Farmertech 372xp wont hold a tune

[TRTermite]

Vents…
Older saws (up to 2005? 10?) or so vented both ways. Epa put restrictions on them so now they can only let air into the tank to replace fuel as it’s used.
If you pull vacuum from the outside and it holds, you can remove the sintered piece and check for a rubber disc inside. And then only reinstall the sintered piece. Removing the rubber check valve makes it to where it will vent both ways.

Pop off pressure in the carb needs to be up around 15 psi (if you still have a 1-way vent) to hold back tank pressure. If popoff is too low, pressure in the newer tanks can push open the needle in the carb and allow fuel to flow into the engine. Most newer Stihls and Huskies have upwards of 25-30 psi pop off pressure to hold back the pressure in the tank

I figured if we bantered around long enough somebody that KNOWS what they are talking about would chime in Thanks

 

[BrettS]

Now be fair, sometimes there is never enough information shared or rather the correct kind of information shared for responders to guess the correct diagnosis.
Then factor in the fact you are asking about a family of "saws" some people dislike the very notion of and thus decide to skip over the posts rather than reply- and a lot of those folk are very good servicers of chainsaws!
Copycat saws are fine for anyone that wants one for personal use and to experience ground up saw builds for the first time- just as you have done.
I despise those that buy the damn things, build them and try to sell them off as OEM.

But all that is neither here nor there, with this particular thread, you have some great advice- knockoff carbs are known to give trouble.
What is perhaps best for you is to find a used OEM 371/372 or 2171/2172 carb and have it kitted by someone that knows carbs and can set it up as near good as factory new- then you can take the carb out of the equation (although I am willing to bet a well set up OEM carb will solve your issues).

Kit saws are fun when they go good- not so good when they do not run well and you cannot put your finger on exactly why that is.

knockoff carbs are known to give trouble.


Kit saws are fun when they go good- not so good when they do not run well and you cannot put your finger on exactly why that is.

I have a "knockoff" carb on my 372, works better than the OEM unit it replaced. No matter what I did to the OEM carb it would not run right, whipped on the "knockoff" carb and whaddaya know, the saw run perfect.

That's the joy of building saws, finding and fixing the problems. Life would be boring if everything worked right out of the box.

 

[9050LX]

So when ya getting the carb? We need some meat on this saga.

 

[TRTermite]

So when ya getting the carb? We need some meat on this saga.

DITTO TAGGART..

 

[Alanmurphy6912]

So when ya getting the carb? We need some meat on this saga.

I ordered a zama carb today. 3 ot 4 day shipping I think so by the 31st I hope. Also ordered an oem tank vent

 

[4CornersPuddle]

Alan, hope you solve this ongoing dilemma with the carb.
I've been fighting a 372 OE rebuild for 3 years now. Symptoms have wandered all over the place. Many times this saw acted as you have described yours acting.
I've tried 3 OEM carbs, checked vacuum and pressure, sprayed brake cleaner around everywhere, checked fuel tank venting, fuel line, impulse by squirting thick oil in the line and cranking the saw over, and more. There were times in the last 3 years when I could tune the saw, take it out to a job, and use it for part of a tank or part of a day. Then it would revert to idling fine, revving okay, 4 cycling for 5 seconds, but then leaning out again.
I scoured all the comments in this great thread of yours for clues.
Well, today I found the problem. A very big heartfelt thank you to you and to all the positive commenters who are helping.
The impulse line, although not noticeably kinked, had sort of a twist in it that was only allowing a small bit of vacuum to pass, so some fuel would get drawn to the carb. Just enough to allow the saw to idle and sometimes run, but not enough to function correctly. I untwisted the line. The saw now develops the famous power that 372s are known for.
Tomorrow I get to fell and process 8 big Ponderosas. I'm hoping my big Dolkita has to stay in the truck, watching and pouting. Haha.

 

[Alanmurphy6912]

To my surprise,that carburetor is out for delivery today already! So I will keep yall posted

 

[Alanmurphy6912]

Alan, hope you solve this ongoing dilemma with the carb.
I've been fighting a 372 OE rebuild for 3 years now. Symptoms have wandered all over the place. Many times this saw acted as you have described yours acting.
I've tried 3 OEM carbs, checked vacuum and pressure, sprayed brake cleaner around everywhere, checked fuel tank venting, fuel line, impulse by squirting thick oil in the line and cranking the saw over, and more. There were times in the last 3 years when I could tune the saw, take it out to a job, and use it for part of a tank or part of a day. Then it would revert to idling fine, revving okay, 4 cycling for 5 seconds, but then leaning out again.
I scoured all the comments in this great thread of yours for clues.
Well, today I found the problem. A very big heartfelt thank you to you and to all the positive commenters who are helping.
The impulse line, although not noticeably kinked, had sort of a twist in it that was only allowing a small bit of vacuum to pass, so some fuel would get drawn to the carb. Just enough to allow the saw to idle and sometimes run, but not enough to function correctly. I untwisted the line. The saw now develops the famous power that 372s are known for.
Tomorrow I get to fell and process 8 big Ponderosas. I'm hoping my big Dolkita has to stay in the truck, watching and pouting. Haha.

