ARRHH can anyone help?

[willy_01]

hey can someone that knows what they are talking about help me out.

Ive got a vf1000f i took it for a ride yesterday, it started fine but would not idle, adjusted idle right up, sweet. took off and knew stright away something was wrong, it had less power than my 250!! I though it might be a crappy jet so revved it out, nup smooth as but just very crap power. so cant be electrical aye otherwise it would not be smooth? anyway took the tank off air filter ect and find the the throttle slides where only a 1/4 open but didnt open anymore when turnning the throttle.:scratch: The butterflies work fine (i can see them work by shinning a torch down the small opening). My question is does anyone know how these front slides open/ are activated, my workshop manual says take it into the dealer, i say bugger that it cant be too hard, umm can it?
anyway its a set of 4 Keihin VD72A, there is bugger all info on the net about them but seems there are a few owners of the vf series in NZ.

Cheers for your time
Sam

[Stopper Dan]

If its a Constant Venturi carb it could be something to do with the diaphrams. I had a similar prob and thats what it was.. Sorry dont really know that much but theres my 2c, hope it helps..

[willy_01]

whats a 'Constant Venturi carb' i thought carbs aways use the venturi affect while in opperation (mind you im pretty dumb) im pretty sure my rg 250 didnt even have butterflies just two slides.

Anyway here is a pic of what im ranting about how are the front 'slides' controlled.

I cant attach a photo for some reason but can be seen here http://groups.msn.com/rg250/shoebox.msnw?action=ShowPhoto&PhotoID=10

[erik]

I'm not sure why they're called constant venturi, but in CV carbs the throttle controls the butterfly, the slides are operated by the vacuum in the carbs. So when the engine is idling, you can twist the throttle and the butterflies will open right up, but because it takes a little while for the engine to rev up, the vacuum in the carbs takes a while to increase. The slides don't start to move until the vacuum starts to increase. It's all to help keep the mixture right as you open the throttle.

I haven't got much experience so I dunno what could be causing the problem. I'd end up checking heaps of stuff and just hope to find the problem eventually. The diaphrams should be under those round steel caps held on with 4 screws that you can see at the bottom of the photo, there should be another two on the other side for the other two carbs. But I'd guess that if the diaphragms were damaged, they wouldn't affect the idle.
When it is idling, get a damp rag and touch it to each exhaust header, you should be able to tell if one cylinder isn't firing if the rag doesn't hiss on one of them.
I might check to make sure there's no water in the tank or float bowls (since that was the last thing that was wrong with my bike :p although I think my bike idled ok, the water just affected it when opening the throttle). Maybe also check you've got spark at all cylinders?
Hopefully someone with more experience will come along and suggest something.