660 won't stay running after a good warm up.

[homervirden]

New 660 build, starts and runs for about a 3rd of a tank then the idle gets lower until it finally won't idle at all. Eventually you can't even keep it running by giving it gas. It also has an oem stihl carb. The spark seems weak, more white then blue, that is all I can see that might be an issue. Gonna change coil next. I don't have a vacum/pressure set up yet but looking to get one soon. Any thoughts? I come back 15 minutes after the saw acts up and it runs good but repeats the issue again after warming up. I had been refueling on the cool down, gonna see if she starts on a half tank today. The p/u tube is always submerged anyways.

 

[Leerod83]

Have you checked the tank vent? After it dies try opening then closing fuel cap and see if it'll start again.

 

[homervirden]

Good idea, I should had remembered/thought of that.

 

[homemade]

I’m going with tank vent. Coils usually don’t slowly die, then come back to life.

 

[ericm979]

Sometimes electronics perform worse or stop working as they heat up. But check the tank vent first.

 

[homervirden]

Doesn't appear to be the vent. I sawed for 5 to 10 minutes, lost idle again. Sat it down, opened fuel lid and would not start afterwards. Got to the plug and it still had fire. Put another plug in and she fires right up and idles fine.

 

[Ozhoo]

Pull the muffler and check for scoring

 

[homervirden]

I checked that, did a compression test that showed 170lbs.

 

[rich450es]

my new built farmer-tec 660 build did the same thing .I thought it was maybe the cheep carb so I ordered a tollotson hs-320a carb off ebay ($50?) I get the carb in the mail and go to install and notice the impulse line is only 1/4 of the way on the barb at the carb (impulse line was made too short in china). I got a factory stihl impulse from my dealer and all in good to go now .

 

[homervirden]

Got a vacum/pressure gauge and found that the bearing and oil pump holes leaking air on the pto side. Strange it wasn't the seal leaking and maybe this is the cause of the original scored piston issue.

 

[Leerod83]

Glad to hear you found the problem. Sticktuitivness I call it. PITA sometimes.

 

[OLDTIMER TECH]

New 660 build, starts and runs for about a 3rd of a tank then the idle gets lower until it finally won't idle at all. Eventually you can't even keep it running by giving it gas. It also has an oem stihl carb. The spark seems weak, more white then blue, that is all I can see that might be an issue. Gonna change coil next. I don't have a vacum/pressure set up yet but looking to get one soon. Any thoughts? I come back 15 minutes after the saw acts up and it runs good but repeats the issue again after warming up. I had been refueling on the cool down, gonna see if she starts on a half tank today. The p/u tube is always submerged anyways.

, ignition coils when they act up will be very quick almost like flipping a switch off that start with Check the tank vent,

 

[homervirden]

So how does one cure air leaks behind the bearing and chain oiler holes?