B&S Model 120000 625 Series

bikerider

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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

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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

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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

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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

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

bikerider

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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

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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

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Thanks again,

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

ILENGINE

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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

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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.
 
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