PWK fuel starvation

[howard]

Since I fitted the PWK's to my R1-Z the bike won't hold more than 7k revs and starts to die, as it's fitted with clear float bowls I can look down and see that there's only a couple of mill of petrol in bottom of the bowl, the bike has a single outlet TZ type fuel tap from Norbo and runs just the same with the TZR tap .
How can I get more juice into the carbs ?

[howard]

Going over to muttsnuts tomorrow to put it on the Dyno so I could try float heights ,

[fatfastroger]

Sure the angle of the carbs aren't the problem? Bowls don't look full enough at that angle.

[tsa]

fit a larger float valve they are available from Allens Performance.

[Deleted]

carb too big for bike, I will give you a tenner for float bowls at dyno tomorrow

[howard]

Bike is just too fast for these tiny little carbs, Whilst at at idle the bowls fill nearly to the top ( more than in the picture ) but when being ridden it just empties to nearly nothing .

[nikfubar]

Apr 11, 2014 21:30:34 GMT 1 howard said:

Bike is just too fast for these tiny little carbs

Don't think so, something must be restricting the fuel supply

[howard]

When the carbs are empty the tap will fill them in a couple of seconds .

[rich]

Have you tried it on prime? Vacuum fuel tap could be a bit lazy.

[howard]

Yes Rich I've removed the TZ tap and refitted the original tap just so I could run on prime and it's the same , tried it with the petrol cap open and checked all the breathers ?

[4l04ever]

It is probably worth looking for alternative inlet rubbers or getting something made to get the carbs a bit more level as they will never be full when sitting at an angle.

[lb]

Thought about Pingle tap?
Wicked makes a big assed bowl for these. With access plug that unscrews for easy changing of the jets.

[howard]

Run it on the Dyno today and once you get to 8,000 + revs the bowl was just emptying but as we never held the throttle fully open for any length of time the starvation never happened , plus I was way too rich with the jetting so hopefully once I road test it I won't have the problem.
Although I do think that the clear bowls might not hold enough fuel, might need to remove the angled spacers so I can get the original bowls back on .

[wallcraft]

Are you running open carbs as in pics, what pilots and mains are you on?
Agree with Kenny try some bigger float valves.

[howard]

I'm running standard airbox with snorkel removed , 40 pilots and 135 mains .

[billyboy]

no fuel filter anywhere ?

[howard]

No filters fitted and I've been out on it today and it's still the same runs out of fuel after 1/2 mile at 8,000 revs ,going to try the original carbs again this week just see if it is thirstier than an E type jag, put it away now and using the 400e instead .

[muttsnuts]

um, that's interesting Steve, so its either draining off or the foaming we saw gets to such a point that the fuel is no longer available to the main jet in the quantities required, if you could get bigger float bowls on that would be ideal, but I know its tight for space which is a right pain, especlaly since the bike has picked up loads of mid-range with the PWK's etc fitted

[LC_BOTT]

Have you tried increasing the float height from what you have now?? might be worth a go, increasing a couple of mm a time, I haven't heard many carbs being a problem with fuel flow etc,(including standard ones) even on highly tuned engines. Is yours standard?

[howard]

The bike has had a road tune by martin77 for more midrange with his pipes to suit , I have measured both the clear and standard float bowl capacity and if anything the clear has slight more , might try lifting the floats this week to see if that helps .
Below is the Dyno chart , red is this weekends and blue was last year with different tune , standard carbs and Swarbricks.

[tsa]

Try the larger float valve this will add fuel quicker when you start to give it some. As an experiment its usually sized in mm you could ream out the ones you have and try it.

[howard]

Raised the floats by 3mm and just been on a quick spin up the by-pass and at 80mph the bowls were still more than 3/4 full , but bike went on reserve so I'll try again later , had to drop the needle one and turn airscrews out another 1/2 turn to get it to pull smooth though !

[rdt400]

hi there mate could you let me know were you got the clear carb bowls from thanks RT

[Deleted]

Howard got the clear bowls on e bay, I was bidding on them too but he won

[howard]

I might sell them though ! I will take £4000 for them with a free R1-Z thrown in .

[matstar]

Never seen clear carb bowls before! Didn't even knew they existed.

[Deleted]

Talk to Norbo Howard he wanted your bike

[db8888]

increasing the float height will give you less fuel............. have you tried increasing the size of the float chamber vent pipes ....

[rdt400]

only wish i could say yes to that deal, lololo

[bare]

Carb angle is 'suspect" imo.. Certainly isn't helping.
Later version PWKS feature a differing design. These incorporate a built in fuel header chamber.
Which is an always full source for the carb to suck fuel from.
BIG feature that, especially so on a Motocrosser spending a lot of time in the air.
Moderne bits have advantage.