Gas leak inside carburetor

[Cedar Row]

I have two saws that have leaked gas inside the carburetors. Gas is apparently leaking past the gaskets. No problem to replace gaskets with carb kit, but I can't figure what is causing the leaks. I have never had this happen before. Anyone have a similar problem? Carbs on Stihl 041 and 021, both were not starting.

 

[DND 9000]

It can be a worn inlet needle (the tip of the needle), or a worn, damaged or clogged needle seat. It can also happen if you didn`t adjust the metering lever properly and therefore the metering diaphragm opens the needle all the time. Also the inlet control lever spring can have not enough force so that the fuel overcomes the popoff pressure of the needle.

 

[Cedar Row]

Y

It can be a worn inlet needle (the tip of the needle), or a worn, damaged or clogged needle seat. It can also happen if you didn`t adjust the metering lever properly and therefore the metering diaphragm opens the needle all the time. Also the inlet control lever spring can have not enough force so that the fuel overcomes the popoff pressure of the needle.

 

[Cedar Row]

Thanks, I'll check these items out!

 

[icontreeservice]

How do you adjust the metering lever? I mean, what is the process so you actually get it right vs. having it too "closed". I've cleaned lots of these carbs, but never messed with these adjustments 'cause I didn't know how.

 

[buzz sawyer]

If you mean it is leaking past the gaskets, are you sure there are no burrs or raised areas on the sealing surfaces? I like to flatten them with some fine sandpaper on a sheet of thick glass. DO NOT do this on the fuel pump section with the raised sealing lines.

 

[sean donato]

How do you adjust the metering lever? I mean, what is the process so you actually get it right vs. having it too "closed". I've cleaned lots of these carbs, but never messed with these adjustments 'cause I didn't know how.

You bend it to the correct height. There are gauges for some carb models, other are set flush to the carb body. The gauges are dirt cheap and factory manuals are pretty readily available for 90% of carbs used on saws.

 

[Okie]

To the OP and icontreeservice.

A blood pressure bulb or a Mity/Vac that will produce up to 5-7lbs pressure is a good tool so as to help test the metering lever needle seat area or a carb for leaks. If it won't pressurize at the fuel inlet you probably have a leaking needle/seat or the metering lever Hiegth is wrong or you did not pay attention when replacing the carb metering diaphragm and got the one with the longer button that holds the metering lever open and you cannot adjust the lever for such. (you having to keep a heads up for this one in the kits, close but no cigar)

Adding some pressure also allows for looking for bubbles if the carb is leaking and submerged under water.

You can get a blood pressure bulb at a reasonable cost. (but should also have a 0-10lb gauge or a compound gauge from the automotive store. (vacuum/pressure gauge that is used to check fuel pump pressure and automotive vac.

 

[Cedar Row]

Good Suggestion! I have the pressure gauge. Never thought about a metering diaphragm being the wrong length.

 

[J D]

These are diaphragms for an MS880 carb. One has a dimple that hooks into the fork on the metering lever, the other does not... that isn't so special in itself, the catch is the metering height each one sits at is about .020" different.
Solution is to either file the larger dimple down slightly or adjust the metering arm appropriately

 

[2StrokeFondler]

View attachment 1112728View attachment 1112729
These are diaphragms for an MS880 carb. One has a dimple that hooks into the fork on the metering lever, the other does not... that isn't so special in itself, the catch is the metering height each one sits at is about .020" different.
Solution is to either file the larger dimple down slightly or adjust the metering arm appropriately

Same thing happened to me on my Stihl 015 carb. Couldn't figure out why it was flooding all the time. Was really lucky that I kept the old diaphragm and checked after trying everything else.

 

[Lightning Performance]

View attachment 1112728View attachment 1112729
These are diaphragms for an MS880 carb. One has a dimple that hooks into the fork on the metering lever, the other does not... that isn't so special in itself, the catch is the metering height each one sits at is about .020" different.
Solution is to either file the larger dimple down slightly or adjust the metering arm appropriately

These take different lever arms

 

[Lightning Performance]

View attachment 1112728View attachment 1112729
These are diaphragms for an MS880 carb. One has a dimple that hooks into the fork on the metering lever, the other does not... that isn't so special in itself, the catch is the metering height each one sits at is about .020" different.
Solution is to either file the larger dimple down slightly or adjust the metering arm appropriately

Where did you get them?
I need to check these pump tips before ordering diaphragms and pumps flappers for my 1124 and 1122 saws.

 

[J D]

These aren't my pic's, I was having issues tuning my 880 & came across this. I have eliminated the dimple height as my issue but still need to kit the carb so may need to address it depending on which diaphragm the kit turns up with

 

[Okie]

Same thing happened to me on my Stihl 015 carb. Couldn't figure out why it was flooding all the time. Was really lucky that I kept the old diaphragm and checked after trying everything else.

Yes about saving the old gaskets and other things at least until you get a good run with the new kit. You really need to keep a heads up and look close at all especially the little button on the diaphragm and I've also seen the needle valves not be the same size.

But if you have never seen one run correctly before You have to keep in mind that Bubba may have installed the wrong parts and you have the correct parts and do not realize such at first.

 

[Mad Professor]

A little vasilene on the gaskets will keep them from sticking to the carb if you need to take it apart again.