Chainsaw won't start when hot

[jefffarq]

I have a Homelite 18 in. 46cc saw, which ran great the first 2 or 3 years I had it. I will admit that I never drained the gas out when not in use, and so this past spring when I needed to trim some trees and started having problems with it, I figured that was why.

The saw would start very easily, usually on the 1st or second pull, but after it got hot it would die and not start again until it had sat and cooled for at least a half an hour.

After doing some reading on this and other forums regarding this problem and finding lots of advice, I have completed the following:

Rebuilt the carburator

Replaced fuel lines, filter, primer bulb

Fresh, high-octane gas

New spark plug

New air filter

Adjusted mixture 1/4 turn richer

After each of those adjustments, the saw still started easily when cold, but after it got hot it would die and not start again until it had cooled off.

The last time I used it I checked the spark after it died (after more reading on the forums), and sure enough, no spark. Forums said "bad ignition coil."

I replaced the coil with a new one, set the gap per instructions found online using a business card. The saw will not start at all now. Thinking I got a bad coil, I put the old one back on, set the gap, but it still won't start at all. In performing the spark test, I get what looks to me like a very weak spark, but a spark nevertheless. But it won't start.

I've searched all over, and the only "specification" I can find for the correct gap is the business card. I'd bet some money that's not how they set them at the factory, but then again I have trouble believing that a couple of thousandths either way would make a big difference. Does anyone know exactly what the gap should be set at?

But, the cotton-picking thing won't start.

What am I missing here?

Thanks,

Jeff

 

[Toyboy]

Business card, matchbook cover are the usual methods.
Try moving the coil closer. Use a sheet of printer paper to gap it and see what you get. I had a similar no spark issue with a different engine, and that made the difference.

 

[/pine]

Just an off the wall thought...I've read some saws have an issue with the muffler and a plate or something that can cause the no start when hot issue...removing the "plate" or cleaning it is the remedy...
...Also, low compression will also cause it to fail to start when hot...FWIW...

 

[davesl708]

Just an off the wall thought...I've read some saws have an issue with the muffler and a plate or something that can cause the no start when hot issue...removing the "plate" or cleaning it is the remedy...
...Also, low compression will also cause it to fail to start when hot...FWIW...

As /pine mentioned a fouled muffler will give you trouble. Clean the screen and I suspect your problem will improve.

 

[yomax4]

Also check your spark plug cap. I had one with weak continuity. Saw started like crap and not at all when hot. Did the continuity test and then changed the cap. It's a whole new world.

 

[stuckmotor]

I've got a Wild Thing that won't start when hot. I only got around 50 psi when I checked the compression. Thinking it might be the guage, I bought a new one today. I'll try to run another test later in the week.

 

[mddorange]

:welcome:
To the TBN forum Jeff. You are lucky. The Homelite I bought a few years ago started being hard to start after a couple of months.

 

[Mysfyt]

Had the same problem on a Stihl many years ago. Did all the same things you did. Turned out to be a weak flywheel magnet. Replaced the flywheel and was good to go. Saw lasted 25 years. Got the tip from an old timer that did chainsaw repair.

 

[jefffarq]

I've got a Wild Thing that won't start when hot. I only got around 50 psi when I checked the compression. Thinking it might be the guage, I bought a new one today. I'll try to run another test later in the week.

Approx. what should the compression be? I don't use the saw very much, just cut up a little firewood now and then; I'm skeptical that I've used it enough to wear out the cylinder/rings.

 

[stuckmotor]

Approx. what should the compression be? I don't use the saw very much, just cut up a little firewood now and then; I'm skeptical that I've used it enough to wear out the cylinder/rings.

If I remember correctly, some people on the web said their saws had compression around 150 psi. My Stihl dealer said I didn't need to check compression, just remove the muffler and look at the piston and rings for dammage. He said the dammage always occurred on the exaust side. I'm a little skeptical of the word always.

 

[sdef]

My experiences may be different than yours as I drain all of the stabilized fuel from my 2/4 cycle utility engines when done with them unless I will be using them again soon, such as the lawn mower during the summer time or when cutting large amounts of firewood.

