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Old November 6th, 2021, 09:40 PM   #8
DannoXYZ
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Name: AKA JacRyann
Location: Mesa, AZ
Join Date: Dec 2011

Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C

Posts: A lot.
MOTY - 2018, MOTM - Nov '17
Quote:
Originally Posted by SuspectPage3 View Post
Hi Danno, so I've opened the airbox and sprayed petrol at the opening (towards the engine side) and waited 30 secs, fire up the bike and it started in one go (after sitting overnight without choke) and I could rev it up right away, I held up the revs to 4-5k for 30 secs and all good.
I put things together and took it for a test ride and as soon as I put in first gear and took off, it tried to die on me,...
Quote:
Originally Posted by Triple Jim View Post
Adding gasoline made it run better, so the air filter box is not clogged with a nest or dirty filter. Something is restricting fuel flow, like a clogged fuel filter at the carb inlet or a tank vent that's not venting, or even dirty carbs.
Yup, good testing! When you bypass carbs and spray petrol directly into engine, it runs great! This shows you've got fuel problem, not enough petrol is getting into engine to run. It won't run that well again until you've fixed your fuel-flow issue.

You've got K&N aftermarket filter, so it's possible you've got some other modifications. Best to verify everything is in stock configuration and factory-fresh clean. Might as well clean K&N filter and re-oil it (lightly, don't drown it).


1. First test is easy. As Jim mentioned, clogged tank-vent can prevent petrol from flowing out of tank. Easy to test riding with tank-cap open. Does it run better?


2. Next should be inspecting tiny filtre inside fuel-inlet port of carb. Remove fuel hose from carb-inlet and look at filtre. If it's clogged or ripped, might as well replace it with external in-line unit.




3. Then test petcock and verify it flows sufficient petrol. Aim fuel-hose into measuring cup. Apply vacuum to port and note vacuum-level where flow reaches maximum. If it's higher than 3-4 in.Hg, diaphragm may be leaking and it may not be opening enough under regular use (this picture is for different bike, ignore numbers).



Also time 30-seconds flow. How much petrol did cup collect?
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