Mastermind Ported Dolmar 6100

[ajschainsaws]

It doesn't have too be that way , sticky back plastic can be a vision of the future ha ha

 

[Terry Syd]

It was getting barely enough. Now after drilling the seat, and the main nozzle I can fatten it up till it gets off the RPM limiter without any problem at all.

So which one was limiting the flow, the main nozzle jet or the needle orifice?

I've never taken one of those carbs apart, but they look interesting with the two welch plugs and the extra brass jet. That brass jet could be a limiter to the low speed circuit or it could be an auxiliary jet for the low speed circuit. - If you take a look inside the carb near the throttle plate, maybe you might find a separate discharge port for that brass jet. If so, it is an auxiliary jet for the low speed circuit and you could drill the jet to increase the low speed flow.

 

[Mastermind]

So which one was limiting the flow, the main nozzle jet or the needle orifice?

I've never taken one of those carbs apart, but they look interesting with the two welch plugs and the extra brass jet. That brass jet could be a limiter to the low speed circuit or it could be an auxiliary jet for the low speed circuit. - If you take a look inside the carb near the throttle plate, maybe you might find a separate discharge port for that brass jet. If so, it is an auxiliary jet for the low speed circuit and you could drill the jet to increase the low speed flow.

I bet the seat was the bottleneck Terry. I've seen that single hole nozzle cause serious issues on the EL42, so I drilled it on thru to make two holes while I was in the carb.

Why in the hell would it just have a .024" seat? Wow.

 

[Terry Syd]

Probably to have a slower ramp in for the fuel of the low speed circuit, but it was just too small for high speed flow, especially on a ported saw.

They could have achieved much of the same ramping by using a larger orifice, but putting in a stronger metering spring to slow the opening. A stronger spring is something you might have to add if it is now a bit 'fat' off of idle.

If you have one of these type of carbs off another saw and you don't mind pulling the welch plugs, we can take a look at the circuitry. That extra brass jet could be a quick way to get some extra low end torque out of the engine.

 

[Mastermind]

Probably to have a slower ramp in for the fuel of the low speed circuit, but it was just too small for high speed flow, especially on a ported saw.

They could have achieved much of the same ramping by using a larger orifice, but putting in a stronger metering spring to slow the opening. A stronger spring is something you might have to add if it is now a bit 'fat' off of idle.

If you have one of these type of carbs off another saw and you don't mind pulling the welch plugs, we can take a look at the circuitry. That extra brass jet could be a quick way to get some extra low end torque out of the engine.

No problem Terry. I'm all for figuring some stuff out. Here's an EL42. Same basic design.

 

[Mastermind]

Looks like the brass jet feeds the transition area under that welch plug.

 

[Mastermind]

Here's a completely unrelated post.

I loves me some Rory Gallagher.

 

[Locust Cutter]

Wow! I'd ever heard of Him, but that was awesome! I love his playing style, almost a mix of blues, bluegrass and rag-time.

 

[Mastermind]

Wow! I'd ever heard of Him, but that was awesome! I love his playing style, almost a mix of blues, bluegrass and rag-time.

He's been gone for a long time now........liver disease got him.

Here's another.....

 

[Terry Syd]

Looks like the brass jet feeds the transition area under that welch plug.

The old "looks like" assumption has messed me around more times than I can count. Taking a look at the picture I can't see where the idle circuit gets its fuel. Where does the taper of the low speed needle exercise its function of regulating fuel flow? Is there a discharge port hidden under the brass jet (and thus the two transition/air bleed holes regulate the air/fuel emulsion out that discharge port?)

I'm going to need a few more pictures before I can figure out that carb - then we may be able to tweak it a bit.

 

[Mastermind]

What other pics do you want? I pulled the brass jet.......it feeds the transition area.

 

[Mastermind]

I'd happily cut this carb into pieces if it helps........

 

[Mastermind]

 

[Mastermind]

The two welch plug areas are connected too.

 

[Terry Syd]

Now we're getting somewhere, it looks like that brass jet LIMITS the flow to the low speed circuit.

I still don't know where the low speed NEEDLE comes in. I suspect it limits the flow from the transition area to the idle, but I can't tell. If so, the low speed needle only controls the idle mixture, not the low speed mixture (jut like on a Zama twin jet or a Mikuni)

If you can confirm that the low speed needle only controls the idle mixture, I think we have a winner!

 

[Terry Syd]

We posted at the same time. Try putting the low speed needle back in and see where it seats.

I expect it is going to seat in the idle circuit and limit the flow to the idle port.

 

[Mastermind]

I'm looking to see where the low speed circuit gets its supply from.

 

[Mastermind]

We posted at the same time. Try putting the low speed needle back in and see where it seats.

I expect it is going to seat in the idle circuit and limit the flow to the idle port.

It seats against the area between the two welch plugs.

 

[Mastermind]

I can't find any supply passage that feeds the idle circuit on this carb. I do remember the 6100 carb having two passages.......one for the high side, and one for the low side. Not this carb though. Weird.

 

[Mastermind]

Here's the 6100 carb.....