<VV> Mower problem - NO Corvair

[Jim Becker]

My first guess would be sticking exhaust valve.

Jim Becker

-----Original Message----- 
From: Grant Young via VirtualVairs
Sent: Monday, November 04, 2019 8:02 AM
To: virtualvairs at corvair.org
Subject:  Mower problem - NO Corvair

This is one of those shots in the dark, but I have struck out in attempts to 
solve a problem with my Toro Zero-Turn mower with a Kohler 27HP V2 engine, 
so I am hoping someone out there might be able to help diagnose. There are 
some Toro help sites, but no help there either. The engine stars and runs 
fine for the first 5-10 minutes, then suddenly goes into some sort of loss 
of power mode and backfires through the exhaust (enough to blow a hole in 
the muffler). Taking the load (blade drive) off helps, but still not much 
power, similar to having water or contamination in the gas. Then for no 
reason, after 5 minutes of this, it will jump back into the power mode and 
be fine for the next 15-20 minutes. Then another bout of power loss and back 
firing for another five minutes, (I just sit and wait, knowing it will 
recover) then I can finish the next 2 hours of mowing without incident.

I have rebuilt the carburetor, changed the plugs and fuel pump, replaced all 
the fuel lines, fuel and air filters, and drained the tanks completely. Fuel 
octane doesn't make any difference nor did a bottle of Heet. I also use 
Sta-Bil ethanol treatment, but tried it once without it.  I could almost 
live with this except for the cost of patching the muffler each time I mow. 
Don't want to put on a new one until I find the fix. It is a fairly low hour 
60" mower.

A private reply is fine. Thanks much,
Grant