1997 Yamaha 70 doesn't start after running out of fuel

[Yammie70]

Hi,

I have an issue with my old 2 stroke - 1997 Yamaha 70HP (70BETO 6H3). I'm hoping the community will have some ideas to help me troubleshoot the problem.

Background:
Motor was running fine until I ran out of fuel.
I swap the tank to a full one but the motor wouldn't start again and I had to get towed back to the ramp... The motor turns and fires but it stalls straight away.
Back at home, I had a look under the cowling and fuel was leaking from the bottom carb when pressing the bulb.
I don't think this is related, but I replaced the fuel line + water separator filter a few days before this happened.

What I tried so far:
- Checked the compression. It is even on all 3 cylinders but a bit low (80-75-75). That being said compression has always been pretty low (~90) in the 3 years, I've owned the boat.
- Installed new kit (gaskets, float needle) on all three carbs. When cleaning the carburetors, they were a bit dirty but I didn't notice anything major, except the float needle was stuck in the bottom carb, hence the fuel leakage, I replaced it with a new one. I didn't have a thin wall socket to remove the float seats so I just cleaned them without replacing.

The bottom carb doesn't leak anymore but the motor still doesn't start. You can hear it firing but it doesn't run.

Over the years, I've learned how to service the motor myself and do some basic repairs by reading this awesome forum and other resources but I'm not a mechanic and I'm not sure what else I can try.

Any pointers or suggestions would be very helpful.

Thank you!

[99yam40]

being a 97 it should have a prime start system and not a choke,
have you tried moving the red lever out of auto/ normal to open or closed to see if that helped?

[brian3006]

I know you say you hear it firing...but have you checked spark on all cylinders just to verify??

along with the red lever on the prime start system that 99Yam mentioned. There is a diaphragm in there that might be worth checking too. Mine just recently tore and was allowing fuel by and basically flooding #2 cylinder. Or the solenoid might be stuck and not allowing extra fuel by to aid in cold starting...

Starting fluid is usually not recommended in 2 strokes...but what about trying a spray bottle with mix fuel in it...spray a shot straight into each carb any trying to start..

[DennisG01]

Did you open the vent on the gas tank?

[Yammie70]

Thank you all for your suggestions.

being a 97 it should have a prime start system and not a choke,
have you tried moving the red lever out of auto/ normal to open or closed to see if that helped?

- Yes it's a prime start system on this motor.
I've tried different position on the red lever...After mucking around a bit, I finally managed to start the motor!
Lots of smoke at first but then it settled and seemed to run fine. Yay!

along with the red lever on the prime start system that 99Yam mentioned. There is a diaphragm in there that might be worth checking too. Mine just recently tore and was allowing fuel by and basically flooding #2 cylinder. Or the solenoid might be stuck and not allowing extra fuel by to aid in cold starting...

Starting fluid is usually not recommended in 2 strokes...but what about trying a spray bottle with mix fuel in it...spray a shot straight into each carb any trying to start..

Thanks, I didn't check the solenoid and diaphragm but Il will next time I remove the carbs (hopefully not too soon).

Why is starting fluid not recommended ? And don't need it in warm days or summer but the motor wouldn't start in winter without it...

Did you open the vent on the gas tank?

Yes vent is opened !


So to wrap up, I can now start the motor but it sounds a bit rough so probably need some adjustments.

- Does running the motor without the black airbox in front of the carbs affect the idle at all or is it just to prevent dust coming in ?

[99yam40]

yes, the silencer might make a difference at high RPM (small restriction), but probably not at idle

starting fluid has no oil for lubrication

[zenoahphobic]

Sounds like initially like you flooded the engine through the float needle sticking and you were adding more fuel rather than withdrawing fuel with your actions!
Can only suggest that there still is too much fuel/oil sitting in the crankcase.
The problem could also have fouled the plugs. Suggest cleaning or renewing them. Otherwise it reverts back to improper carby cleaning and clean again, and Ofcourse proper setting up, synchronising, and mixture adjustment. Older two strokes can be a pain sometimes as they need to run in order to adjust!

[brian3006]

Why is starting fluid not recommended ?

sry for the delay. basically starting fluid is not usually recommended in a 2 stroke because it can "wash" the lube from the oil off of the surfaces in the crankcase and piston.

There are some starting fluids that claim to have lubricant in them... they may be worth trying if you need to use starting fluid.

All that being said....I have used starting fluid in many 2 strokes over the years.. I just try to be very sparing with it.. don't overdose it and keep using it if it won't start. once it gets running, the lube in the fuel is returned...