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Stihl 034 AV

Skippydiesel

Skippydiesel

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Jul 10, 2021
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47
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The Oaks
I have a Stihl 034 AV electronic quick stop, fitted with a Zama carburettor.
Was running fairly well but could have been better.
Stripped the carb, cleaned thoroughly & fitted with a new (Stihl) carburettor kit, air filter & spark plug.
Cylinder now floods (a lot)
Checked & triple checked the carburettor assembly - all good.
Thought it might be a perished pulse tube - replaced - no improvement.
Checked for damaged piston/bore by removing exhaust box - a bit warn but looks functional (compression great)
Completely out of ideas.

All suggestions welcome
 
Skippydiesel

Skippydiesel

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Messages
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Still say carb.
Leaking needle?
Gaskets/diaphragm in wrong order?
Diaphragm jammed on lever?
I agree it must be the carb.
Diaphragms/gaskets all checked and rechecked several times - all correct.
Don't know how one could be jammed on valve leaver.
 
Wood Doctor

Wood Doctor

Edwin
Joined
Jan 10, 2008
Messages
11,653
Location
Omaha, Nebraska
Getting a new carb for the 034 is like finding a needle in a haystack. The carbs they have for sale are for the 036 and they do not work very well. And, the air filters for those carbs don't even fit inside the 034 carb cover.
 

J D

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Apr 19, 2020
Messages
681
Location
NZ
Don't know how one could be jammed on valve leaver.
If the metering lever is set too high or the gaskets are the wrong way around the diaphragm will be jammed against the lever. It sounds like if anything you have the lever set too low. I have seen saws that ran fine with the lever set too low, but only because they had the gaskets around the wrong way as well.

Could be and yes to compressed air .
Have dismantled check valve three times looking for damage/foreign material - all looks okay but still a possibility
This is the nozzle check valve I'm referring to...
download (1).jpeg download (2).jpeg
Compressed air can damage the little disk inside. These are not typically considered a serviceable part.
 
Skippydiesel

Skippydiesel

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Joined
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Messages
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Location
The Oaks
If the metering lever is set too high or the gaskets are the wrong way around the diaphragm will be jammed against the lever. It sounds like if anything you have the lever set too low. I have seen saws that ran fine with the lever set too low, but only because they had the gaskets around the wrong way as well.


This is the nozzle check valve I'm referring to...
View attachment 918659 View attachment 918660
Compressed air can damage the little disk inside. These are not typically considered a serviceable part.
You guys are amazing - I had a Eureka moment last night - "there must be a valve or restriction on the crankcase pulse system" - having dismantled this carb so many times in the last few days I am sure that there is no obvious valve/restrictor on the carb - if there was one I have "blown" it away.

Q. Should there be such a valve/restriction, fitted to the carb, on the pulse system??

JD - the location of the nozzle you refer to looks to be in the carb throat (?) - I will check for such a nozzle however the carb you have in the photo does not look like my Zamma.
 

J D

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Apr 19, 2020
Messages
681
Location
NZ
View attachment 918704

(This is a very similar carb to mine - may not be exactly the same)
See the spring loaded ball bearing above the valve No 2 - mine is missing. I assume this is the pulse control valve?
I believe that spring loaded bearing is just there to put location pressure on the choke shaft so it stays where it's put.
I think the nozzle check valve is the component below the number 5 in that diagram. Often it is under a welch plug but that doesn't appear to be the case here. These valves can be tested & sometimes even repaired or replaced. If the issue is definitely over fueling I'd be looking at the metering & adjustments first. Have you tested for carb leaks & pop-off pressure?
 
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