60 Sport starving for fuel

[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.

[Dave K]

I can't imagine how it would be the rotary valve. When the engine stops, is the spark plug wet or dry? Do you have spark? In other words is the coil heating up and shorting out and it takes it about 10 min. to cool down and make sparks again? As soon as it stops, make sure you have fuel getting to the engine. That the carb. is not plugged in any fashion. If you were to give it a shot of ether as the engine is dying, will it continue to run? No fuel it won't run, no spark it won't run, it has compression or it wouldn't have run now. Hmmmmmmm Some may think it is a crank case seal. But usually that will allow you not to even start the engine and as it warms up, the heating and expansion "may" actually seal it up again.

[OldSwartout]

I've had a couple of similar experiences over the years. 

One was a CB350 Honda with a petcock that had varnished up the internal screen and the layer of varnish was acting like a flapper valve - it would let fuel flow slowly, but at highway speeds, it closed off the internal screen and starved the carb. It would run slowly and idle all day long, just wouldn't run with a lot of throttle for long.  It would die completely, then refire after a few minutes. It acted just like a plugged gas cap vent, except, like yours, it still happened with the gas cap off.

The second was a Suzuki X6 that would run fine up to about 3/4 throttle, but when you tried to run with more throttle, it would starve and die - turned out it was just the float level set too low, so it didn't keep up with high flow demand.  That one would come back to life as soon as you backed off the throttle for a few seconds, though.

[ddavis]

Hello, Just joined this sight. I have two old Bridgestone Motorcycles. The one that is in good shape I beleive is a 1966 90cc or 100 cc model. I beleive the other is a 1971 9cc or 100 cc mountain model, it is in poor shape. I am into Triumphs and Honda's. I bought these hoping to restore but have decided to sell them instead. Would any one be interested in them. located i nthe Texas Panhandle. Thx D.Davis

[hmmmnz]

why dont you start your own thread?
i'd be interested in the 60cc carb