Topic: Perplexed! please provide input: photos attached

[KingCustomCycles.com]

No comments on my drawing that looks like a 3 year old did it?  I am losing faith in the abrasive nature of this forum...

[Gordon]

No comments on my drawing that looks like a 3 year old did it?  I am losing faith in the abrasive nature of this forum...

We generally try not to poke fun at something that another member obviously spent hours and hours of hard work on and pored his soul into.  You could really hurt someone's feelings doing that!

[Spanner 1]

O.M.G....I believe I solved it!!...blocked vent-tube...the give-away was fuel appearing in the carb. throat, that should not happen 'cos the top of the vent-tube is below  this and would drain any excess fuel.!

[TwoTired]

O.M.G....I believe I solved it!!...blocked vent-tube...the give-away was fuel appearing in the carb. throat, that should not happen 'cos the top of the vent-tube is below  this and would drain any excess fuel.!

The stand pipe behaves like a vent until there is something in it, like fuel, etc.  All the bowls have a separate vent (sometimes ganged with others) at the top of the float chamber.

Cheers,

[KB02]

Occam's Razor

Is that from "Galaxy Quest"

I think it's "Igthar's Hammer." 

Never give up! never Surrender! - Hey, that's a good slogan for our bikes as well. 


My one thought as to why the bike was running well(ish) with the upside down float is that the PO somehow got it locked open so there was always fuel in there.

Sounds to me like all you need now is a good carb sync and tune up and ride the heck out of it. 

[Spanner 1]

Surely, TT, the 'stand pipe' is also designed to drain excess fuel in the bowl to the ground via its drain tube, before the fuel level rises to the carb, throat and spills on yer motor.
Otherwise why would it be there if there is a " separate vent in the top of the float
 chamber "?

[TwoTired]

Surely, TT, the 'stand pipe' is also designed to drain excess fuel in the bowl to the ground via its drain tube, before the fuel level rises to the carb, throat and spills on yer motor.
Otherwise why would it be there if there is a " separate vent in the top of the float
 chamber "?

In normal operation there are two vents to outer atmosphere for each carb bowl.  The stand pipe behaves as one until it contains "something" that prevents pressure equalization.

The vent at the top of bowl chamber connects to the adjacent carb via a tube or "log" type manifold that interconnects with all four carb bowls.  Other Keihin designs used on the SOHC4 also provide a separate tube as an atmospheric vent.  While the  PD41/2 series does not appear to have the tube to atmosphere directly (it is awkward to examine these closely in my garage at this time), this interlink manifold ensures that all four stand pipes must be plugged before pressure equalization can cease.  I suppose it is arguable whether this specific carb design assigns primary value to the standpipe as either bowl vent or overflow safety function.  However, Keihin's other carb designs on the 500/550, 350/400, etc. since 1971 had separate tubes for bowl vent function, making the primary function of the standpipe on all these other designs, overflow safety.  I've not examined Cb750 carbs prior to 77 for the bowl vent implementation.  So, I don't know for certain if they had a separate bowl vent tube to atmosphere.

Cheers,

[Don R]

Congrats on a job well done by all involved.  I would be very surprised if the float and it's metal tab had not been bent in some manner to make it work upside down or just bent by the act of bolting the bowl on with the float like that. If it's working OK you must have gotten it though!