Mac 84 and remote mixture needle

[Mark]

I ran my Hummingbird for the first time today (at last!) and would like to know what is happening. I have a Speedmaster remote needle opened about one and a half turns from closed, when I open the throttle on the stand it bogs down a little then revs hard, when I close the needle a little and rev it, the thing screams it's head off even with the throttle in idle position for about a full second or 2 but otherwise it revs up nice. When I open the needle a little it bogs worse. So I drop it in the water with about 2/3 throttle and away it went up on plane, to me it looked a little slow but was still moving fairly quick, I did about 2 or three laps then thought I would adjust the mixture on the transmitter and as soon as I touched the button it bogged down almost instantly. The amount I moved the servo on the mixture wouldn't have been more than about 1mm. Then it went about 20 to 30 metres and stopped. It feels like it has a delay when I make a mixture change on the stand but can't understand why it died on me after running ok at speed when I only made a small adjustment at full throttle.

Do the direct carbs that have a mixture control on them work more consistantly. When I bought the thing I was thinking that these things would have a delay because of the fuel line between the needle and the carb.

BTW the pressure line was still on the pipe nipple when it stopped so no fuel supply problem there.

Can anyone help?

 

[Don Ferrette]

If there are no leaks in any lines, no trash in the needle, etc. then the needle is not delivering enough volume. The CMD/Kalistratov is the best needle for the MAC engines. The MAC engines need to be rich on the shore & you will idle it higher than you may be used to. B)

 

[boaterbill]

Don,

You're right about the needle.

Bill

 

[Mark]

Don,

How much should the throttle be open on idle? Is 1/3 to much. Why did the engine die so suddenly? Was it running so lean that it didn't have enough fuel supply?

 

[Don Ferrette]

Mark, my 84's are open a little more than 1/3 & set rich. It died from no fuel delivery.

 

[Mark]

Don,

I worked out why my engine died yesterday when I touched the mixture control.

The needle adjustment by hand is on a fine thread while the control horn of the remote neeedle for the servo is on a really really course thread which makes 20 or 30 clicks on my transmitter third channel move the actual needle inside about one full turn of the fine adjustment by hand.

Now that I know how much throttle opening I need for idle and to richen it up heaps the thing should kick ass now. It was ok before but now it should be really fast especially when I put the 1667 prop on. I'm using a H prop of some sort thats about 7mm or 8mm smaller in diameter than the 1667. Was told it's a good prop to run the engine in with and get used to the boat before I start going really fast.

Even though I had little use on Sunday (only one run because my old starter crapped itself) it was good fun. It's much different to my 1/8 and 1/10 scale cars.

I'm getting a new starter on Friday. Hope to get out again on Sunday.

I would also like to get a good 1/8th scale hydro so I can run in 2 classes. I see a lot more scale boats locally than I do 90 Riggers.

 

[Ed Radz]

Mark

Andy Browns needles are the only way to go with a MAC. I have a MAC 45 & was using a BVM remote needle. I could rarely get it to be consistant. I changed a few weeks ago to Andys needle & Boater Bill (Bill Heacock) flowed it for me on his flowmeter. My first pass it was too lean. I richened up 3 clicks with the radio & it was a rocket!

Later!

Ed Radz