Installed a Bing 48 carb on my 036

[Backtroller]

A cleaner one I just picked up from Dave

 

[Canadian farm boy]

The 038 intake boot I'm using is AM. I got it off eBay from the Greek. (Didn't want to pay oem price for an experiment) The inside is knurled. The one thing I did notice about the boot is that at the cylinder end the inside of the boot is more rounded then the other 038 boots I've seen. You can see the outlet end of the boot in one of the pictures I posted back on the first page. The eBay ad listed it as also being for a ms380 or 381. Most of the 038 boots I've seen have kind of a square corner in the outlet end, shaped just like the Venturi in the Bing carb.

 

[Canadian farm boy]

Something else I'll mention is that with the 038 boot and Bing carb I'm having issues with the idle. It's extremely touchy to how it's tuned on the L side.
After making a cut (hot saw) the saw will return to idle as it should but if it's allowed to idle for approximately 10 seconds or so the idle will begin to drop off. Sometimes the saw will stall. I figure that what's happening is that its loading up with fuel just like if the L side was tuned to rich. I think that the larger 038 boot is lowering the intake velocity. Maybe the 036 intake boot would help this? Or maybe like Al said the intake port needs to be a bit higher. Idk for sure. Just thinking out loud here

 

[Stihlbro]

There are a few options you can do.

1.) reshape your low needle to make the low adjustment more tuneable. Picture a gradual taper vs. a blunt end.
2.) you can notch the throttle blade in small increments to balance out the fuel setting.

This is presumed you have tried to adjust it and it still acts up.

 

[jacob j.]

Are you getting any fuel spitback?

 

[Canadian farm boy]

Are you getting any fuel spitback?

I've run the saw without a filter for a bit. At idle I don't have any real noticeable spit back. At wot throttle no spit back. Now when I rev the saw off idle it does spit back a bit. I've seen other saws spit back worse that don't have any tuning issues.

 

[Terry Syd]

The 'wetside' is a term that is used to describe the side of the carb with the metering lever. A picture of the inside of the wetside will show any jets, welch plugs and the like.

 

[Backtroller]

Sorry

 

[Terry Syd]

OK, looking at the picture we can see that the main discharge nozzle has an auxiliary jet drilled in the back of it. That is used to set a base line fuel flow for the High Speed circuit.

There is also a hole drilled down to in front of the High Speed Needle to allow the needle to adjust the final fuel flow through the High Speed circuit.

So where does the Low Speed circuit get its fuel?

The welch plug over the Low Speed circuit will have to be pulled and the circuits traced out. I suspect that the Low Speed circuit gets its fuel from that same hole drilled in the carb (that is an unusually shaped welch plug), but NEVER assume anything when modding carburetors.

Perhaps someone with a junk carb could pull the welch plug and post a picture so a good carb doesn't have to be rebuilt.

 

[RI Chevy]

Just asking, would an 044 intake boot fit on there?
I can bring one to try if you think it would fit.

Would an 044 i take boot fit?

 

[Canadian farm boy]

Would an 044 i take boot fit?

I suppose you could use a 044 intake boot but you would have install a separate impulse line for the carb.

 

[RI Chevy]

I thought all Stihl saws had separate fuel lines and impulse fuel lines?

 

[Canadian farm boy]

I think if I was gonna try the 044 intake boot I would probably use a different carb(maybe a 044 carb) because the carb would already be set up for a separate impulse line

 

[RI Chevy]

Ahh. Ok

 

[Canadian farm boy]

I thought all Stihl saws had separate fuel lines and impulse fuel lines?

There's actually several Stihl saws that use the impulse line setup like the 036. The 034,036,038, maybe the 028? I believe several of the smaller clam shell saws use a similar set up as the 036

 

[RI Chevy]

Wow. I didn"t realize that.

 

[Terry Syd]

If no one wants to pull the welch plug to check the circuits, then I'd suggest trying a longer and stronger metering spring. After re-tuning, I expect the low speed circuit to pick up some extra flow and it may be all the carb needs.

Although, I notice that BOTH the low speed and high speed circuit appear to be getting their fuel through the single hole in the carb. That may be a potential issue just like the Walbros where the low speed circuit gets its fuel out of the main discharge nozzle tunnel. Perhaps a second hole placed in front of the low speed needle seat could help to get a more uniform fuel flow during operation (like the mod with the Walbros).

 

[Backtroller]

Here you go

 

[Terry Syd]

I expect there is a hidden tunnel/circuit that feeds the low speed needle, but I can't see where it has been drilled from either end of the carb. If you close the low speed needle all the way in, then measure the length of the needle that is sticking out of the carb, then remove the needle from the carb and place it on top of the wet side so the length is the same - we can see where the needle seat is in the carb.

OK, there are no extra jets in this carb, what we have for the low speed circuit tuning is the metering spring. When you go to a stronger spring with more pre-load (longer spring) it will lean out the idle when you first fire it up. You then have to re-tune the low speed needle to get it to idle (you have to make it richer). That increases the fuel flow in the low speed circuit, so you will have to lean out the high speed needle to get the same WOT.

What that change does is change the relationship between the two fuel curves in the carb. Generally, it will give the saw more low end torque and if you get the blending of the two curves right, you will get a stronger torque peak.

EDIT: If this carb can be modded to perform as well, if not better, than the Bing - a metering spring is a lot cheaper than a whole carb.

 

[drf256]

I expect there is a hidden tunnel/circuit that feeds the low speed needle, but I can't see where it has been drilled from either end of the carb. If you close the low speed needle all the way in, then measure the length of the needle that is sticking out of the carb, then remove the needle from the carb and place it on top of the wet side so the length is the same - we can see where the needle seat is in the carb.

OK, there are no extra jets in this carb, what we have for the low speed circuit tuning is the metering spring. When you go to a stronger spring with more pre-load (longer spring) it will lean out the idle when you first fire it up. You then have to re-tune the low speed needle to get it to idle (you have to make it richer). That increases the fuel flow in the low speed circuit, so you will have to lean out the high speed needle to get the same WOT.

What that change does is change the relationship between the two fuel curves in the carb. Generally, it will give the saw more low end torque and if you get the blending of the two curves right, you will get a stronger torque peak.

EDIT: If this carb can be modded to perform as well, if not better, than the Bing - a metering spring is a lot cheaper than a whole carb.

Where does one buy a metering spring assortment and how does one tell how stiff the current one is?