According to the box it came in, The carb I bought was a C3M-DM11D
Farmertech 372xp wont hold a tune
- Thread starter Alanmurphy6912
- Start date
Help Support Arborist Forum:
What spark plug are you using? I have seen where the Torch plug that comes with the kits will give intermittent problems that can mimic carburetor issues. Switch to an NGK or Bosch and it is often cured. It sounds like you've tried everything else. I would also run another leakdown test before I threw more money @ carburetors and the like.
Agreed.Anyone with experience riding 2stroke motorcycles will tell you NGK or nothing,in my opinion.Not hard at all to foul a spark plug in a 2stroke engine.
Alanmurphy6912
ArboristSite Operative
I put an ngk plug 8n the saw when I built it and still the same plug in it now. I can try to swap.it out with a different plug and see what happens.i think it's a BPMR7A but don't quote me. Is that what this saw should be running? A 7? And looking at the plug it looks to be burning okay most of the time rich if anything which is how I like to tune them especially while breaking it in. I believe it has only had maybe a tank or 2 tops ran thru it and all at different times like I've not been able to run a complete tank thru it at once due to it running erratically. And one step ahead of you on the pressure vac test I did again yesterday morning and still holding tight on vacuum and pressure. I truly hope an oem carb will fix it if I can find one that's not crazy expensive, because if not I'm gonna be completely at a loss of what to do.
Plug sounds right.Sometimes the best thing thing is to step away from the problem for a few days.Sleep on it,When that doesnt work run it over with the tractor, lol.
Alanmurphy6912
ArboristSite Operative
Yes sir NGK for the win,and klotz 2 cycle oil always in my 2 strokes. Bikes saws etc.
Plug wire ok? switch out coil again?Coil gap ok?Sounds like carb though.You will probably kick yourself when you find the problem.I assume compression is OK.I wont mention the tank filter, lol.Wouldn't hurt to blow out the fuel line for peace of mind.
Alanmurphy6912
ArboristSite Operative
Yes I actually took an oem coil off my 460 rancher and put on the saw and made no real difference from the chinese that came with the kit. I did pull the boot off re pinch the coil into the wire and yes gapped the coil with a business card lol. And I hope so on the kicking myself thing. The weather is starting to break and I want to use this saw. The 660 is great but its heavy. I do have a 029 that runs great and is on a fresh top end but no full wrap handle and so forth. Something about building these kits has me addicted to building them and wanting to work them like an oem saw. Love it and would build saws daily if I could afford it.
Alanmurphy6912
ArboristSite Operative
And actually I did just replace the fuel line and impulse line yday also while I was at it and filter. I have no checked compression but I'm sure it's good. It wouldn't hurt to check it tho and see. My 660 has my compression guage saying 190 psi which is nuts but I dont expect this saw to have that much probably closer to 140 or 150 is my guess.
Getting a good reliable impulse? 2 turns out on idle seems excessive. Check valve in carb there? Gaskets in the carb are in the right location?Disconnect kill switch wire, lol.Something stupid somewhere.
Alanmurphy6912
ArboristSite Operative
I havent actually ripped this second chinese carb apart yet I dont think, other then just the cover to make sure the metering lever height was right I will do that again today and see what is up. It seems to run the same regardless of which cheap carb I throw on it. I dont have a good oem carb to try out or I would. Lol I hope to find it soon also. Itd be great if it wasn't the carb and was something stupid that I missed somehow,thatd keep me from throwing more money at it and making other forum goers mad lol
You've probably checked already, but make sure the decomp valve is doing what it should.
Also, I'm sure your sick of hearing this, but make sure the tank is vented properly.
Also, look at the tab inside the spark plug boot to make sure it's not making poor contact with the wire it's crimped to.
How is the end play and run out on the crankshaft? Any movement in-out, or up-down?
Did the finger porting and such look okay when you assembled it?
Is the fuel line or pulse line kinked or pinched anywhere?
Has the ignition switch been replaced with a known good switch?
Did you blow out with modest air pressure, then flush out with diesel fuel, the crankcase before assembly, as well as after assembling the the short block?
.
Also, I'm sure your sick of hearing this, but make sure the tank is vented properly.
Also, look at the tab inside the spark plug boot to make sure it's not making poor contact with the wire it's crimped to.
How is the end play and run out on the crankshaft? Any movement in-out, or up-down?
Did the finger porting and such look okay when you assembled it?
Is the fuel line or pulse line kinked or pinched anywhere?
