HELP. 3120xp Won't start when hot.

[deye223]

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.

If It's a brand new stock saw with less than 8 hours on it take it straight back to the dealer

 

[Hinerman]

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.

You have to get the saw to run cooler if possible to prevent heat soak into the carb. If you don't want to mod the muffler and the carb, you might try running a littler richer mix (32:1) or taking the top cover off. Maybe somebody else will have some other ideas. Otherwise, you are going to have to rechoke the saw after a long cut; not really a big deal other than yanking on a 3120 starter is not on my top 10 list of favorite things to do.

EDIT: not 32:1, see post below

 

[kneedeepinsaws]

Try running at 50:1 instead. Should cool it down some

 

[kneedeepinsaws]

You have to get the saw to run cooler if possible to prevent heat soak into the carb. If you don't want to mod the muffler and the carb, you might try running a littler richer mix (32:1) or taking the top cover off. Maybe somebody else will have some other ideas. Otherwise, you are going to have to rechoke the saw after a long cut; not really a big deal other than yanking on a 3120 starter is not on my top 10 list of favorite things to do.

Running at 32:1 will actually lean the saw out, you are mistaken.

 

[Hinerman]

Running at 32:1 will actually lean the saw out, you are mistaken.

Thanks for the info. I edited my post. My reasoning is flawed, lol

 

[kneedeepinsaws]

Thanks for the info. I edited my post.

No worries it is a very common misconception

 

[Mastermind]

Vapor lock. Modding the muffler will help. The stock carb will be fine as it is. They are too fat as is....

I'd braze a 1 1/4 pipe in it off to the recoil side.

 

[Hinerman]

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

Yes, they are successful

 

[Hinerman]

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.

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

In case Navy Vet wants to do it himself:

How To Add A High Speed Circuit To A Walbro WG Carb | Outdoor Power Equipment Forum (opeforum.com)

Simplified---Adding A High Speed Circuit To A WG Carb | Outdoor Power Equipment Forum (opeforum.com)

 

[Lightning Performance]

If the dealer gets it after a muffler mod it does void any warranty. Better to get a new one made from a member here and bolt that on.
No need to mod the carb for your use.
Milling with my saws they are set so fat they just puke out oil cold @32-1. I could easily go to 40-1 but good oil is cheap insurance pulling 166 dl of 404. The 660s are going on 32-1 when ported. No need to beat up bearings with long bars.
25-1 if you buy cheap oil. Lifting in the cut takes out the motor heat. I do it often on long bucking cuts. Just ease up every twenty seconds to here it blubber and keep going.

 

[rogue60]

I did own a 3120 at one time had it a few years was 100% stock it never did vapor lock even in 40c heat but that was back when fuel was good and had additives to increase the boiling point.
Even e free has a lower boiling point now day's and any fuel with ethanol in it makes vapor locking even worse.
What fuel are you running? Vapor lock is the fuel boiling a fix could be as easy as changing the fuel you are using.

 

[US Navy Vet]

I did own a 3120 at one time had it a few years was 100% stock it never did vapor lock even in 40c heat but that was back when fuel was good and had additives to increase the boiling point.
Even e free has a lower boiling point now day's and any fuel with ethanol in it makes vapor locking even worse.
What fuel are you running? Vapor lock is the fuel boiling a fix could be as easy as changing the fuel you are using.

I've been running shell 91 octane ethanol free mixed 40:1 with husky oil. I know its not the best but I got a gallon of mix oil with the purchase of the saw.

 

[Mastermind]

I've been running shell 91 octane ethanol free mixed 40:1 with husky oil. I know its not the best but I got a gallon of mix oil with the purchase of the saw.

Try some canned fuel.

 

[US Navy Vet]

If the dealer gets it after a muffler mod it does void any warranty. Better to get a new one made from a member here and bolt that on.
No need to mod the carb for your use.
Milling with my saws they are set so fat they just puke out oil cold @32-1. I could easily go to 40-1 but good oil is cheap insurance pulling 166 dl of 404. The 660s are going on 32-1 when ported. No need to beat up bearings with long bars.
25-1 if you buy cheap oil. Lifting in the cut takes out the motor heat. I do it often on long bucking cuts. Just ease up every twenty seconds to here it blubber and keep going.

I understand the warranty side. If I can't keep it running stock than I'm willing to make improvements. I ran it today for a few long cuts and it seems the same. I shut it down with the choke on the third cut and it did start better but definitely still having issues.

 

[US Navy Vet]

Does anyone have any experience with the aftermarket mufflers on amazon or ebay? I find them around $40 to $45 and if decent would be worth a shot to see if it corrects the problem.

 

[US Navy Vet]

Try some canned fuel.

Any specific brand? I have VP 40:1 that I can try out. It's new in the can but I can't justify the cost for milling.

 

[rogue60]

Any specific brand? I have VP 40:1 that I can try out. It's new in the can but I can't justify the cost for milling.

Yes run the VP if the saw does not vapor lock you found the problem.
Then the fun part will be getting it to run and not vapor lock on cheap pump fuel sounds like modding the muffler to get more heat out works as said above.

 

[Mastermind]

Any specific brand? I have VP 40:1 that I can try out. It's new in the can but I can't justify the cost for milling.

That will do.

 

[Lightning Performance]

Good idea

 

[davidwyby]

I just got a H jet modded 3120 from @Armbru84
I haven’t milled with it yet.
He might have some ideas.