Walbro carb.

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I am having running problems with my Stihl 361, changed the diaphragms but still awful, anybody got the diagram including blow up of the Walbro 21-477 5.2?
 
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  • #5
Were the old diaphragms stiff? What sort of running problems?

They were a little stiff and slightly stuck down which is why I changed them, before I did change them the saw would run fine but to start it you didn't need to choke it, if you did it would flood the engine.

Now it is difficult to start, runs for a while then cuts out and it won't tick over, I have cleaned the carb with carb cleaner, taken out the mixture screws, cleaned, ripped out the plastic limiters, removed the needle valve, clean.

Fuel filter in tank looks OK, could it be a air leak? saw is second hand but has not done a huge amount of work.
 
You could have the spacer gaskets on the wrong side of the check valves or the metering diaphragm spacer out of order .

I'm not trying to insult you but I've done it myself and I should know better .Chit happens . Not only once,mind you but twice in the same day .:(

Take a peek at Mike Acres site and look up Walbro carbs.There is a parts list that shows proper assembley order .If it isn't that it could be the metering lever is set incorrectly .
 
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  • #7
No problem Al, that's what I was thinking, the wrong order, I have changed the order but alas, no improvement.
I will investigate further on these matters with a clear head.


That, will take a while.
 
Another thing popped up in my mind .Some of the Walbro kits contain double check valves .One set is a brown fiberous material and the other is a black softer material .

The black one goes towards the carb body with the brown as a back up .They will actually work without using the backers with just the soft black one .

If you don't get it pretty soon give a shout and I'll take one apart and post the pictures .
 
How did you clean the carb? Did you soak it in a dedicated carb cleaner. You can not get the very tiny metering orifices clean without soaking overnight. Sometimes these orifices will plug up with varnish. This is very hard to see on these smaller carbs.
 
On the order thing, usually it's opposite on the diaphragms. The metering one is above the gasket, and the one on the other side is below the gasket.

Did you check the metering lever height against the carb body? Altering it will require readjusting the mixture screws.

I've put the metering lever diaphragm in upside down too. That works swell. :roll:
 
That thing might be new enough to have a compensating carb on it."intelli- carb" or something like that .

That being the case I would assume it works something the the 200 T and takes an air suction from the filter box to the vent side of the metering diaphragm ..It the filter starts to clog it shuts down the flow of gas from what I gather . That might have some thing to do with the problem or may not .:?
 
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  • #12
On the order thing, usually it's opposite on the diaphragms. The metering one is above the gasket, and the one on the other side is below the gasket.

Did you check the metering lever height against the carb body? Altering it will require readjusting the mixture screws.

I've put the metering lever diaphragm in upside down too. That works swell. :roll:

OK, metering lever height was maybe a little low but by the tiniest of margins, saw runs, throttles up but stays revving fast when throttle released, will eventually slow to tick over but will eventually stall.

Al, do you mean I can discard the backer and just leave the soft rubber one?

I am sure the diaphragms are in OK, Walbro has pdf of an HA carb but not the particular type on my saw.
 
Revving high like that could be an air leak. Forgive the lame question, but did you adjust the low and high speed screws? What you are describing could easily be the low speed adjustment too lean.
 
Al, do you mean I can discard the backer and just leave the soft rubber one?
You can but if they are working don't fool with it .You are better off leaving the backers in .

The newer kits seem to use a harder black plastic material for the checks I've noticed . Perhaps this material is more suited for the funky gas we have now ?

That reving most likely is an air leak . I had that on the Rocky special .I had torn the top anti vib and tore the boot but for some reason didn't see it for a while .Lucky I didn't smoke the engine .That would have been a sad day had that happened .
 
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  • #15
Revving high like that could be an air leak. Forgive the lame question, but did you adjust the low and high speed screws? What you are describing could easily be the low speed adjustment too lean.

Screws are adjusted to factory settings, I am going to make a coffee then check the boot.
 
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  • #16
OK this is the order...gasket metering diaphragm (on the carb) , diaphragm assem'y metering.


Soft diaphragm fuel pump, gasket circuit plate, harder gasket.

The boot is fine.
 

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Factory settings can be off, especially on older saws, and when the metering lever has been altered....needle seats getting worn......

If you get it assembled and still have the problem, richen up the low speed little by little, starting with an 16th-8th turn counter clockwise. Look for smoother acceleration and running. If that was the problem, your high speed needle might be off as well.

Low speed only a quarter turn out, wow, that is unusual. Something with the newer carbs?
 
Yep,that's a compensater carb .

Something doesn't look quit right on the third picture to me . The thing looks like it has two spacers on the check vaves . I would have thought the checks fit right against the carb body but maybe not :?
 
Aha,just as I thought .This is a model HD Walbro,fixed jet but the idea is still the same .

From the carb body out ,check valves,spacer gasket ,cover .
 

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Slow return to idle. I think your high speed screw may be to lean. Try to richen it up about 1/8 turn and see if it returns to idle quicker. Lean mixture could also be caused by an air leak.
 
If he has a spacer on each side of the checks it won't run worth a hoot because the checks won't seal properly .

I got the order wrong once on an 042 and I could start it okay but it would fall on it's face about 15 seconds into the cut and about drove me nuts .

Made me so mad I stuck that thing on the shelf for about 3 years untill I got my pout . When I popped the carb off last May I knew exactly what I did wrong and felt rather foolish about it .

If you look at the stack up on Walbro carbs on Mike acres site it shows only one spacer gasket . However on some of the kits they send all kinds of extra parts ,maybe just to confuse you .:lol:
 
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  • #25
So, I changed the set up so I have just the one hard check so it's like your picture Al.

Check, seal, cover.

Started it up and it ran fast as I had the idle screwed in, shut it off and it kept running!
Bastard! I thought, must be a ignition problem, checked the plug again and nothing, it was a weak spark before when I checked, you could feel it, just, but you could not see it, the guy in the saw shop said it was not unusual, not to see the spark...hmm I wonder.

So now it's on the shelf while I contemplate it's future, it's beginning to get upsetting now.
 
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