excessive fuel consumption...

[Nige W]

Just a fuel-consumption question... my Arrow seems to go through petrol like it's going out of fashion. In the 200 miles I have put on it in the past couple of months of ownership, I have more-or-less filled up the tank three times (a total of around 8 gallons). This works out at around 25mpg!!! A 30 mile ride yesterday saw it consume well over a gallon of fuel.

I haven't been able to find any leaks anywhere. Petrol tap is shut and the carb run dry after every run. Can't smell petrol whilst it's stood in the garage.

Could it be that the carb is worn out? - though the engine runs well, accelleration is pretty good and revs out in first three gears. It does surge a bit when warmed up (ie revs don't drop off quickly when throttle closed) and idle a bit quicker, but if that was a vacuum leak then it'd be running lean if anything, surely?

Have noticed some fuel staining on front of headers (though not excessive), but does tend to gather oil at exhaust/silencer joints and at the end-caps.

Any thoughts/ideas much appreciated (probably cheaper to chuck in a new carb than to keep filling it up tbh).

Cheers

[ian williams]

hi Nige ;
you should see at least 50mpg but its more usual to get 70mpg out of the leader or arrow .
my leader easily does 70mpg and it doesnt make much difference how its ridden .
im using the 7/8" carb .

if you have a 1 1/16" carb and the engine has high compression heads and has had a bit of tuning work done to it you should still find mileage figures well above 50pmg .

the float height is fixed on these carbs but seems to be quite high when i checked mine , it might be that you have an issue with fuel getting in due to a "flooding" action connected with float height .

what i did to mine was to machine the screw in float needle seat/fuel pipe connection down a bit and shim it so i could lower the float level a little ,but i only did this for my own testing and cant say what the result of this would be for anyone else .

check that the float is shutting fuel off when the float is up and also check the float itself .

i know john ellis said he had a plastic float swell up once due to the ethanol in the petrol causing this and he had to sand the float down to get it to swing free as it wasnt working previously and caused problems .

the new floats by amal uk are ethanol proof but some older plastic floats dont seem to be .

brass floats seem fine though but you need to see they still float .

only other thing is to check if you have a leak in the tank somewhere but i guess youd smell the petrol and see a stain from it .

my guess is its something to do with your float and associated parts .

ian .

[Nige W]

Thanks Ian. I must admit that I haven't checked the (brass) float operation fully (though a visual inspection would indicate that it's sound, and no fuel inside it). As I have other carburation questions I'm going to start a new post - thanks again.

Nige