Was able to get a bit of garage time today. Found a spot using carb cleaner somewhere under the intake manifold, radiator side. Vacuum gauge went up 1 to 1.5 cm Hg and RPMs dropped. Definitely a leak there. Buttoned everything back up. Adjusted carb, still Idling about 900-950ms with a vacuum pressure 17.5
Now it is decision time. Might drive it until I have the coin to buy a sniper. Whether or not I decide on carb rebuild or sniper, it’s gonna have to be taken apart at some point.
Now I’m confused. I have not had time to investigate this further until tonight. Bought another can of carb cleaner. Fired up the 40 and let her warm up. Began checking everything with more carb cleaner.
Seems to me there were times when I sprayed carb cleaner on certain areas that the idle went up.
I thought that when an intake leak was sealed temporarily by the cleaner the idle would drop. What am I missing?
I don’t think the carb cleaner (very flammable) seals leaks/gaps, it actually gets sucked in (vacuum “leak” which is actually sucking ) and gets burned rapidly, so your adding fuel. Hence the idle jumps up.
Yup. If you spray water (some do because it’s not flammable) you’ll get a rpm drop because it reduces fuel-to-air mixture. Carb cleaner (flammable) increases fuel-to-air mixture.
Now, at full disclaimer, if you literally dump carb cleaner into the carb/inlet system you’ll probably choke the engine (briefly) due to too much fuel, but that’s nearly impossible to do while spraying a fuel source at a vacuum leak. Vacuum “leak” phraseology is from the engine’s perspective. From our perspective they are an increase in “sucking.”
The engine will pull whatever it can get based on its displacement and what’s available to burn in the cylinders (fuel-air mixture), so when you get or have a vacuum leak there’s more air available, so a lower fuel-to-air mixture results, and the increased air flow into the intake system will draw more fuel as well (if the carb has the circuits for such, which most do ), hence a higher rpm. You‘re no longer “running“ on just the idle circuit. The issue then becomes when you give it throttle you now have excess and a typical symptom is a bog.