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Stihl 034 AV

tomalophicon

tomalophicon

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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?
They are sometimes pressed in, sometimes threaded as far as I have seen.
 
Skippydiesel

Skippydiesel

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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?
Hi JD -

The area/part/opening I am looking at, faces the cylinder head (ie in the other side of the carb to the choke) and lines up with the pulse tube opening.
 
Skippydiesel

Skippydiesel

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Surely you could jig up a spring and ball that aren't specifically designed for the carb.
1626488719006.png
This is a Walbro - however it would seem to me that Part Nos. 50146 84-1 & 50145 84-1 are what is missing from my Zama. Not suggesting these are the right size - just that this carb obviously has a pulse metering system that is missing from mine.
 
tomalophicon

tomalophicon

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View attachment 918769
This is a Walbro - however it would seem to me that Part Nos. 50146 84-1 & 50145 84-1 are what is missing from my Zama. Not suggesting these are the right size - just that this carb obviously has a pulse metering system that is missing from mine.
If it has no pulse it can't be getting fuel surely.

I think logically you'll need to eliminate what you've changed on the carb that has stopped it running badly.

Also as a minimum id recheck you're getting spark. Sometimes other stuff will go wrong coincidentally.
 

J D

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View attachment 918769
This is a Walbro - however it would seem to me that Part Nos. 50146 84-1 & 50145 84-1 are what is missing from my Zama. Not suggesting these are the right size - just that this carb obviously has a pulse metering system that is missing from mine.
The parts you are referencing (I think you have the second number wrong) are doing the same thing as previously discussed... Pressure on the shaft to keep the choke from moving itself. As far as I'm aware "pulse metering" (or restriction) is governed solely by the size of the orifices leading back to the pump diaphragm (at least in every small 2 stroke carb I can recall working on).
The pulsing pressure causes the pump diaphragm to vibrate which causes fuel to be pumped as there are one way valves (flaps) on the fuel side of the circuit. If a spring & ball valve where to be used on the impulse side it would trap pressure preventing pulses & probably destroy the pump diaphragm in very short order.
The impulse hole on the cylinder side of your carb should port through to the top of the pump diaphragm without restriction.
Short of a hole where there shouldn't be one, if there was a problem with the impulse side of the carb you'd have less fuel not too much
 
Skippydiesel

Skippydiesel

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To all of you knowledgeable people; You are correct (of course) - I now think the problem must be the "nozzle check valve" referred to by JD

download (1).jpeg


download (2).jpeg

My apologies for persisting with the idea that there must be a valve/reducer on the pulse system. Mine looks quite different to the above (JD supplied photo) being a brass fixture with a hole/nozzle facing the inlet side of the combustion chamber. I agree, this is a poor excuse for not taking your advice sooner.

The question now is;
  • Can this be repaired?
  • Replaced?
If the answer to the above is no - what is the solution(s)
 
tomalophicon

tomalophicon

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To all of you knowledgeable people; You are correct (of course) - I now think the problem must be the "nozzle check valve" referred to by JD

download (1).jpeg


download (2).jpeg

My apologies for persisting with the idea that there must be a valve/reducer on the pulse system. Mine looks quite different to the above (JD supplied photo) being a brass fixture with a hole/nozzle facing the inlet side of the combustion chamber. I agree, this is a poor excuse for not taking your advice sooner.

The question now is;
  • Can this be repaired?
  • Replaced?
If the answer to the above is no - what is the solution(s)
The nozzle check valve is more likely to result in inability to idle rather than flooding.

I'd still recommend undoing what you did for it to stop running and see what happens.
 

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The nozzle check valve is more likely to result in inability to idle rather than flooding.

I'd still recommend undoing what you did for it to stop running and see what happens.
+1...
What makes you so sure it's flooding?
How many turns out did you set the adjustment screws?
If it is indeed flooding first look at the metering & adjustment needles & seats
 
Skippydiesel

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The nozzle check valve is more likely to result in inability to idle rather than flooding.

I'd still recommend undoing what you did for it to stop running and see what happens.
Hi Tom,

All have done is;
  • A complete strip
  • Clean using carb cleaner & compressed air
  • Install carburettor kit (two complete kits just in case the first one was incorrect/defective)

Not possible to undo the above
 
Skippydiesel

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+1...
What makes you so sure it's flooding?
How many turns out did you set the adjustment screws?
If it is indeed flooding first look at the metering & adjustment needles & seats
JD;
Flooding - ,
  • When I do manage to get it to start, wont respond to throttle, just struggles along blowing a lot of smoke, dies as soon as throttle closed
  • Wet plug,
  • Copious amount of fuel in crankcase & combustion chamber
Adjustment screws -
  • Initial one full turn back from full in
Adjustment needles & seats

  • Both look to be in good condition - impossible to swap so in correct location
 

J D

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I'd start by putting pressure on the fuel inlet. Should be able to pump it up to at least 10psi before it "pops off".
If it doesn't hold pressure drop it in a jar of water & look for where the bubbles are coming from.
If it passes the pressure test you can test the nozzle check valve by pressing a straw or tube onto it & gently suck on/blow into it... Should only flow freely towards the venturi.
As previously stated, even if the nozzle check valve has an issue, there has to be something else amiss to cause over fueling
 
Skippydiesel

Skippydiesel

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Gentlemen - there is no doubt that far too much fuel is getting into the combustion chamber. It can only be coming from the carburettor. As it was working before strip down, it is reasonable to suggest that I have damaged something in the clean & rebuild. It must be one or more systems, that will allow very large quantities of fuel into the inlet.

If damaged are the following capable of delivering large amounts of fuel:
  • The main nozzle check valve
  • The metering lever (remember it is currently sitting just below the edges of the carb - I believe this to be correct)
  • The metering lever valve/needle itself
  • Damaged bore causing excessive blow by - I have inspected that part of the bore & piston/ring that can be seen through the exhaust port - looked okay but what of the unseen portion??
 
huskihl

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Gentlemen - there is no doubt that far too much fuel is getting into the combustion chamber. It can only be coming from the carburettor. As it was working before strip down, it is reasonable to suggest that I have damaged something in the clean & rebuild. It must be one or more systems, that will allow very large quantities of fuel into the inlet.

If damaged are the following capable of delivering large amounts of fuel:
  • The main nozzle check valve
  • The metering lever (remember it is currently sitting just below the edges of the carb - I believe this to be correct)
  • The metering lever valve/needle itself
  • Damaged bore causing excessive blow by - I have inspected that part of the bore & piston/ring that can be seen through the exhaust port - looked okay but what of the unseen portion??
On the metering side, are you certain you have the gasket and diaphragm in the correct order?
 
Wood Doctor

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Can't you just switch out the compensator cover and use the compensator carb on the 034
I tried that and it failed. However, I could have done something wrong. I bought an 034 air filter and fitted it to the 036 carb. Then I plugged the 036 carb's end cover with foam that let in some air, and that seem to work. But, it's just a band-aid job. Not sure how long that will last.
 
Mad Professor

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I tried that and it failed. However, I could have done something wrong. I bought an 034 air filter and fitted it to the 036 carb. Then I plugged the 036 carb's end cover with foam that let in some air, and that seem to work. But, it's just a band-aid job. Not sure how long that will last.
No, you switch the end cover ON the carb with a non-compensator one. You can do same with WT- 026 carbs
 
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