Stumped!!

Bike starts then cuts out straight away. So I thought fuel, sorted fuel lines,float bowl, cleaned carb and reeds still the same problem persists. So I pressure tested the bike got roughly 155psi. There's a spark and when I took the plug out if wasn't to filthy just right. The Problem started a week a go as I wanted to take her out for a little ride however got 10-15 minutes down the road as I gave it some juice it just backfired and died. Since this it doesn't want to start for more than 5seconds. Left me in a position where to me it's a stab in the dark. Any help appreciated

 

Could be an airleak on your intake manifold, get some new gaskets or some gasket goo, worth a try

 

ignition problem ?

 

try another set of reeds if you have them? my runner did the same, i started it an it idled lovely

gave it a rev and it popped and spluttered and then ran like crap and wouldnt rev

turned out to be the reeds

 

his starts for 5 seconds and cuts out could a loose fly wheel cause the problem i had a similar issue on a aprilia rs 50 where the fly wheel nut had come lose and had caused the to back fire tightened it up ran like a dream after that

 

i have heard of people having the woodruff key snap and cause all manor of issues!

 

yeah me too mine was all down to a loose nut on the flywheel side , lets hope the wood ruff key hasn't snapped and chewed the threads on the crank

 

you pressure tested the engine to WHAT? thats 10 bar! Is this a 4 stroke? I wouldn't go over two for fear of blowing the crank seals off....
off hand I'd look at the ignition like steeve says (damn he's good!). A faulty ignition runs into trouble when the temperatures &pressures get high - and the spark gets 'quashed'.
just an idea.

 

155psi seems high but pretty correct for a compression test?

 

ah - Compression test. OK. Makes more sense. Thought we were talking crank case & finding leaks.

 

my stalker does this if i dont let it warm up long enough ?

 

Right. In my limited experience - electrics are the culpret. But in the case of qwerann - If it works fine when warm - it's probably a bit poor somewhere - probably with the mixtrure screw - or there's a choke issue.

 

yeah i think its mixture as still not got it set up right... i have a 54 plate which run delly 17.5 carbs with small air box..... but, also have the older model webber carb with big air box in the shed... dunno whats better? alot of the lads i know who use them as stunt bikes run the webbers

 

It might sound proper daft, but you don't have the tick-over down too low?

It can give the symptoms you describe of starting for a few seconds and then dying. Obviously this can be tied in too with your mixture screw setting as one will effect the other.

 

It could be:-

Water in the carb float bowl, carb float height incorrect, carb auto-choke stuck, air leak at the exhaust connection to the engine, as well as damp in the electrics.

 

Sorry for the late reply lads, been busy, I've tried taking the carb off n cleaned again.. Took the stator off n cleaned connections... I took the vacuum bit off the boost bottle and covered it up the suction was good and it started for a few seconds more so I think it's a air leak or a problem around this area... Is it possible to of blown fuel back up the pump and blocked it

 

Doubtful. If you've had the carb apart, my money is on the float height being wrong, stopping the float bowl from refilling once it's emptied. You'll get a couple of seconds running before it empties.

Check how you've fitted the float needle on the float and try blowing into the carb with the float bowl removed, to check that the float needle opens and closes the fuel flow as you adjust the float height. The jet that the needle goes into might also be partially blocked, so check that too.

 

I cleaned it out again put it back together and it run sweet, rid it for a bit then fuel got low it bogged n died then just about got me home, think there's crap in the petty tank gunna give that a go and go over it all again