Jerry D's MAC 21 OB

[Jerry Dunlap]

Happy Easter Sunday Everyone,

Well after returning from church services this morning, I had an opporunity to unbolt the CMB 21 LS from the Law Outdrive and bolt on the MAC 21 OB. Have to say the two engines do share a similar appearance - however, since the MAC is black and the CMB green, don't think I'll have a problem telling them apart.

The header for the MAC is just a cooper plumbing elbow with two holes and ears sticking out of the top of the elbow for the ends of the spring to hook into. I think I paid like $.39 for the elbow at the local Ace Hardware store.

The pipe is the new Irwin Muffled pipe. I will also test the HTB Silver Bullit, but I wanted to try the Irwin first because that is what I'm running on the CMB LS 21.

The motor mount is from Precision Boats Racing, thanks, Tim. And the lower unit is a Law Less 21 from R Mfg. I stuck a brand new K&B flex cable in the lower unit. This cable is one of the latest from K&B and is more flexible than some of the previous cables. The prop is an Octura X640 cut down to 37 mm diameter.

Just to see if the motor would start, I filled the Power Surge Rqcing Products fue cell with 65% Wild Cat fuel, and turned on my new Futaba 3PK radio. Hey, this starting to sound a lot like a NASCAR interview, isn't it??!!

The MAC 21 fired up on the second appliction of the starter to the starter cone. Didn't run it much, just enough to know it was going to run.

So, tomorrow I'm hoping to get it on the water. I'm hoping I can attach a couple of photos.

Jerry D.

 

[Jerry Dunlap]

Hey, cool, it worked.

O.k., here's a rear view.

JD

 

[Jerry Dunlap]

Since I'm on a roll, here's a shot of the boat and motor. FYI, this is the 30" version of the JD WOF 28/30. You too can build this fine hull. If Grim can plug his products, Ol' J.D. can do the same. Plans are available directly from me for a few more weeks.

 

[Mike Hughes]

Hey Jerry

I was able to get mine out yesterday at Waughop. I put it on my Sundowner with a hyperperformance lower. I ran the Silverbullet pipe. The first few runs I was not able to get the third needle to get lean enough. Brought it back in the adjust the servo linkage. I was starting to make some power. The only problem being that the boat did not like the prop being that far back than the standard K&B lower. It is 1.25" further back. When I was going down the straights all of a sudden hard right and I did not even touch the wheel. I tried a few changes to the the setup with no success. It is going as fast as the NR was (that is right before it does its hard right loop out). I believe the motor with the standard lower is going to surpass the NR no problem. I am happy with my purchase. Now all I need is a Van Houtton.

Mike

 

[Kris Flynn]

Anyone with a Mac...is there much of a weight difference between the Mac OB and the NR or CMB?

JD, looks pretty nice on that boat

Kris

 

[Jerry Dunlap]

Kris,

I don't have a scale readily available, but I don't think there's any weight difference between the MAC and the CMB.

Jerry D.

 

[lohring]

I ran my new MAC 21 yesterday as well. It replaced the modified K&B on my Leecraft XTR-21. As expected, the MAC had less low end and needed a good launch. However, it's lots more powerful and the setup needed adjustment before I could keep the boat on the water. If it stops raining today, I'll try to get some radar speed readings. Some other testers report GPS speeds with the MAC/Leecraft XTR-21 combination in the mid 50s. The engine looks like a winner.

Lohring Miller

 

[Mike Hughes]

There is a 1/4 oz. difference between NR and the MAC. But then again my scale weighs in 1/4 oz. increments so it could be less. NOT A FACTOR.

Mike

 

[Jerry Dunlap]

Well, the first time out with the MAC 21/JD WOF 30 was a little disappointing. First, there was a drizzle type rain falling. Second, the lake where I tried running the boat had been raised and there was all kinds of stuff floating in the water.

The good news is the motor started easily. The bad news is the skeg was continually snagging debris and hindering performance/handling. I managed about 15 total minutes of running, but the motor never really came up on the power band. Dragging stuff on the skeg probably didn't help. Might still need more run in time.

Hope to try it again in the next day or so.

Jerry D.

 

[[email protected]]

Hey to all you guys sponsoring Jerry you must be happy, Jerry you have me cracking up w/all the brand recognition. Hey I'll mail you some Doritios or Fritos to eat the next time you do an interview or another project! That should really help my sales next week! LOL

 

[Jerry Dunlap]

Had another opportunity to run the MAC 21 OB/JD WOF 30 today. Much better weather and water conditions. I went to a different lake to run.

I made three good runs with the boat testing three different props: X440(full, sharpened/balanced), X637(full, sharpened/balanced), X640(reduced to 37mm diameter.)

The motor ran on-pipe with all three props. The X637 seemed to run the best. I could definitely hear the motor begin to break in while running that prop. I didn't have time to try the reworked 1440. Also, the bracket for my mixture control broke.

Some comments after this second outting:

1. The motor really starts easily.

2. It might take four or five tanks of fuel to get the motor running really hard.

3. The motor is pushing the boat well, but at this time,I don't think it's any faster than the CMB LS 21 Greenhead I previously had on the boat.

4. As time allows, I will test the Silver Bullit tune pipe and different props.

5. After probably 30 minutes of run time, the K&B 1L still looks good. The wire is pulled to the side just a little, but it still lights brightly.

6. A visual inspection of the cable revealed no broken strands.

Jerry D.

 

[lohring]

I also just got back from MAC 21 testing. I am running the same setup as for my modified K&B; an Irwin pipe, 1440 prop, and engine 3/16" above the sponson bottoms. It was obviously faster than the K&B with radar readings around 46 mph. The engine got smoother running as I ran several tanks through it. I tried an X-437 earlier in the testing, but I didn't check the speed. I think some fooling with props will pay off. Several boaters are reporting speeds in the low to mid 50s. They aren't seeing huge improvements over the Nova Rossis the MAC replaced, but they have not had time to fool with the setup.

Lohring Miller

 

[Jerry Dunlap]

Spent a considerable amount of time testing the MAC 21/JD WOF 30 today, Wednesday, April 30. Tried a bunch of props, reworked 1440, reworked X442, X640 cut to 37 mm diameter, stock X440, and stock X637.

Played with tune pipe length and prop depth. Here's what ended up working the best:

1. The stock X637(balanced and sharpened).

2. The Irwin Quiet Pipe with a 1/4" gap between the pipe and the cooper elbow header pipe.

3. Prop height 5/16" above the bottom of the sponsons. I know that's way up there, but the boat was handling fine. With the R Mfg LawLess Outdrive, I find I run the props higher.

4. Prop thrust maybe 1 degree postitive, pretty close to neutral.

I've now run at least 5/8 - 3/4 gallon of 65% fuel through the motor. I'll need to replace the K&B 1L next time I run. The plug still lights and the element has been pulled to one side and slightly outward.

The flex cable still looks fine.

I will have an opportunity to race this motor/boat combination this weekend. Will be interesting to see how it does.

Jerry D.