Need help

[jasonspeedy]

Hey guys, I need some serious expert advice, especially from AB if he's out there. I've got an older MAC .67 with very low hours. I first put it in a scratch-built rigger that was running on 5 points. No matter what the needle, the boat would eventually go into what seems like a lean bog, only quicker with a leaner needle. I thought I may have a load issue, so I went to a smaller prop, tried different stingers, got rid of the rear sponsons, etc...I even drilled the spraybar. I decided that my boat was crap, until I bought a sprint cat. The motor exhibits the same symptoms. I literally replaced everything in the sprint-cat, piece by piece, to isolate the problem, but the MAC does the same thing over and over. The only difference in setup is that the OPS (which runs great in the cat) has a cooled header. I've tried pipe lengths of 11 to 11.5 inches. I think I'm missing something or looking at the problem in the wrong way. The MAC motor appears to be fine...no leaks, compression is good, hc is about .011, but I just can't figure it out. Any ideas? The only thing I haven't done is change the water lines from medium to large.

Jason

 

[AndyBrown]

Jason,

I sent you an e-mail about that last week, but it bounced back.

Let me know if it's OK to resend.

 

[Bob Kensill]

The early Mac engines had a cooling problem. This was solved by cutting a circular groove down into the head button to add more water volume. They also had a "non-bushed" drum rotor housing. This can gall and cause a lean mixture. The rear transfer port also needed to have the angle changed at the top to direct the fuel/air charge toward the glow plug better. If all of this has been reworked on your engine, then I am at a loss for what to check next.

 

[Preston_Hall]

The early Mac engines had a cooling problem. This was solved by cutting a circular groove down into the head button to add more water volume. They also had a "non-bushed" drum rotor housing. This can gall and cause a lean mixture. The rear transfer port also needed to have the angle changed at the top to direct the fuel/air charge toward the glow plug better. If all of this has been reworked on your engine, then I am at a loss for what to check next.

I don't remeber the transfer port thing, not saying it isn't true, but a friend had these symtoms, he had the rotor bushed and the cooling head done and nothing changed.

 

[jasonspeedy]

Hey Andy-sorry about that, try [email protected].

The motor was originally non-bushed, but Andy gave me a bushed front housing to try. It didn't change anything. I think it was a mute point anyway, since the original drum had an excellent fit. I think my choice of motor and boat may have exceeded my skills, and I'm overlooking something. I don't really understand the whole dynamic of pipe length/prop diameter/prop pitch/temp/and mixture. Tell me if this is wrong or right: bigger prop/more pitch=longer pipe, lean=high temps, more load=richen the mixture, etc. I don't know...maybe I should buy a sail and call it a day. I'd see a dramatic cost reduction in glow plugs and nitro!

Just a note, when the MAC did come on...it was WICKED SILLY FAST!!!

Jason

 

[RaceCraftBearings]

I to this day run the first run of Mac 67 and 84 in the original design and to this day do not have any problems with them as they came in the box. Not to dispute what Krp is saying but it just isnt so with my motors.

Run LARGE fuel lines and depending on your local water temp Large water lines which are a must in Florida.

Good Luck!

 

[jasonspeedy]

Yeah...seems like a good idea, but if the nominal i.d. of the medium fuel tubing is at least the size of the fuel tank fittings, needle, and carb inlet, would it make much of a difference. I'll try it if you think it's worth a shot. What about water, could it be leaving the jacket so fast that it doesn't have time to soak up any heat?

 

[TimD]

What needle valve are you using Jason?

 

[Don Ferrette]

What needle valve are you using Jason?

85660[/snapback]

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I was going to ask the same thing. I addition to the needle what prop, what pipe & pipe length?

 

[jasonspeedy]

I'm using a CMD needle valve, and that reminds me of something...the other day when I was having the problems, I checked the needle. I had it so rich that the o-ring was nearly out of the housing, which I thought was odd...hmmmh? How in the world can a motor be that rich and still starve? Now you're thinking that it was SO far out that it was sucking air at the needle, but I checked that to. I checked the needle by pressurizing the tank with my mouth, and the fuel was a gushin', so I don't think it's a starvation induced lean.

