Fuel starvation or something else?

[harvey_s]

My NC21 has been unused out of necessity for about the last 9 months...a few weeks ago finally felt OK enough to take it out and it died about 200 yds from the house.
A bit of hunting around showed the rubber vac hose to the tap had disintegrated, checked the tap diaphragm as well, that looked OK but there was no spring inside, so found one in rough spare tap and replaced that as well.
Tried it today and starts and runs...however once on the move, any large throttle openings cause the engine to bog down and although the bike will accelerate, when its done under any real power it kind of feels like its being held back with the fuel being turned on/off...
I did use rubber pipe for the replacement vac hose - if this was too soft would it cause an issue?
Tank and internal filter were cleaned and checked as well.
Just wondering if I've still got a fuel starvation issue, done something silly inside the tap or the carbs need attention after its lay up...?
Any ideas?...thanks for any input...

[Neosophist]

your spring could be too hard for a start keeping the diaphram patially closed, the stock spring is very wide and quite weak.

vac hose could be collapsing on itself yes.

can take your spring out and see if it fixes it, if so your spring is too stiff

[harvey_s]

Thanks for the advice...
Will try both and see what happens - presumably I can work on the tap in the OFF position without draining the tank.

[harvey_s]

Tried having another look today and realised that I'd put the vac hose onto the vent pipe instead of the diaphragm side of the tap....what a numpty I thought and promptly reattached to the correct connection.
Chuffed with myself, went for a road test and bugger me, its exactly the same...

Off on holidays tomorrow, so will have wait now till I get back...but now just wondering now if there is any vacuum in the pipe. and that's why the last owner took the spring out?
or is the vac in the pipe quite noticeable with finger over the end?

Might have to try a swift ride with a length of pipe in my mouth

[harvey_s]

Just to update this thread and to say thank you for the advice...
Finger over vac pipe proved vac OK and hose not collapsing.
Took tank off and onto workmate, hose on tap into fuel can and vac hose with me on the end proved that the tap worked perfectly as well with enough fuel flowing to keep a motoGP engine happy.
So carbs off and whilst they didn't look too bad internally, there were missing seals on the air screws, very small mains (98's), chewed heads on the emulsion tubes and other issues.
Mine is a vfr400z and the silencer has been modified, the air inlet has had the restriction removed and pipercross air filter element fitted.
So using two other sets of carbs I had as spares, I cleaned up the all parts using a cheap LIdl ultrasonic cleaner and a cut down milk container as per an old Practical Sportsbikes article to increase the capacity for the carb bodies and made one good set with nc24 needles and 5 hole emulsion tubes, 110 mains and tried again.
It now runs absolutely peachy and the best it ever has - no hesitation, no flat spots or fluffiness....very happy bunny now.

[cbr400rrn]

I'd forgotten about that issue of practical sportsbikes so will have to dig it out, can you remember which month it was so I don't have to trawl through every issue from the past couple of years?

[harvey_s]

It's still on the bedside table... Issue 28, Feb 2013