mac 21 o/b(recap)

[dizzy dean]

running redmax 50%, mc 9, irwin pipe, lawless and x437/3 not pitched. runs great but if i lift, it's hard to get it back on pipe! am i doing something wrong or is this normal. i'd rather not lift but sometimes you have to in order to get out of trouble.

thanks tim

 

[HOOTERS Racing]

try a stock abc 40x53 2 blade and see how you go

cheers ian

 

[LarryConrad]

How deep are you running your prop? Macs like to rev.

 

[Joe_Knesek]

I had the same problem until Rod G reworked the stock carb.

 

[dizzy dean]

How deep are you running your prop? Macs like to rev.

hard to be exact without setup board. time to make one, turn fin is what is stoppping me from just putting it on a board.

thanks tim

 

[Tim_Duggan]

try a stock abc 40x53 2 blade and see how you go
cheers ian

Depends on what pipe and how long it is, but yes this prop worked on several of the MAC's at our pond, with stock or CMB L/S carbs. The X637 works well too.

 

[Rokieboater]

running redmax 50%, mc 9, irwin pipe, lawless and x437/3 not pitched. runs great but if i lift, it's hard to get it back on pipe! am i doing something wrong or is this normal. i'd rather not lift but sometimes you have to in order to get out of trouble.
thanks tim

Let us know if you get it figured out. I run a similar combination and the only way I could slow down and get back on pipe is to change the carb to one modded by Rod. Good Luck.

Robert

 

[Grimracer]

This is what I have found.. I have had this happen to me from time to time.

You need more fuel at low throttle.

Make sure you have the low speed needle either backed all the way out or removed. Try to use a carb that has a bore no larger then about .3”

Next

Stick with a low pitch prop for now.. not so much dia but pitch. I like the GrimRacer 40X52/3 or Octura X437/3 for my 21 tunnels. When you get your boat to come back on pipe you can start to pitch it up a tad.

Can you let us know what pipe you are using? I would try the standard Silver Bullet at first and once its rocking you can go to the short.

Keep us posted

Grim

 

[dizzy dean]

as stated, irwin pipe(i believe), s&b 437/3 prop, center of prop is 3/8 inch above sponson bottom with 1 degree pos(up).carb is stock no low end just remote os needle. change degree on sunday to more pos, then i had an airplane in about 40 feet, people love to see it fly.

thanks tim

 

[153stars]

running redmax 50%, mc 9, irwin pipe, lawless and x437/3 not pitched. runs great but if i lift, it's hard to get it back on pipe! am i doing something wrong or is this normal. i'd rather not lift but sometimes you have to in order to get out of trouble.
thanks tim

Haven't run one but when alot of talk was going on about them a couple years back,I read they like a lot of heat, some filling the water jacket with epoxy of some sort and lapping it, cutting an air cooled head way down,a gasket between the PTO AND LOWER END to build better heat, Irwin composit lower for more heat ,,ect

 

[Joe_Knesek]

The stock carb bore is .295. After watching my sons boat have the same problem Rod suggested that the stock carb is not able to draw fuel well enough to recover when the boat comes off pipe. He then reworked the carb & without changing anything the boat can be off pipe for an entire lap and snap right back up.

 

[dizzy dean]

The stock carb bore is .295. After watching my sons boat have the same problem Rod suggested that the stock carb is not able to draw fuel well enough to recover when the boat comes off pipe. He then reworked the carb & without changing anything the boat can be off pipe for an entire lap and snap right back up.

well i guess i need to talk to rod g., wonder how long and how much?

thanks tim

contact info for rod please

 

[LarryConrad]

[email protected]

He reworked the carbs on both my mac OB's and restricted the water through the heads (I run them aircooled now).

I had work done on several engines at the same time so I don't know for sure how much he charges to tweak a carb. He uses a flow bench and optimizes the carb to the motor.

Larry

 

[dizzy dean]

[email protected] reworked the carbs on both my mac OB's and restricted the water through the heads (I run them aircooled now).

I had work done on several engines at the same time so I don't know for sure how much he charges to tweak a carb. He uses a flow bench and optimizes the carb to the motor.

Larry

thanks larry, i'll email him and find out. may throw on the air head before the weekend.

tim

 

[LarryConrad]

[email protected] reworked the carbs on both my mac OB's and restricted the water through the heads (I run them aircooled now).

I had work done on several engines at the same time so I don't know for sure how much he charges to tweak a carb. He uses a flow bench and optimizes the carb to the motor.

Larry

thanks larry, i'll email him and find out. may throw on the air head before the weekend.

tim

Is your air head stock from CMDI? The one I have has all but three fins cut off and the diameter turned down. The motor I have on my boat uses the stock water head with no water hooked to it.

Larry

 

[dizzy dean]

[email protected] reworked the carbs on both my mac OB's and restricted the water through the heads (I run them aircooled now).

I had work done on several engines at the same time so I don't know for sure how much he charges to tweak a carb. He uses a flow bench and optimizes the carb to the motor.

Larry

thanks larry, i'll email him and find out. may throw on the air head before the weekend.

tim

Is your air head stock from CMDI? The one I have has all but three fins cut off and the diameter turned down. The motor I have on my boat uses the stock water head with no water hooked to it.

Larry

yes, stock from cmdi. guess i'll disconnect the water. first i need to send to rod, takes about a week turn around. thanks for your help again.

tim

 

[TUNLBOTR]

running redmax 50%, mc 9, irwin pipe, lawless and x437/3 not pitched. runs great but if i lift, it's hard to get it back on pipe! am i doing something wrong or is this normal. i'd rather not lift but sometimes you have to in order to get out of trouble.
thanks tim

Tim

Its possible the outlet on the pipe could be too large inside diameter wise. My backup Irwin is shimmed down to .290 with brass, JB welded in, and at the time scrapped the stock carb and went with one of Rods .285 bore carbs. Rocketship with full response, smaller in, smaller out..... Justa thought. h34r:

Randy

 

[dizzy dean]

running redmax 50%, mc 9, irwin pipe, lawless and x437/3 not pitched. runs great but if i lift, it's hard to get it back on pipe! am i doing something wrong or is this normal. i'd rather not lift but sometimes you have to in order to get out of trouble.
thanks tim

Tim

Its possible the outlet on the pipe could be too large inside diameter wise. My backup Irwin is shimmed down to .290 with brass, JB welded in, and at the time scrapped the stock carb and went with one of Rods .285 bore carbs. Rocketship with full response, smaller in, smaller out..... Justa thought. h34r:

Randy

mine has a brass insert that measures .255 +/-, once i get the carb back i'll work from there, one change at a time. i've watched people make to many changes at one time and get nowhere. always consider all replies. <_<

thanks again.

tim

 

[dizzy dean]

is this in fact an irwin pipe? <_< i been going off pics, and what others said they had. never had it confirmed.

tim

 

[Geraghty]

is this in fact an irwin pipe? <_< i been going off pics, and what others said they had. never had it confirmed.
tim

Yes.....that is an Irwin......