Installed a Bing 48 carb on my 036

[Stihlbro]

I checked the pop off pressure on my Bing carb. It pops at 16-17 psi.

Just for comparison I also checked 2 Zama C3A carbs. The one Zama pops at 25 psi and the other is 30+psi( my gauge only goes to 30)
The 2 Zama carbs have different looking wet sides. I'll post a couple pictures in a minute

If it were me, I would put a stiffer spring in the Bing and retry. It should make it behave better at idle.

I, would also try the first carb you posted picture of, it looks to have independent fuel circuits. When running, I would open the low side adjustment up and see how much fuel the circuit can deliever. In other words see if the low side delivers fuel at wot.

The carb I posted picture of, does not feed fuel to the low side circuit from the main nozzle. The low side is fed from the fixed jet. The fixed jet supplies fuel to the under the Welch plug. I would drill the divot that is inline with the low needle and give it a try. This would make fuel more availability for tuning. Clean up then Venturi (oversize some), clean up the throttle blade and screw for flow.


Other than that, unless you lived closer, I'd say swing on by the house and I could help more. We could cut down the neighbors tree for testing. (Hahahahaha)

 

[Terry Syd]

This thread was getting interesting. What happened?

 

[dall]

mike told me this morning he was gonna run saws today so we should have some answers soon terry

 

[Canadian farm boy]

Time wasn't on my side today. I did manage to get a couple videos of the 036 with the non epa Zama

Video#1. Saw is tuned to 15600. 25# pop off pressure. Average cut time was 8.8 sec

 

[Canadian farm boy]

Video#2. Saw is tuned to 14600, 25# pop off pressure. Average cut time was 8.7 seconds

 

[Canadian farm boy]

I was beginning to run out of daylight so I didn't try the 30+# pop off spring.

I'm not sure what to make of the results. It would appear that the fatter tune was just a touch faster but the results are extremely close

 

[Terry Syd]

Those times were way behind the initial testing. Is it a different log or chain?

 

[Canadian farm boy]

Those times were way behind the initial testing. Is it a different log or chain?

Same log, same bar and chain.
Only thing different is the carb

 

[Terry Syd]

That doesn't seem right. I don't know what the heck is going on, maybe the non-EPA carb was for a smaller displacement engine. Perhaps you could post the part number and we can find out if it is for a smaller displacement engine.

The fact that the nozzle does not have a jet drilled in it (blocked off) on the non-EPA carb indicates that it doesn't require extra fuel through the high speed circuit.

Perhaps we need to try an EPA carb that has been drilled like Stihlbro indicated. Heck, that's what most guys would be using anyway.

 

[RI Chevy]

Thanks for taking your time to do these tests for all of us. [emoji106]

 

[Canadian farm boy]

That doesn't seem right. I don't know what the heck is going on, maybe the non-EPA carb was for a smaller displacement engine. Perhaps you could post the part number and we can find out if it is for a smaller displacement engine.

The fact that the nozzle does not have a jet drilled in it (blocked off) on the non-EPA carb indicates that it doesn't require extra fuel through the high speed circuit.

Perhaps we need to try an EPA carb that has been drilled like Stihlbro indicated. Heck, that's what most guys would be using anyway.

Your probably right about the carb coming from a smaller saw. It likey originally came off a 034.

The next time I go out to test this saw I'm gonna have to find another log.

I'll set a baseline with the Bing carb and then repeat the testing with the original Zama carb and the different metering springs

 

[Terry Syd]

We may have a non-EPA carb with different transition holes in the circuit for a smaller saw. The smaller transition holes creates a practical limit to the amount of fuel we can get from the low speed circuit - it will tend to run lean at idle and we can't bump it up to where we want it without creating a too rich idle.

Other carbs are much more easy to jet. The C3M carbs were easy by just drilling the jets. Likewise, the Dolmar 6100 and EL42 on the 357 were easy as the circuits were entirely different to the 036 carb. The 'limiter' jets on those carbs affected the entire low speed circuit - and the idle circuit was a separate circuit. You can tweak the low speed fuel flow on those carbs without changing the idle circuit. Randy had some success drilling the jets on those carbs.

If you try a quick mod (drilling the bypass hole) on the EPA carb, we may be able to tweak it from there.

 

[Canadian farm boy]

Unfortunately I don't have any micro drill bits. I'am however looking into getting a set. May take some time to actually get the drill bits.
Maybe someone else with one of the Zama carbs has a micro drill bit set and we can keep this ball rolling.

 

[paragonbuilder]

Unfortunately I don't have any micro drill bits. I'am however looking into getting a set. May take some time to actually get the drill bits.
Maybe someone else with one of the Zama carbs has a micro drill bit set and we can keep this ball rolling.

I've got some Mike. If you don't have any before the gtg.

 

[Canadian farm boy]

That would be awesome. Thanks Dan. It would be pretty cool to have everyone involved. The more brains the better.
I'll bring everything I have here, carbs, saw, extra fuel tanks etc.

 

[Terry Syd]

Drilling the bypass hole on the 036 carb doesn't require a set of micro drills. Just use a small drill (about 1mm will work). All you're doing is opening up the flow to the low speed needle.

If you get into changing the air bleed/transition holes, then the micro drill set would be needed.

 

[Terry Syd]

Here's a way to test whether the low speed circuit can use some extra fuel. Just keep opening up the low speed needle and re-tune the high speed needle - sounds easy, but the engine won't idle. So you have to keep screwing the idle adjustment in to keep the engine running.

It can become dangerous as the chain will be moving, be careful. If the extra fuel in the low speed circuit helps, then there are a couple of things that can be done to fix the idle.

Unfortunately, we already have a strong metering spring, so putting in a stronger spring is out.

Removing the welch plug and drilling an air bleed hole a bit larger will work (done on the C3M under the idle jet).

We may be able to tweak the throttle plate to allow more air at idle, usually just drill a small hole in the throttle plate (you can only go so far with this mod).

 

[Terry Syd]

Going back to the two carbs with different pop-off pressures, the springs in the two carbs could be identical.

Pop-off is not only determined by the pre-load on the spring, it is also related to the size of the metering orifice. The larger the metering orifice, the more area of the metering valve is subjected to the pressure. For example, you have two carbs with identical springs, one carb has a metering orifice with twice the area of the other. The carb with the bigger orifice will have half the pop-off pressure of the other carb.

The best thing to do is to look at the springs and see how strong the springs are (pitch and wire diameter) and how long they are.

 

[Deets066]

Finally got time to read the rest of this thread. I gotta say there is some awesome info here. I'm workin over the shafts and screws on a 36 zama. I have a new zama for an 038 too, maybe tomorrow I'll open em both up and see if I can contribute anything to this thread

 

[CR888]

As I am waiting for my $2(delivered!) set of nipper pliers from China, I was only able to drill the idle jet & auxiliary but I cannot remove the idle jet to get to the air bleed hole and open it up to 0.55mm without nipper pliers. I decided to install the carb back on the 6400 and give it a run without doing the air bleed but having drilled the idle to 0.3mm & aux to 0.35mm. It ran well with good power but idle would not stay constant, every 20ish seconds it would lean right out and I would have to throttle it up to keep it running. I'm hoping drilling the air bleed will fix this, we'll wait & see.