B&S Model 120000 625 Series

[bikerider]

I've got a DR Trimmer Mower with a B&S 625 190cc engine.

The engine was running perfectly for about 8 hours of use over 3 days last week. I shut it down when I went to eat lunch on the third day and now it will not start, and pops or backfires when I pull the starter cord.

I've gone through the carb a few times, it's got a new air filter and spark plug, and new gasoline. I pulled the plug and it's getting a spark. I can spray carb cleaner through the carb throat and get the backfire.

I removed the cover on the top of the engine and the flywheel key is not sheared.

Does a backfire necessarily indicate an electrical or timing problem?

Is there something that I've missed??

 

[ILENGINE]

Did you change the spark plug before or after the problem started. Some of the newer briggs engines take a special gap plug that will foul out in a moments notice, and will appear to spark but won't under compression.

 

[bikerider]

Thanks for the reply.

My trimmer is 2 years old. Before I used it this season I changed the filter and plug. DR sent a package with the machine that included a new air filter and a new spark plug.

I set the gap to match the old plug. I wasn't able to find the recommended gap specs.

 

[bikerider]

Is it possible that something has happened to the valves?

I'm no mechanic - obviously, but today I pulled the plug one last time and poured a small amount of gas into the cylinder to try and get it to fire.

Looking into the spark plug hole, I can see one of the valves - possibly the exhaust valve(?). The valve appears open. When I pull the starter cord, the valve doesn't move. Shouldn't it be moving up and down when I pull the cord? There also seems to be less resistance at the starter cord - indicating reduced compression.

Would stuck valves cause the engine to backfire and not start?

Thanks for any help.

 

[ILENGINE]

You may need to pull the head and take a look around.

 

[bikerider]

Thanks.

Is pulling the head off, or unsticking a stuck valve super difficult?

Or can it be accomplished with regular hand tools?

Or.....should I take this to a repair shop?

 

[ILENGINE]

Normal hand tools are fine. May need to get a hold of a torque wrench for torquing the head bolts afterwards, If you remove the valve springs that can be a bear to get back on without a compressor, but it can be done.

 

[bikerider]

Thanks again,

Do you have any idea about warranty? Will I void the warranty if I start getting into the engine?

 

[ILENGINE]

If less than 2 years old then take the unit to your local Briggs authorized lawnmower dealer and let him figure it out. Because you could void the warranty if it is that new.

 

[bikerider]

I took the machine to a B&S authorized service place today and the mechanic asked if I changed the oil after the initial 5 hours of use. I told him I did not and he then told me that B&S would not honor the warranty since I failed to follow written maintenance guidelines. He also told me that the work that he would have to do would just about equal the cost of a new engine. Anyway......

So I came home and took the head off myself. Sure enough, the intake valve was not moving. I might have done something stupid, but I took a block of scrap pine and a light hammer and gave the wood and thus the valve a light tap just to see what would happen and the valve dropped back into it's seat. And now when I rotate the engine with the starter rope both valves move like they should.

But the damn thing still will not start.

Could I be missing something less obvious....like a vacuum leak....a faulty carb intake gasket......or maybe an electrical issue? When I remove the spark plug and ground it and turn the engine there is a spark. Maybe the gap is too small? Using carb cleaner as starting fluid does nothing.

I'm going nuts.