Vanguard 20hp question

I have rebuilt the Briggs and Stratton V-Twin 20hp Vanguard on my generator. It had blown the head gasket on #1 cylinder and sucked the intake valve on the #2 cylinder. All went very well on the reassembly and the engine starts easily, even the first time. It has an ignition switch and the problem is when the key is in the run position it attempts to run too fast, popping and backfiring a little, when the key is turned to the off position it will not shut off but runs perfectly at the proscribed rpm. Even when under load (tested it with my stick welder when running with the key in the off position). I have triple checked the wiring and everything is in the correct position. It is a new ground wire loom on the ignition modules (I have not tested the diodes on it yet) and a new ignition switch. Just for comparison I put the old ignition switch on and it repeated the same behavior. I am suspicious of the rectifier/regulator being messed up but I'm not sure how that might be affecting this particular issue. It seems to run perfectly when the key is in the off position, very smooth and steady. Being that it powers a generator it does have a mechanical governor. Any thoughts or more questions would be very welcome. I'd like to get some ideas before I just start replacing parts. Thank you very much for any help or insight that you can give.

Seems to me that when you put it all back together you hooked something up wrong......... You did a good job on getting the genny itself off of the engine.... Those are a bugger at times..........

Try and retrace your steps on the wiring... It might be easier to see all of it if you take the gas tank off.......

Let us know Mon Ami ~!~!

Check that there is a ground connection to the ignition switch.
The switch should connect M ( magneto ) to G ( ground )
Check that the switch is actually doing this and that the terminals are in fact connected to the magneto kill wire & ground respectively.
When doing this is is a good idea to disconnect the magneto just in case you accidentially send battery voltage down the kill wire which will kill the magneto, for good.

OK here is a follow up for anyone who has followed this thread. The engine is running perfectly now but it took a little bit of work to figure it out. As can be typical it was a couple of things interacting that was causing the problem. First off the wiring was correctly placed and functioning well (for the most part, more on that later). I thought the engine might be running a bit fast so I purchased an optical rpm reader, placed a piece of reflective tape on the flywheel and found that the engine was running at 4800 rpm, about 1200 rpm more than the recommended unloaded rpm. This got me checking the governor and even though it had been reassembled exactly as it had been, on engine reassembly the adjustment had gotten off just a little bit. All that was necessary was to loosen and reset the external rotating arm that attached to the governor's rotating shaft that exits from the crankcase. I took this time to verify the correct placement of the primary and secondary control springs on the rotating control arm and then set the correct and final rpm with the adjusting nut. So far so good, now the engine was running smoothly at the proscribed rpm (3600)

Next was trying to solve why it would not shut off, at the elevated rpm I was not able to discern that it was only running on one cylinder when the key was turned off. When set at the correct rpm it became evident that when the key was turned off it was still running but just on one cylinder. This would be a symptom that one of the diodes on the engine wire harness was bad. Pulling a spark plug wire isolated that it was the #1 cylinder that continued to run so a close look was taken at that side of the wiring harness. As a note, this was a brand new wiring harness that had been placed just a few weeks ago. When removing the lead from the ignition module I noticed something just didn't look right so I removed the insulation off of the connector and found that the wire had broken inside the insulation. I re-crimped and re-soldered the wire to the connector and placed new shrink wrap insulation. I placed the connector back on the #1 cylinder ignition module, started the engine which still ran very smoothly at the correct rpm then switched the key off and the engine shut off correctly. Hooray!! Success and all systems are operating correctly and well.

I did use a factory shop/repair manual which was very helpful in sorting everything out and confirming correct placement of all components and wiring. If attempting an extensive repair like this I strongly recommend purchasing a manual. Thank you for the input and I hope that this can help someone else. Greg

Great information, tks.

Very dissapointing about the harness.
Well done "Mr Homes"
And thank you for final "all Good Now" post as it closes the thread and makes it a valuable resource for others.