OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines GMC Mower - with a Briggs and Stratton Engine

Just after a few thoughts on this GMC Mower with a Briggs and Stratton Engine. The previous owner indicated the mower had problems when the engine got hot (apparently after about 20 mins of mowing). He indicated it would suddenly stall and then become hard to re-start.
My initial thoughts were in relation to the ignition coil however he indicated a new coil had already been installed. I must admit I haven�t given the engine a full once over yet as I was after some thoughts before I start.
The mower and catcher are in good condition and appear to have been reasonably well looked after.
As it is the mower starts relatively easily however I haven�t taken it for a good run yet.
I also have a small dilemma with a catcher flap which needs to be repaired.See the photo. Any thoughts on the repair process would be appreciated. I was thinking of riveting a small section of plastic to the cover however I�m open to thoughts. I would like the end result to be neat and tidy
Sorry Grumpy I don�t have the exact engine codes on me at the moment however I will get them tonight and post them up.
Thanks

Hi Jaffa, here are some ideas. Start with the simple checks before you get into the more complex stuff. Determine whether the problem is ignition or fuel related, and finally whether it's a mechanical issue.. Hot run it and let it die as he says, prime it 2-3 times:- does it restart, check for spark, try a new plug, check the kill switch is not shorting out(i believe most of those models had the safety brake so the kill switch has been re-routed to the throttle plate up front if it did):- does it restart, check flywheel to coil airgap, check the keyway.
When you try to restart after its hot does it spin freely or is the engine binding, like its overheated or partially seized. Is there oil in it?
I cant see it being anything toooo major. good lck and let us know how you get on.

Thanks Theo.
I started with the basic checks like I normally do in order to assess the condition of the engine.
1) Gave the unit a thorough clean (pressure wash and air compressor afterwards)
2) Re-gap the coil and replace the spark plug
3) Cleaned the carby and replaced the diaphragm.
Everything else visually looked to be fine however upon trying the engine it wouldn�t start up. It popped lightly and tried to start but didn�t. I then went to check the spark and it was weak and erratic. That is the best way I can think to describe it.

It led me to believe the original coil was never replaced like the previous owner indicated. I think he may have been quoted a price and never followed through with the repair. The original coil was also corroded on the surface so this led me to believe it was never replaced.
I then switched over the coil and voila the engine ran perfectly. I then gave it a good test to try and simulate the previous faults and nothing���.. no faults whatsoever.
Iv included some pictures of the finished product. Apart from a pretty flimsy catcher, it chewed up long grass with ease down the back of my suberb. The 4hp motor now runs really well!
Next question, can something cause failure of the coil and is there a reliable test I can conduct to determine the coils condition as I have not found a failed coil on this type of unit before.

Peter, failed coils are not all that common on these bad boys, although even if we had the "thing" that tests the coil, yours would probably show up as ok, until it got hot. So in my opinion, and in the absence of a coil tester, the best check is to hot run it. if you can work the mower for 20-30 mins and the coil doesn't fail then it probably wont fail at all. They normally fail within the first 10-15 mins of running when they're dodgy.
Looks like you've got another one there ready for a new home.

Appreciate the explanation. I hot run all my mowers over at least 15 to 20 minutes to ensure they are right to go so if I keep following that principle I should be right!

Excuse the thousand questions, I like to be thorough.

If you want to process a run-of-the-mill engine like that one and get it out of the place fixed, the quickest way in my experience so far, is to keep a set of "known good" comparison parts. So, first do the obvious simple tests: does it have spark, does it have compression, will it run briefly if primed with petrol? Usually the problem is obvious at that point, but if you suspect a problem that only arises under load or after warm up, change the component you suspect is at fault with your comparison part (in this case, the Magnetron, but more often, the complete carburetor/fuel tank/air cleaner assembly). Give it a decent test run with the comparison part installed, and if the fault has gone, you know with high confidence which part was at fault. Do not leave the comparison part on the engine though, or you'll no longer have a known-good comparison part for next time. Remove it, empty the fuel out, clean it, and put it away safely.

Thanks Grumpy,
I am slowly getting together a good collection of working parts which I keep as spares to do testing with faulty mowers. Its only a hobby for me so it will take some time. I am in no rush.