Help tuning/setup Mac 84

[ktl]

I'm new to boating but not rc(planes,helis,cars,trucks) and I have a couple of questions which I haven't been able to find answers for. I have a Dumas 1/8 Circus with a Mac 84 (I built this for fun) and a Brown 84 muffled pipe set at about 11.5 inches and the 3rd channel course valve. I've run a gallon of 25% through the engine at a very rich setting and just let the boat cruise around the lake at lower RPM's. Now I have 45% nitro. Today I tuned the motor to run rich at idle (1/3 throttle opening as per Andy a couple of weeks ago) and ran the boat. When first in the water boat ran pretty good and I was able to accelerate but nowhere near what this motor will do. It seemed sluggish accelerating and seemed to pick up speed when turning. After about 6-7 min the motor lost power and all I could do idle around the lake, the motor would not accelerate but again the boat seemed to pick up speed when turning. I believe I need to lean it out more. Is this correct? Also, right now I have the needle mounting so I can easily make ajustments and do not have it hooked up to the 3rd channel. My question is how do I go about setting the needle to work with the 3rd channel. Right now the needle is almost 2 turns out. When setting up the remote how do I set the needle? The course adjustment seems it will make a big difference in the needle position.

One last question, I have my strut running about 1 1/4 down. Is this about right? What effect does the strut height have on performance?

Thanks for all your help. It's been a struggle to get this far but I haven't given up. Probable should have researched boats better and started with something a little easier but then again I like challenges.

Thanks

Keith

 

[Don Ferrette]

For starters what prop are you trying to push? :blink:

 

[Lay26]

and what size fuel tubing do you have in there?

 

[ktl]

x460/3 and large fuel line but I have not redone the tubing in the tanks. I am running a 1oz header tank. Thanks

 

[Don Ferrette]

Is this the silver 84 parabolic? If so did you drill out the stinger?

 

[ktl]

Don - The package says Brown 84 Muffled Pipe and it is silver and no I did not drill out the stinger. What size should I drill it out to and what other problems do I have if any? thanks

 

[Don Ferrette]

Don - The package says Brown 84 Muffled Pipe and it is silver and no I did not drill out the stinger. What size should I drill it out to and what other problems do I have if any? thanks

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Actually you are drilling the baffle just behind the actual stinger. Drill it to the same size as the i.d. of the stinger itself. Then richen the needle & run it again.

 

[ktl]

That baffle you see when looking in the end of the pipe?

 

[Don Ferrette]

That baffle you see when looking in the end of the pipe?

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That's the one. Be extra careful to shake all the drilling chips out of the pipe when you're finished.

 

[gil sonsino]

Hi Keith

All my riggers have CMD 3rd channel and that's I use to do:I open the needle about 1 1/2 turn and make sure that with less than 1/2 turn via radio the engine receives enough fuel to run rich.Then i close it via radio until get the engine in the pipe.....normally it is less than 1/2 turn positioned.The CMD is very sensitive and precise just make sure you are using the coarse one with large lines.

Set your strut at the same level of the front sponsons with 1,5 degree down .The X460/3 must be easy for the .84 Mac and open the baffle of your pipe as mentioned.The Dumas Circus Circus is a heavy boat so you can try 12" for your pipe and see if it runs good to then shorten it .

Gill

 

[ktl]

Thanks for everyone's help. I will make these changes and try and run it later this week.

Keith

P.S. - Anyone have any idea on how fast this boat will run if I can keep it on the water?

 

[gil sonsino]

in the 60's with a right set up.

Gill

 

[ktl]

Today I opened up the stinger, set the carb to run super rich and set the pipe just shy of 12 inches. The boat ran a litle better but not up to full potential. I can only get about 1/2 throttle, anything more doesn't make a difference. When the motor warms I seem to lose a little power. Should I be running leaner or richer? Also, when I pulled the plug 2 of the coils were pulled out which I believe is a good thing. Thanks for all your help.

 

[Don Ferrette]

Today I opened up the stinger, set the carb to run super rich and set the pipe just shy of 12 inches. The boat ran a litle better but not up to full potential. I can only get about 1/2 throttle, anything more doesn't make a difference. When the motor warms I seem to lose a little power. Should I be running leaner or richer? Also, when I pulled the plug 2 of the coils were pulled out which I believe is a good thing. Thanks for all your help.

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Richen it up more, still sounds lean to me. The throttle will be over a 1/3 to almost 1/2 open to get it to idle when you are rich enough.

12" pipe length does seem a tad on the long side, you'll probably wind up around 11 1/4" to 11 1/2".

 

[AndyBrown]

If it is slowing down after two or three laps then it is most likely lean, richen it a little to be sure, but also I think it just may not have enough load. If the load was correct and it was too lean it would burn the plug.

The easiest way to get more load is to just shorten the pipe a little (1/4") at a time.

This added load will gain more rpm as you open the throttle past the 1/2 open point.

Anyway make it richer first. If it gets better, continue to richen until is slows down a little then begin to shorten the pipe.

Also, Don is correct! The carb will need to be nearly 1/2 open to get a decent idle on the beach if the mixture is rich enough.

 

[ktl]

OK, this is where I'm at. I don't get to run the boat that much, so I make adjustments, run it once and go home. The boat is a rocket when in gets into the turns, gets on pipe and just takes off. Enter the straights, falls off pipe and slows down. Strut is set at 1 1/4 inch down. I've run the pipe from 12 to 10 1/4 inches and can't seem to get enough load on it in the straights. I really haven't messed around with the strut height or prop. Third channel is set up and air/fuel adjustment and is not the problem (tried rick/lean ect.). What do you guys recommend trying? Thanks - Keith

 

[Don Ferrette]

OK, this is where I'm at. I don't get to run the boat that much, so I make adjustments, run it once and go home. The boat is a rocket when in gets into the turns, gets on pipe and just takes off. Enter the straights, falls off pipe and slows down. Strut is set at 1 1/4 inch down. I've run the pipe from 12 to 10 1/4 inches and can't seem to get enough load on it in the straights. I really haven't messed around with the strut height or prop. Third channel is set up and air/fuel adjustment and is not the problem (tried rick/lean ect.). What do you guys recommend trying? Thanks - Keith

Set the parabolic pipe at 11" & play with different props. Don't be afraid to go down in prop size if need be to get it going. I always start out on the smaller size range of props on a new scale & progress up once hull is dialed in.

 

[MikeP]

OK, this is where I'm at. I don't get to run the boat that much, so I make adjustments, run it once and go home. The boat is a rocket when in gets into the turns, gets on pipe and just takes off. Enter the straights, falls off pipe and slows down. Strut is set at 1 1/4 inch down. I've run the pipe from 12 to 10 1/4 inches and can't seem to get enough load on it in the straights. I really haven't messed around with the strut height or prop. Third channel is set up and air/fuel adjustment and is not the problem (tried rick/lean ect.). What do you guys recommend trying? Thanks - Keith

I had the same symptoms with a parabolic pipe as you on a rigger, I found I had too much pipe pressure. It would rocket around the turns then go rich mostly towards the end of the straights. I had the baffle drilled out. Then I cut 1/2" off the stinger and fixed the problem.

I have read stuff about a cold engine causing the same symtoms, heat up and lean out in the turns then go cold in the straights.

Mike