371xp carb issue

[old CB]

I picked up a 371xp recently. Cleaned & put a kit in the carb, & replaced fuel line & filter. (Walbro carb 21-477)

It runs fine, cuts well, but doesn’t like to idle. With the idle screw backed out entirely, it’s still turning the chain at a good clip. The end of the mixture screws looked good. It’s got a good snappy throttle response, and the plug is a nice tan-brown.

Any ideas what causes this condition?

 

[272super]

Does the idle drop down quickly from full throttle? If not you might have an air leak. If everything seems normal,then the throttle butterfly is probably worn on the side and it's allowing too much air to pass and causing a fast idle situation.​

 

[old CB]

Yeah, air leak was my first thought. But I don't have the means to test that. I'll run the saw today and see if I can get any more clues.

 

[Westboastfaller]

Maybe its a cluch, clutch spring or bearing issue causing it to race? Idk

 

[HiOctane]

Your fast idle is steady or goes up and down ?If quite steady,then check if throttle flap is not worn each side or the shaft throttle itself.If up and down,then air leak somewhere.

 

[decableguy2000]

Have you adjusted the throttle screw until it stops spinning the chain the low screw adjusts the fuel ratio.

 

[old CB]

Thanks for all the replies. This is exactly the kind of help I came looking for.

I didn't run the saw today, but from recent use I know that the fast idle is quite steady so I suspect a problem w/ the throttle butterfly. I'll have a look the first chance I get.

 

[Westboastfaller]

Its got good response? then low jet shouldn't be to far clockwise? Yeah just manually push back on the nylon where the throttle hooks in to make sure its going back out of the throw completely ?

Is that a waldro carb kit?
I got one once and it had 6 different countries to where the parts may have come from and it ran worse.
Where's the quality control there?
I just got another one and it just says Waldro and nothing about 6 countries
So I'm hoping it will be good.
First 371 I bought new in '96 had an air leak in the manifold.
Recheck the manifold bolts...hopefully you didn't over tighten either aslo the four carb top plate too.
So is it hard to start when you put heat into it? Or will it start first pull?
If it starts good warm then the low sounds good.
You can flex the manifold putting side presure each way and that will give you an idea if its a faulty manifold prehaps for future reference?

No it doesn't sound like an air leak at all
Is the clutch black from heat? Could be weak clutch springs or if the rollers in the bearing aren't rolling then it will do that too, or hip chain thread or Kevlar in
there, does still happen with the internal clutch? Theres a few things we've collectively come up with.
Good luck, let us know where you're at with it....also would be good if needed! trying another carb off someone if some of these quick checks don't work out?

 

[old CB]

Westboast,
The saw starts hot or cold. I did check the throttle cable travel and it's good. Clutch is fine, no issues there. From what I can see, the manifold looks okay, but that doesn't mean much of course.

I found a NOS carb on ebay and got it for $25 last night, so I hope that will be the cure. If I mount the new carb and find it still races, I'll know what the problem is.

 

[lone wolf]

I picked up a 371xp recently. Cleaned & put a kit in the carb, & replaced fuel line & filter. (Walbro carb 21-477)

It runs fine, cuts well, but doesn’t like to idle. With the idle screw backed out entirely, it’s still turning the chain at a good clip. The end of the mixture screws looked good. It’s got a good snappy throttle response, and the plug is a nice tan-brown.

Any ideas what causes this condition?

What rpm is the chain turning at is the first question? It could be the clutch springs you need to put a tach on it first. Unless the idle is so fast you are sure it is way too high?

 

[old CB]

Hey Wolf--

That's a good thought. But I'm pretty sure it's too fast, as sometimes I can dog the chain into wood and eventually it will settle to a slow idle. I'll try the tach. Idle I always set by eye/ear, but 2700 should be about right, no?

 

[lone wolf]

Hey Wolf--

That's a good thought. But I'm pretty sure it's too fast, as sometimes I can dog the chain into wood and eventually it will settle to a slow idle. I'll try the tach. Idle I always set by eye/ear, but 2700 should be about right, no?

2500 maybe right. Look at the butterfly and the linkage and make sure it is closing all the way. Something might be bent or out of whack. Still check the rpms.

 

[Westboastfaller]

Yeah for sure try the carb? I don't no anything about the quality of the carb you are referring to, others would though.
Hopefully its good and your not chasing your tail? you got it so hopefully all is well ..erm..for a while...lol

What do you mean the clutch is good?
IT doesn't show signs of being hot I'm assuming thats what you mean...
Did you have it off and chech the bearing rollers And grease/oil or replace?
If not I would just slap that carb on and hopefully its a wrap...should be.

 

[old CB]

I ran the saw yesterday for a bit. At first it idled as it should, no chain spin. But after a while the rpm crept up and chain was spinning when it shouldn't. About that time the muffler came loose and I set the saw aside and went back to my 372. After I get the muffler tightened and new carb installed, I'll find out where I stand.

 

[old CB]

New carb installed. It idles, 2500 rpm. I'll put it to work tomorrow, and hopefully this saw comes off probation.