B&S Vanguard spark problem

[rstrauss]

I need some help on this problem. Engine is a stock 20HP Vanguard, horizontal shaft, Nikki 2 bbl carb, model 351447-1180-A1.
I bought it used. It would start and run.

After getting it home I pulled the spark plugs. #1 was black, smelled of gas. #2 looked good - nice light brown color.
I put a spark tester between the #1 plug wire and plug - plug was firing. But, if I pulled #1 plug wire off when the engine was at idle, the engine ran at the same rpm - no change at all. If I pulled #2 plug wire off the engine stopped.

I switched spark plugs from side to side. Same conditions applied, except the black plug changed to light brown when put in #2 cylinder.

I tested #1 magneto: 5.8K ohms.
Valves are adjusted to 0.005"
I checked the diodes in the kill wire and both are good.
The magneto is set at 0.010" from the flywheel magnet.
Carb idle mixture screws are turned out 3/4 turn.
Idle speed is 1200 rpm.
Compression is 140 psi in both cylinders
I have cleaned the carb (ultrasonic cleaner), new float needle, checked that the float does indeed float level in a container of water.

With the muffler off, I can see occasional blue flame at #1 cylinder exhaust port. Not so much at #2 exhaust.
Engine rpm wanders, some times increasing, settling back to idle.

So, I'm asking for possible solutions to my problem. I think it's ignition related. Other opinions?

 

[bertsmobile1]

First step is to remove the cut out wires and see if that makes a difference
Remember you will need to put one back on or use a jumper to earth to stop the engine.
Problem gets better then replace the cut out wires & diodes.

No joy then sap the coils over they are usually identical.
Problem moves to No 2 then you have a duff coil.

Still no joy the measure the height of the valves, fully open & fully closed.
Chances you have a bent pushrod or sticky valve on No 1

If the exhaust does not open fully you will still get a nice high compression reading but it will choke the engine.
usually you will see blow back through the carb but this is hard to pick now that decompression also blows back through the carb.

 

[NorthBama]

not saying this is your problem but I had a B & S with 2 barrel Nikki that was only sucking fuel into cylinder on one side. Engine would only run on one cylinder. Could be something to check if you have good spark and good compression.

 

[pugaltitude]

So you know the problem is cylinder one.

Try swapping the coils. A spark tester would give a quick easy test to know the coils are working.
I would go with a compression related component like valves or possibly a valve seat.
The seats can and do fall out.

3 components that are common on both cylinders is ignition timing, crankcase pressure and usually carb (if single barrel) so that would effect both cylinders.

Components not common would be coil, and compression components for each cylinder (valves, head gasket, rings).