Briggs 18 ignition problem

BuggyBrain

Hello:
I wonder if anyone could help me with a problem a friend is having. The cart is a Yamaha G9 with a Briggs Vanguard 18 V-twin.

What happened: Cart hit hard bump at high speed & died.

What we did:
1. Cleaned carb which was full of dirt & installed an inline fuel filter. Pump is good & motor getting plenty of gas.
2. Motor then ran on only #2 cyl until twisting the plug wire around & then it ran fine on both cyls. Twist wire one way & #1 misses. Twist other way & #1 hits. Bad plug wire &/or coil, right? No.
3. Both plugs are good & both fire. (New set).
4. Replaced coil on #1 cyl.. Motor now started & ran on #2 cyl. only. Cart now won't shut off.
5. Checked & replaced both grounding wires to both coils. Same problem, won't shut off & runs on #2 cyl..
6. Checked ground (shut-off) wire from key switch. No problem there, grounded when off, no ground when on.
7. Put original coil back on. Engine now runs on #1 cyl again & #2 is now dead.
8. Put new coil on #2 cyl. Cart now won't start at all. Backfires thru carb & exhaust.
9. Unhook ground wire to #2 coil & cart runs perfectly (#1 cyl. will now shut off with key leaving motor running on #2 as expected.)
10. Unhooked both ground wires from main wire to key switch. Cart runs perfect. Ground #1 wire & #1 cyl dies. Ground #2 wire & #2 continues to fire. Touch both ground wires together & it kills both cyls. dead.
11. Tested all coils with tester & all test out good.
12. Switched coils (new back on #1 & old on #2) & same problem exists on #2. Problem stays with #2 cyl.. Engine runs perfect with neither coil grounded. Ground #1 coil seperately & #1 cyl dies. Ground #2 coil seperately & it continues to fire as before. Touch both ground wires together & motor dies.
13. Gaps between coils & flywheel are good. Both plugs are good (tried another set to be sure).

I hope this makes sense. Have tried to break it down as clearly as possible. Any thoughts? Had a small engine mechanic (Briggs parts dealer) looking at it & he ran out of ideas other than perhaps a sheared flywheel key. The only thing is, it runs perfectly when neither ground wire is hooked up & indeed runs fine if you hook only #1 ground wire to key switch (#1 will then shut on & off with the key). Touch #2 wire to #1 wire & both cyls die. Gound only #2 & nothing happens at all. #2 runs along on it's merry way. In short, if #1 & #2 wires touch either directly or via ground circuit, engine dies whether key is on or off. Unground/unhook #2 ground wire & engine purrs. Just won't shut off. Note: Engine charges fine & have checked all plugs/connections. Have found nothing. What gives?
Mike (BB)

2stroke

From what I can understand, problem lies in ground wire to #2.

Barracudas

We think we have the solution to this problem now, I want to say a BIG THANK YOU to Buggybrain. It was our vanny that he was trying to fix.

Barracuda

TheNewGuy

Hey Barracudas, haven't seen you on in awhile.

What was the solution??

Ron

If you can't run with the BIG DOGS...stay on the porch

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Barracudas

Yeah, it's been a while. Grad school and my restless 5th graders keep me busy, and the crime in the city keeps my husband's job the same way. It turns out we need to replace the whole wiring harness since the wires have these "diodes" in them that prevent the problems that we were having from occuring. Hope to pick up the part from a briggs dealer today.

Cuda'

TheNewGuy

I can barely remember 5th grade LOL (some time ago) I feel sorry for you!!!!

Let us know how the wiring harness goes. I haven’t had any problems with
my 18 hp so far…..knocking on wood!!

Ron

If you can't run with the BIG DOGS...stay on the porch

Please Visit Our Sponsors

TheBadBoyG9 * Frame Mod * New Exhaust
Marathon Project

Barracudas

Will keep everyone posted. This whole thing started when DC was showing off to some buddies of ours and he hit a bump real hard. The cart just quit, the airfilter was trashed, the box was full of dirt and dust and some dirt got into the carb. (See BB's post) then next after all that was the ignition. Just hope to get it running again and home for the winter soon, so it can get some TLC.

Cuda'

UBERCART

Check the diode thats goes in between the 2 coils.

Barracudas

All fixed, new harness is isntalled. Runs like a champ again.

Cuda'