MAC.84\CF Rigger

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Looks like this weekend may be good for a test drive. I just need to finish the prop. Reducing the diameter of a 1667 and adding a little cup. This will give me 7 weeks to get a reliable heat race setup before the big road trip race down south.

-MikeP
 
I threw it in the water today, inspite of the weather. I took the day off because they forcast 70's. Well it was 50's and raining. The first launch failed because it was too rich, I got it going on the second launch and it wouldn't get on the pipe. I reduced the cup from 5.7" to 5.2 and it took off ;D ;D ;D ;D everything worked good the pond seems alot smaller now. The only problems I have are with my 12volt starter. I need more starting power. I am going to check the boat over tonight and go back out in the morning.

-MikeP
 
I use a goldbee 120 with all my boats. Cranks over .90s on 12V (I use a car battery though) with now problems. They are cheap, too. Try loosening your plug. Tighten it up after you take the plug booster off, or POW. It will put a hole in your head if it's in the way.

Hammer
 
Are we gonna see some vids of the CF riggers soon? I would like to see them in action.

Hammer
 
I think my OS 9B carb cannot flow enough fuel for the MAC .84. I checked the spray bar in them. The stock carb is about 2.15mm inside diameter. The OS 9B is about 1.72mm. I am considering drilling it out. Any opinions on this?

-MikeP
 
TimD is pretty good at doing work on 9Bs. Check out the last 2 pages of Riggers in Japan. You will see some of the work he did.

Hammer
 
Hey Mike,

Those are some nice pic's!

Regarding your 9B - have you hooked up a flow meter to it?

If you have access to a flow meter, measure the flow @ full throttle on the MAC carb and compare it to the OS item. that will give you an idea if the diameter is too small. Also, if you are using the low end needle, I set them so they sound a little on the rich side at idle. when you punch the throttle from idle it will hesitate a little before cleaning out. If your problem apears after a few laps on the pipe I would suggest trying to richen up the low end needle first.

Then, If all else fails, then drill out the tube to the same diameter as the MAC carb.

Hope that helps a little....

Hammer san,

Don't sell yourself short dude, you have been using OS carbs more than me!

Tim.
 
Mike,

The 9B's have been used on many 90's (like Hammers!) and works quite well, I doubt it cant supply enough fuel. Do you have large bore fuel lines and large bore pressure lines? I use Prather water outlets with O-rings as pipe pressure fittings with my A-90 and K-90.

I would look at other aspects of the fuel system before you drill out the spraybar. I think that would affect the operation of the low-end needle as well.

You could also try asking Andy Brown about the problem, I seem to recall some discussion about the pipe stingers being to restrictive for some applications.

Ian.
 
I don't have large bore on my pressure side. Med fuel line and a standard pressure fitting. I made a post on the other board to see what came up. A guy name Ron says that Andy told him the OS remote needle that fits in the carb isn't good for anything over a .45. What are you guys using on the k90's. Do you even use radio needles?

I don't have a flow meter, but I can just put the stock needle back in and retest.

-MikeP
 
Mike,

I personally dont use a radio needle, I use a remote mounted needle that OS make for the 9B carb, and it seems to work very well. Without a flow meter I dont know how you could verify whether the radio needle you have will flow enough.

But what you are describing with the engine going off after a couple of laps sounds a bit like what some people were describing on the listbot when they suggested that the stingers may be too restrictive.

Maybe try the original non-radio needle first, then try large bore pressure line. Do you have another pipe you can try?

Ian.
 
Hey Mike,

I REALLY doubt that the pipe is the problem, but I do know a few people that have opened them up a bit. What is the bore of the stinger?

On my MAC 45 I flow at 8.5 on my meter. For reference my K90s flowed at around 7.8. The MACs like alot of fuel. I'd swap the carb back and see what happens. It will idle just fine with the stock carb, just set it up so that the barrel is open about 1/3 at idle and if it's rich enough it will just burble along.

Chris
 
I have the stock carb and the CMD remote needle. I am going to set them up. I really think this will fix the problem. **** I really like the OS carb.

-MikeP
 
Tim! That is what I do on the K90. I have the low end needle set a little rich. It doens't hesitate anymore after the engine has been floored a few times. Just when your starting it. My friend who has a MAC .84 swears that the level of the tank in reguards to the engine has a lot to do with the performance. The Tank shouldn't sit too low or too high in the hull. The bottom of the tank should be level with the bottom of the engine. I don't think you should encounter this problem with a rigger, though. My friend has had nothing but troubles with his Mac .84. He might not be doing it right, or he has a lemon. Also with the K90, I have a collar epoxied into the throat of the intake manifold. Instead of increasing the diameter of the carb, I have reduced the diameter of the throat.

Also Tim! Mike was talking about drilling and rework. I have never reworked any of my 9Bs, so I can sell myself short in that respect.

How did you do at the ACTS anyway?

I heard you won at least one heat. Gonna go check that thread out now,.

Hammer
 
Here is what I got from my investigation of the MAC .84.

From the CMD message board Andy stated in there several times that the OS and K&B remote needles don't work with the bigger MAC engines but is ok on the .21.

Chris states that his MAC .45 flows more than his K90.

Hammer, What does your friend with the MAC .84 use for a needle?

-MikeP
 
Mike,

Are you using the 9b and the inflight needle?

Here is what I've done with my 9B on my Blue head 67EXR. I removed the main needle valve assembly completely from the side of the carb. I have replaced it with the blanking screw that comes with the OS remote needle assembly. (you could use a screw with a washer if you don't have the OS one). I have a remote fuel doctor type valve mounted to the side of the tub a short distance from the carb. I also had Ian make me an adaptor that angles the carb up at the front so that it is level with the top of the tank. (not needed on a MAC or K90!)

While it is true that MAC's like a lot of fuel, they still get away with running the same size fuel tanks, which makes me think the difference is not that dramatic or they would all run out of fuel too early.

The Parabolic pipes I have seen appear to have a very small stinger and everyone here who I know that run's MAC 84's had to drill the stinger out to 1/2 inch id to stop them fading and / or eating plugs. (All the guys running MAC 84's seem to be going to different pipes now too!)

If it were my dilemma, I'd be trying to track down the use of a flow meter before I blame the carb outlet. If you can't get your hands on one I have one here but I'm not exactly local ;D

Maybe try the CMD needle assembly with the 9B first before going back to the original carb.
 

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