PT425 ran great yesterday, won't start today and backfiring through the carb

[NC1]

PT425 ran great yesterday, won't start today and is backfiring through the carb. It will try to start, pop, and sputter, but can't get her going. Tried a little starting fluid in the carb and it tried to start and backfired through the carb and cought the overspray on fire-- small fire, just blew it out. It is 15 degrees cooler today, but she has run fine in the past when it gets cooler.

Any tips/suggestions?

 

[ponytug]

Sorry to hear it.

I don't have a 425, so this is just general advice to tide you over until someone who really knows can step in.

Did you check the oil level to make sure that you didn't have a gas leak into the oil overnight?

If it were me, I would start by checking that the choke and throttle are working correctly.
Then, I would check the plugs and wires for loose fit, spark, and gap. Sometimes just getting colder can cause an issue. If there is a noticeable difference in the plug condition, I would change the plugs and try to fix whatever might have been causing the issue, like a bad wire or connection, or valve adjustment.
If the plugs and wires are good, my next thought is that overall it sounds like a timing issue, so my guess would be have a look at the valves to make sure that the are functioning properly, and that nothing is loose, and that the camshaft is opening and closing the valves roughly in the right place.

All the best,

Peter

 

[MossRoad]

What engine is in it?

 

[seville009]

Older and longer thread link that might give you some ideas

the saga continues... PT-425 engine problem at 10 hours?

After doing about 2 hours of loader work today the PT started sputtering. Thinking I was about out of gas I rushed back to the garage to fill it up. It still had almost half a tank, but filled up anyway. I also checked to make sure the fuel line didn't get kinked from where I replaced the gas...

www.tractorbynet.com

 

[NC1]

Sorry to hear it.

I don't have a 425, so this is just general advice to tide you over until someone who really knows can step in.

Did you check the oil level to make sure that you didn't have a gas leak into the oil overnight?

If it were me, I would start by checking that the choke and throttle are working correctly.
Then, I would check the plugs and wires for loose fit, spark, and gap. Sometimes just getting colder can cause an issue. If there is a noticeable difference in the plug condition, I would change the plugs and try to fix whatever might have been causing the issue, like a bad wire or connection, or valve adjustment.
If the plugs and wires are good, my next thought is that overall it sounds like a timing issue, so my guess would be have a look at the valves to make sure that the are functioning properly, and that nothing is loose, and that the camshaft is opening and closing the valves roughly in the right place.

All the best,

Peter

Checked the oil level, it was a tad low. I'll check the other things. Thanks

What engine is in it?

The Subaru

 

[LittleBill21]

if it repeatedly backfires through carb, pull the valve cover, sounds like the intake valves may be bent, compression check should catch this as well

 

[MossRoad]

Checked the oil level, it was a tad low. I'll check the other things. Thanks



The Subaru

My Kohler did something similar a few years ago. Turned out one of the rocker arm nuts came loose, the rocker turned and let the push rod fly. Only damage was a cracked rocker cover.

As others have mentioned, you might want to pull your valve covers and have a look-see. But before you do that, study up on the valve cover gaskets and if they have to be replaced if you pull the covers, or if they're reusable.

 

[NC1]

Older and longer thread link that might give you some ideas

the saga continues... PT-425 engine problem at 10 hours?

After doing about 2 hours of loader work today the PT started sputtering. Thinking I was about out of gas I rushed back to the garage to fill it up. It still had almost half a tank, but filled up anyway. I also checked to make sure the fuel line didn't get kinked from where I replaced the gas...

www.tractorbynet.com

That thread had a lot of great info, thanks.

I took the carb off and cleaned it, still would not start and still backfiring through the carb--much cooler looking at night!

I then checked the compression and have 160 on the right and 155 on the left.

maybe timing/valves?

Advice on next steps?

 

[Lnk]

Is it me Robin Subaru engine? If so they don't like the cold. I try to not start it when it is the coldest part of the day. I have a wood stove in my building, and will warm the area up ahead of time when I am planning to use it. I will say this, turn it over without the choke on a few times, then when going to start it, close the choke as I turn it over. When I get to the bottom of choke travel or closed. Open it right back up. I love my 425, this is the only issue. A block heater would help.

 

[MossRoad]

That thread had a lot of great info, thanks.

I took the carb off and cleaned it, still would not start and still backfiring through the carb--much cooler looking at night!

I then checked the compression and have 160 on the right and 155 on the left.

maybe timing/valves?

Advice on next steps?

Install a fuel shutoff in the fuel line and close it.
Leave the choke off.
Leave the throttle off.
Pull the spark plugs and crank the engine for 10 seconds to clear anything out of everything.
Reinstall the spark plugs.
Open the fuel shutoff and try and start the engine with no choke or throttle.
Slowly close the choke while you're cranking the starter and it should eventually fire.
If it's spraying fuel out of the carb with no throttle or choke, then I would suspect a valve issue first, followed by a timing issue. These things don't usually go out of time unless something breaks or is disassembled. Suspect the valves first:
Stuck valve
Valve adjustment
Broken-defective rocker
Bent push rod
Things like that.

Hope that helps.