Smoking the carburetors: I was expecting no smoke from the carburetors on a cold engine and the throttle shafts disconnected from the throttle bar. Am I doing something wrong, are my expectations inaccurate or are all three carburetors not sealing correctly? Have a looksy at the short video.
With the intakes open like that the smoke will take the path of least resistance, which is through the intakes. You won’t find the leak like that with a smoke tester.
Tape the intakes of all 3 carbs closed (sealed off completely), then try the test again - the smoke will come out of any leaks.
I find spraying the carbs with a water mister (like a windex sprayer) while the car is running the easiest way to find leaks - if the idle changes then that means water is getting pulled in where the leak is. If the idle doesn’t change, then that means either you have no leak, or your water spray hasn’t reached it (yet).
[quote=“Andrew_Waugh, post:2, topic:350704”]
When is it appropriate to have the engine running while performing a smoke test? I would think that air sucked into vacuum leaks would oppose smoke leaking out?
I did block the carburetor intakes with duct tape but smoke still leaks, not as bad. I was able, however, to see smoke come out from the butterfly shaft of the suspect carburetor. I think I will build some carburetor intake blocking blades (metal + rubber) and try it again. I shall be back.
Robert,
As far as I know, a smoke test is only ever done with the engine off.
We’re trying to find a leak in the carbs/intake area. The volume between the Air filter and the inlet valves should be a closed chamber. Ideally, air can enter into this chamber only by passing through the air filter. With the smoke tester you are injecting smoke into the chamber (with the engine off) and looking to see if it escapes anywhere other than the air filter or the exhaust pipe.
The other way to check for a vacuum leak is to run the engine and get it to pull something other than air in through the leak. While the engine is running the whole volume between the air filter and the intake valve(s) is under a vacuum. If you then spray some material (water, propane, starting fluid) which will change the way the engine runs onto a leak then it will be pulled into the cylinder and mix with the A/F mixture which will in turn cause the idle speed to change.
I prefer water in a squeeze pump. It is cheap, readily available, and won’t set fire to your engine if something goes wrong.