OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S Quantum no spark

Hi all,

Time has come to brush the dust off the mower and tidy up the backyard a bit after winter.

I have a Morrison Briggs and Stratton Quantum, that will not start.

It seems I am not getting any spark to the spark plug. I have tried 3 different plugs and none of them get spark (I know they work as I tried them in other machines).

How is the spark created and what can I check?

Cheers
Sam

Please post the Model, Type and Code for your engine. These will be stamped on the cooling air cowl.

Essentially your engine has a Magnetron electronic ignition module, mounted just in front of the flywheel under the cowl. A magnet attached to the flywheel generates electricity as it passes the magnetic yoke which is part of the Magnetron. The same magnet triggers the spark as it passes the trigger unit of the Magnetron.

The usual cause of no spark with a Magnetron ignition is that the kill wire is grounded when you are trying to start the mower. The purpose of the kill wire is to ground the trigger unit, to stop the engine. However if the insulation is worn through or the governor plate connection to the end of the kill wire is messed up, the ignition might be killed all the time, rather than only when the speed control is in the stop position.

I suggest you trace the black wire that is attached to the governor plate (where the engine-end of the speed control cable connects) and watch its end terminal get grounded in the stop position, but not be grounded in any other speed control position. If it is working properly, trace it back to the Magnetron checking for insulation damage. If there is none, disconnect the cable completely and secure it so that it cannot touch anything, and test for spark again. If there is still none, you will need to check the grounding of the Magnetron, the condition of the high tension wire from the Magnetron to the spark plug, and the size of the air gap between the Magnetron and the flywheel (which should be the thickness of a business card). If none of these is the problem, it appears you will need to replace the Magnetron. This is a fairly rare outcome, though - Magnetrons are very reliable.

Thanks Grumpy for your reply.
Model: 100708
Type: 0140 01
Code: 87092205

I will check the things you suggested and get back to you.

Cheers
Sam

Is that the 3.5 hp quantum with vertical pull starter? For some reason I have had several of those with failed ignition units, if memory serves me right if the kill wire hasn't shorted to the engine a ignition coil from most quantums will fit.

Sam, your engine was made on 22 September 1987 in Briggs' Poplar Bluff, Missouri, engine plant. Because this date is later than 1982, it has a Magnetron ignition system. (Prior to that, Briggs engines had breaker points inside the flywheel.) Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6olxBVJ1DajI.pdf

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/mspCEM-K_ny7tH217FzoPu.pdf

As Joe thought, that model has a vertical pull starter. He has a great deal of professional experience repairing these engines, so from what he has said, the possibility of a failed Magnetron on that particular model is higher than I had thought. Nevertheless, I suggest you make those other checks first rather than risk buying a fairly expensive part that you turn out not to need. If you do need a replacement Magnetron, I suggest you report it here - Outdoorking members will probably have second-hand ones that might offer a better deal than buying one from a dealer.

Thanks guys,

yep it's the vertical pull start model. Turns out the kill wire was earthing out somewhere. Gave it all a good clean and put it back together and we have spark again

Starts fine and runs pretty well, it does have a bit of a miss every 30 seconds or so or sometime more frequently. I had another briggs that did much the same thing.

It's not really a big deal but is there anything I can do about it?

Cheers

Sam, in my experience Briggs side valve engines always miss an occasional shot, particularly at idle or light load. This appears to be simply due to rather marginal scavenging, which is probably to be expected in a side valve engine with a high bore diameter to stroke ratio. However except at idle it should be occasional, not frequent. (At idle I'd expect a miss about once a second, and at full speed light load, probably one every 10 to 15 seconds.) If you are irritated by that, the only cure I can suggest is what I did: get rid of all of your Briggs engines and buy only OHV Hondas henceforth. If in decent condition they simply never miss a shot.

haha,
thanks for that. yeah it does bother me a bit but now I know that it's fairly normal I' m not so worried.

I was just hoping there was an easy known solution, maybe I will keep and eye out for an OHV Honda.

Cheers

Just one point, Sam: I said OHV Honda, not OHC Honda. I think as a discriminating mower user, you would not be happy with an OHC model.