Hot Starting/Vapor Lock Issues (E10?)

[Chris-PA]

chris- l love ya bro, but you're thinking like an engineer, not a mechanic. a mechanic doesn't know the root cause until he's solved the problem, or to use big, 25 cent words, you don't except a hypothesis until you can support it with repeatable experimental data. believing is an obstacle to finding the truth. i like your idea of using a heatsink. better ventilaton might help too. i don't see why a poulan clamshell should run hotter than a more conventional saw, maybe the lack of an integral oil tank as a heatsinking mass? in my experience an overheated motor always floods when you use the choke. i don't see any hard data supporting vapor lock for that matter, only that you think, no you're sure that is the cause.

You're not reading what I wrote carefully - the clamshells don't run hotter nor do they vapor lock more easily, rather they are easier to get out of it due to less hot metal around to conduct heat to the fuel system.

Also, I am an engineer and troubleshooting is what I do best, and I teach people to always start with a hypothesis built from your best understanding at the time - whatever you've got. You begin with your best theory of what is happening, and carefully watch what happens as you go. If anything you see does not match your theory, then that theory must be modified or scrapped. You cannot proceed until you understand what you saw and why it doesn't fit. In this way you converge on an answer - otherwise you flap randomly in the wind, and hope maybe you'll stumble into a solution by chance.

So yes, in your experience an overheated motor always floods when you use the choke, and that was once my experience too. But when mine will not restart I can get them going, and sometimes have them continue to run, on full choke. So you must reconcile what is observed with your starting assumption. Obviously if the fuel were still liquid the saw would flood, but it doesn't and even after a few pulls on full choke the plug is dry. The carb fuel pump cannot pump vapor, and the venturi does not work with vapor. Blocking the intake with the choke plate and letting the engine pull directly on the tank is the only thing that does.

 

[heyduke]

You're not reading what I wrote carefully - the clamshells don't run hotter nor do they vapor lock more easily, rather they are easier to get out of it due to less hot metal around to conduct heat to the fuel system.

Also, I am an engineer and troubleshooting is what I do best, and I teach people to always start with a hypothesis built from your best understanding at the time - whatever you've got. You begin with your best theory of what is happening, and carefully watch what happens as you go. If anything you see does not match your theory, then that theory must be modified or scrapped. You cannot proceed until you understand what you saw and why it doesn't fit. In this way you converge on an answer - otherwise you flap randomly in the wind, and hope maybe you'll stumble into a solution by chance.

So yes, in your experience an overheated motor always floods when you use the choke, and that was once my experience too. But when mine will not restart I can get them going, and sometimes have them continue to run, on full choke. So you must reconcile what is observed with your starting assumption. Obviously if the fuel were still liquid the saw would flood, but it doesn't and even after a few pulls on full choke the plug is dry. The carb fuel pump cannot pump vapor, and the venturi does not work with vapor. Blocking the intake with the choke plate and letting the engine pull directly on the tank is the only thing that does.

two things, then i gotta go do some real work.

my trouble shooting technique has always been to create a binary question, is it a or b? eliminate one with an experiment than divide the other one in half and do the same again. it's a power of 2 thang and gets you to your answer before the boss gets mad. that and engineers made me a wealthy man. i thank them.

second, i'm not saying this is true, just brainstorming again. my experience is that when a saw needs the choke to run rather than just to cold start. it's because one or both "jets," really metering orifices, are not working properly and need the extra vacuum supplied by the choke plate because the venturi doesn't supply enough. usually it's because they have been damaged by ethanol and/or its biproducts. maybe try a new carb or a verified good one. so as i said, i still don't see hard data supporting "vapor lock," just a saw that won't start on a hot day that might start if it were cooler. not arguing but trying to offer alternative ideas since you seem stuck. first thing i would do is try some good fuel on a hot day. then if you "vapor lock" you can tell me to piss up a rope and i'll do it, maybe even post the vid.

 

[lone wolf]

 

[GeorgiaVol]

My Echo weed eater does this from time to time. And down here in Georgia, 95 degrees with 90% humidity is pretty common. I find when my trimmer acts up, usually after 1 or 2 hours of use, I have to restart it as if I am starting it cold. This means depress the primer bulb 6 times, move lever to cold start (choke), pull a couple times till it fires, then move it to run, pull one or 2 more times and it runs like normal. I do notice when I press the primer bulb when it's hot the fuel is full of air. The 6 times pressing it gets the fuel line full of fuel again with no more foam.

 

[GeorgiaVol]

I will add that just refueling isn't long enough to cause the problem. It happens when I set it down for 10 to 15 minutes. Maybe the same problem, maybe not.

 

[Chris-PA]

it's because one or both "jets," really metering orifices, are not working properly and need the extra vacuum supplied by the choke plate because the venturi doesn't supply enough. usually it's because they have been damaged by ethanol and/or its biproducts. maybe try a new carb or a verified good one.

