Piston Rings? Valves? Timing? All Three?

[Big T]

The most common cause is overfilled oil, or gas in the oil
Could you post up a picture of all four of your spark plugs?

 

[Isoparmesan]

Spark plugs are all sooty, it’s definitely running rich (surprising with pods). I’m going to try to dial them in again next week since I need to rebalance them anyway after that slide adjuster bolt came loose.

I’m at a bit of a loss when it comes to adjusting the fuel screw on the bottom of the carbs. Can I treat it like the air screw? Turn it both directions until I see a drop in revs and then go for the middle? Or do I really have to tweak it and check the plugs repeatedly?

 

[Steve]

Most here will tell you that you set the fuel screw ONCE, based on your intake/exhaust equipment, then do all fine-tuning with the air screw.

While looking at the carb diagram to see how they work, I question that, but have virtually no experience with VM carbs, so I have no way to verify my theories.

In the BS-series carbs (also know as "CV" carbs), you have a fixed air jet and a fixed fuel jet to provide a set mixture. The amount of that mixture that is admitted to the main airstream is adjusted with the pilot screw (also known as the "mixture" screw).

Your VM carbs have a fixed fuel jet. Air is mixed with that fuel, the amount of air is controlled by the pilot air screw. That mixture then passes the "fuel" screw to get into the main airstream. The only functional difference that I see is that the air/fuel ratio of the mixture is variable.

VM carb:

BS carb:

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[Guest]

After setting and re-setting and re-setting and ..... (you know how it goes) my VM slides I have screw number 3 in Steve GS Whisperer's picture set at 1/2 turn from VERY lightly seated and screw number 1 in said picture starting at 1 turn out. once the bike was well warmed up i fettled screw 1 until the revs rose and fell and left it at the highest revs. This took a bit of practice but i got there in the end. These figures worked the best on my carbs, they may not work as well on others but it's a starting point. I have a Marshall deeptone exhaust 4:1 (on the bike when I bought it) and foam filter pods.

 

[Steve]

Those pictures are from the factory service manuals.

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[Isoparmesan]

After setting and re-setting and re-setting and ..... (you know how it goes) my VM slides I have screw number 3 in Steve GS Whisperer's picture set at 1/2 turn from VERY lightly seated and screw number 1 in said picture starting at 1 turn out.

From
just did the same. Here?s what?s a new plug in cylinder 1 looked like after 30 or so minutes of riding. I flipped the kill switch at high revs before pulling the plug. I was getting kind of a lumpy idle after riding a bit longer. I?m still going to rebalance (have to borrow a manometer) and also take another look at the ignition timing.