How to cause a 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.

 

[user 122190]

Lack of tank ventilation.

 

[Big Block]

My 346 vapor locked today I left it in the sun off after a pretty big cut and thought I'd never get it started again. And then my arms cramped and I looked like t rex for about a minute. I think it was mostly due to getting my ass kicked by the pole saw. I never did have a problem with my 372 though.....hmmmmmm

 

[CoreyB]

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.

 

[wde_1978]

Lack of tank ventilation.

I don't think so!

1980's Sachs-Dolmar 105 (103 / 108) - magnesium PH that incorporates a fully encased fuel tank.


Boiling fuel is a common occurrence with these saws and other than dangerous refueling it never seemed to cause any running issues!

Horizontal cylinder design, muffler exhaust port to the right side.

My Dolmar PS-7900 is prone to vapor lock though , while my Dolmar PS-6400 is not.

 

[sunfish]

If ya don't have a vapor lock problem why in the hell would a person worry or even care about it???

 

[CoreyB]

I don't think so!

1980's Sachs-Dolmar 105 (103 / 108) - magnesium PH that incorporates a fully encased fuel tank.
View attachment 510119

Boiling fuel is a common occurrence with these saws and other than dangerous refueling it never seemed to cause any running issues!

Horizontal cylinder design, muffler exhaust port to the right side.

My Dolmar PS-7900 is prone to vapor lock though , while my Dolmar PS-6400 is not.

That is interesting and baffling not much difference between the 7900 and 6400.
Does the 7900 run noticeably hotter?

 

[CoreyB]

If ya don't have a vapor lock problem why in the hell would a person worry or even care about it???

My self is the why factor as well as I wanted to see if my saws where prone to it.

Looking at vapor lock from the outside sounds like it would be something definitive and sometimes an easy fix. However it seems to be pretty elusive in some cases.
You seem agitated do you have vapor lock problems?

 

[sunfish]

My self is the why factor as well as I wanted to see if my saws where prone to it.

Looking at vapor lock from the outside sounds like it would be something definitive and sometimes an easy fix. However it seems to be pretty elusive in some cases.
You seem agitated do you have vapor lock problems?

Not agitated & have never had vapor lock problems. Thanks for the explain.

 

[Andyshine77]

Not agitated & have never had vapor lock problems. Thanks for the explain.

Neither did I until the other day. Do you ever cut in hot water? I'd be interested if your 562 has these issues.

 

[wde_1978]

That is interesting and baffling not much difference between the 7900 and 6400.
Does the 7900 run noticeably hotter?

I don't think so, but I can not be certain without having a proper temperature measuring device.

Then again the PS-7900 sports the bigger top end meaning there is lesser material left to pick up the heat.
The PS-7900 also burns considerably more fuel in comparison to my PS-6400, about 1/3 more!

Oddly my PS-7900 received a muffler mod, while my PS-6400 didn't.
That alone should help expel at least some of the PS-7900's heat a bit easier, but it doesn't seem to affect the vapor lock issue.

The vapor lock phenomenon was an unknown issue to me before I got my PS-7900, and even now it only seems to be an issue while running the saw at high outdoor temperatures.

All my saws get the same fuel mixed at the same ratio, usually out of the same mixing canister.
I use unleaded E-free EuroSuper95 from the local pump (have been for as long as I cut wood with a gasoline power chainsaw).

I'll try to remember to video document any future bucking sessions in order to capture any vapor lock phenomenon.

 

[Andyshine77]

I've used my 7900 in hot weather for a decade and have never had any vapor lock, or starting problems. I did however have a bad carb that did cause some tuning issues, it was a poorly sealing welch plug. Also early production models have a foam tank vent filter that would easily clog up. It was replace with a porous plastic disk that pressed into the tank.

 

[wde_1978]

My PS-6400 is built 2001. and my PS-7900 2003.

Other than preemptively replacing the piston and piston ring on my PS-6400 (due to some carbon scoring and blow by), both saws haven't had any issues requiring repairs.
I can't be 100% sure about my PS-7900 though as I purchased her used.

 

[Andyshine77]

My PS-6400 is built 2001. and my PS-7900 2003.

Other than preemptively replacing the piston and piston ring on my PS-6400 (due to some carbon scoring and blow by), both saws haven't had any issues requiring repairs.
I can't be 100% sure about my PS-7900 though as I purchased her used.

I would check the tank vents, the foam cover would often fall off. I replaced the vent filter and vent on my older 7900 and 5100.

 

[sunfish]

Neither did I until the other day. Do you ever cut in hot water? I'd be interested if your 562 has these issues.

I've done a fair bit of cutting in 80+ degree weather, but never at 90 or above. I chose not to.

Never any of these issues with my 2011 562.

 

[blsnelling]

A couple years ago I ran my 346XP quite a bit down in Florida. It was well into the 90s and humid. It ran horribly. It wouldn't hold a tune at all. I didn't do any scientific testing, but I blamed it on the heat. My 390XP ran flawlessly in the same conditions. Otherwise, I've never had trouble with vapor lock. With that said, I rarely run my saws in that kind of heat.

 

[wde_1978]

I would check the tank vents, the foam cover would often fall off. I replaced the vent filter and vent on my older 7900 and 5100.

Might do, have a spare OEM one sitting on the shelf!

 

[CoreyB]

Cutting in 90 + deg heat sure does zap you. But splitting loading and stacking is down right cruel. But hey makes a great weight loss program.
On topic it really is intriguing how it seems to be no rhyme or reason to some of these.
I tried a bit with my 192 yesterday but I ran out of steam and got discouraged when I realized how many branches and small stick I had to pick up. I have been loading and stacking wood all day trying to catch up.
On the plus side the wood pile is looking awesome!