Vapor lock?????

[CoreyB]

What causes a vapor lock?
Is it something a person can re create?
As I understand it is mainly heat
So run the saw like I stole it.
90+ degree day.
Shut it off in a cut.
Let it sit in sun for 15 min.
Will this cause a vapor lock.
I am really interested and would like a better understanding.
I want to try and see if my saws are prone to this.
If it is able to be re created I hope it will give a better understanding of how to prevent it.

Well I deliberately tried. Sweating my but off, killing the saw directly after noodling.
I noodled and stumped for 30 min in 91 degrees and humidity that was nasty.
Let it sit for 15 min in direct sunlight. 91 octane e-free fuel with dolmar synthetic oil. Oak tree and the second tank of fuel on that chain.

Now I understand some saws are more susceptible to this then others but it seems like some who come across this problem have a very hard time finding a solution and some saws just can't get around it.
What are some solutions?

 

[mdavlee]

Some that do it can be fixed by choking them to shut them down. The metal tank saws are way more likely to happen to.

 

[CoreyB]

Some that do it can be fixed by choking them to shut them down. The metal tank saws are way more likely to happen to.

Choke to shut it down really! That is interesting. So does it just load the carb with cooler fuel to disperse the heat from the lines and carb better.

 

[mdavlee]

That seems to pull more fuel to the carb. A splash down the intake can usually get them going too.

 

[Mycamaro_68]

In my experience in automotive repair, vapor lock had more to do with the fuel lines. I have had decent luck rerouting fuel lines as far away from any heat sources (exhaust manifold, coolant hoses, the engine block itself). I even replaced fuel lines on a snow blower last year, ran the new line along the engine in the same route as factory and it would vapor lock. I ended up routing the line away from the engine and the problem was solved. Maybe different saws are more prone to vapor lock because of the fuel lines being closer to the engine?

 

[TJ the Chainsaw Mechanic]

I've never had a vapor lock issue. I have to wonder if it has to do with the tank vent? Excessive heat and pressure build up and the vent it not allowing the pressure and heat out? I have no solution. X2 with using the choke to shut the engine down. When my saws are hot I'll rev them and then shut them down while holding the trigger at full throttle.

 

[Wilhelm]

The Dolmar PS-6100 is a rather modern saw with reed valves which might help prevent vapor lock.

When I get my firewood logs I'll try remember to intentionally cause vapor lock on my PS-7900 which shouldn't be a problem as she seems to be very prone to it in summer heats.

Vapor lock on my PS-7900 doesn't require 15 minutes, nor does my PS-7900 have to be sitting in the sun!
Scenario:
- run her hard, bucking cut after bucking cut continuously for up to a tank of fuel
- shut her off
- refuel bar oil and fuel
- tension the chain
That is like 5 minutes give or take.
She usually doesn't start willingly after that!

My Dolmar PS-6400 is not affected by this behavior!

EDIT:
I think vapor lock is a carb issue, gas vapors building up or entering the carb prevent the diaphragm to pump fuel.
That's just my view at it.

 

[huskihl]

In a vapor lock, here's my take on what happens. Maybe I'm way off.

When you shut the saw off in a position where the transfers aren't open, added heat pushes through the impulse line into the carb and makes its way through the carb to the fuel line, pushing fuel out of the carb and into the tank. Seems logical to me why a splash of prime fixes it quicker than choking it

 

[Chainsaw Jim]

Has anyone checked the case pressure on one of these problematic saws while hot?
Or pressure tested the carb check valve?