Strange Intermittent Starting Problem

[dan4081]

I have a mid 80's Force 85HP that has been really reliable, except.....a strange starting issue once in a while. And it always seems to happen as follows:
When I first put it in the water it starts right up, usually first, maybe at worst second turn of the key.
It then runs great all day until the gas tank runs out, and the engine stalls because of no gas. I switch to the next tank, pump the ball, and sometimes it starts right up, sometimes it takes 5, 6 7 or 8 tries or more!
The strange thing is when this happens if I tilt the engine up out of the water it usually starts right away.
Also, if I turn off the motor before I run out of gas and switch tanks it starts first time every time.

So the problem is obvious...when the engine runs a tank dry it is harder to start back up.

The questions then are:
Why does it usually start easier tilted?
What should I look at first that might help the re-start issues?
Fuel pump? Diaphragm?

Thanks for any suggestions.

 

[CharlieB]

Re: Strange Intermittent Starting Problem

I suspect that the crank seals between cyl's are drying out when you run it out of fuel, they then leak just enough that engine vacuum is reduced just enough that it does not pull quite enough fuel to start normally, tilting the motor up lowers the water in the leg, reducing the back pressure on the exhaust and allows the motor to pump a little more air, then enabling it to draw enough fuel to fire.

Once restarted and the crank seals are again wetted, the seal is again adequate for normal starts.

In order to prove this the carbs and exhaust would need to be plugged and each cyl pressure tested to measure the leak to each adjacent cyl.

This is NOT necessarily reason enough to rebuild the motor until the seal becomes so poor that idle quality is gone.

 

[dan4081]

Re: Strange Intermittent Starting Problem

Thanks for the post Charlie.
One thing I forgot to mention above is that the engine also starts easier in the driveway, on muffs, if it is tilted as opposed to in the down position.

 

[dan4081]

Re: Strange Intermittent Starting Problem

Any more ideas?

 

[john from md]

Re: Strange Intermittent Starting Problem

+1 on what Charlie told you. As for starting easier on muffs, you have no back pressure when on muffs as the snout is not in the water. Just switch tanks before running it dry and you won't have a problem. It doesn't take much to look at the tank gauge.

John

 

[CharlieB]

Re: Strange Intermittent Starting Problem

Low float levels and/or slightly lean idle mixture settings also contribute to hard starting.

Tilting the motor tends to artificially raise the floats, causing flooding out the front of the carbs.

If tilted during cranking then a richer mixture would become available to the air flow thru the carb.

Clean your carbs and pay careful attention to the float settings.

Idle mixture should be adjusted while on-the-water IN Forward gear PLUS another 1/8 turn out, test by slamming throttle WOT, if ANY, even the slightest, hesitation or bog, then open idle mixture screws another screwdriver blade width and retest, repeat until perfect.

Carry an extra tank and check your fuel level, don't run out!

That few moments while the fuel levels are getting low are enough to MELT pistons.

 

[dan4081]

Re: Strange Intermittent Starting Problem

+1 on what Charlie told you. As for starting easier on muffs, you have no back pressure when on muffs as the snout is not in the water. Just switch tanks before running it dry and you won't have a problem. It doesn't take much to look at the tank gauge.

John

Thanks John
my boat has 3-6 gallon portable tanks. 2 are underneath the back deck area, so it isnt very easy to look under there and check the gas, though I can do a better job of checking it then I have been. I dont have a gas guage.

I'm confused on what you guys are saying about the back pressure as it displays the exact same symtoms in the driveway on muffs as it does in the ocean. It starts easier tilted up then it does in running position. So with or without any back pressure, it is the same.

 

[dan4081]

Re: Strange Intermittent Starting Problem

Low float levels and/or slightly lean idle mixture settings also contribute to hard starting.

Tilting the motor tends to artificially raise the floats, causing flooding out the front of the carbs.

If tilted during cranking then a richer mixture would become available to the air flow thru the carb.

Clean your carbs and pay careful attention to the float settings.

Idle mixture should be adjusted while on-the-water IN Forward gear PLUS another 1/8 turn out, test by slamming throttle WOT, if ANY, even the slightest, hesitation or bog, then open idle mixture screws another screwdriver blade width and retest, repeat until perfect.

Carry an extra tank and check your fuel level, don't run out!

That few moments while the fuel levels are getting low are enough to MELT pistons.

Ouch, that last sentence has me worried.
I have 3-6 gallon tanks on the boat and always change from one to the next after a tank runs out. I didnt know this was dangerous to the motor.

 

[CharlieB]

Re: Strange Intermittent Starting Problem

Thnk about what goes on when the fuel pump stops pumping, the fuel level in the carbs starts lowering, the fuel MIXTURE is LEANING OUT more and more as the level drops, RAISING COMBUSTION TEMPS higher and higher until there isn't enough fuel to fire.


It only takes less than a MINUTE to MELT a piston at WOT.

It is NOT recommended to run out of fuel at WOT.

 

[john from md]

Re: Strange Intermittent Starting Problem

Opps, I missed the part about being tilted in the driveway. In that case, I would say your problem is definitely float level adjustment. The only thing you are changing when tilting an engine out of the water is the fuel level in the bowl.

John

 

[dan4081]

Re: Strange Intermittent Starting Problem

Opps, I missed the part about being tilted in the driveway. In that case, I would say your problem is definitely float level adjustment. The only thing you are changing when tilting an engine out of the water is the fuel level in the bowl.

John

Is this something I should adjust or is a carb rebuild in my future?

And again, Big Thanks to all who have posted suggestions.

 

[john from md]

Re: Strange Intermittent Starting Problem

You can adjust the floats but you have to pull them off and separate them so why not rebuild them at the same time? The kits cost about $14 each and chances are that you have the old type rubber needle seats anyway which eventually swell when using E10. This is a good time to replace them and preclude having to pull the carbs apart at a later time.

John

 

[dan4081]

Re: Strange Intermittent Starting Problem

Looks like a rebuild of the carbs is in my future then.
Thanks

 

[john from md]

Re: Strange Intermittent Starting Problem

While you have them apart, blow out all the passages with brake cleaner or air if you have it. Also, pay attention to how the balance spring is attached to the float.

John