Vapor Lock????

[Further North]

I have a 1989 Johnson 150 GT on a 1991 Lund 1800 Pro-V...

The motor has been running great, no problems at all...

Sunday around noon with the temperatures way up outside, it becomes hard to start.

Monday evening, temps around 95?, it won't start at the ramp, so I fished with the trolling motor...2 1/2 hours later with air temps down to about 75? it started and ran fine.

Tuesday with air temps right at 100?, it starts at the ramp but dies halfway across the lake...sounds like it's starving for fuel.

Any thoughts are appreciated!

 

[oldcatamount]

Re: Vapor Lock????

Check the vent on you fuel tank(s). Air temp shouldn't effect the motor but will affect the expansion of fuel in a tank.

 

[HighTrim]

Re: Vapor Lock????

Were you running the motor in the morning before it got hot?

Heat soak primarily affects the 60 degree, 90-175hp motors because of their compact design and the fact that they use plastic in the carbs and manifolds. They retain heat longer than their aluminum equivalent parts.

Factory tests have shown that when a motor is shut off, residual engine temps,especially in hot weather, can get above 200 degrees. This causes the gas in the motor to boil away.

Then when the motor is restarted, it is actually running on the vapours, as opposed to the liquid gasoline like it is supposed to. The engine may idle, but will have no power when you accelerate.

Make sure you squeeze the primer bulb, and let the motor idle a little longer than normal. This will allow fresh, cool fuel from the tank along with a venturi effect to cool things down to where they should be.

Alcohol and various other fuel additives aid in this problem, due to their lower boiling point.

Linc n sync, proper plugs and gap, and richening up the idle screws seem to aid in this, along with squeezing the primer bulb and longer idle warm up time.

 

[Further North]

Re: Vapor Lock????

Check the vent on you fuel tank(s). Air temp shouldn't effect the motor but will affect the expansion of fuel in a tank.

Will do, thanks.

 

[Further North]

Re: Vapor Lock????

Were you running the motor in the morning before it got hot?

We were running it on Sunday, off an on all morning, including some 5-6 MPH runs to do side scanning of cover.

On Monday, the motor had not run all day, and would not start unli late in the day (8:30-ish). It started and ran fine after that.

On Tuesday, the motor had not run at all, fired up and ran fine on idle and was fine until it just sort of petered out about half way across a mile wide lake.

In the latter two cases, the priming bulb was nearly empty.

Heat soak primarily affects the 60 degree, 90-175hp motors because of their compact design and the fact that they use plastic in the carbs and manifolds. They retain heat longer than their aluminum equivalent parts.

Factory tests have shown that when a motor is shut off, residual engine temps,especially in hot weather, can get above 200 degrees. This causes the gas in the motor to boil away.

Then when the motor is restarted, it is actually running on the vapours, as opposed to the liquid gasoline like it is supposed to. The engine may idle, but will have no power when you accelerate.

Make sure you squeeze the primer bulb, and let the motor idle a little longer than normal. This will allow fresh, cool fuel from the tank along with a venturi effect to cool things down to where they should be.

Will do - especially on the idling - I normally idle just long enough to warm everything up.

Alcohol and various other fuel additives aid in this problem, due to their lower boiling point.

Linc n sync, proper plugs and gap, and richening up the idle screws seem to aid in this, along with squeezing the primer bulb and longer idle warm up time.

Thanks!

 

[Further North]

Re: Vapor Lock????

Marina went through everything and found nothing out of whack....On the lake this weekend to see what happens.

 

[Fed]

Re: Vapor Lock????

Don't be afraid to re-prime with the fuel bulb, use the fast idle lever & even some choke.

 

[Further North]

Re: Vapor Lock????

Will do.

Had the Marina go through everything - nothing out of whack.

We replaced the primer bulb as a precaution, and I ran the motor off and on all afternoon Sunday, it ran fine...but it was not hot out.