Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

   Got a Mastercut riding mower with a 12hp Briggs I/C engine.    The factory number is rubbed off its tag.  If anyone has one of these please post the factory number.

   The maker tag has AeroIndustries but I think it was made by MTD.  I'm not sure when MTD tookover AreoIndustries so it may be AreoIndustries made.  If you have a Lawnboy or some other brand with the same features then it's MTD.  The year is around 1985-1989.  The closest I've found so far is an Agway 300 which is an MTD #137-332-019.

   The engine on this seems shot.  The compression is 30psi.  I can turn the flywheel easily by hand through the compression stroke.

UPDATE: Got it started and it runs very well.  Cut a big section of lawn and no engine sag.  Went up a steep hill cutting and no sag.  The engine seems fine.  ??  Ran it up and down the street and it ran fine.

Trouts, 

What year is the engine?   That should narrow down the search a bit...(The date of engine is the year of unit or engine date plus 1 year)

Do you have any of the sticker numbers from under the seat?

Friiy

Does that engine have compression release? That would explain the bad readings on an engine that runs well. I think Mastercut was Aircap Industries and MTD acquired them in '86.

Yes it does,  but it was mostly a dirty valve face (carbon),  or a slow/ gummy valve stem that made it feel so weak.

Friiy

The sticker number under the seat has been worn off.  The engine is 1988.  I found a group of drawings which match the machine all from 1987.    They match except for one belt which is a problem. 

 

The blades are always engaged.  When the deck is disengaged the belt does not go slack enough to let the belt slip on the drive pulley.  There is no tensioner pulley.  What I think happens is the engagement level lowers the deck and at the same time moves the deck back slightly which is probably how the belt gets tensioned.  It may be working properly but the belt on there may be too tight. 

 

 The belt on all the drawings of machines similar all have a deck drive belt of 754-0280.  The MTD site lists that belt at ½  x 53 ½ inches.  That size would never work on this machine.  The belt on there is 754-0329 listed as .625 x 69.28.  Some non-MTD  sites list the 754-0280 as .700 x 53.17 which also never work.  The belt on there measures about 70 inches, is too tight and not the right part number, it’s754-0329. ??

 

I’d like to get a belt that works but that will probably have to be done by trial and error.  It makes starting the thing harder because of the blades being engaged. 

 

The compression is 30psi and way to low even with compression release.  I think your right Friiy, that something is going on with the valves.  It could also be a sheared key and the flywheel only slightly off but most  likely valves.  With the air filter off there seems to be a slight mist in the throat which much be caused by the intake valve leaking.

 

Bill_H,

   The sticker under the seat has AirCap Industries on it but the rest is worn off.  Given the 1986 and the drawing match to MTD it’s MTD made.

 

Not a bad rig for $100 and it came with the double cloth bags and blower hose.  The guy had the solenoid wired to the ground post of the ignition switch for some reason.  He ran a separate wire to do that.  The original wire was inplace but unconnected.  ?? 

 

Friiy, you mentioned these carbs were weird.  It has a 4 inch tube with small holes you can unscrew and remove from the top of the carb which was partly plugged.  Never saw such a tube before.  Clearing that made it start and run a bit better. 

    I think I understand what's going on with the belts.  The original deck was 32 inches.  The guy replaced the 32 with a 38.  Both are MTD and look similar.  The difference in the deck size is probably why the belt tension is off. 

    The bigger deck does not move back as far with the engagement lever set to disengaged allowing the bladed to turn without great power.