Discussion in 'Chainsaw' started by Andyshine77, Jun 24, 2016.
Great thread..,have you concluded it to be a design issue? Im having the same problems with mine
Yes it is a design problem, it is one of the major reasons why the 550xp and 562xp are being completely redesigned. In fact the new 550xp mark II is expected to be in dealers any day now.
Getting the heat out of the carb box area is the best solution. Opening up the exhaust and plugging the decompression valve also helps.
I just read through every page of this thread. I have the same problem on my 550, primer bulb pumps air, and saw will not start or will but dies with any throttle.
This happens after leaving the saw for about 2 minutes +
After reading all the posts this is def a heat issue due to design. I was looking at the 550 mk2 and it seems that the cooling fins for the cylinder are further away from the carb. Fins are at a different angle but piston angle is the same, maybe this was huskys fix?
Bobe8888 I have seen your other video with an insulated carb box plate, did this work?
I have two ideas myself if this does not.
Make another hole in the air injection shaft at the lowest point possible. Then make a small slit on the top of the cover on the side just in front of where the filter sits.
When the saw stops without this mod, heat soaks from the cylinder through the wall causing vapour lock. But with this mod it could allow convection currents to do the cooling for you, cooler air rises and now that there is a place for it to go it dissipates heat.
I think the key here is to make sure that the holes are not to big on the top cover so that air flow is not robbed from cooling the fins of the cylinder.
My other idea is to insulate the fuel line itself, I was thinking of sleeping it with larger rubber tubing to insulate it from heat.
After reading this thread and google searching it appears that gas evaporated rapidly above 30 degrees C. It can boil as low as 60 C maybe less.
I’ll have to take a look at my unit and see if these ideas are even possible, but I really want to here what bobe has to say about his insulation trick.
Ok the air injection port is low enough for sure to allow cool air to come up through convection. But as I mentioned there needs to be a hole for these currents to flow...
I added these three, if need be I can plug them off. You can see in one of the shots these holes are in obstructed by the air filter and have a straight line of sight to the Top of the carb boot.
Air should flow when the saw is off from the air injection port, to the hottest side of the carb, to the holes.
If I could get an idea for some kind of way of measuring temperature, I could do a test of before and after.
Eliminating variables would be
Same day (hot around 30C/90F)
Same fuel/mix (91 AKI)
No wind conditions for hottest effect
Variable would be
Ten mins with the holes plugged
Ten mins without the holes plugged
Temperature readings before and after the test for both situations
I figure the probe for the temp would be mounted on the carb itself as it has the greatest thermal conductivity. Suggestions welcome
Another dealer informed me that sometimes the fuel line can collapse when it tries to suck fuel, so replacing the fuel line has alleviated a issue for some. I never liked a few lines on these saws are way too pliable.
When it comes to testing carb temps it sure would be nice is we could buck the saw up to the common service tool, but Husky and Stihl dropped the ball there. A temp gun may work, but I fine them somewhat inaccurate, a thermal coupler would probably be the ticket. I likely wouldn't try insulating the fuel line, I don't think that would do much, but than again anything is worth a try.
So are you still having the issues with the heat tape?
Yes I was thinking a thermocouple style probe... I think a computer style one would probably be best, they are the size of a match head.
I could even stick my meat digital thermometer in one of the holes I drilled and watch the temps...
Went out today, it was 28C out with no wind.
Stuck the meat thermometer in the car right hole and tried to center it.
The coolest it got in the air box was 115F this was at full load bucking cookies like no tomorrow. Saw got very hot, wood chips were starting to smoulder on the exhaust.
When I turned it off and let it sit the temp inside slowly climbed, as high as 171F
In the picture this was where it started to slow down in its temperature climb, but a minute later reached 171.
Heat is soaking into the air box from the cylinder slowly, this is probably why it takes about 4 minutes to reach this temp.
I tried to restart and nothing, the air holes are not good enough. Primer bulb was pushing air. However... when I put it into half choke it did run, and after about 10 seconds of this it did not die and was responding to throttle.
I plugged the other two holes for another test after it was shut off when really hot. The temperature climbed one degree every 5 seconds. With the holes un plugged it rose one degree every 11 seconds.
