Vanguard v twin problem.

[fleehillfarm]

Hi everyone, I have a problem that's driving me mad. I have a Cub Cadet ride-on mower powered by a Vanguard V twin 20hp Briggs and Stratton engine. It will only start with a squirt of easy start and then runs normally for about 1 minute and then starts to smoke quite badly. Bluish or white smoke. I have done a compression test and both cylinders have 120 - 125 psi. A leak down test shows only 20% loss. So all appears to be good. Carb has been stripped down and thoroughly cleaned. Both magnetos have been adjusted. Good spark at one plug. The other had no spark until I removed the kill switch wire. So it does have a short somewhere  but that wouldn't cause the smoking or reluctance to start. I'm fairly good with the running of small engines but this one really has me beaten. Any advice or ideas would be much appreciated. Many thanks - Richard

[roys]

The only thing I can think off that you haven’t done is the inlet and exhaust valve clearances.

The carb on my Vanguard V twin needs stripped and cleaned about once a year, that is even after I added an inline fuel filter and a fuel preserver.

[fleehillfarm]

Sorry roys forgot to mention that I have adjusted the valve clearances on both cylinders. 

My first suspicion when the problem arose was obviously a blown head gasket but can an engine return a reading of 125psi with  a blown head gasket? I'm reluctant to take the head off to find out but maybe it's the only thing left to do. The carburettor is the Nikki type with fixed idle mixture valves and limiters in the top so that doesn't help as you only have a very limited amount of adjustment and they come to a stop. Maybe they have moved. If I forced them beyond the limitation does anyone know whether I would break something? Also could a bad idle mixture cause the smoking? Many thanks.

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[spudulike]

Now, bearing in mind the only Vanguard I know are the US investment specialist....was this engine playing up before you made any adjustments to anything?

Assuming not....white smoke...what does it smell of, burning oil smells like burning oil😬, It could be diesel in your fuel....that smells like paraffin as combustion leaves.... paraffin to exit the exhaust, water in the fuel can give all sorts of issues with running so drain off a bit from the carb float bowl in to a glass and look for the water at the bottom of the fluid...it is pretty obvious.

It could be a stuck choke, as I said, I don't know the engine but if the choke is stuck shut, white smoke and stalling is the symptom you get 100%.

Compare both cylinders for compression, leak down and plug colour. If the head gasket has gone in one, there will be a significant difference.

When you stripped the carb, did you pull the main jet AND the emulsion tube...those little holes can get blocked up.

I can't say I know that much about mowers😉

Good luck

[fleehillfarm]

Thanks for your thoughts spudulike. There's no water or diesel in the fuel and both cylinders were almost exactly the same in compression one was 120psi and the other was 125psi. In the leak down test both returned 20%ish leak which is quite  good for an engine 20 years old. Yes all jets were checked when the carb was off. Choke isn't stuck moving freely. Quite a puzzle this one.

[openspaceman]

Over full with oil? Can you  take crankcase breather off the carb and block the hole into the carb?

[fleehillfarm]

The oil level is correct. If I take the breather off the back of the carb and block the hole up what does that achieve? Sorry but I'm not familiar with that . Thanks for the input.

[openspaceman]

1 hour ago, fleehillfarm said:

The oil level is correct. If I take the breather off the back of the carb and block the hole up what does that achieve? Sorry but I'm not familiar with that . Thanks for the input.

If oil is not frothing out of the crankcase nothing.

[spudulike]

Have you looked at the plugs after the machine stops? Wet or oily plug on one cylinder may lead to a fault one cylinder. 

Blue smoke is usually oil and white is excessive fuel. 

It could be one cylinder not firing after a minutes running so dodgy coil....does it have two coils, is the coil to magneto gap nice and close as a large gap may make the coil only work when stone cold....seen this before on chainsaws.

[fleehillfarm]

Both plugs are looking the same. Both cylinders are working as I pulled off the spark plug covers when it was running. Smoke still absolutely pouring out of the right hand cylinder exhaust. So it's definitely the one cylinder that's the problem. Going to have to take the cylinder head off. Thanks for all the advice.