Dumb carb question

[andym]

TL;DR: if the fuel tap outlet is below the carb inlet by 4-5cm.... would it cause fueling issues at higher revs?

I haven't had the chance to do any testing to find out for myself, so figured I would ask instead.

The last time I worked on the dirt bike I removed the starter motor so I could get access to the mixture screw on the carb, while the engine was running (stupid place to put it IMO), going from 1 turn out to 3 turns out (using 1/4 turns each time), the exhaust went from clear to smoky.... although not a lot of difference in the idle strangely. The one thing that remained though was the lack of getting past half throttle before it coughed, spluttered and a lot of the time died.

The carb has been cleaned numerous times, so I know that shouldn't be the problem.... so now I'm thinking it may be the fuel line that could be the issue. The fuel tap outlet sits below the carb inlet, add to that the 1-2cm drop from the tank, then 6-7cm (over the frame otherwise the hose kinks) rise then 1-2cm drop into the top of the carb... would the engine be creating enough of a vacuum to draw fuel through the fuel line?



I know I could easily test this by removing the tank and holding it above the carb level.... but at the moment it's dark when I fall out of bed and dark when I get home.

[Pete.]

The outlet height is largely irrelevant, the fuel level in the tank is what provides the flow to the carb. If the level of the fuel in the tank falls down to near the float bowl fuel level then no more fuel will flow to the bowl. The nearer the two levels are to each other the more the fuelling will be affected when demand is high.

If it has an inline filter, check that (as in remove it).
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Nobby the Bastard]

^ What he said.

If the top of the float chamber is below the bottom of the tank (not the tap) then so long as the tank has fuel, the carb will.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[stinkwheel]

Bikes which have a fuel level below the float height have fuel pumps. Usually electrical these days but mechanical ones do exist.

These are simple to fit but will show up any inadequecies in your needle valve.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.