Fuel starvation

[Mrs Reject]

My Kwak GT750 decided to break down twice today on my way to uni. It sounded like it was running out of fuel (loads in the tank), got it going the first time by priming it then put the fuel tap back on normal. It did it again about half a mile later and didn't seem to like pulling away much. As it started up again on prime I decided to leave it on prime and it went a treat, in fact it was the best it's been since I got it which leads me to believe the fuel tap is blocked somewhere preventing enough fuel getting through, I haven't tried it on the reserve setting yet.
Does anyone else think there is a problem with the tap alone or could it be something else and will I damage it if I ride around on the prime setting? It's been tempramental since I got it re: pulling away and I can only usually pull away from stationary in 1st gear, with the tap turned onto prime it pulled away in 2nd and even 3rd great!

[Mad Dog]

Sounds like the vacuum tap or the pipe leading to it is leaking and therefore not operating the tap properly.

Leave it on prime or throw it away and get a regular manual tap.

[dracken1]

vacuum taps were fitted to bikes so that if a float got stuck whilst parked you did'nt end up with 3 plus gallons of fuel on the road.
running your bike in the "prime" position is the same as the "on" position on a non vacuum tap bike.
by rights the prob you have when in the on position should also happen in the reserve position.
either the vacuum from the carb inlet is'nt working (partially blocked) or leaking as maddog stated or the diaphram in the tap is stuck.
so yes its fine to ride it in the prime position but when you park up turn it to on or reserve

[Mitch]

I think... we've just found the problem (this is my idea anyroad) - the pipe that goes from the tap to the Vacuum Nozzle (for want of a better word) on the carbs is really weedy and thin compared to mine - it's also about 4 inches longer. My tubing is about one and a half times as thick.

Would I be right in saying, the whole thing works like a syphon tube and that if the pipe is too thin, the suction compresses the tube forcing it to close, therefore no suction can take place and Mrs R runs out of petrol?

[dracken1]

if it takes less vacuum to collapse the tube than it does to move the fuel tap diaphram,then yes the tube will collapse, giving you the prob

[Mitch]

Cheers Dracken and MD for your help... one less problem to worry about. :D

... see you Sunday MD?

[Mrs Reject]

Thanks guys, took her out for a blatt this evening and at last the bike handles like she should, no struggling to pull away, pulls away in second and a pleasure to ride, after all this time - 7 months it's taken us to figure it out!!! None of the garages we took it to could figure it out either.

[Gypsy]

i have had this problem a few times... always the bloody vacuum pipe :D

[Mad Dog]

I can confirm that Gypsey has had this problem. :)

And, Mitch, I'll be there Sunday.