Oh man I'm sorry to hear that on the 3 year timeline! Thatd drive me up a wall! I've got an atv giving me fits that I've had for about a year and I know it drives me nuts not knowing or being able to figure it out. So i understand your fatigue. But I'm glad you found your issue! I'm very thankful to all those who have been helping me thru this problem and a previous problem I had with a customers 272xp i had problems with. So that's awesome you found your issue. Hopefully I figure mine out as well. I now will take a third look at my impulse hose and make sure it isn't kinked or anything. It sorta runs thru a rubber hole that sticks off the side of the intake book on my saw so it may be pinched in there a little or something I'm not sure. I've changed it twice

 

[Bob Hedgecutter]

Oh man I'm sorry to hear that on the 3 year timeline! Thatd drive me up a wall! I've got an atv giving me fits that I've had for about a year and I know it drives me nuts not knowing or being able to figure it out. So i understand your fatigue. But I'm glad you found your issue! I'm very thankful to all those who have been helping me thru this problem and a previous problem I had with a customers 272xp i had problems with. So that's awesome you found your issue. Hopefully I figure mine out as well. I now will take a third look at my impulse hose and make sure it isn't kinked or anything. It sorta runs thru a rubber hole that sticks off the side of the intake book on my saw so it may be pinched in there a little or something I'm not sure. I've changed it twice

Have you replaced it twice with known OEM impulse lines?
Cheaper copy ones could be collapsing and sucking flat under vacuum.

 

[Alanmurphy6912]

So when ya getting the carb? We need some meat on this saga.

So the carb came yday and everything looked okay except 1 thing. The hole for the choke lever isn't big enough. And turns out that metal on a zama carb appears to be stainless or something super hard to drill..

 

[Alanmurphy6912]

Have you replaced it twice with known OEM impulse lines?
Cheaper copy ones could be collapsing and sucking flat under vacuum.

Yes the last time I replaced it was with stihl impulse line I bought by the foot.

 

[Alanmurphy6912]

So the carb came yday and everything looked okay except 1 thing. The hole for the choke lever isn't big enough. And turns out that metal on a zama carb appears to be stainless or something super hard to drill..

 

[9050LX]

Don't remember if mine was needing drilled or not.Can't expect they use stainless or a hard steel for that.Use a new cobalt bit and/or lots of lubricant.

 

[huskihl]

The new carb you bought is for a 7900. It’ll work for it, just gotta drill or ream the hole.

 

[Alanmurphy6912]

Don't remember if mine was needing drilled or not.Can't expect they use stainless or a hard steel for that.Use a new cobalt bit and/or lots of lubricant.

Yea whatever material it is is super hard. I broke a few bits last night and only got 1 hole drilled at 1/8 inch. And need to be roughly 3/16 or a size smaller I believe. But at the rate of drilling I'm gonna need some newer better bits. And maybe use my drill press so I can get some leverage. Always a fight lol

 

[9050LX]

Dont' make it too big or the plastic grommet will fall out.I noticed mine slips out once in a while, maybe its because I drilled it too big.I honestly don't remember drilling it.I am going to find a circlip that fits tight on the choke shaft thats inside that hole. Drill pretty slow.

 

[9050LX]

Another suggestion:If the throttle cable doesn't allow enough play you can take a fine hacksaw blade to trim the plastic insert slightly.Run it in the cable groove lightly until you have enough play.

 

[4CornersPuddle]

Good ideas for helping keep coming in. Good thread.
My 372 update: ran the saw, felling and bucking to firewood lengths, several Ponderosas yesterday. Saw performed flawlessly.
I also ran the big Makita on a few trees, just so it wouldn't feel deprived. And cut a couple of medium pondos with my recently modified H 455. That did well, too. Much narrower power band on the 455. Gotta focus on the rpms more.

Also did some minor limbing with my newly acquired and rebuilt CS400 (big grins) and an older H 350 that continues to cut well, rev well, 4 stroke out of the cut, but just will not idle slow enough to stop the chain from spinning. That saw is the next long frustrating project to cure.

 

[camel2019]

Vents…
Older saws (up to 2005? 10?) or so vented both ways. Epa put restrictions on them so now they can only let air into the tank to replace fuel as it’s used.
If you pull vacuum from the outside and it holds, you can remove the sintered piece and check for a rubber disc inside. And then only reinstall the sintered piece. Removing the rubber check valve makes it to where it will vent both ways.

Pop off pressure in the carb needs to be up around 15 psi (if you still have a 1-way vent) to hold back tank pressure. If popoff is too low, pressure in the newer tanks can push open the needle in the carb and allow fuel to flow into the engine. Most newer Stihls and Huskies have upwards of 25-30 psi pop off pressure to hold back the pressure in the tank

Kinda like the EPA gas cans that seem to be more prevalent in the states then here in Canada at least in Ontario I can still buy vented cans.

 

[huskihl]

Kinda like the EPA gas cans that seem to be more prevalent in the states then here in Canada at least in Ontario I can still buy vented cans.

Give the EPA half a chance and they would **** up a soup sandwich