Stihl 024 air leak

[spudulike]

Blimey.....big bucks, don't remember ever being paid them:confused1:!!!

 

The compensator is the cover that fits over the diaphragm, in the later ones, it has an O ring round a fitting that pushes in to the air filter - I have only seen them on 026s and 260s but are fitted on later models. Non compensator models have a flat plate cover held in place with four screws.

 

All carbs will leak air around the throttle valve shaft, I would expect the air to leak down over a number of seconds and not to stop you getting any pressure in to the crankcase - I use a bicycle pump so you get a fair bit of air in each pump but you should see a reading on the gauge and the needle slowly descending to zero as air escapes.

 

It would be very strange for a new carb to have this issue if it is a new Walbro one - the Chinese ones can be a bit hit and miss. I thought the carb was an old one and now you have said it is new have confused me some more:confused1:

 

I think we are missing something here, I can't see air coming out of the NEW throttle valve shaft that fast that you can't get a reading at all???

 

Where are you in the country - wheres that phone box - I look good with my underpants on the outside of my trousers and wearing a cape!

 

I am coming to the end of what I can do - the carb test you explain will show any leaks in the carb but have no figure to work on as to what is right.

 

Bugger - think I have an idea - your impulse line isn't sited correctly, it has a flange on it - look at the pic below - the red vertical lines are the back plate of your air box, the bit to the LEFT of the vertical lines, sticks out in to the air box, the far left lines are where the impulse line plugs in - have you got it the wrong way round or not pushed in correctly - if it is too long, it will hold the carb off the rubber inlet boot:001_rolleyes:

 

Hope this helps - try it!

[spudulike]

It may help if I posted this:001_rolleyes:

[ihatesaws]

The impulse hose is in the correct position as shown in your diagram. The carb is fully inserted and making contact with the boot.

 

We've moved on from getting no reading at all. Since I've started using the steel plate, the choke side of the carb is better sealed and I can get the gauge up to 7psi by constantly pumping. It quickly drops back to zero though if I stop pumping. I'm using a pump like this one for the pressure and vacuum tests:

http://www.werkstattportal24.de/fotos/r-parts/40.40.34-1.jpg

Now that I can get some pressure into the saw it is alot easier to see bubbles of air coming out. I guess that when I pressurize the carb separately I will see how quickly the gauge needle drops. If it is very quickly like when it is on the saw with bubbles only at the throttle valve shaft this would indicate that the main leak is within the carburetor. If on the other hand it is a slow drop to zero I will have to look again at the seal between carb and boot as being a factor as well.

 

I'm in Ireland so you don't have to worry about me landing on your doorstep with a box of saw parts anytime soon. I don't think you can do anymore. Some things you just have to have in front of you to examine in order to figure out what is going on. I'll keep you posted. Thank you very much for your help so far.

[spudulike]

The impulse hose is in the correct position as shown in your diagram. The carb is fully inserted and making contact with the boot.

 

We've moved on from getting no reading at all. Since I've started using the steel plate, the choke side of the carb is better sealed and I can get the gauge up to 7psi by constantly pumping. It quickly drops back to zero though if I stop pumping. I'm using a pump like this one for the pressure and vacuum tests:

http://www.werkstattportal24.de/fotos/r-parts/40.40.34-1.jpg

Now that I can get some pressure into the saw it is alot easier to see bubbles of air coming out. I guess that when I pressurize the carb separately I will see how quickly the gauge needle drops. If it is very quickly like when it is on the saw with bubbles only at the throttle valve shaft this would indicate that the main leak is within the carburetor. If on the other hand it is a slow drop to zero I will have to look again at the seal between carb and boot as being a factor as well.

 

I'm in Ireland so you don't have to worry about me landing on your doorstep with a box of saw parts anytime soon. I don't think you can do anymore. Some things you just have to have in front of you to examine in order to figure out what is going on. I'll keep you posted. Thank you very much for your help so far.

 

No Worries, had hoped you were local or at least on one of my beaten tracks but you are well away from that!

 

Your problem is a bit baffling - the pump you are using looks like a vacuum pump to me, does it also pump air out to pressure check as well as sucking air out to produce vacuum? does the saw leak vacuum at the same rate as pressure - usually air leaks around boots or splits show less under vacuum as it pulls leaking joints togther!