Has the ignition switch been replaced with a known good switch?
Did you blow out with modest air pressure, then flush out with diesel fuel, the crankcase before assembly, as well as after assembling the the short block?
.
Alanmurphy6912
ArboristSite Operative
Ok yea I put an oem decompression valve in the saw when I built it but how exactly do i test it? Also I've been suspecting the tank vent a few times as that why i bought a different rear handle that has the actual vent in the side instead of the rubber hose with the spring on it. Now instead of fuel leak9ng out all the time I have pressure when I open the fuel cap which I think is somewhat normal. I'm not sure how to test it otherwise? I know it let's plenty of air in the tank not any out tho until u loosen the cap. Also already re crimped the plug boot and wire into coil is freshly cut and re threaded in. No crank movement, all the porting looked okay, it has ran great a couple times but then when it becomes warm it no longer runs good or even the next time u start it cold it runs like crap again. It acts like it starving for fuel sometimes with a big when hitting the throttle but then when it's hot and in the cut and starts acting up.it acts like its flooding due to no rpm. No on the pulse line,and fuel line, just replaced, and I d9nt have another switch to try I dont think. I've unplugged it tho and still same symptoms. And no I did not flush it out after assembly. I let it sit overnight to let m motoseal cure and that was it. I used 2 cycle oil for assembly lube
Crack the fuel cap when it acts up.See if it normalizes.
John Stryker
ArboristSite Operative
Hi Alan,
just a wild guess but, I think you may have it tuned too rich. Your description of low revs at wide open throttle sounds like it's overly rich. In my experience with the 372xp's, they run well with around 1 1/4 turns of the low jet, and 3/4 turn of the high jet. I usually start with a setting of 1 turn each and then fine tune it when completely warmed up. If you have flooded it, it will take quite a bit of cranking and running to un-flood it; or you could take the plug out and crank it while holding the saw upside down to clear out the extra fuel.
Another thing to check would be a kink in the fuel line between the tank and air box floor.
just a wild guess but, I think you may have it tuned too rich. Your description of low revs at wide open throttle sounds like it's overly rich. In my experience with the 372xp's, they run well with around 1 1/4 turns of the low jet, and 3/4 turn of the high jet. I usually start with a setting of 1 turn each and then fine tune it when completely warmed up. If you have flooded it, it will take quite a bit of cranking and running to un-flood it; or you could take the plug out and crank it while holding the saw upside down to clear out the extra fuel.
Another thing to check would be a kink in the fuel line between the tank and air box floor.
As Above...May be loading up at idle when warm, although somethings still fishy. tune at idle when warm and good throttle response,may be lean without partial choke until warmed up.
Alanmurphy6912
ArboristSite Operative
I did a few times and it doesnt seem to really change anything. Its almost like once it's hot and acting up it's just gonna keep acting up. Then it will cool I'll put it down and forget about it for a day or 2 and fire it up again, sorts let it warm up and tune it and then I'll go and actually use it cutting and a few cuts in it will then start running like a turd and wont idle etc. I really just need to get a good oem carb to try
Alanmurphy6912
ArboristSite Operative
Yea I only have the low jet out so far because it wont even run at 1 turn out and was starving for fuel. It only starts that bogging and being super rich after it becomes hot and after a few cuts and at that point I'll lean it out and it still acts funny. I believe the Chinese crap carbs I have are junk because the low jet seems to affect the wot rpm s also and a little bit of vise versa and it shouldn't have that large of an impact on wot In my experience. I've gotta get ahold of a good oem carb to try and hopefully that will answer some questions,or leave me with more questions than I started with lol
9050lx just stated what I was thinking soon after I made my original reply, but forgot to post... crack the fuel cap open when it acts up.
***I thought if the tank is vented, it should not hiss and blow off pressure when opened.
Secondly, stryker reiterated what I first brought up... check for fuel/vacuum hose kinks.
.
John Stryker
ArboristSite Operative
Try to re-tune it when it's hot; I still think it could be too rich. Also, it is normal for low and high jets to affect each other; when you adjust one, you will have to adjust the other also to balance the total amount of fuel at wot. That's why it's best to start with the factory suggested settings, which are 1 low, and 3/4 high I think.
Similar threads
Latest posts
-
Scrounging Firewood (and other stuff)- Latest: sean donato
-
Fiskars Handle on Super Splitting Axe
- Latest: AmateurSawer
-
-
-
-
-