Installed a Bing 48 carb on my 036

[Terry Syd]

Yeah, drill the air bleed/transition hole and you won't have any further idle issues.

I suggest grinding the jaws of the nippers down until they come in flat on the jet. A lot of the nippers have an edge on them where the 'bottom' of the edge is ground at an angle. Get them FLAT and then put the notch in the edge on both sides. Then all you have to do is get the jet turning before you start to pull it out (the movement is like you are 'unscrewing' the jet).

 

[CR888]

Thanks Terry, that is exactly what I wanted to hear. I know what you mean about the sorta beveled edge like on some cutter pliers. I think flattening the area and notching would result in perfect custom jet removal tool.

 

[Deets066]

New 038 zama

 

[Deets066]

There doesn't look like any plugs anywhere on the outside where a new passage could've been drilled. It has 3 transition holes in the bore and one in the Venturi

 

[Terry Syd]

Another carb configuration, ya gotta wonder how many variations these engineers can come up with. It appears to be a basic design without any EPA trickery - just the needles to regulate the fuel flow. I note the main discharge nozzle has an extra jet drilled in the back of it. That may mean that the low speed circuit was designed with a lower flow rate and the extra jet was needed to provide enough fuel at WOT without the high speed needle being turned way out.

If you can get hold of some extra metering springs, you can play around with the low speed circuit and see if you can improve the powerband. If you get real ambitious, you can pull the welch plug and drill the first transition hole after the idle port a bit larger. That will lean out the idle and allow you to run more low speed flow - try the springs first, they are a lot easier.

It has 3 transition holes in the bore and one in the Venturi

I bet if you were to check under the welch plug the three transition holes will be one idle port and two transition holes. I don't know what you mean by a transition hole in the venturi.

 

[Deets066]

Ok it's hard to see, but the 3 holes in the bore are clear and there is another small hole in line with these in the Venturi

 

[Terry Syd]

Maybe it does have a third air bleed/transition hole up behind the discharge nozzle. On many of the Walbros the second transition hole isn't in the bore, it is up further in the tail end of the venturi. I've just never seen a saw carb with three transition holes. Some of the Mikunis have three transition holes, but they are set up for part throttle work in boat racing.

If it did have three transition holes, the carb would be flowing a fair bit of fuel in the low speed circuit in order to have to compensate for the extra air provided by three air bleed holes.

Without pulling the welch plug, it is difficult to know how it is configured. I'd try some metering springs to see what you can get from the carb. Perhaps you got a good one and won't have to do any drilling.

 

[Deets066]

Maybe it does have a third air bleed/transition hole up behind the discharge nozzle. On many of the Walbros the second transition hole isn't in the bore, it is up further in the tail end of the venturi. I've just never seen a saw carb with three transition holes. Some of the Mikunis have three transition holes, but they are set up for part throttle work in boat racing.

If it did have three transition holes, the carb would be flowing a fair bit of fuel in the low speed circuit in order to have to compensate for the extra air provided by three air bleed holes.

Without pulling the welch plug, it is difficult to know how it is configured. I'd try some metering springs to see what you can get from the carb. Perhaps you got a good one and won't have to do any drilling.

I haven't tried this carb yet, it's of an 038 goin on a 36 so it'll take a bit of linkage work.

3 holes are visible in the bore and one in the Venturi totaling 4 holes. Could they be anything else?

 

[Terry Syd]

I've warned a number of times in this thread about assuming anything about a carb's circuitry. For example, it took a while to work out that the brass jet on the 036 carb was a limiter jet on the low speed circuit, for a while it appeared to be an auxiliary jet.

You could remove the low speed needle and squirt WD-40 in the hole. You might have to block off the other three holes with a finger. If fluid comes out the 'venturi hole', then it is connected to the low speed circuit.

 

[Terry Syd]

I just checked the displacement on the 038, 038 Special and 038 Magnum. They start at 61cc, 66cc and then 71cc. I suppose someone could check the specs for the carbs and see if they are all the same.

The fact your carb has a jet drilled in the back of the nozzle may indicate that it is off one of the larger 038s.

 

[Scott0154]

I'm late to the party but this could solve the choke issue http://www.davesmotors.com/Choke-for-up-to-3-4-Hole-PBCK-75.html . It would probably fit with the oem filter

 

[Stihlbro]

I think what Deets is referring to are the three holes under the welch. First hole idle, second hole is transistion and third hole is the emulsion. Fourth hole is the main nozzle.

 

[Canadian farm boy]

I just checked the displacement on the 038, 038 Special and 038 Magnum. They start at 61cc, 66cc and then 71cc. I suppose someone could check the specs for the carbs and see if they are all the same.

The fact your carb has a jet drilled in the back of the nozzle may indicate that it is off one of the larger 038s.

I have a 038 super that has the exact same Bing 48 carb we've been playing with. The Bing 48 carb I've been using on my 036 is from a smashed 038 super carcass I had.

 

[Deets066]

I think what Deets is referring to are the three holes under the welch. First hole idle, second hole is transistion and third hole is the emulsion. Fourth hole is the main nozzle.

I was talkin about the small holes in the bore and one in the Venturi, I posted a pic earlier today.

Your right Terry about assuming, I don't know much about carbs but enjoy learning about them. Just hope some of this knowledge sticks with me.

 

[Terry Syd]

Once you get your head around how they work, then modding them gets easy. Ya have to know how something works before you can make it better. Some guys are 'parts changers' other guys become 'tuners'. The 'tuners' can even make a few bucks with their knowledge.

The Bing 48 carb I've been using on my 036 is from a smashed 038 super carcass I had.

Perhaps the Bing being off a 66cc engine was jetted a little fatter. I'm sure it flowed more fuel in the low speed circuit than the EPA approved Zama with the limiter jet. Bypass that jet and dial in the tuning and maybe they work the same.

 

[Canadian farm boy]

is this the limiter jet?
When I spray wd40 in the low speed screw hole it comes out here as well as the 4 holes in the carb bore after the Venturi

 

[Stihlbro]

What you are pointing at supplies fuel to the low side circuit and to the nozzle. It will always supply. ( my thoughts are at wide open throttle it doesn't give much to the low side)

The other brass piece in the upper left corner is the limiting jet. It supplies fuel to the secondary transistion hole is primarily for part throttle.

I could go more but I'll keep it simple for the moment.

 

[Terry Syd]

No, that's the main discharge nozzle for the high speed circuit. The other brass jet was said to the limiter jet. Somethings not right, you shouldn't get any spray out that nozzle.

The high speed circuit should be separate from the low speed circuit - unless the circuits were joined together with that extra circuit with the plug (that may be the case).

 

[Stihlbro]

Terry, the main nozzle with hole supplies the low circuit. The limited jet is a additional transistion circuit. His carb has one transistion under the Welch plug and the secondary is slightly behind the one under the Welch plug.

Again, I believe the type carb shown does not supply much fuel from the low circuit when wide open throttle. I could be wrong.

 

[Canadian farm boy]

I just rechecked spraying wd40 through the low speed screw hole. I definitely get fluid out the hole in the back of the main discharge nozzle. I'm also getting fluid out of two of the holes in the carb bore furthest from the Venturi. (Idle circuit holes???)

I also sprayed wd40 into the limiter jet. I only get fluid coming out 1 of the 2 holes closest to the Venturi. I'm guessing this is the transition hole and the second hole is the air bleed?