1983 70HP blue band shuts down at 5000 RPM

[smittylv1]

Motor will perform OK at 4000 RPM and under. Accelerate to 5000 RPM and it runs like a scalded dog for about 5 minutes and shuts down and refuses to start until the next day. It's like someone turned the key off....fuel bulb collapes...I presume due to the high vacuum created fron the sudden shut down. Motor has no thermostat, water pump is new. Any ideas would be appreciated.

 

[Texasmark]

Re: 1983 70HP blue band shuts down at 5000 RPM

Fuel bulb collapsing is a clog in the fuel line between it/in it if defective, and the gas in the tank......period. Don't read something into it.

The fuel pump is sucking against an obstruction. It can't suck in the volume of fuel it is designed to. Therefore the suction against the resistance creates a vacuum and this vacuum collapses the bulb as the interior pressure is lower than the atmosphere.

With what you said, your tank vent is probably clogged. That sounds like about what a clogged vent would cause.

Mark

 

[smittylv1]

Re: 1983 70HP blue band shuts down at 5000 RPM

Mark...thank you...however, vent is not clogged, fuel lines, bulb and fuel pump are all new, carbs have been rebuilt

 

[Bondo]

Re: 1983 70HP blue band shuts down at 5000 RPM

Mark...thank you...however, vent is not clogged, fuel lines, bulb and fuel pump are all new, carbs have been rebuilt

Ayuh,... Welcome Aboard,... That may be true, but the bulb is tellin' ya, there's a restriction Up-stream....

Try a different tank...

 

[Texasmark]

Re: 1983 70HP blue band shuts down at 5000 RPM

Regardless, the vacuum doesn't lie. Bondo has a good idea. Borrow one if you don't have another.


Mark

 

[smittylv1]

Re: 1983 70HP blue band shuts down at 5000 RPM

Thanks!!....can I substitue a plastic gas can? Does the fuel can or tank have to be lower than the carb?

 

[Chris1956]

Re: 1983 70HP blue band shuts down at 5000 RPM

A lot of built in fuel tanks have antisiphon valves in the fuel pickup. Some have screens, some do not, but all can clog. This will cause the fuel primer bulb to be sucked flat...

 

[CharlieB]

Re: 1983 70HP blue band shuts down at 5000 RPM

The restriction in your fuel supply allows enough fuel flow for the motor to operate up to 4000, any more than that and the fuel pump needs to move more fuel than the restriction will allow.

Like Chris said, check the fuel tank dip tube and the tank fittings, I've found stuff like a cigarette filter sucked in, causing a restriction, filtered the fuel and accumulated at lot of crud, which increased the restriction even more.