Approaching the hot starting problem only, sometimes my Husqvarna semi pro/pro saws can be hard to start when hot due to me not paying attention to proper hot starting procedures. You may need to verify your hot start procedures if not done so already. When this happens to me I switch to another saw until the first one cools down or... I ensure the choke is open, place the throttle into wide open position and pull the starter rope until it fires, which usually takes 10 or 15 pulls (sometimes more) on the rope; just like starting an old carbureted automobile that was flooded. My oldest saw is ~ 15 years old and never fails me as long as I do my part. The newest saw that uses a computer is more touchy to me following proper hot starting procedures.

You have replaced quite a few parts. In my experience, if my chainsaws start and run fine when cold and run fine when hot, the hot starting problem is caused by me. Of course, whatever is causing your current no start problem could have been causing your hot start problem.

 

[dfkrug]

I'm a little skeptical of the word always.

The intake side of the piston and cyl can get scored from sucking dust. Not as common as the
damage you see at the exhaust port, yes. I have seen it several times, from bad or missing air
filtration.

I am with MYSFYT and YOMAX: weak spark can come from weak magnets, bad cap, or bad wire.
Weak magnets are extremely rare in my experience, but excessive heat can damage them. That
is why you don't use a torch to pull the flywheel.

Also, at least one large saw maker had a recall from hot-start issues. It was due to flooding the
carb when a hot saw was turned off. Tank pressure buildup overwhelmed the rubber valve in the
carb. Some tanks have only one-way vents.

 

[jefffarq]

If I remember correctly, some people on the web said their saws had compression around 150 psi. My Stihl dealer said I didn't need to check compression, just remove the muffler and look at the piston and rings for dammage. He said the dammage always occurred on the exaust side. I'm a little skeptical of the word always.

Tested the compression, it runs between 125 - 140, depending on how well I can hold the saw/tester and pull the rope.

 

[Oldpath05]

Chainsaw won't start when hot<<< Neither will I, sounds like the 1970s Partner chainsaw, guess it was called vapor locking.
I have a 3 year old Husqvarna 550XP with a make believe Auto Tune system, that can start miserable hot or cold, sometimes I don't know whether or not to choke my saw or no or throw it the brush pile, 3 pulls it can flood, gas comes out the exhaust, sometimes, 1 pull and it runs.

 

[jefffarq]

I finally got time to fiddle with this some more, I pulled the muffler and sure enough, the top of the piston is badly scored.

So, in trying to determine what's next, I guess my next question is - what is the likelihood of the cylinder being damaged? I see pistons and rings are fairly cheap, the cylinder not so much. I haven't had time to disassemble the whole engine; and I don't want to just for the exercise, but I know I can't tell whether the cylinder is bad or not without taking the whole thing apart.

 

[Oldpath05]

I'd say since the piston is scored it must of scratch the cylinder and should be fixed to if it doesn't cost more then the saw's worth. The other option is boat anchor or hang it on a limb at 300ft and use for target practice, I'd go with the target idea, tannerite and shotgun slugs.

 

[4570Man]

I had a lawnmower that would die and wouldn't restart until it cooled down. The coil was bad.

 

[4570Man]

I'd say since the piston is scored it must of scratch the cylinder and should be fixed to if it doesn't cost more then the saw's worth. The other option is boat anchor or hang it on a limb at 300ft and use for target practice, I'd go with the target idea, tannerite and shotgun slugs.

Will shotgun slugs detonate tannerite? They recommend a minimum of 2000fps, and their website says shotgun slugs will not reliably detonate it.

 

[stuckmotor]

I had a lawnmower that would die and wouldn't restart until it cooled down. The coil was bad.

I had one with the same symptoms. It caused me so much frustration that I ditched the mower and cut my vines with a swing blade. I used the slasher on the yard.

 

[4570Man]

I had one with the same symptoms. It caused me so much frustration that I ditched the mower and cut my vines with a swing blade. I used the slasher on the yard.

Except I didn't have a tractor at the time which left me little choice except get it sorted out. It also caused lots of frustration and took me a while to figure it out. I could mow about 15 minutes before it shut down.