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Briggs Opposed Twin's


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#1 kenbhall OFFLINE  

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Posted September 01, 2012 - 02:08 PM

Anyone ever had a problem with a Briggs opposed twin not starting after running for a while and being shut off ? I have acquired my second twin with this problem everything seems to look good but I seem to get a weak spark after the engine gets worked. I should explain that they both run fine until you shut them off , they just won't restart till they cool down.

#2 bowtiebutler956 OFFLINE  

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Posted September 01, 2012 - 05:41 PM

Almost sounds like the plugs are getting a little fuel fowled, and have to dry out before it will restart. Have you tried pulling the plugs when it won't start, to see what they look like?

Matt
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#3 kenbhall OFFLINE  

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Posted September 01, 2012 - 06:10 PM

I have previously replaced the plugs while the engine was still warm and had the same results. its not a big problem but I really dont like being stumped by a small engine.

#4 Rock farmer OFFLINE  

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Posted September 01, 2012 - 06:17 PM

I don't quite understand, it cranks but won't fire?
Or doesn't want to crank?
I've had problems with the starter/ignition switch which will do that.
Corrosion, loose posts, things like that.
What's it doing?

Joe
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#5 kenbhall OFFLINE  

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Posted September 02, 2012 - 05:25 PM

It cranks just fine just weak spark but only after it has run for a while and has been shut off. it has never died while running,as a matter of fact it runs strong till you turn it off . It seems like a strange problem to me.

#6 John@Reliable OFFLINE  

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Posted September 02, 2012 - 06:24 PM

I would test the coil when it happens again. But first I would take apart all all electrical connections to clean and re-tighten, don't forget the grounds. Also look for bad wires/wiring.
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#7 Tennblue59 OFFLINE  

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Posted September 05, 2012 - 04:18 PM

Coil going bad. I had a craftsman (briggs l head 18hp) that did the same thing. Ran fine as long as you want UNTIL it shut off, then had to cool off before it would start again - poor spark. It was explained to me (sounds plausible...) that the coils on some of these engines are in a spot where they get a lot of heat, which tends to break the insulation down over time. As they get warm, the situation gets worse.

As long as the engine is running, it turns enough rpms and power to keep the spark going. But the demands at startup (lower voltage, voltage to the starter, lower rpms, etc) cant get past the coil's internal leakage. Eventually the coil would fail altogether.

I replaced the coil in mine and it ran fine for a few more years until the body rusted out from under it.....

If it is hard to CRANK when hot, that may be valve adjustment or weak starter/electrical system. But if it spins fine, I would check the coil.
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#8 wvbuzzmaster OFFLINE  

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Posted September 05, 2012 - 07:52 PM

No coils on those bad boys that I know of. I know my Briggs opposed twin has issues restarting. I rebuilt the carb, replaced the plugs, and done all but rebuild the motor. I learned one thing about them, best to just let them sit running when you get off to do stuff, unless you plan to stay at least 20-30 minutes. Get to know your machine's quirks, and learn to live with them, and love them for them. Don't try to fix them all, just refine how you deal with them.
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#9 Tennblue59 OFFLINE  

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Posted September 05, 2012 - 09:21 PM

WVBuzzmaster, many of the opposed twins used a magnitron armature-magneto - that is what I am talking about as a "coil". Older ones used a points setup, newer ones used a capacitive ignition built into the magnetron.
Sorry, should have used the proper terminology....

On my craftsman/briggs (a 42A707 19hp L head opposed twin), there was ONE magnetron coil that supplied both cylinders and had two sets of plug wires coming out of it - one for each cylinder.

Edited by Tennblue59, September 05, 2012 - 09:28 PM.

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#10 DH1 OFFLINE  

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Posted September 05, 2012 - 09:35 PM

I believe that these engines fire both plugs at the same time, every RPM,
Only 1 cylinder will fire, power stroke, then next RPM the other cylinder fires on it's power stroke.
I have one of these engines, 18hp opposed twin and I find it reliable, predictable, starts every time, but you need a good battery to start it when it's cold.
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#11 larrybl OFFLINE  

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Posted September 05, 2012 - 09:46 PM

OK, Just chiming in, I own three of these, all rebuilt. Granted, they don't like to start when warm/hot. They do not have a compression release, and the valves are not adjustable (stem grinding is required). with that said.... My Red is acting the same way. I plan on upgrading the battery from a 235 CCA to a 420, That worked wonders on my "Blue Money Pit". Make sure all your connections are good - including grounds, Airfilter is clean, Carb is adjusted, (wouldn't hurt to install new plugs) and the Starter in good shape.
The flywheel needs to spin fast when starting for the magnatron to provide a healthy spark.
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#12 wvbuzzmaster OFFLINE  

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Posted September 05, 2012 - 09:48 PM

WVBuzzmaster, many of the opposed twins used a magnitron armature-magneto - that is what I am talking about as a "coil". Older ones used a points setup, newer ones used a capacitive ignition built into the magnetron.
Sorry, should have used the proper terminology....

On my craftsman/briggs (a 42A707 19hp L head opposed twin), there was ONE magnetron coil that supplied both cylinders and had two sets of plug wires coming out of it - one for each cylinder.

I have fried one of those, and had to replace it. I also replaced spark plugs, all my electrical system, and rebuilt the carb. All has helped in starting it, but it still doesn't like to restart, so it is just a matter of learning to live with your machine's quirks.

Edited by wvbuzzmaster, September 05, 2012 - 09:49 PM.

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#13 DH1 OFFLINE  

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Posted September 05, 2012 - 10:17 PM

Here's a Video of my 18hp B&S starting after just finishing cutting grass, and the motor is hot.


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#14 DougT ONLINE  

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Posted September 06, 2012 - 07:14 AM

I agree with the coil problem. Had the same thing happen on my JD 116. The coil does fire both plugs every time. It was recommended to run the plug gap at .025 instead of .035 to have less stress on the coil.
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#15 kenbhall OFFLINE  

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Posted September 06, 2012 - 02:37 PM

thanks for all the input guys I feel better knowing I'm not the only one experiencing this :laughingteeth: , I do love the Briggs twins pleanty of power and they do run good. the latest one is on a used walk behind mower I picked up real cheap as a back up mower for my son's lawn care business. So frequent starts and stops are the norm for it. maybe I will just switch engines on that and keep the twin for a later transplant




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