Briggs 31P777 0293 Ei Backfiring

Reply

  #1  
Old 05-23-14, 10:30 AM
Member
Thread Starter
Join Date: May 2014
Location: USA
Posts: 6
Question Briggs 31P777 0293 Ei Backfiring

I have a Yard Man Rider mower with the 18.5 HP OHV engine that won't start. When I try to start it sounds like the timing is off & pops back through the carb. I have adjusted the valves. Pulled the head & cleaned & reseated the valves. Tried different coils. Cleaned & went through the carb. Replaced the flywheel key. Adjusted the valves 3 or 4 times. I'm fairly new to working on mower engines but worked on cars & truck for 40 + years. Has me confused. Any help would be greatly appreciated. Thank

I'm a newbe to the group. I retired after owning & working my Auto Repair shop for 38 years. Got bored after a year or so & started working on Riding mowers last year. Married to my girlfriend for almost 46 years. Have 1 son who's in his 40s. We live in Sunny Western New York.
 
Sponsored Links
  #2  
Old 05-23-14, 09:27 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,821
Have you tried a new plug? Sounds like you've done everything else that would possibly cause your problem. If it's an NGK plug, take it out and put a champion or autolite in.
 
  #3  
Old 05-24-14, 08:38 AM
Member
Thread Starter
Join Date: May 2014
Location: USA
Posts: 6
Forgot to put that in the list. I did try 2 new plugs. Could the wrong magnetron cause it to pop back through the carb? Once in a while it attempts to start at real low throttle position. It will try to run a little then it pops back though the carb again. Oh I only use Champion plugs in all my engines. I've been told it's an internal problem but I can't figure out what could be wrong inside. I don't think the cam gear could spin on the cam shaft but that is the only thing I think could cause it to act like it does.
 
  #4  
Old 05-24-14, 06:32 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,821
What happened prior to this? Was it all working fine and one day you went to start it and this is what happened? How far do the valves open and close? It sounds a lot like it could have a wiped out cam lobe.
 

Last edited by cheese; 05-25-14 at 08:24 PM.
  #5  
Old 05-25-14, 11:06 AM
Member
Thread Starter
Join Date: May 2014
Location: USA
Posts: 6
Briggs 31P777 0293 Ei Backfiring

It was supposed to be running then 1 day then it quit. I checked the valve movement & it goes through the 4 strokes in proper order. Int, comp, power & exh. I pulled the head & it looked like the intake valve wasn't seating. I reground the valves & lapped them in. They were seating good. Put it back together & adjusted the valves to 004 intake & 005 exhaust. Tried to start it & it will attempt to run as long as I keep cranking with the starter. I tried starter fluid & it does the same thing. If I hold my hand over the carb I can feel it sucking. Tried different spark plugs, coils, went through the carb 2 times. I'm totally confused. HELP!!!!
 

Last edited by calc1941; 05-25-14 at 11:47 AM. Reason: wording
  #6  
Old 05-25-14, 01:26 PM
Member
Join Date: Dec 2006
Location: Canada
Posts: 528
Is it possible that you are flooded? Perhaps the float or needle and seat in the carb are not working. That can create a condition where it papumps a few times when cranking but just won't start. It also eliminates the success of using starter fluid.

The best test for this would be to install a manual fuel shut off valve between your gas tank and fuel filter. Turn it off. Take out the spark plug and crank over the motor 10 or 15 times (be aware of the fire hazard here) to blow out any liquid fuel. Put the spark plug back in, open up the fuel shut off valve and quickly give her a go. If it starts up for you and quickly chokes and dies afterwards, then it is flooding. Remove the carb and see what's wrong with the float or needle and seat. If it starts up fine and runs fine after that, then just remember to shut off the fuel shut off valve when you are done mowing and you might not need to fix the carb. It just depends on how big the leak is.

If it doesn't start right up, forget everything I said.
 
  #7  
Old 05-25-14, 08:25 PM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,821
I understand it is going through the cycles, but how far are the valves moving?
 
  #8  
Old 05-26-14, 02:32 AM
Member
Thread Starter
Join Date: May 2014
Location: USA
Posts: 6
Thanks, That does seem to be what is going on .I've had the carb apart a few times & the float seems to be moving easily. I did put a shut off in the line but haven't tried it the way you suggested. I'll give it a try later today. I might have another carb to try.
 
  #9  
Old 05-26-14, 08:12 AM
Member
Join Date: Dec 2006
Location: Canada
Posts: 528
OK let us know how it turns out.

I should probably add that if I am right and the mower starts up, you probably should not run it too long. If it was flooding, some of that gas will probably have made it into the crankcase and dilute your oil. So you may want to change the oil when this problem gets resolved, if flooding was happening.

You should probably give the oil level a check to see if the level has risen and/or if it smells like gas. If it does, change it out before you run my test. It is only a few bucks worth of oil and you probably know the cost if that oil is too thin and diluted.
 
  #10  
Old 05-26-14, 10:52 AM
Member
Thread Starter
Join Date: May 2014
Location: USA
Posts: 6
By the movement of the rocker arms the valves are opening close to 1/4" to 3/8".
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes