Mastermind Ported Dolmar 6100

[Mastermind]

The 620 is getting real close to the bench. I'll get a good chunk for the bar size I have....

 

[Terry Syd]

I'm going to post some pics of that carb, and see if we can figure it out as well as we did the EL42. Then decide if we can add a little more fuel to the transition circuit.

Yeah, I'm still unsure about the 6100's circuits. Hopefully, the idle circuit is split away from the transition circuit like on the Zama and Mukuni, it makes tuning simpler when all the functions/circuits can be tuned separately without affecting another circuit.

If the Low speed needle only controls fuel to the idle circuit, then it will just be an idle mixture needle. The low speed circuit flow will be controlled by the brass jet feeding into the transition circuit. It will be interesting to see how big that single brass jet can be modded on a 60cc engine.

If it starts getting really fat off of idle, you're probably going to need some stiffer metering springs to slow the ramp of fuel down.

I see Poleman is monitoring this thread, he can probably add a few things with the number of carbs he's done.

 

[Mastermind]

It has the same configuration as the EL42 Terry. That "mystery" hole is for the primer bulb return.

 

[Mastermind]

The smallest bit I have is .015", and that is bigger than the hole in the brass jet.

 

[Mastermind]

To enlarge the brass jet, and make it mean anything, I would also need to enlarge this passage.....

 

[Mastermind]

Or.......I could just drill a .015" hole in the transition welch plug.

 

[Mastermind]

I'm gonna think this over............

 

[Terry Syd]

You need to get one of those 'micro drill' sets that starts at .3mm and goes up to 1.5mm. I figure as a WAG that the jet size will end up around .35-.4mm. I could be wrong on that, perhaps Rich has an idea. Too bad he isn't visiting with you, he now has the 'feel' for modding carbs and he could probably dial it in real quick.

I'd wait until you have the micro drill set. If you hog it out now, not only will it likely be too large, but you won't have the opportunity of experience of slowly increasing the flow to start getting the 'feel' of the mixture change. After you do this first carb, the rest will become a lot easier.

 

[Terry Syd]

The .015" drill equates to a .381mm (using a handy calculator). I expect the stock jet probably starts at .25mm as that seems to be the size that keeps popping up (probably an EPA regulation). The first pass with a .3mm drill takes a bit of time and patience, after that they go through a lot faster.

You may want to try the .015" drill and if it is too much fuel, then you could put the old brass jet from the EL-42 in the carb.

 

[Mastermind]

I have several micro drill sets. .015" = .381mm

 

[Mastermind]

The .015" drill equates to a .0381mm (using the a handy calculator). I expect the stock jet probably starts at .25mm as that seems to be the size that keeps popping up (probably an EPA regulation). The first pass with a .3mm drill takes a bit of time and patience, after that they go through a lot faster.

You may want to try the .015" drill and if it is too much fuel, then you could put the old brass jet from the EL-42 in the carb.

I didn't get the brass jet out without killing it.

 

[Mastermind]

I just ordered a set of 10 bits (2 each) Size: .20mm to .40mm 2 each: .20mm .25mm .30mm .35mm .40mm

 

[Terry Syd]

Great, it's a bummer having to wait for the drills, but I think you'll feel more confident in the long run.

To get those brass jets out easily, you need something that can grip down low on the jet (I use a set of modified wire cutters) and then TURN the jet as you pull it out. The turning or moving back and forth as you pull is the secret to get them out without any damage.

 

[Mastermind]

I used a set of nippers.......but they were not the right thing evidently. They cut the top of it right off. lol

 

[WKEND LUMBERJAK]

I used a set of nippers.......but they were not the right thing evidently. They cut the top of it right off. lol

Gorilla grip.

 

[Mastermind]

Gorilla grip.

I'm sure you watched this video Kenneth, how does the 6100 I did for you seem compared to this latest one?

 

[Terry Syd]

They cut the top of it right off.

Yep, sounds like my first brass jet removal. After I chopped the top off the jet, I had to grind down into the carb body with a small Dremel bit to get another area to grab on to. I think Poleman did the same thing, must be one of those 'rites of passage' type things.

 

[WKEND LUMBERJAK]

I'm sure you watched this video Kenneth, how does the 6100 I did for you seem compared to this latest one?

Looks stronger with the chain you have on it. If I remember right you had a very aggressive chain on mine in your video.

 

[Mastermind]

I think this one is the best one I've done yet. I've only done four or five, and as I learn more about them, they tend to get a little better.

 

[Terry Syd]

I was thinking about your comment about drilling the transition chamber welch plug. Sounds like a good idea for testing.

You can put a dab of GB Weld on the brass jet and then start drilling the welch plug. Eventually you will go too big in your testing. No biggie, put a dab of GB Weld on the welch plug hole and then drill out the brass jet to the size you want.

If you don't have some washers to shim up the metering spring, it might be a good time to order some. You can get a bag of them cheap and you can use them on every carb that you want to mod. You just drop one, two, whatever into the metering spring well and then put the spring on top of them. It increases the pre-load on the lever, like having a longer spring.

The spring RATE is the pitch of the spring and the thickness of the wire. The spring rate and the size of the metering orifice will determine the angle/steepness of the ramping in of the low speed circuit. The pre-load of the spring will determine when the metering valve starts to lift and the ramp begins.

If the metering spring rate is in the ballpark, the cheap washers should be all you need to tune the throttle response.