cap / coil.

The best way to determine which cylinder has the issue is to use the exhaust manifold temperatures, either with a laser/thermometer or a spitty finger...

Once you can answer the above. you can work through to determine exactly what the problem is.

[j0nes]

I swapped 4 cylinder spark plug and HT to cylinder 1. Still 1 cylinder is not working so the problem is on carb/fuel issue.  I will make manometer on the weekend when i get T connectors. If i take carburetors out and clean all the jets. Will the mixture remain the same if i just screw all jets to same position as they were?

[Disorderlypunk]

i have a strange feeling some crap has got through and blocked up carb 1 slightly
but you said 1 carb had less fuel so when you clean your carbs definatly check your float levels
i say this as you have not specified drain order or if on center stand or side stand
remember when you drain your carbs you will also drain the fuel line and the last you drain will always hold the least amount as the fuel line is drained by that point from the other carbs (hard to explain but it is due to air getting in to replace the fuel in the line)
might be worth backflushing the fuel filter to remove some of the crap but do this with caution
Dont do it if you feel uncomfortable doing it....

[j0nes]

I took carbs out and then i drained them empty.
Draining order and how much there was gasoline:
1 carb 7ml
2 carb over 25ml
4 carb over 25ml
3 carb 25ml
I havent yet tear down the carburetors but clearly there is a problem in 1 carbutetor.

[Disorderlypunk]

draining off the carb always best way to go where posibleooh yeah thats your problem right there
go straight to the float and float needle valve my guess is its simply closing far too early or even just sealed shut and that 7ml was just sitting there
or there could be some crap behind the needle valve but a quick blow through the fuel line will show that (just block the other 3 fuel needles)