Head scratcher PROBLEM SOLVED!!!

[Stevetheboatguy]

Have a head scratcher.

XS 2071 (371/372 oe) saw runs great until you let it idle. If you let it return to idle after a cut. It will sit and idle until the cows come home. When you pick it up and go to make another cut. It falls on it's face and dies. Doesn't matter if you feather the trigger or gun it.

I have had the carb apart and everything seems fine. New fuel line, filter and impulse. Haven't swapped the 390 carb and intake out for the regular 371 carb yet but thats where I'm leaning to try next.


Anybody run into this before? It's a new one for me.


Steven

 

[Cat 525]

Maybe air leak?

 

[Stevetheboatguy]

Maybe air leak?

Haven't done a p&v test but it runs wot, idle at all angles even upside down without changing. I'll prob check that when I pull the carb off again.


Steven

 

[jacob j.]

Is it puddling fuel in the intake boot somewhere? The MS-440s had that problem for a while, it turned out the intake boots were getting distorted during installation.

 

[Stevetheboatguy]

Is it puddling fuel in the intake boot somewhere? The MS-440s had that problem for a while, it turned out the intake boots were getting distorted during installation.

This sounds interesting. I will take a look at that. Thank you sir.


Steven

 

[huskihl]

Check the impulse line for a kink or a wear mark where the top cover may have pinched it.

 

[huskihl]

You can also send the carb up here for a few bucks shipping and I can clean it and run it on a 390 here and see if it’s bad. I have other used 390 carbs I could send back if yours is no good

 

[Stevetheboatguy]

You can also send the carb up here for a few bucks shipping and I can clean it and run it on a 390 here and see if it’s bad. I have other used 390 carbs I could send back if yours is no good

10-4. I appreciate the offer. Might take a stab at it again tomorrow. Thing flat out hauls azz. But if I set it down for more than a few seconds it wont come off idle without stalling. Let it sit for 10 min and it will start right up and haul again. Funny thing is it will idle for as long as you let it. I wonder if JJ is on with it pudling fuel at idle. Going to try looking at it in the morning.


Steven

 

[JohnnyBlade]

I had the almost exact same prob on a 350 i built. It wound up being the tank vent. And a few others that gave me probs too. Jred 670 and the 272 platform saws only cuz i dabble in them i suppose. But its came to my attn enough and made me throw fits that im just about to put it on my list of must change items when i build a saw. I guess i just over looked them
As not being a wear item, but hey guess what?THEY R! And i have prob a few more gray hairs because of them

 

[drf256]

Nozzle check valve?

The valve can fail, or be thrown out of nozzle if you used compressed air. It’s function is to stop air from going back into the wet side when it calls for fuel at idle. At WOT, the nozzle will maintain negative pressure. The negative pressure in the wet side should only pull up on the diaphragm, but it will pull air back through the nozzle instead. Sometimes you’ll get enough fuel to stay idling, but not enough for WOT cuts.

It’s one of the few head scratchers I’ve encountered while going through a carb and getting bad results.

Try to swap in another nozzle If you have one Steve. Obviously, check the fuel line/impulse/boot also.

 

[Nutball]

I'd think it would lean rev at some point before dying if it was the check valve, maybe not, but I'll give another vote to pooling fuel. It was what first came to mind.

 

[Mastermind]

You can also send the carb up here for a few bucks shipping and I can clean it and run it on a 390 here and see if it’s bad. I have other used 390 carbs I could send back if yours is no good

This is how it's done fellas.

Taking care of the customer should top priority.

Thanks for being awesome Kevin.

 

[Stump Shot]

I would hazard to say that if the saw was left to idle for a time and then picked up by the rear handle so the saw is pointing down, if it dies this would indicate the puddling. If not, then the carb is then most likely the culprit. This should help diagnose the issue @Stevetheboatguy

 

[Stevetheboatguy]

You can also send the carb up here for a few bucks shipping and I can clean it and run it on a 390 here and see if it’s bad. I have other used 390 carbs I could send back if yours is no good

This is how it's done fellas.

Taking care of the customer should top priority.

Thanks for being awesome Kevin.

So I want everyone to know and be clear. I didn't buy the saw from Kevin. Wasn't a saw that I sent to him. Just a used saw from the trading post. The seller has already gone above and beyond for my troubles with the saw. There are no sour grapes on my end. I appreciate all the help and offers. I really want to get the saw running consistently that is the reason for my post. Once I get it sorted out I will definitely post up what the problem ended up being. Been a while since I have been puzzled but I think we are on the right track.

Again thank all you guys. And if anyone else thinks of anything please let me know. Today was a bust for looking at it but I will be back on it again soon.


Steven

 

[Stump Shot]

So I want everyone to know and be clear. I didn't buy the saw from Kevin. Wasn't a saw that I sent to him. Just a used saw from the trading post. The seller has already gone above and beyond for my troubles with the saw. There are no sour grapes on my end. I appreciate all the help and offers. I really want to get the saw running consistently that is the reason for my post. Once I get it sorted out I will definitely post up what the problem ended up being. Been a while since I have been puzzled but I think we are on the right track.

Again thank all you guys. And if anyone else thinks of anything please let me know. Today was a bust for looking at it but I will be back on it again soon.


Steven

Ported saws need serviced just like stock saws do. Good luck with finding the issue.

 

[Stevetheboatguy]

Problem solved. I swapped the carb with one from a 385 and like someone flipping a switch it runs spot on now. So that leads me to believe that Doc is correct. The main nozzle must be messed up in some way.


The donor



Now hopefully I just need to get a main nozzle for the bad carb. Any pointers on where I can order one?


Steven

 

[Terry Syd]

I always like it when I finally find the problem. When it could be a number of things and you have to work your way through them it can be a real pain - but then! - you find it.

I used to get a lot of parts from M&D mower. They had good parts diagrams and a big list of parts. Bought a few different carbs and heaps of nozzles, springs, etc. from them. I haven't used them for years, but they may have something available.