# Saw acting up again quits when hot.



## Coldfront (Jan 31, 2014)

I have been struggling now for about a week thought I had it fixed up now acting up again.
Chainsaw info.
Husqvarna 372xp year 2007
965 70 23-00
Sn. 07 2000769
Walbro carb.

I flushed gas tank replaced fuel filter and new gas.
New spark plug, new air filter.
Fuel line and impulse line ok
took apart carb cleaned and new diaphragm gasket kit.
Put back together and ran great, adjusted carb per specs and tune up video's.
I cut one tank of gas saw run good. 
2nd tank of gas saw cuts good low idle good, high speed good.
*Then* I cut a few rounds then the saw just quits like it run out of gas, and won't start.
Spark is good.
Next day I bring it in house go over the carb adjustments again. Saw starts right up I let saw warm up set the low idle, perfect, start cutting into some big oak logs and set the high speed, I get that perfect, cuts smooth and starts 4 stroking when I let up on cut, seems to be running perfect. Low idle good. high speed good.
*Then *after my high speed cuts and saw running good I set down for a 30 seconds saw dies. I get it started again but as soon as I hit the throttle dies, now it won't start. I had both the carb adjustments perfect and throttle speed perfect. I pulled the spark plug it looks great on one side nice tan color, but other side of plug looks dark and carbon? 
Not sure where to go from here?


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## Philbert (Jan 31, 2014)

Fuel vent?

Philbert


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## Coldfront (Jan 31, 2014)

I am concerned about the way the spark plug looks nice and tan on one side of the insulator, but dark and almost looks like the insulator is starting to get pitted and dark on the other side of the insulator? Pitted or some kind of dark build up?


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## Coldfront (Jan 31, 2014)

How do I check the fuel tank vent? It has been about zero temp outside could the vent be icing up? Bring it inside warm it up for a hour take it outside it runs good again for a while. I see the vent tube coming out of the tank makes a horse shoe the goes down inside the plastic case? How can I check if its plugged up? Does that vent tube just pull up out of the gas tank, is it hard to stick it back in if I pull it out?


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## Coldfront (Jan 31, 2014)

Also I tested compression 1st pull 45psi, 2nd pull 60psi, 3rd pull 65psi, 4th pull 75psi , 75 max.


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## nmurph (Jan 31, 2014)

Compression sounds low.... pull until it stops climbing and report back.

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## Coldfront (Jan 31, 2014)

nmurph said:


> Compression sounds low.... pull until it stops climbing and report back.
> 
> Sent from my C771 using Tapatalk 2


I did 75psi max.

I let it sit inside for a half hour just took it outside it started 3rd pull, I let it warm up and cut 12" oak logs for about 10 mins. no problem runs great again, idle and high speed good. One of these kind of headache problems, I'm thinking maybe that vent tube. In my normal cutting I am maybe 30-45 seconds between cuts, when I am setting high speed I am cutting cookies one after another, that seems like when it happens? If I can get it to do it again I will open the gas cap let air in that should eliminate the vent if it still does it right? It might take some hard cutting to get it into a vacuum in the gas tank? When normal cutting, time in between cuts lets the vent slowly let air through?


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## Philbert (Jan 31, 2014)

If opening up the fuel tank releases a vacuum and lets saw start again, it is likely a clogged fuel vent. I am not familiar enough with this saw to guide you to it, but someone here on AS can. Or look on a parts diagram (IPL).

Philbert


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## Coldfront (Jan 31, 2014)

After looking at several diagnosis pictures of spark plugs, i guess it looks more normal than the rest of the pictures.
Yea if I can get it to do it again I will open gas cap and see what that does. I tried pulling the vent tube out on the front bar side I think the rear side is where it goes down into the gas tank. It won't pull out easy I don't want to break the tube in half, I can start it pulling out of the rear side I think is the gas tank side but I am afraid if I pull it out I won't be able to get it back in.


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## Marshy (Jan 31, 2014)

Seems like a double post to your other one askin what the life is of rings... Pull your muffler and check for scoring. A saw will be hard to start with low compression and might run for a little while before it dies. Might need new piston and rings...


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## nmurph (Jan 31, 2014)

It sounds like a vent problem but very low compression could do something similar.

