Briggs and Stratton 3.5hp lawnmower engine wont start.

G

grover

Forum Newbie
Joined
Sep 27, 2016
Threads
2
Messages
8
  • / Briggs and Stratton 3.5hp lawnmower engine wont start.
I have been given a lawnmower with a B & S 3.5 engine but I cant get it to start,
I checked the sparkplug and its new, I checked the spark with a tester, and thats good, I replaced the petrol tank and carb, with one from a good lawnmower.
As I was trying to start it, it kept on backfiring out of the carb, so I thought the timings a bit out. I checked the blade for damage, and its ok, so I removed the flywheel to look at the key, and it was perfect, not a mark on it.
Then I thought if its backfiring through the carb the inlet valve is not closing properly, or sticking. So I removed the head, and reground the valves, and set the valve lash. When I tried again to start it, it was just the same. Anyone any ideas of what it could be gratefully received...
 
Boudreaux In Eunice La.

Boudreaux In Eunice La.

Lawn Addict
Joined
Jul 22, 2017
Threads
21
Messages
2,154
  • / Briggs and Stratton 3.5hp lawnmower engine wont start.
Intake tube might be loose or cracked causing it to suck air !!!!!
 
W

WyrTwister

Member
Joined
Aug 1, 2017
Threads
2
Messages
17
  • / Briggs and Stratton 3.5hp lawnmower engine wont start.
If it had hit something , with the blade , it is common for the key between the flywheel and top shaft , to sheer & the flywheel move ( rotationaly ) in respect to the top shaft . Rhis throws the ignition timing off .

Pull the rope starter assembly off and check . I made a puller to get the flywheel off ( after I removed the nut at the top shaft ) .

The keys are inexpensive and available at Ace Hardware & other places that sell mowers & supplies .

God bless
Wyr
 
Boudreaux In Eunice La.

Boudreaux In Eunice La.

Lawn Addict
Joined
Jul 22, 2017
Threads
21
Messages
2,154
  • / Briggs and Stratton 3.5hp lawnmower engine wont start.
Grover you said you reground the valves.... Were you very careful not to get any grinding compound down in there ??

The only other thing to keep it out of time is the cam shaft is damaged in some way. Those plastic cams are epoxied together and can move on you. Example The lobes will be in a different spot because the gear wheel can rotate on the shaft part of the cam. You will have to compare it with a known good cam and look at it very closely.
 
G

grover

Forum Newbie
Joined
Sep 27, 2016
Threads
2
Messages
8
  • / Briggs and Stratton 3.5hp lawnmower engine wont start.
WyrTwister said:
If it had hit something , with the blade , it is common for the key between the flywheel and top shaft , to sheer & the flywheel move ( rotationaly ) in respect to the top shaft . Rhis throws the ignition timing off .

Pull the rope starter assembly off and check . I made a puller to get the flywheel off ( after I removed the nut at the top shaft ) .

The keys are inexpensive and available at Ace Hardware & other places that sell mowers & supplies .

God bless
Wyr
Click to expand...

Hi Wyr, Ive checked the blade and key, and its ok, and also like you I made a puller, to get the flywheel off.
The key was one of the best I have seen, not a mark on it. I was disappointed as it was my last hope after I had done the valves, so I will have to investigate further, but have put this on the back burner for now, as I have a good lawnmower to use. Thanks for taking the time to reply.
Best regards Grover.
 
G

grover

Forum Newbie
Joined
Sep 27, 2016
Threads
2
Messages
8
  • / Briggs and Stratton 3.5hp lawnmower engine wont start.
Boudreaux In Eunice La. said:
Grover you said you reground the valves.... Were you very careful not to get any grinding compound down in there ??

The only other thing to keep it out of time is the cam shaft is damaged in some way. Those plastic cams are epoxied together and can move on you. Example The lobes will be in a different spot because the gear wheel can rotate on the shaft part of the cam. You will have to compare it with a known good cam and look at it very closely.
Click to expand...

I cleaned the valves & seats etc well before re-assembly. I am coming to the conclusion like you say that its some sort of problem with the camshaft/gears.
I will remove the bottom plate and have a look, but I have put this on hold for now, as I have a good lawnmower to use.
Thanks for your help.
Best Regards Grover.
 
G

grover

Forum Newbie
Joined
Sep 27, 2016
Threads
2
Messages
8
  • / Briggs and Stratton 3.5hp lawnmower engine wont start.
grover said:
Thanks, for that I will have a look at it.
Click to expand...

I had a look at the tube and it was ok. The bolts holding it on were slightly loose, so I tightened them, but it made no difference.
 
You must log in or register to reply here.

Footer Links 1

Top