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Thread Like Summary
Beach, Gordon Gray, gREgg-K, NickL, RF Whatley
Total Likes: 6
Original Post (Thread Starter)
#851617 06/14/2021 10:52 PM
by Hillbilly bike
Hillbilly bike
I have been riding around a bit on the A10 project bike... Runs perfect ...except...after about 20 minutes the engine starts to misfires badly on both cylinders. This occurs at 3500 rpm regardless of throttle position or engine load. Below 3500 rpm it runs great and idles nicely. Fiddling with the manual advance does not clear the problem.The inductive electronic tach needle goes nuts when it misfires. engaging the cold start makes no difference...
The plugs look ok, no signs of obvious carb problems...
The K2F magneto was fully rebuilt, rewinding etc by a man i have used in the past. It came with a test report..
Non resistor NGK iridium plugs, solid core wires with non resistor terminals and so on...
I am going to change the plugs and check the points tomorrow...
Anyone have a mag act up like this?
Liked Replies
#851625 Jun 14th a 11:41 PM
by NickL
NickL
Capacitor packing up.
1 member likes this
#852962 Jul 3rd a 04:31 PM
by Magnetoman
Magnetoman
Originally Posted by Beach
No ignition coils on magneto bikes.
This comes as shocking news to me.
1 member likes this
#851636 Jun 15th a 03:03 AM
by Magnetoman
Magnetoman
Originally Posted by Hillbilly bike
after about 20 minutes the engine starts to misfires badly on both cylinders. This occurs at 3500 rpm regardless of throttle position or engine load. Below 3500 rpm it runs great and idles nicely.
Rather than the capacitor, it sounds like when it gets hot the insulation is giving up at higher rpm (i.e. higher voltage).
1 member likes this
#853115 Jul 6th a 12:08 PM
by RF Whatley
RF Whatley
This is why you need a magneto armature tester. You can "run" the armature on the bench at varying speeds, look for insulation breakdown, and swap out the capacitor while it's breaking down.

[Linked Image from i.imgur.com]

The machine doesn't lie.
1 member likes this
#853141 Jul 6th a 04:46 PM
by Magnetoman
Magnetoman
To put in a, ahem, plug for magnetos, the one for my Ariel sat totally neglected on the shelf for nearly three years, but the bike started on the first kick once the bike was back together. Try that with a battery ignition system.
1 member likes this
#853157 Jul 6th a 09:03 PM
by Hillbilly bike
Hillbilly bike
The double engine racer I built has sat in my rider's pub since It's last race on July 25 2018. it has a onboard lithium iron battery that has not been charged since July 2018...with Pete Suchawreck from this site as a witness, I pressed the starter button , the Harley starter motor turned over two high compression Triumph engines with Pazon Smartfire ignitions with no problem. The engines started so quickly we both jumped back....The bar patrons also were startled, some beer was spilled, lol. I had no idea a lithium battery could hold a charge so long.
But a magneto can still fire some engines after dozens of years...
1 member likes this
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