SOHC.co.uk Forums > CB750

Probably last ride this year

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Bitsa (Ralph Wright - RIP):
Rich
Have to say I am with you on the not be beaten bit but I just cant remember my UK K2 having double tap.It must of had but do remember, like you not well off and switching to reserve loads of times I don't remember what your having happen.Do remember while racing with a Jag the open cable snapped shutting down dead nearly went over the bars.From new the shop I worked at sent all new bikes out on reserve with just enough fuel in to get you to the nearest garage.You know this will turn out to be a real silly thing.Keep plugging mate you have all winter to sort it.
Cheers
Bitsa

RGP750:
I haven't tried another tap ,anyone got one i could borrow? i'll happily pay your postage,
 must be cheaper than buying a new one at the mo.
Just to try the pipe route i swapped them over on the tap last time  i tried to sort it
and either pair connected to the front pipe were starved of fuel.
Rich
PS just had answer from previous owner never had a problem with reserve.
it must be something daft.

K2-K6:
I've run both K2 and K6 reliably down through reserve and can't ever remember any supply problems. Also run them so low of fuel that it's emptied one side of the tank to the point where I've stood them on a curb and lent it over far enough to get what's left of the fuel over to the tap side of the tank and would then run up to about 10 miles further.
I'd go through all of the carb breathers to make sure that there is no restrictions to carb filling at all, you are right that it shouldn't do what you describe.

RGP750:
It has to be a tap problem ,tank on bench,attach a length of tube 6", to both pipes
on the tap,put tap on reserve,fuel will flow from rear pipe but not front,put finger
over rear pipe and fuel flows from the front pipe.
As Lobo says you would think when the two carbs being filled by the rear pipe are full the fuel would flow from the front
but this dosen't happen for some reason.
 as for breather pipes the carbs were rebuilt this year and if i swap the fuel pipes over whichever pair is fed by the front pipe is starved. weird!!!

Lobo:
Rich,

A possible explanation...

The tank fuel enters a common chamber within the petcock, and from here exits straight out the 'aft' nipple, and via a couple of 90 degs bends the forward nipple. With the petcock ON all is well...

When set to RES, fuel only flows out the Aft nipple (easiest route), but not out the forward. However, if the Aft is restricted, it'll then flow normally out the Fwd nipple...

So... this implies (to me) that there is a restriction in the reserve tank feed, ie it is unable to supply enough fuel to BOTH forward & aft nipples simultaneously.
Ie... The reserve filter is likely clogged, or it's fuel gallery clogged prior to the common fuel bowl.

Perhaps a new filter, sonic clean or air line?

Simon

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