Scooterotica

I'm running a genuine Keihin PWK 35mm carb on my reed valve malossi MHR 221 & I'm suffering fuel starvation in the upper part of the rev range (even on a full tank of fuel)... the carb has been properly jetted in & set-up on the dyno & runs nice & crisp through the whole range - but when holding it open in 3rd the motor will just suck the bowl dry?
I've got a BGM fast flow fuel tap fitted, which I've tested & am getting over a pint per minute of flow - but it's not enough to keep the bowl full @ higher revs...
The PWK is quite a compact carb when compared to other types of 35mm carb, and I'm wondering if the issue is down to the size/volume of the bowl on the PWK carb being too small?
Has anyone else experienced similar problems running one of these carbs - and would fitting a vacuum fuel pump be the way to alleviate the issue?...


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A vacuum pump is the way to go, you can take the vacuum feed from the reed block to save splitting the casings. If you do a fuel loop system before the carb you may need to fit a restrictor in the circuit to avoid over fuelling or a smaller float jet.

PWK type carbs are prone to fuel starvation issues. Make sure yours is flowing sufficient fuel with the carb fitted and bowl removed. A genuine PWK shouldn't need drilling out though. The other issue is that as the float bowl is as you noted, a bit on the small side the angle that the carb sits at is quite critical. Tilting backwards might be ok but try to keep it as upright as possible in the other plane. Playing with the float height might help too.

Cheers for the replies lads... am gonna have a go @ fitting a vacuum fuel pump once I've done a bit of research on how best to do it - but in the mean time will also check the flow through the carb with the bowl removed.
Should I be looking for the same sort of flow rate through the carb as I'm getting @ the tap?...


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