Kind of a red neck way to check for intake/bottom end leaks:
Because the problem is from a leak in the engine, ether on the intake parts or in the bottom end of the engine, you will be losing vacuum and letting "fresh" air get into the engine. Im not going to get into the problem with air getting into the engine as you probably already know why thats not good. Possibly dieseling, lack of lubrication, loss of power.....
The quick way to check if you have a vacuum leak is to spray flammable spray onto the parts you want to check for leaks. What this will do is if you have a leak the engine will differ in RPM. Most likely increase, but it could decrease. Whats happening is the flammable liquid is entering through the leak and acting as fuel, thus burning like fuel. If you have no leaks, there should be no change in rpm.
In this particular case you will have to make sure the engine is NOT DIESELING, so keep it on the trailer and have it in water. Then when the RPM's are steady, spray small amounts of spray on parts of the intake. Wait a few seconds, if no change, spray a different part. if you hear change, then you found the leak.
Obviously people are going to disagree with this, because it to dangerous, or sounds crazy. BUT it does work. Iv done it many times on dirt bikes and small engine stuff. I usually find it works on carb parts like intake boots and idle/mixture screws. Little different then a ski, but same principal. A two stoke is simple.
Id maybe have a hose ready or fire extinguisher. but common sense is best dont spray at a spark.
USE brake clean, parts cleaner, or carb cleaner.
