SOHC.co.uk Forums > CB500/550
Wont exceed 4,500 rpm then stalls and wont restart - on route to MOT
totty:
Hi,
Having a bit of an MOT disaster today - It started bogging at around 3,500rpm on route and wouldn't go any higher unless I was very gentle on the throttle then refused to pass 4,500rpm. When I stopped outside it was holding revs, I turned it off while some space was cleared, it then started but ran really flat and wouldn't pull up the hill, stalled and wouldn't restart.
I'm thinking that it possibly overheated, but not sure if the cause is ignition or fuel related (vacuum leak maybe), or it could even be oil flow as I'm yet to trace why the oil pressure light doesn't work.
They're going to leave it to cool for a couple of hours before trying to start it for an MOT and I'm arranging a van to take it home :(
Any tips would be great, I've got a strobe so the ignition should be easy to test.
Cheers
Allan
UK Pete:
Sounds fuel related, i had a problem like this on one of my other bikes, try all the obvious things in fuel system starting with checking enough fuel is coming from tank, check the filter if you have one, mine turned out to be a blocked breather tube in the fuel tank so the petrol only dribbled out.
Pete
totty:
The good news is it not only started for the MOT but passed and got me home ;D
Do you know what the flow rate should be or should I just look for a steady stream?
I've sprayed a bit of carb cleaner around to confirm that it's not a vacuum leak. I noticed the symptoms after riding just about 50 yards on the way home so I don't think it could be a symptom of overheating.
F2 Paul 876:
Hi
Make shaw the fuel cap breather hole is clear and not blocked over time this gets dirt in it and if you use a tank bag it can bloke it off. all so i had once a badly fitted air box rubber this let air in and stopped it reeving and was just like yours was, refitted it correctly and was instance 100% better.
Paul
totty:
Which bit do you mean by "badly fitted air box rubber" ?
The rubbers on the carb to inlet side are quite hard but spraying carb cleaner around then doesn't affect the tickover so they aren't leaking. I can't get my head around how the carb to aribox or even the join from the airbox to the filter housing could have an effect but I'll definitely check them.
I've also just remembered that the fuel level is quite low as I only put 5L in it, but I did run it with the tap set to reserve.
Cheers
Allan
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