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By Jamesy
#82660
That problem I had and it was down to a faulty fuel tap.I would also check fuel and the inner fuel tank for any crud.
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By Wheaters
#82674
Jamesy, Thankyou but please see my original post - all that had been considered and dealt with before I posted.


What I found last night: I stripped the carb and confirmed the float height was correct and that the spring in the float needle was working.



However, I also removed the float needle jet to inspect it (it was perfectly clear) but I did find something else! The external fuel inlet tube on these carbs sits offset from the central float needle assembly. To connect the inlet to the float chamber, the carb body is drilled at an angle from the outside to make a narrow port which breaks into the threaded aperture in the centre of the float chamber, where the float jet screws in. After the port is drilled, the outside is sealed with a plain brass plug. Looking from the inside, I noticed that the bottom of this hole didn't seem clear; there was a small "tag" of metal from where this drilling breaks into the threads of the needle jet aperture - poor manufacturing quality control. I tried to see how the brass plug could be removed hoping to re-drill the port to clean it up; I couldn't see how that could be done. Instead I used a 2.5mm drill bit from the inside of the float jet aperture, in my hand drill, to clear away the tag of metal and drilled a little further up into the port.

After I'd finished, everything was blown through with an airline.

I'm keeping my fingers crossed that I've finally found the fuel flow restriction to the carb.
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By Adrian
#82676
If the petrol can get into the carb faster than it can get out through the main-jet, you're winning...



A.
By papasmurf
#82677
2.5 mm? That is in running an engine on methanol territory. (If you fit a main jet to the carb to suit.)
By Norm
#82678
Doesn't matter how big the hole is the float controls the fuel flow
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By Adrian
#82680
But if the float is starved of fuel by a partial blockage upstream it can't do its job properly.



A.
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By Wheaters
#82684
Adrian, precisely so. I don't have a 2.5mm main jet but turbulence caused by a restriction upstream can restrict a smaller orifice further downstream, especially in a gravity fed setup. Or we could just fit the main jet in the fuel tank, couldn't we?

To the doubters, ever wondered why a plumber fits a 22mm diameter pipe on a long run of hot water pipe to a bath tap, rather than the 15mm pipe fitted to the cold one?
By p
#82685
Is the little "lowest point" tag allowing your float to fall far enough to allow full flow through the float valve? I have known insufficient scope restricting max fuel flow.
I regard the mikuni manual as the bible for the micarb clone setup :http://www.mikuni.com/pdf/vmmanual.pdf
Paul.
By Norm
#82687
Sorry Adrian, I should have been a bit more precise, I was meaning the fact it doesn't matter how big, the hole or hose is above the float, I was commenting on Papasmurfs previous post
By Norm
#82688
Wheaters, are you people still using gravity feed hot water units? They are so yesterday.

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