boxer 421 problem

**karl_karpets** · 09-01-2009, 09:27 AM

On one of my boxer 421's the engine runs great, but when i put a load on the vacuum it bogs down and almost shuts off. I changed the spark plugs checked the air filter, cleaned out the heat exchangers, the blower seems to be fine. Im usually very good at fixing these problems but i'm totally stumped. Any ideas for me?

**darylbrown** · 09-01-2009, 11:25 AM

It sounds like what is happening is you're running on one cylinder. The machine will sound fine and even normal until you put a load on it. Start the machine up and pull one of your spark plug wires. If it dies you found the problem if there is no change the plug it back and try the other wire. If you find this is the problem then the fix is to replace the ignition coil which you have to pull the front of the motor off to do but not as complex as it sounds.

**Chris Sheldon** · 09-01-2009, 01:02 PM

Be sure to check the spark before you start changing the ignition coils. Also check the air gap on the coils before replacing them and adjust them if need be.

You can also pull the valve covers and check to see if you have a bent push rod. Also check the valve clearances.

Good Luck!

-Chris

**Chris Sheldon** · 09-01-2009, 01:24 PM

Oh yeah, you may also want to check your fuel delivery, because if you aren't getting enough gas it will exhibit the symptoms you described. Try pulling the choke out when it is bogging and if the rpm's come back up this maybe a sign that you have a fuel problem.