mcnicol
Hero member
- Location
- Safety Harbor, Florida, USA
I bought a Japanese commuter for use while my Jota is being dismantled and bits sent to the far corners of the earth, and I'm having a problem that's beyond my experience, looking for advice. 1995 Honda CB1000, watercooled UJM, runs fine except after a while it runs out of fuel in the float bowls and stops for a minute or so until more fuel drains in. Not fun in traffic.
Has a single central vacuum-controlled fuel valve under the tank. There's some rust in the tank, PO has fitted an inline fuel filter (replaced). I dismantled and cleaned the fuel valve as much as possible (partially riveted together) and got it working a little smoother than before. When I run the bike with an external fuel tank and connect the vacuum line from the inlet to the vacuum port on the fuel valve, the fuel valve does exactly what it's supposed to on main and reserve and off positions (I can blow air through when it's supposed to pass through, no air flows in off position).
When I put it all back together, petrol in the tank, I can see fuel flowing in the fuel filter at first to fill the bowls. But after a while the fuel flow mostly stops, and fairly soon after the bike starves and dies. It appears that vacuum can hold the control diaphragm open when there's no petrol, but won't hold it open when there's petrol present.
I'd like to fix it properly, but I could just completely bypass the vacuum control (the fuel valve does have an off position), plug the vacuum line on the valve and the inlet port, and just ride the damn thing. Is this a good or bad idea?
And what can I try to fix it properly?
Ken
Has a single central vacuum-controlled fuel valve under the tank. There's some rust in the tank, PO has fitted an inline fuel filter (replaced). I dismantled and cleaned the fuel valve as much as possible (partially riveted together) and got it working a little smoother than before. When I run the bike with an external fuel tank and connect the vacuum line from the inlet to the vacuum port on the fuel valve, the fuel valve does exactly what it's supposed to on main and reserve and off positions (I can blow air through when it's supposed to pass through, no air flows in off position).
When I put it all back together, petrol in the tank, I can see fuel flowing in the fuel filter at first to fill the bowls. But after a while the fuel flow mostly stops, and fairly soon after the bike starves and dies. It appears that vacuum can hold the control diaphragm open when there's no petrol, but won't hold it open when there's petrol present.
I'd like to fix it properly, but I could just completely bypass the vacuum control (the fuel valve does have an off position), plug the vacuum line on the valve and the inlet port, and just ride the damn thing. Is this a good or bad idea?
And what can I try to fix it properly?
Ken
. 
. There actually is a tank vent, but it's under the tank; I know it's open at the tank because fuel spilled out of it when I took the tank off (damn thing holds nearly 25 litres!). But the vent line may be a different matter. Like most UJMs this thing probably has 10km of hoses wrapped around it, but I'll trace the vent hose and see if it's clogged.
