16hp briggs help needed

[hybridv8]

Hi,i am having a problem with my 16hp briggs on my simplicity tractor and am in need of advice/help,it has not run for a couple of years and was mothballed because of erratic running issues,so I decided to spend some time on it and bought a brand new flojet carb and a new electronic coil,I fitted the coil and carb and fired her up she ran a bit erratically which I expected as the carb needed tuning while turning the fast jet screw it started popping back through the carb so I wound it in again and it stalled now when I go to start it as soon as it fires it locks up and chews up the plastic teeth on the starter as soon as it happens it is free again until it fires again then immediately locks up for a second any thoughts would be appreciated.

[4x4forks]

sound like the ignition timing is too advanced. it was ok with it being rich mixture as it was a slower burn. Now you have leaned out the mixture is is a much more efficient and faster burn and is having the effect of locking up. Try retarding the ignition timing .

[hybridv8]

When I first fitted the coil it ran quite well until you increased the revs then started popping back through the carb,after it stalled I turned the fast jet screw back to where I started but then the locking up started I didn’t alter the timing from when it was running ok at idle,I have just been on the briggs and Stratton web site and they are suggesting that popping back through the carb is usually a sheared key on the flywheel which would alter the timing,so could be an engine out job as I cant get to the flywheel in situ

[charlie]

Are the valves and seats in good order?

[hybridv8]

I took the head off late last night and the valves seem in good order they seem to work properly ( they go up and down as the engine is rotated ) but when the magnet on the flywheel is directly below the coil the piston is almost at the bottom of the bore surely that’s not right.I am assuming that when the magnet passes the coil it generates a spark so for combustion to occur the piston needs to be somewhere up top, I am not really a petrol person so not sure most of what I have is diesel apart from these and they only come out occasionally, (should get them out more ).

[trusty220]

You really do need to remove the flywheel to check the key hasn’t sheared. The keys are made of aluminium so that they can shear if the engine encounters a shock loading (like the mower blades hitting a brick); if the key was of the more usual steel type the shock loading would cause the flywheel to crack instead.

If you find that the key has sheared don’t be tempted tp replace it with a steel one- the proper aluminium ones are cheap enough and readily available.

[hybridv8]

I removed the engine and with a good puller and a lot of heat finally got the flywheel off to reveal a sheared key,after looking online it appears the keys can shear for no other reason than a backfire,hopefully when I have sourced new keys I can have another go at sorting the carb out,many thanks to all who replied.

[hillsider]

If you can do so it would also be a good idea to return the carb settings to their initial setting positions. With a new key fitted you may find the engine will run better any way and not need too much adjustment once the timing is correct.

For future reference it is helpful to let us know the Model,Type and Code numbers of when seeking advice about Briggs and Stratton engines it helps with identifying the engine and then giving the correct information.
Good luck.

[Author]

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