PT422 Engine shaking / sputtering

[KMA]

I started up the PT422 today (Robin engine) and there was a slight bogging down that happened briefly while idling, but nothing too bad. I parked it for a while and started it up again later in the day. It ran okay, but I thought I could almost hear a dull banging sound over the engine like something large and heavy was loose. I figured I was hearing things... It went away for a minute and then the engine started to shake violently and sputter, with a little bit of black smoke coming out of the muffler. I shut it down immediately. I started it up again with no throttle and it ran, sounding a little bit "off", but as soon as I increase the throttle it starts to shake again.

I didn't want to hurt anything more, so I figured I'd post up here and see what you guys think it could be. The only thing I've done recently was take off the filter and spray some carb cleaner inside. I did that last time I ran it (about a week ago) and mowed for about 2 hours without issue.

Anyone know what this could be?

Thanks for your help.

 

[Marks481]

Check the level of oil. Oil too high could be caused by the carburetor flooding out and draining to the crankcase. Could give you symptoms like that.

Robin specifies using a fuel shutoff valve between the tank and the engine to prevent this from happening, but PT chose to make that an optional item...

Optional as in allowing the enduser to install one himself if he felt he should follow the engine manufacturer's specifications....

If that isano-go, then try Measuring the compression of each cylinder, if you have a compression gauge ($30 at auto zone). That will help rule out the expensive, nasty things like stuck exhaust valve, frozen piston with a hole punched through it by the connecting rod, etc.

 

[KMA]

Checked the oil level and it wasn't high. I took off the top of the carb and tried cleaning it again just in case something got stuck somewhere. I blew it out and then sprayed some carb cleaner. I took out the plugs and re-gapped them (one was way off for some reason). I started it up and it ran fairly rough and then cut out and wouldn't start again. I took the plugs back out again and noticed one side looked pretty dry like it wasn't getting any fuel when I was cranking it. The other side looked normal.

I have the EH65 manual and I'm going to look through it for a clue. Unfortunately I don't know enough about the engine to know why one cylinder is dry (assuming that is the main problem).

Thanks again for your input.

 

[KMA]

YouTube - PT422 engine trouble

Here's a video on youtube I made today. It's kind of hard to tell how it sounds exactly since I recorded it with my phone, but I varied the throttle while it was running. You can see towards the very end when I bring it down to an idle it really starts shaking. At full throttle it doesn't sound that bad (other than I know what it normally sounds like and that isn't it...) but you can sort of hear some strange metalic sounds mixed in. I don't know if it is the engine or the mounts creaking as it shakes. It doesn't sound good. If I drive it, it has very little power like there's not much compression. Maybe it's only firing on one cylinder?

Any input/ideas would be appreciated.

 

[toy]

Is both plugs firing? I would put new plugs in it and see if that helps. Black smoke, can you smell a strong gas odor? Is both plugs firing?

 

[BobRip]

I had the shaking issue and turned out to be a miss firing plug. You can pull a wire off a plug while the engine is running. The engine will die immediately if you pull the good plug. If there is no spark between the bad side and the plug (hold the wire near the plug) then you may have a bad coil. I would just go ahead and replace both plugs. This may clear up the problem. If that does not work stick a screwdriver in the bad side and while cranking see if there is spark with the screwdriver shaft held near a ground. If there is no spark, it is probably the coil for that side. Good luck.

 

[KMA]

Thanks for the input guys... I will try replacing the plugs tomorrow and let you all know how it goes.

 

[washita]

your video shows the same operating condition my 425 exhibited last winter
check compression in engine mine had a broken rocker arm in addition to a mouse chewing insulation off of the coil grounding wire which would intermittenly short out the coils hope this helps

 

[coolconnection]

KMA Kevin,

Sure looks like you have been leaking some gas around your gas cap as well. Mine was doing the same thing so I took an old inner tube and cut it the same size as the cork gasket that is already on there. I reassembled it with rubber gasket first then the cork gasket and then the gas cap. It hasn't given be any problems since and no more gas stains on the tank.

 

[KMA]

your video shows the same operating condition my 425 exhibited last winter
check compression in engine mine had a broken rocker arm in addition to a mouse chewing insulation off of the coil grounding wire which would intermittenly short out the coils hope this helps

I still need to get a compression tester... I will have to check it out this week. Can you describe where the mouse chewed through some wires? I definitely have lots of mice around here, and they chewed a bunch of wiring on my ATV causing it not to run. Thanks for your help.

KMA Kevin,

Sure looks like you have been leaking some gas around your gas cap as well. Mine was doing the same thing so I took an old inner tube and cut it the same size as the cork gasket that is already on there. I reassembled it with rubber gasket first then the cork gasket and then the gas cap. It hasn't given be any problems since and no more gas stains on the tank.

I'll have to give that a try. Alot of the staining is from the recent problems since it shakes the tractor so much, but it's always been a minor issue. Thanks!

I've attached a photo of the new spark plugs after being installed and ran for one minute (same shaking/sputtering/etc). The one on the left is from the left cylinder (looking from the back of the tractor). Can anyone read the spark plug "tea leaves" and diagnose what's happening? I tested spark with both the old and new plugs and they are all firing.

Thanks again for your help!