# 18 hp briggs no spark



## weverling (Sep 21, 2008)

I have an old (1985) briggs and straton engine that has no spark when it gets warm. After it cools off, it starts fine, then either dies as I'm cutting the grass or upon a restart when hot. Any thoughts?


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## Midnight Tech (Dec 31, 2001)

Does it have a point-type or Magentron ignition system?


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## MrChooks (Apr 19, 2008)

:wave: These kind of come & go problems can be a total PiA - :upset:

You need to check on the ignition type as suggested by Midnight tech - coz if you are lucky - it might be no more than a dud condenser or transistor (depending on ignition type) - and whilst a bit of a fiddle to replace - they are usually relatively inexpensive. - so worth a shot as a 1st approach. 

Also - before buying any new parts - thoroughly check that every part of the ignition circuit components are securely connected - that means that the wire connectors are good and tight and that where ever the component/s casings (particularly the condenser if fitted) is properly grounded. To do this - just unscrew the mounting screw - rub the connection surface with some fine sand paper and reinstall. (I mention this coz years ago I had a vile Villiers engine that did the same thing and after years of messing about - I finally stripped the mag and found that the condenser wasn't mounted tightly to the frame - that meant that when the engine (magneto) got hot - the earth connection would fail and the @#$%n engine would just stop and refuse to restart until it got cold:upset::upset::upset:


If that doesn't work - one would have to start suspecting the magneto coil / windings - and that is a major PiA - sorry but it is:sigh:

Pls let us know how you get on


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## weverling (Sep 21, 2008)

Thank you both for the advice. I take it the condenser is under the flywheel, which means, among other things, it has to come off. Right now, it won't start at all, although it cranks great. I even tried disconnecting the wire from the ignition switch and other devices that kill the engine with no luck. Again, thank you all for your help.


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## weverling (Sep 21, 2008)

another quick question, is can a brigs 12 hp engine go where a 18 hp was. Meaning is the shaft the same size and I assume the frame was stamped for more than one engine.


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## MrChooks (Apr 19, 2008)

:wave: Yea - all that ignition stuff is under the flywheel :sigh: (you can try the B&S web site for a parts list / exploded view which should show you where all the bits sit).

OK just for completeness - before starting the ignition system strip down - take the plugs out - leave the ignition leads connected and hold the side of the plug against the engine block (to earth) whilst cranking the engine you should see the plug spark across the gap - if no spark (as we suspect) then you will need to get into the ignition system 

To get the flywheel off YOU MUST USE A FLY WHEEL PULLER!!! coz attempting to pry it off will cause damage. :4-thatsba:4-thatsba 

Fly wheel pullers are usually no more than a piece of flat steel with a couple of outer engaging holes to secure the flywheel and a centre threaded bolt hole & bolt that you screw in to gently force the flywheel off the crank shaft. If you are a little handy - they are easy enough to make - just measure the hole spacings, drill the flat bar steel and get the correct bolts to engage all the threaded holes. B&S site might have a diagram of a flywheel puller - but their layout should be fairly obvious once you have a good look at the flywheel face

On the 12hp vs 18hp question - that is a HUGE difference in power output - so whilst it might fit shaft daim etc - I would be surprised if it would come near pulling the load that the 18 hp engine was installed on.

Whilst I would not recommend do it - if the load is a mower or shredder etc - and you are desperate - it might be worth a try provided you were EXTREMELY GENTLE with it. 

*If its on a generator set - just forget it* Coz the alternator would be designed to "pull" about 80+% of the 18hp output and if you were to connect a 12hp in its place - the voltage / current output would be a mess (read = trash all your connected appliances)


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## MrChooks (Apr 19, 2008)

Hold on - I might have lead you astray:sigh::sigh: if so - many apologies - 

You might be in luck - I just checked and depending on your engine model your ignition coil and parts might be on the outside of the flywheel - saving the need to remove it - if so, they may be located just under the flywheel cowl - in which case the whole job gets a lot easier - see link below

http://faqs.custhelp.com/cgi-bin/faqs.cfg/php/enduser/std_adp.php?p_faqid=3426&p_created=1098407641


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## weverling (Sep 21, 2008)

Hey, thanks again. I'm going to start tearing into this mower tonight so I'll let you know what type of configuration it has. I did put a inline voltage tester ( neon bulb) to see if I was getting any spark. During the day, I couldn't see any spark at all, but at night, the faintest glow was seen. I really don't think it's enough to do anything though.

Anyway, thanks again!


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## MrChooks (Apr 19, 2008)

:wave: OK the neon was a test that at least confirms the problem area - so once you get into the ignition and satisfy yourself that all the leads and connections are OK - next items are the replacement of the transistor unit (as a 1985 build I assuming that your engine is equipped with a transistor ignition) as magneto coils rarely fail - and are generally more expensive than the transistor unit.

Good luck with it and let us all know how you get on


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## weverling (Sep 21, 2008)

The electronic ignition must be in the coil because there were no points on this thing. Anyway, to make a long sad story shot. I ended up replacing the coil and also rebuilding the fuel pump in the carb. I think the big one was the starter though. It had a egg shaped bushing in the starter that might of been the smoking gun. It was causing the starter to drag and lower the battery voltage. After repairing the above, the darn thing works like a song. Who would of thought? 

I do appreciate all your pointers and help. Thanks again


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## MrChooks (Apr 19, 2008)

:wave: Well done indeed

Sorry none of us picked up on the starter motor issue - although that shouldn't have affected the magneto spark - so my guess is you efforts with the magneto got your spark sorted out and your efforts with the starter have headed off a future impending problem - so well done indeed ray:


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