I once a owned (and liked) the silver .60 parabolic pipe that Andy makes, but I slung it aloose, and now it's on the bottom of Blue Lake, with the rest of my 401K. I currently have the black AB .60 pipe at @11.25" with an H-32.

Nothing I have is weird or on the edge, it's all pretty typical stuff.

I'm lost, although I do like the "open up the water jacket idea"...that'd give me a reason to fire up the 'ole lathe and screw up a perfectly good water jacket!

Thanks guys, Jason

 

[TimD]

Are you using a MAC's product's 90 degree pressure fitting in the pipe by any chance? Another thought - are you using the reducer bushing in the black pipe?

Is your CMD needle valve the COURSE one?

Are you running a metal tank or a plastic one?

 

[Roxyflash]

Try running the pipe at 12 inchs you said when it turned on was wicked fast then fell off?Do you plug the plug element down the last two coils ?Make sure the pressure tap on the pipe is open and you have the right nipples on your tank hooked up right.

 

[AndyBrown]

Jason,

For the rigger in cool weather if that's when you were running it, the stock cooling is fine. For the cat, cutting a groove in the top of the head will help, but not much.

But this is not the real problem.

Proper pipe restriction and fuel delivery is the key.

Do you have stinger bushings for the AB 67 (black) pipe? They are a must. For the cool weather you'll want the .410" bushing. As the weather heats up you will need to go to .430" or .450". This may be your problem now because the Brown 67 (parabolic) pipe has more restiction, so it was working better.

I think this is your only problem.

One more thing. If you are using two plastic tanks with 1/8" brass tubing (stock), this is adding to the problem. Install 5/32" brass and use large fuel line.

 

[Chris Wood]

jason,

I had the same problem with a cmb of mine, come to find out that the 90 degree pipe pressure fitting was plugged, pulled it apart cleaned it out and away we go..

check it out. not say that is it, but it is something to look at

hope i helped

chris

 

[jasonspeedy]

Whoa...that was a lot of info at once...

Let's see, I don't know whether my needle valve is course or fine. I'm assuming that by stingering the black AB pipe I'm richening the mixture, which sounds good, and I've never thought about using larger brass in the fuel tank, that's a good idea too. I've never considered the size of the pressure tap on the pipe, but I see how that could affect delivery. Geeze, you guy's act like you run model boats or something. I guess I need all the fuel and water I can pump...at least that's the idea I'm getting. Thanks a bunch. I'll try some of this stuff.

Jason

 

[jasonspeedy]

One more thing...the tank is a v-bottom plastic sullivan, and yes I take the plug every time, without fail.

Jason

 

[troymcintire]

A friend of mine had the same symtoms. Found CMD needle leaking air.

Everything was clean and sealed going into the needle, and coming out of the needle fuel line was full of bubbles.

 

[TimD]

Jason,

Dismantle the tank, drill the end cap and stopper to accept 5/32 brass tubing for the fuel line. (if you use K&S brass tube - anneal it first). Run the large dia. fuel tubing thru to the needle valve and then to the carb.

The reason I asked if the pipe fitting was a Mac's products 90 degree is because some of them will close up when you screw the fitting on the end. I slot them with a dremel to prevent it closing off.

Tim.

 

[EatMyShortsRacing]

Further questions..... what plug and fuel are you using?

Sounds like the plug is losing some of its element fairly quickly which is the same as my early MAC 67 did (still without a bushed rear housing). I think the motor will be over compressed and damaging the plugs as soon as it comes on. The short pipe would accelerate that but also the pipe restriction will help ease this problem.

The other option is to cut down on the nitro a little.

just my guess though

 

[EatMyShortsRacing]

... or maybe a colder plug????