So it is working, it’s just not big enough or something else is happening here...
I did pull the cap off at one point when it was vapour locked and I was getting positive pressure. This tells me that it can’t be a line collapsing problem... unless it’s getting kinked in the tank or something?
The tank did not seem hot at all, and when I pulled the cover the carb was just a little warm to the touch...
I’m gonna make the hole in the air box larger by squaring it out.. I might even add another hole to the bottom of the air box for better convection currents.
Could this issue be due to too low a pop off pressure on the carb? Liquids under pressure increase their boiling temp...
Still issues with the tape, but it helped. The lines are real soft and could get pinched, doubt that's your issue though. From what I know the carb internal temps have shown 130°F or better when info was pulled from the ECU. Some of the heat is likely coming straight from the engine up tge intake boot, that's not something we can really stop from happening. It would be interesting to see what larger holes in the cover would do, I believe a new covers like $30 so not a huge loss.
Yes that’s what I was thinking, if the holes do not work no huge loss.
That’s a good theory about the carb intake carrying heat back to the carb from cylinder.
And yea nothing we can do about that! Wonder if the mark 2 has a more horizontal carb boot?
I also noticed very little air coming out of the holes at full throttle, so I don’t think making them bigger will rob cooling from the cylinder
As I wrote upthread the carb box is conected to the flywheel and cylinder through the turbo clean duct. When you try to restart a heat soaked & vapor locked saw it pulls in extremely hot air right of the aluminum flywheel, and near the cylinder fins. So the carb does not cool off by pulling in fresh cool air and it stays vapor locked.
You need to add enough of a fresh air hole that it does not pull in hot air, and possibly block the turbo clean duct. You may need to restart on choke, but once it gets some cool air flowing through the carb it will cool off fast.
I liked turbo clean and converted some of my saws to it, but it was a bad idea for hot weather. Especially with the E10 I run. It is essentaily carb heat on steroids. None of my saws without turbo clean have this issue, and with a 3/4" hole right off the filter my Poulans don't either now.
As I've mentioned in another thread, the aluminum tape firewall has made the greatest impact on hot start issues for my 2013 562xp. I used simple aluminum foil tape sticky one side. The thermal tape others speak about might be better but I haven't seen or used it.
When I removed the tape earlier this year cause it started looking a little ratty, it got tough to hot start again even though my case hole is cut a little larger than the stock new 562 case and muffler in and out holes are double size. So once again I wrapped 2 layers of aluminum tape fully around all possible entry exit points into the carb area making a decent aluminum firewall and she settled right down again.
Haven't been out in blistering hot weather this year as I did most of my firewood back in June/July, but I left her sitting in the sun between bucking up logs steady (run hard without pause for 3/4 tank at a time) and she pulled over easy every time I shut down for refill or between logs.
I just ran the saw for 4 minutes straight edging a log with the 20” bar buried. Was very hard on the saw using 3/8 milling chain and she got very hot. I won’t do this again cause I’m gonna burn it out if I keep it up. However saw sat for 3 minutes and it fired up after 2-3 pulls with no priming and no fast start. Revved up.
This is hardly conclusive but it was 27C out today and I was right in the sun. Heat tape on the primer lines and on a bit of the carb along with knocking out a hole in the bottom of the air box are the only other changes made. Oh yes I did put the heat tape on the inside of the air box on the divider instead of on the cooling fin side.
I’ll continue to use it and post results
Ive only had one hot start issue this summer with my 562, it was 36 degrees celcius outside with a humidity index of like 42. I felled, limbed and cut up like 2 cord of wood with the saw that day. It was HOT, way too HOT for saw work.
My 044 amd 365 would also not restart that day either so I chocked it up to me being silly that day. Those 2 saws always restart..
My 562 is a 2014, if I follow the manuals hot start method the saw starts every time when its hot no issues. If temps are below 28c i can just pull the cord like any other saw and it fires up.
If its super hot out and I forget to prime it and put it on fast idle its a toss up if it will start.
I may try a divider soon to see if it changes how the saw starts.
Separate names with a comma.