MAC Troubleshooting

[Russell Bear]

Here's what I have. Scratch built scale wood hydro that weighs 15.2 lbs. 2005 MAC 67 (Big bore carb) with head clearance of .008” with the AB black pipe @ 11 1/2". Running 45/18 Byron's fuel and a Mark Sholund X460/2. The engine has close to a gallon through it so it's fairly new.

What we are seeing is that the engine doesn't like to rev all that much when on the table or underway. When starting the easiest way to get it started is to pinch the fuel line, and when it does run it is sloppy rich. Have to keep the engine at least half throttle or better to keep it running. When on the water it will run pretty good for a couple laps and then starts to fall off the pipe in the corners and then wakes up again until the next corner. It’s hard to keep on the pipe. We tried a number of different props. The ones that did get up on plane did the same thing.

After the run we looked at the plug. Some plugs were slightly pulled and in better shape than others, but there were a few that were burnt black and the coil was pitted badly. I can only get one or two runs on a plug.

I am attaching a couple pictures of the head button and the top of the piston. I am seeing quite a bit of pitting on both, but the bowl looks good, just pitting around the perimeter of the button.

So anyone out there know what I should try to get this MAC running?

 

[RaceCraftBearings]

Russell, this sounds alot like my recent problem with the same combo a Mac67/Scale/460-2 blade. I ended up getting good performance with the Parabolic pipe with internal stringer drilled out the same diameter as the stinger. I also have the Black A/B pipe but have not tried it yet I was so pleased to get it running with the Parabolic that I just haven't tried the other yet.

The problem ended up being that my old pipe/muffler combo was to restrictive and not letting heat escape.

Good Luck!

Ron

 

[dave roach]

I see a problem from the start .008 head clearance is to tight for a 67. Open up the head clearance.

My 02 cents

Dave Roach

 

[Douglas P Shepherd]

Russell, this sounds alot like my recent problem with the same combo a Mac67/Scale/460-2 blade. I ended up getting good performance with the Parabolic pipe with internal stringer drilled out the same diameter as the stinger. I also have the Black A/B pipe but have not tried it yet I was so pleased to get it running with the Parabolic that I just haven't tried the other yet.

The problem ended up being that my old pipe/muffler combo was to restrictive and not letting heat escape.

Good Luck!

Ron

Two years ago I tried for 3 months and 5 gal of fuel to get the Mac 67 to run with the AB pipe in a scale (Andy built) I had no luck with the AB pipe on the MAC. There where also some top scales that was working on the same set up. I also have seen they have moved on as well !! Pipe works Great on a CMB Green head

Good Luck Doug DPS Racing hulls

[

 

[SayMikey]

Russell, this sounds alot like my recent problem with the same combo a Mac67/Scale/460-2 blade. I ended up getting good performance with the Parabolic pipe with internal stringer drilled out the same diameter as the stinger. I also have the Black A/B pipe but have not tried it yet I was so pleased to get it running with the Parabolic that I just haven't tried the other yet.

The problem ended up being that my old pipe/muffler combo was to restrictive and not letting heat escape.

Good Luck!

Ron

Two years ago I tried for 3 months and 5 gal of fuel to get the Mac 67 to run with the AB pipe in a scale (Andy built) I had no luck with the AB pipe on the MAC. There where also some top scales that was working on the same set up. I also have seen they have moved on as well !! Pipe works Great on a CMB Green head

Good Luck Doug DPS Racing hulls

[

Id try a parobolic cmd pipe thats what i run on my mac and prop it down a little start with a x457. Put the head cl up near .014 and make sure you are using big fuel lines and a high flow needle. Too small a needle will be ok till it hits the water and needs fuel,these motors suck fuel more than a green head but if its a late version it will rock....Mike

 

[Russell Bear]

***Correction to the head clearance. It is at .012" already, not .008".***

:blink: :blink: :blink:

Russell, this sounds alot like my recent problem with the same combo a Mac67/Scale/460-2 blade. I ended up getting good performance with the Parabolic pipe with internal stringer drilled out the same diameter as the stinger. I also have the Black A/B pipe but have not tried it yet I was so pleased to get it running with the Parabolic that I just haven't tried the other yet.

The problem ended up being that my old pipe/muffler combo was to restrictive and not letting heat escape.

Good Luck!

Ron

Two years ago I tried for 3 months and 5 gal of fuel to get the Mac 67 to run with the AB pipe in a scale (Andy built) I had no luck with the AB pipe on the MAC. There where also some top scales that was working on the same set up. I also have seen they have moved on as well !! Pipe works Great on a CMB Green head

Good Luck Doug DPS Racing hulls

[

Id try a parobolic cmd pipe thats what i run on my mac and prop it down a little start with a x457. Put the head cl up near .014 and make sure you are using big fuel lines and a high flow needle. Too small a needle will be ok till it hits the water and needs fuel,these motors suck fuel more than a green head but if its a late version it will rock....Mike

Got the Prather large fuel lines with the CMD large mix valve. I replaced the 1/8" fuel tank pickup's with 5/32". Your right, it does suck the fuel! :huh:

 

[P THOMAS]

Here's what I have. Scratch built scale wood hydro that weighs 15.2 lbs. 2005 MAC 67 (Big bore carb) with head clearance of .008” with the AB black pipe @ 11 1/2". Running 45/18 Byron's fuel and a Mark Sholund X460/2. The engine has close to a gallon through it so it's fairly new.

