HELP. 3120xp Won't start when hot.

[US Navy Vet]

New here but not new to saws. I have a new (less than 8 hours) 3120xp that will not re-start when hot. I use it mostly for milling. I run 40:1 and have verified the spark plug and factory carb settings. To be perfectly clear, it will pop and snort but will not run. If it does pop it immediately dies. I tried squirting some fuel in the carb but it will not stay running. Starting from cold, it runs perfect and stays running until it runs out of fuel or I shut it down. Any input is appreciated.

 

[Czed]

New here but not new to saws. I have a new (less than 8 hours) 3120xp that will not re-start when hot. I use it mostly for milling. I run 40:1 and have verified the spark plug and factory carb settings. To be perfectly clear, it will pop and snort but will not run. If it does pop it immediately dies. I tried squirting some fuel in the carb but it will not stay running. Starting from cold, it runs perfect and stays running until it runs out of fuel or I shut it down. Any input is appreciated.

Next time open the gas cap see if there is excess pressure.
Indicating a bad vent

 

[US Navy Vet]

Next time open the gas cap see if there is excess pressure.
Indicating a bad vent

I opened the fuel cap and there was pressure but no more so than the 395xp or dolmar saw I was using today. I can hear it vent out of the cap but it doesn't blow fuel out of it.

 

[US Navy Vet]

After more research, is it possible the coil isn't gapped correctly from the flywheel? I cannot find an actual measurement spec for it.

 

[Czed]

Check and see if the fuel line is collapsing

 

[Lightning Performance]

An air gap of 8-10 is fine. Business card works.

Remove the coil if all else fails and replace it.
Fix the old one with a magnum if needed.

 

[US Navy Vet]

An air gap of 8-10 is fine. Business card works.

Remove the coil if all else fails and replace it.
Fix the old one with a magnum if needed.

Thanks. The air gap is around 8 thou. Not sure what else to try. If I start it with the throttle lock on, it speeds up and immediately shuts down.

 

[MACHINE]

After more research, is it possible the coil isn't gapped correctly from the flywheel? I cannot find an actual measurement spec for it.

.007 is what I use.

Have a spark tester??

Sent from my SM-G975U1 using Tapatalk

 

[US Navy Vet]

Check and see if the fuel line is collapsing

Best as I can tell the fuel line is no collapsed but it is difficult to see it when trying to get it running while hot. I can't really look at it while cranking but it looks normal after it pops and fails to start.

 

[Canadian farm boy]

Have you tried a different spark plug?

 

[drf256]

Mine did the same thing.

Pretty sure it’s vapor lock. Only happened when milling in the hot sun. I’d have to choke it to get it to run again, then she would be perfect.

Opening the muffler more cured my issue.

 

[Hinerman]

Mine did the same thing.

Pretty sure it’s vapor lock. Only happened when milling in the hot sun. I’d have to choke it to get it to run again, then she would be perfect.

Opening the muffler more cured my issue.

^^^^this.

 

[US Navy Vet]

So far I have verified good spark, fuel line is perfect and changed out spark plug. No changes... With vapor lock, I have seen this on old chevy engines but have never dealt with it in a chainsaw. Is there any way to help? More oil (going from 40:1 to 32:1) or doing the muffler mod as suggested by drf256? Will a muffler mod hurt the engine without the ability to tune?

 

[Lightning Performance]

So far I have verified good spark, fuel line is perfect and changed out spark plug. No changes... With vapor lock, I have seen this on old chevy engines but have never dealt with it in a chainsaw. Is there any way to help? More oil (going from 40:1 to 32:1) or doing the muffler mod as suggested by drf256? Will a muffler mod hurt the engine without the ability to tune?

Do you have flood limited carb?

If you don't know post up the carb numbers.
Tuning the high side is not critical. They flood at high RPM on newer carbs. Tuning the low is easy. Getting the heat out is important.

Try feeding your saw a shot of fuel in a minute right after shutdown. A shot to flood it a bit. Like one ounce or more. Start it at idol not WOT. It will take some pulls but usually overcomes the vapor lock if that is indeed your problem. It needs to idol for five or ten seconds to recover the fuel and prime up the fuel pump and carb. If it runs fine your cooking the carb on long hot runs. Be ready to shut down, refuel and prime with a shot fast as possible. They pull, pull and pull

PIA but it will give you feed back.

If it fails to run on ten pulls you got other issues most times.
Twenty pulls with no go and you can bet something is out of whack there besides the fuel system.

 

[US Navy Vet]

Do you have flood limited carb?

If you don't know post up the carb numbers.
Tuning the high side is not critical. They flood at high RPM on newer carbs. Tuning the low is easy. Getting the heat out is important.

Try feeding your saw a shot of fuel in a minute right after shutdown. A shot to flood it a bit. Like one ounce or more. Start it at idol not WOT. It will take some pulls but usually overcomes the vapor lock if that is indeed your problem. It needs to idol for five or ten seconds to recover the fuel and prime up the fuel pump and carb. If it runs fine your cooking the carb on long hot runs. Be ready to shut down, refuel and prime with a shot fast as possible. They pull, pull and pull

PIA but it will give you feed back.

If it fails to run on ten pulls you got other issues most times.
Twenty pulls with no go and you can bet something is out of whack there besides the fuel system.

I'm not sure on the flood limit carb. It's a brand new stock saw with less than 8 hours on it. I tried to start it at idle when hot but it would not fire. I put it on the throttle lock hoping to feed it fuel. When I put a shot of fuel it the carb, it pops but doesn't stay running.

 

[Lightning Performance]

I'm not sure on the flood limit carb. It's a brand new stock saw with less than 8 hours on it. I tried to start it at idle when hot but it would not fire. I put it on the throttle lock hoping to feed it fuel. When I put a shot of fuel it the carb, it pops but doesn't stay running.

It's a flood carb

 

[US Navy Vet]

It's a flood carb

Any ideas on how to troubleshoot this that I have not covered? I will be milling this afternoon and would like to figure this out. Thanks

 

[Czed]

@beaglebriar
Thoughts?

I'd muffler mod and retune so it'd flow better

 

[US Navy Vet]

@beaglebriar
Thoughts?

I'd muffler mod and retune so it'd flow better

I don't mind doing the muffler mod but you cannot adjust the high side of the 3120 carb and I don't want to burn it up under a lean condition. I also do not want to spend another $200 to get the carb modded to make it adjustable.

 

[Czed]

@Mastermind
You talked about a carb mod for these
Was it successful?