I don't think you tester is accurate if 75psi is all you get. 100psi is pretty much the bare minimum to get a saw to run. Pull the muffler and have a look.

You are not getting meaningful info from pulling a plug and staring at it. It has to be done in a very specific way to yield a valid result. Otherwise, you are looking at how the saw has been running for the last xxx number of hours but not how it has run for the last five minutes.


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## Coldfront (Jan 31, 2014)

nmurph said:


> It sounds like a vent problem but very low compression could do something similar.
> 
> I don't think you tester is accurate if 75psi is all you get. 100psi is pretty much the bare minimum to get a saw to run. Pull the muffler and have a look.
> 
> You are not getting meaningful info from pulling a plug and staring at it. It has to be done in a very specific way to yield a valid result. Otherwise, you are looking at how the saw has been running for the last xxx number of hours but not how it has run for the last five minutes.



The last time I checked the plug I was running it wide open while cutting a good 12" oak log as soon as the cut was finished I hit the kill switch and pulled the plug. I'm pretty sure that is how you check plugs?
I'm leaning towards the vent plugged or icing shut. The saw still runs strong, and starts up good after I letting it sit for a while. I have seen what spark plugs look like if you burned a piston, I have replaced many a piston on snowmobiles, and done one piston on a husky 55 rancher before for a friend. I did look down the spark plug hole with a pen light at bottom of the stroke, the top of the piston did not look bad, and the cylinder wall looked ok also. I will get the correct compression tester because now I am curious. Do you like the one that threads in, or just the one you push the rubber nose cone on the spark plug hole?


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## hamish (Jan 31, 2014)

75psi you gauge is done or your top end is, plain and simple, resolve this first, then go from there.

For a chain saw, unless your a magician you need a compression tester that threads in the plug hole.


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## nmurph (Jan 31, 2014)

To check a plug in a saw-

warm the saw
install new plug
run WOT in a log
cut throttle at WOT
pull plug
look at base of insulator


I would not consider a rubber nosed compression tester.


Run your saw until it stops,then crack the fuel cap to release the vacuum. If it is the vent you should be able to get it to crank up immediately.


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## Coldfront (Feb 1, 2014)

I bought a new compression tester today, max. I can get on a cold engine is 130psi
Plus I confirmed the gas tank vent is plugged. I had the saw inside the house all night, and when I opened the gas cap it was under pressure, as I loosened the cap I could hear air pressure coming out of tank, I mean I could really hear it. If the vent was working that shouldn't happen. Go to "372 gas tank vent tube" thread. http://www.arboristsite.com/community/threads/372xp-gas-tank-vent-tube.251633/


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## RedFir Down (Feb 1, 2014)

What happens when you blow INTO the tank vent line?

Like mentioned before that is a one way check valve, it should not let fuel/air out of the tank (only allows air to be drawn in). 
When the saw was inside warming up the fuel was expanding (kind of like leaving your gas can in the sun on a warm day) that is why there was a pressure build up.

Am I making any sense?


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## Coldfront (Feb 1, 2014)

ok yes so pressure inside the tank is ok / normal, after bringing inside warming up. But when I tried blowing through the hose into the tank it was also a no go, couldn't blow into the tank either, but maybe that was because the tank was already under pressure, I will try blowing through it again with the gas cap off.


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## Coldfront (Feb 1, 2014)

Ok I just tried blowing air through the vent hose *into *the gas tank with the gas cap off, I still can't blow through it. Or is the check valve such a small orifice it feels like I can't blow through it? Would I f it up if I try and blow compressed air through it with a blow gun with the gas cap off?


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## RedFir Down (Feb 1, 2014)

Coldfront said:


> Ok I just tried blowing air through the vent hose *into *the gas tank with the gas cap off, I still can't blow through it. Or is the check valve such a small orifice it feels like I can't blow through it? Would I f it up if I try and blow compressed air through it with a blow gun with the gas cap off?


I would not blow compressed air through that!!!
Im going out to check if I can blow through mine...one minute.


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## krushing73 (Feb 1, 2014)

You said spark is good. Did you spread the tip of the plug and assure it'll jump the gap when hot ? My saw had a bad coil and looked good until I spread the top and it wouldn't jump it when hot. A saw that won't run hot is usually the coil.