How about using a x455/3 and the pipe at 12 -12 1/2 You need to lessen the load and let the motor rev. The macs are touchy to fuel draw problems you need 5/32 tubes in your tank pickups and larger than standard fuel line. That black pipe may be to small the parabolics are bigger but still need to be drilled out. A pipe that i found works real well is a MAC 13cc muffled

 

[Will Gallagher]

I would try a stinger reducer bushing. The AB pipe has a stinger ID of .470. Reduce it to .430 and see what happens.

Just my 2 cents

 

[Mark Stein]

I got one more thing to add to phils statment about the fuel tank. Use Aeromarine large tubing - Prather tubing is too small for the .67 CMB or MAC and check all those fuel fittings bigger is better. MY CMB .67 wouldnt run 2 laps until I increased the fuel flow.

 

[Duck899]

Head clearance should be .012" and pipe around 12" for that X-460/2. Macs will pour fuel into the carb when starting and need 1/2 throttle to run. I would go to a X-457/2 or even better as Phil mentioned, the X-455/3 to start off with. Macs will rev to the moon.... Work your way up to the X-457/3 and hang on.....

3 blade props work better in the corners on a scale......

Have fun......

 

[ALLAN YUEN]

Better use Carburtor .510 bore with head clearance of .012" to.014" shims. Set up AB black pipe 11.750 +/- .250 inches play( depend on size propeller) also put piece stinger bushing reduce .410 or.430( depend on weather) Great good working

Good Luck! Have Fun with boat

 

[stanosmax]

Although you said you only ran about a gallon of fuel through it,,I would check the bearings. That motor is running pretty stressed from the looks of the head button.Falling off the pipe frequently could be a sign of bad bearings,overheating(you stated a couple of plugs were burnt black),or too big of a prop ,as others have stated.Too lean of a mixture will also do that kind of damage.Whatever you do,do it soon!

 

[Brian Schymik]

This is the funniest dang post.....everyone chipping in their two cents.

All have good ideas, but here is the thing....listen to the people that have run what you are running.

Doug, Phil, Mike and I have all run your combo with NO success. Motor is fine..get a different pipe. I spent way too much time on that combo with exactly your results.

Get A parabolic or MAC 13 pipe and it will be fine. All of the stuff about the fuel lines is true also.

Don't be stubborn and waste time on that combo.

Now if I have convinced you, I will buy that AB pipe. It does work great on a greenhead!!

Brian Schymik

US-1 scale 2004

 

[Grub]

Get A parabolic or MAC 13 pipe and it will be fine. All of the stuff about the fuel lines is true also.

Ditto that Brian.

I've currently got a MAC 67 with MAC 13cc pipe at 11.75 inches, large fuel tubing and running a X-462 in my Miss U.S. Karelson round nose.

Boat is now ballistic when the mixture is right.

Gotta love the MACs

Grub

 

[carlnoki]

Russ;

LISTEN to Brian!!!!!!!!!!!!!!!!!!!!!!!!

I have seen his combo work BEAUTIFULLY in Evansville when i went to the races there. WORKS FANTASTIC!!!!!!!!!!!!!!!!!!!!!!

carl cisneros

 

[Douglas P Shepherd]

Get A parabolic or MAC 13 pipe and it will be fine. All of the stuff about the fuel lines is true also.

Ditto that Brian.

I've currently got a MAC 67 with MAC 13cc pipe at 11.75 inches, large fuel tubing and running a X-462 in my Miss U.S. Karelson round nose.

Boat is now ballistic when the mixture is right.

Gotta love the MACs

Grub

Very well put Brian!!!!!!! If you got a friend with a CMB green head, make his day! Lot's of power and big top end Great low mill speed

 

[Douglas P Shepherd]

Get A parabolic or MAC 13 pipe and it will be fine. All of the stuff about the fuel lines is true also.

Ditto that Brian.

I've currently got a MAC 67 with MAC 13cc pipe at 11.75 inches, large fuel tubing and running a X-462 in my Miss U.S. Karelson round nose.

Boat is now ballistic when the mixture is right.

Gotta love the MACs

Grub

Very well put Brian!!!!!!! If you got a friend with a CMB green head, make his day! Sell him the AB pipe and save your self alot of time and money It dosnt work in a scale with a Mac 67 in it..................

 

[ALLAN YUEN]

Get A parabolic or MAC 13 pipe and it will be fine. All of the stuff about the fuel lines is true also.

Ditto that Brian.

I've currently got a MAC 67 with MAC 13cc pipe at 11.75 inches, large fuel tubing and running a X-462 in my Miss U.S. Karelson round nose.

Boat is now ballistic when the mixture is right.

Gotta love the MACs

Grub

Very well put Brian!!!!!!! If you got a friend with a CMB green head, make his day! Lot's of power and big top end Great low mill speed

Tell me What size of carburtor bore for CMB green head?

 

[Douglas P Shepherd]

I am getting .470 just inside the carb on the mounting side.

 

[ALLAN YUEN]

I am getting .470 just inside the carb on the mounting side.

That's Why! your small bore because MAC67 stock carb .550 not good for scale (not enough airflowing room cowling) also change small carb.510 will be working.