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60 Sport starving for fuel

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millbuna:
I have an old 60 Sport that I got running a few years ago but it has a recurring problem I can't figure out. I take the carb out, remove the float bowl and reassemble. The bike runs 3 to as much as 10 minutes then the idle speed climbs and sounds as though bike is starving for fuel, then it quits. If I disassemble the carb/float bowl and reassemble, it repeats the same way. There's fuel in the line and when I open the petcock with the carb out and needle/seat open fuel flows out. Any ideas?? Thanks

Dave K:
Is the vent in the tank cap clear? If it is plugged, you will start a vacumn in the tank and fuel will not flow. Carefully run the bike with the gas cap off and see if that works. Is the needle and seat clear and allowing fuel to flow when the float is in a lowered position. This should have the needle and seat open allowing gas to flow. Do check the float lever and make sure it is adjusted properly. Too high and no gas will flow, too low and it will flood the carb, that is if the needle and seat are clear and working properly. Let us know!

hmmmnz:
im running the same engine in my mini bike, unfortunatly im running a tk carb (like in th old kawasaki mowers and weed eaters) so i can't really comment, but what dave has said sounds about right
good luck

czmike:

Hello millbuna,

It does sound like it empties the float bowl and then stops (it also sounds like its rich at idle, if the speed climbs much as it runs out of gas).
There is a simple check you can do that will check your gas flow, including the tank cap vent (it has to let air in as the gas runs out).

Get a graduated measuring jug (quart size will do) and aim the carb gas hose into it
Turn on gas tap while you make note of the time on your watch
Turn off gas tap 60 seconds later
Measure gas level collected in jug
Should be 6 or 7 US Fluid Ounces at least (or 200 milliliters) for a small bike
Without having removed the tank cap run this same test again to check for a blocked vent in the cap.

Bigger motors need more flow, e.g. Honda 900 or CBX 1000 gas taps provide about 34 fl. oz (1 litre) per minute. This is an important check for any two stroke motor. The motor doesn't use gas at this rate but you need some headroom to cope with all conditions.

You should have gas hose connected to the float bowl top for this test so you are checking the flow all the way into the carb. Hold open the float bowl needle valve while you run the test.


If it passes the flow test then it may be an air-leak that gets worse as the engine warms slightly.
Crankcase sealing would be the likely suspect I think.


Let's know how you do please.



Best Regards,

Mike Munday

millbuna:
Thanks for the replies. I have run the bike with the fuel cap off suspecting a plugged vent, but the bike still quits. Carb is clean and float bowl vent is clear. With the floats and needle removed fuel flows freely through the seat...but I haven't tried a flow quantity test as suggested. I'm not familiar with how the rotary valves work but know a 2 stroke will run poorly (if at all) with bad reed valves. Could it be that the rotary valves are worn and when the bike warms up they no longer work/seal causing the bike to quit? I haven't done a compression test although when the bike is running it seems to have decent power.

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