Well if this was theory A, you'd need to go to B because it doesn't fit the symptoms here - I do have the advantage of having been working on this problem for a long time now, and carb problems were something I looked into a lot. In this video from my other thread the saw had just vapor locked badly minutes before the first two cuts. I had to do the whole full choke routine and nurse it back to running. But there's nothing wrong with the carb, and if I shut it off I could start it right back up again - provided I don't wait too long. The second two cuts are a different carb which runs virtually identically.

I will add that just refueling isn't long enough to cause the problem. It happens when I set it down for 10 to 15 minutes. Maybe the same problem, maybe not.

That's exactly it. If you shut it off long enough the fuel boils in the carb. Shorter times don't do it.

 

[GeorgiaVol]

Well it seems like the problem is the carb can't run on fuel "foam" so until the fuel flow is restored the engine runs like crap. If you don't have a primer I'm not sure of the best way to restore a solid fuel flow. I would think a saw would run hotter than a string trimmer, considering there is really no load on a trimmer.

 

[Chris-PA]

Well it seems like the problem is the carb can't run on fuel "foam" so until the fuel flow is restored the engine runs like crap. If you don't have a primer I'm not sure of the best way to restore a solid fuel flow. I would think a saw would run hotter than a string trimmer, considering there is really no load on a trimmer.

Full choke will pull fuel better than the purge bulb. The trimmer actually does have a decent load. In fact those kinds of spinning loads are less linear than a chainsaw, in that they tend to hit a wall and just can't spin any faster.

Just broke the driveshaft on my old Echo SRM-2410 - I'm gonna have to order another. That trimmer doesn't owe me anything!

 

[GeorgiaVol]

Been loving mine. Im sold on the Echo Brand at least for trimmers. Probably going to try the CS590 next year. I need (or want if you ask the wife) a new saw.

 

[GeorgiaVol]

I thought that the load of pulling the teeth across some hard wood would need way more torque than a string trimmer. That's why I assumed they would run hotter.

 

[Chris-PA]

I thought that the load of pulling the teeth across some hard wood would need way more torque than a string trimmer. That's why I assumed they would run hotter.

I'm sure the saw requires quite a bit more total power - I was referring more to the characteristic of the load where it builds to the point where it becomes a brick wall at some point. Blowers are even more extreme that way. When I used to ride a bicycle a lot I had one of those fan trainers for it. You could put all the energy you had into it but you just could not spin it faster than a certain speed. The saw load is larger but more linear.

Anyway, most trimmers have pretty small engines, but still you have an engine made of metal, all of which is hot, and the whole package is under plastic covers with the carb and the fuel system. The carb is cool when running, but when you shut it off the heat radiates out from the hot engine, and the cool carb starts to heat up. Doesn't take too long to cook out the little alloy carb body. If the boiling point of the fuel is low enough, there you go.

 

[Chris-PA]

It's that time of year and I've been dealing with vapor lock on heat soak again, and it appears other are as well. I believe I figured out the issue, and thought I'd stop by and post that info.

All the saws I have that vapor lock on heat soak have some form of centrifugal filter system, or otherwise pull air from near the flywheel. When the saw shuts off the cylinder and flywheel fins heat the air in this chamber, then when you try to start the saw the carb pulls in this superheated air and never cools off. You have to get it going enough to get the flywheel to pull enough cool air into that part of the case, so that in turn the carb can pull in enough air to cool itself off.

Often it will chug away on full choke at low rpm for quite a while without really cooling enough to run properly.

The saws I have that pull intake air to the carb/filter box from other paths don't have this issue much.

 

[Huskybill]

These are newer saws right? They are set leaner to meet emissions. Over heating causes vapor loc in the hotter weather. How about porting the muffler so it gets rid of the exhaust faster. What about the intake are the intake openings allowing enough cool fresh air into the carb. The air filter must be kept clean too.

My older husky saws never had this problem.

 

[lone wolf]

Its winter gas!

 

[Huskybill]

Its winter gas!

You think?

 

[lone wolf]

You think?

Well I don't know all the details but It sure happens to me this time of year. Winter gas is around still in some stuff. You can tell, leave the can in the sun sealed and see how much it gets agitated when you open it.

 

[CentaurG2]

Never seen the difference myself but I did look it up. I would think the 2 stoke oil would have a huge effect on this.


https://www.popularmechanics.com/cars/a3180/summer-blend-vs-winter-blend-gasoline-whats-the-difference-13747431/

 

[Huskybill]

Well I don't know all the details but It sure happens to me this time of year. Winter gas is around still in some stuff. You can tell, leave the can in the sun sealed and see how much it gets agitated when you open it.

In the springtime, my “mount everwood” as the neighborhood kids called my 50 cords of wood unsplit yet. My point is all my two stroke mix that’s left over (winter gas) goes into the log splitter. I wonder how long it takes the pump gas to change over to the summer blend? I only use high test gas too.

 

[Chris-PA]

Its winter gas!

That's a major problem, but the switch over should be around the beginning of May - I know I have gas that old, but it should be working it's way through the system by now. I usually have trouble all summer thanks to running E10.

 

[Huskybill]

I been running the husky 50:1 per mix in the quart cans. I add more husky two stroke oil to it so it’s 40:1/38:1.