 

Good luck with it - shame I cant get to look at the little tinker:lol:

[ihatesaws]

That is not the exact pump I have. It's broadly similar but at the front you can

rotate between In and Out to go between vacuum and pressure. It seems even harder to draw a vacuum than to pump in air so I suppose that supports the case for the carb boot interface not being at fault.

 

I took the wt-194a off the saw, made a second rubber and plate and removed the inlet needle from the carburetor. I used two collar screws to clamp the plates to the carburetor sealing the venturi. I attached the pump to the fuel input line and stuck the carb in a bucket of water.By constantly pumping I was able to get the pressure up to maybe 5psi. This dropped quickly to zero when I stopped pumping. There was a constant stream of bubbles out of both sides of the throttle valve shaft and nowhere else.

 

This doesn't look very good for the throttle shaft but maybe they are all like this. For comparison would you be able to test in a similar fashion any carb you have there from a saw that idles well? Maybe it's just the carbs made for 024/026 that are bad idlers.

[spudulike]

Is this carb, a brand new off the shelf from a known dealer, boxed carb or an ebay special:blushing:

 

I find it difficult to accept that the throttle shaft leak would stop a saw holding any pressure - it will let through some air but small amounts, the wear would cause an uneven idle that you do have.

 

If I get time, I do have a second hand carb for and 026 in my collection and if time allows, will try it out.

[ihatesaws]

It is a new carb that came in a box from Sägenspezi in Germany:

Vergaser Walbro passend für Stihl 024 024AV AV MS240, 56,50 € - SÄGENspezi

It says the carb is from walbro and made to a high quality standard.

 

What if I somehow seal the throttle shaft temporarily with some kind of sealant, put the carb back on the saw with the plate behind it and do the pressure test again? Would that hylomar gasket sealant I have be worth a try? I could try and squirt it around the shaft inside at the throttle butterfly.

[spudulike]

It is a new carb that came in a box from Sägenspezi in Germany:

Vergaser Walbro passend für Stihl 024 024AV AV MS240, 56,50 € - SÄGENspezi

It says the carb is from walbro and made to a high quality standard.

 

What if I somehow seal the throttle shaft temporarily with some kind of sealant, put the carb back on the saw with the plate behind it and do the pressure test again? Would that hylomar gasket sealant I have be worth a try? I could try and squirt it around the shaft inside at the throttle butterfly.

 

I would hope if the casting says "Walbro" it is genuine.

 

I was thinking of a test like you mention, the pressure would force the sealent or a heavy grease in to the shaft gap so is worth a try by all means - it may give you an idea if this is the only problem area.

[ihatesaws]

The cover on the fuel pump side of the carburetor does say Walbro.

 

I put in the hylomar behind and infront of the throttle butterfly. I sealed the carburetor with the two steel plates. I could pump up to 10psi and it took about 15 seconds for it to drop to zero with a few bubbles still coming out of the throttle shaft.

 

I then put back in the inlet needle and put the carburetor on the saw, sealing behind it. I pumped up the saw through the impulse hose to 7.5 psi with only two pump actions and it took more than a minute to gradually drop to zero. I could only draw a small vacuum however. I presume this is due to the pump sucking the hylomar away from the shaft allowing air to enter.

[spudulike]

The cover on the fuel pump side of the carburetor does say Walbro.

 

I put in the hylomar behind and infront of the throttle butterfly. I sealed the carburetor with the two steel plates. I could pump up to 10psi and it took about 15 seconds for it to drop to zero with a few bubbles still coming out of the throttle shaft.

 

I then put back in the inlet needle and put the carburetor on the saw, sealing behind it. I pumped up the saw through the impulse hose to 7.5 psi with only two pump actions and it took more than a minute to gradually drop to zero. I could only draw a small vacuum however. I presume this is due to the pump sucking the hylomar away from the shaft allowing air to enter.

 

Well it looks like you have now found out where the air leak is - your carb is looking a bit suspect to me, can you try another carb out to see if it works better? The loose shaft will explain the varying idle speed - wonder if the seller is putting Walbro covers on Chinese carbs???