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## Coldfront (Feb 1, 2014)

Ok I started my air compressor and shut it off at about 30 psi, with the gas cap off I blew some air through the hose into the tank vent line, air is coming through, the hole in the check valve is very small but I can hear air coming in. It is still very possible that with all the snow and setting the saw down in the snow that I did ice up the bottom where the vent sucks its air from. Plus the snow spinning off the chain when cutting snow covered logs. I'll run it some more and see what it does.


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## Coldfront (Feb 1, 2014)

If it does it again now that I know everything is clear with the vent, compression should be ok with 130 psi cold. I will check spark again if it dies out, and try with jumping a bigger gap. I just put another new spark plug in it as well. It is warmer out today a tropical heat wave clear up to +15f


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## RedFir Down (Feb 1, 2014)

Ok I opened the fuel cap and I was able to blow just a little bit of air through that vent. It was not alot, and it took quite a bit of force... more so than blowing up a ballon (if you can relate to something along those lines)
I know mine is in good working order... the saw has less than 3 tanks of fuel ran through it.


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## Coldfront (Feb 1, 2014)

Ok thanks, I ran the saw for a while today so far so good. I will give it a good test tomorrow.


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## krushing73 (Feb 1, 2014)

Coldfront said:


> If it does it again now that I know everything is clear with the vent, compression should be ok with 130 psi cold. I will check spark again if it dies out, and try with jumping a bigger gap. I just put another new spark plug in it as well. It is warmer out today a tropical heat wave clear up to +15f


Very good video on checking coil





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## Philbert (Feb 1, 2014)

I have a short wire with alligator clips on both ends: one goes to the spark plug, one to a grounded part of the saw, to avoid the spark plug jumping around. like in the video.

Philbert


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## krushing73 (Feb 2, 2014)

Philbert said:


> I have a short wire with alligator clips on both ends: one goes to the spark plug, one to a grounded part of the saw, to avoid the spark plug jumping around. like in the video.
> 
> Philbert



It has a space in the middle ? 


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## Philbert (Feb 2, 2014)

krushing73 said:


> It has a space in the middle ?



Nope. Plain wire with alligator clip at each end.

In the video, you see that the spark plug is still attached to the spark plug wire, and he is grounding out the base against the outside of the cylinder (but sometimes it slips off). He is watching for the spark to jump between the electrodes. I use the wire to make a positive connection between the spark plug and the saw, and watch for a spark in the same place.

Advantages are that it maintains a positive connection even if the saw moves while pulling the starter cord, and lets me position the plug better.

*Note that this rarely happens, _but sometimes_, when guys are troubleshooting a saw, they test for a spark and ignite a bunch of gas fumes from a flooded saw. Can get exciting. Good practice to stuff a rag into the empty spark plug hole, and to move the plug away from that spot, if possible. I guess the commercial spark testers with the enclosed windows help protect against this as well.

Philbert


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## Coldfront (Feb 2, 2014)

I have seen guys weld a big alligator clip right to the steel on a old spark plug for testing. When I worked at a boat marina they had spark testers you can adjust the length of the gap if you want.


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## Philbert (Feb 2, 2014)

If you ground out the actual plug, you are testing both the coil _and_ the plug. Some of the testers will let you check the coil by itself. If I was in the business, I probably would have a few different types of testers. If I don't get a spark in the field, I swap out the plug and try again - I have heard of weak plugs that still emit a visible spark, but cause problems.

Philbert


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## Coldfront (Feb 2, 2014)

Philbert said:


> If you ground out the actual plug, you are testing both the coil _and_ the plug. Some of the testers will let you check the coil by itself. If I was in the business, I probably would have a few different types of testers. If I don't get a spark in the field, I swap out the plug and try again - I have heard of weak plugs that still emit a visible spark, but cause problems.
> 
> Philbert


Yes I had a dirt bike that once had a spark plug that would spark just fine when out of the engine checking spark, but when in the engine under compression would not spark. I took it to the dealer to get fixed when they called me the next day and said it was ready, I asked what they found? When they said they replaced the spark plug I felt pretty dumb.


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