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My 15 year old (well maintained, and has always run well upto now) just died/stopped. I replaced the plug and air filter at the beginning of the season. This is my 3rd time using it this year. After about 20 minutes of running just fine as always, it backfired twice and stopped. I've tried to re-start several times; it makes a backfire / "throaty" sound but does not start.
Any ideas or suggests?
Answer -
Hi Steve,
A valve problem may have suddenly developed but let's try the easier things first.
You will need to determine if the problem is a lack of spark or a lack of fuel flow. Remove the spark plug, reconnect the wire and lay it against the engine head. Pull the engine over and watch for spark at the plug's electrode.
If good, then try to start it while squirting fuel or starting fluid into the carb intake. If it starts and you can keep it running by adding fuel, then the carb most likely has dirt, debris or gummed fuel inside.
First, check the gas cap to make sure it is venting and not causing a vacuum in the tank. If that's okay, you will need to remove the carb, disassemble it, clean all the small internal openings and blow it out with compressed air. Probe each and every hole with a small wire. A carb rebuild kit wouldn't hurt either.
If the spark and fuel are good then do a compression test to check the valves.
Let me know how you make out.
Michael
Michael,
I have a little more information... I read somewhere that you can test compression on a B&S by turning the blade backwards. You should feel a "bump" resistance. I tried this and feel some resistance but NO bump of any kind. I do hear a hiss of air escaping on each revolution. What are your thoughts on this?
Thanks,
Steve
Answer -
I have not heard of this, so I can't comment. Sorry.
Michael
Michael,
Here's where I read about testing the B&S compression...
http://faqs.custhelp.com/cgi-bin/faqs.cfg/php/enduser/std_adp.php?p_faqid=3433&p
Here's where I am now...
I replaced the headgasket, but did not help the problem.
I've watched how the valves are opening and closing and find that the exaust valve seems to NOT seat completely as it closes. I noticed there is a 1/16 (plus) gap at the valve stem end and the tappet when fully retracted. If I press on the face of the exaust valve, it will then close completely. I suspect the valve stem is binding, but the spring may also be weak. The intake valve seem to close completely on it's own. Does this sound like the cause of the bad compression? How do you suggest I proceed?
I also noticed that the underside of the intake valve seems to have a lot of deposits built up, but it doesn't seem to cause any seating problem. Should I be concerned about this? clean it off?
Also, I've removed the engine from the mower. Would you suggest opening the case and checking inside there while I'm at it? I was wondering if the time gear driff key might be a problem, but most likely not since I believe my problem centers around the lack of compression.
Thanks,
Steve
AnswerHi Steve,
Yes, if the exhaust valve does not close completely it would loose compression. There might be carbon build up on the stem. I would remove and clean it. The spring may be weak also. There is a spec for the uncompressed spring height.
The intake valve should be okay as is. I wouldn't open the case. The flywheel key may be partialy sheared and you could look at that but unless it kicks back while pulling the recoil rope or backfires out of the carb I wouldn't be concerned about that.
Keep me posted.
Michael
