twin mac 84 problems

[Drew St. Amant]

Tried to to run our twin this weekend to get ready for an upcoming race in September. The first run went great other than the water line popped off it was brought in the next lap after it happened the motors where a little hotter than normal but nothing alarming. When we tried to run it again we very quickly lost the inside motor. Checked the flow on the needles and that motor was all the sudden way lean went from 55 to 80 on the flow meter. so we sprayed wd40 through the needle backwards and got some trash to come out and the flow went back to where it should have been tried to run it again and same problem we lost a motor and had trash in the needle. so we decided we needed to clean the tanks out better (this boat had been sitting a while so it wasn't all that surprising to find trash in the tank). while we dissembled the boat one motor felt a little weird so we took them apart and one feels almost new and its pretty tight at the top the other feels significantly more worn. What I'm wondering is should I be looking for new pistons and liners or should we try and run the boat again with cleaned tanks and then see how the motors do.

 

[RaceMechaniX]

Clean the tanks and replace the bearings if they fell iffy. Get some brake cleaner and flush both the tanks and needles throughly. While you have the motor apart check the deck clearance and look for other signs of worn out parts. Since replacement P&S's are very hard to find for those motors do everything else first.

 

[Drew St. Amant]

Would anyone happen to know what is a good head clearance for those motors we have several macs in several sizes but we had so few issues in the past with them I don't think I've ever checked the head clearance on them

 

[Mike Hughes]

I ran at 12-14 with 50%.

 

[Drew St. Amant]

OK I'll check it and see where I'm at thanks guys

 

[Drew St. Amant]

Also one more think what do you guys think about swapping motors side to side to see what that does not sure if that can hurt anything?

 

[Walt Barney]

Also one more think what do you guys think about swapping motors side to side to see what that does not sure if that can hurt anything?

 

[Walt Barney]

If the tanks are Tin or Brass toss them as you will not be able to clean them enough to stop the needles from plugging up if they are Stainless Steel wash them out with Laquar thinner if you still have problems
check your fuel
Walt Barney

 

[Drew St. Amant]

Thanks for the suggestion Walt. The tanks are actually your tanks we bought the boat from a friend so we didn't buy them from you directly all of you tanks are stainless correct?

 

[FloridaScaleBoater]

Thanks for the suggestion Walt. The tanks are actually your tanks we bought the boat from a friend so we didn't buy them from you directly all of you tanks are stainless correct?

No, Walt made tin tanks also,

 

[Walt Barney]

No, Walt made tin tanks also,

NO I made tin tanks several years ago,Put a magnet on the tank to see what they are.
Walt

 

[Drew St. Amant]

OK I'll give that a try

 

[Tim Kish]

Inline fuel filters!

 

[ALLAN YUEN]

what kind of needles ? Reason O ring worn out or swell then leak or vibrate near engines cause air bubbles fuel line

 

[Drew St. Amant]

Bob violet needles and we wanted to install filters but there's not much room. Since we've had this issue we are definitely planning on making room though

 

[FloridaScaleBoater]

Bob violet needles and we wanted to install filters but there's not much room. Since we've had this issue we are definitely planning on making room though

Drew, not sure if you mentioned it as a "to do" or not?
But I would disassemble at the least the engine that has lower compression.
Also, I would put the largest plastic tanks you can fit it the boat, just for testing purposes

 

[ALLAN YUEN]

Bob violet needles and we wanted to install filters but there's not much room. Since we've had this issue we are definitely planning on making room though

what size of fuel line silicone ? S , M or L How old tube ? If you show any pictures. thanks

 

[Drew St. Amant]

I believe from the tank to the needle is large from the needle to carb is smaller not sure if it's med or small we did disassemble both motors you could see on the motor that was loose the liner was almost mirror polished right up to where the piston stops and on the tighter motor the liner you could still see the honing marks I'll get some pic up of our needle setup soon

 

[Tom Foley]

Filters for sure . Disassemble both needles , blow out with brake clean., wipe off needle with a clean paper towel etc to get any haze off . Reflow the needle to your good number . Two new or good plugs . Clean filter after.EVERY fill up without fail
Not full disassembly but brake clean it and put the flowmeter back on it until you get consistency. The large main bearing should be changed fairly frequently , front small bearing every 3 rears . Close off one end of the needle with a hemostat and blow.into the needle with a spray of wd 40 or fantastic around the needle to make sure it's not leaking .

 

[Drew St. Amant]

Does anyone know where I can get O rings for my needles if I knew what size I they are I could probably get them from McMaster