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How do I diagnose problems with the Vacuum systems
QUESTION: Does anyone know how to diagnose problems with a cars vacuum advance
system.
OK from my previous post about my Suzuki engine you might understand some
of the symptoms. In any case now that the engine is running again I would
like to turn my attention to the vacuum system. The engine produces
mysterious whoosing, popping sounds coming from the distributor
carburettor direction. These usually occour when decelerating, shifting
gear or when going down hills. I suspect that this is due to a problem
with the vacuum system.
There are a large number of small rubber tubes and I am guessing that one
of them has a hole or small crack. Does anyone have any ideas as to how I
can diagnose problems with this area of the engine. i.e. figure out which
little tube has a hole or crack in it so I can find a replacement. Usually
with gas systems one covers the part with soapy water and looks for the
bubbles. As this is a vacuum system it seems that this would be an
exceedingly bad idea and wouldn't tell you anything anyway.
Any ideas please email me (you can guess what kind of spam block I've got
going):
ANSWER: I use carb cleaner spray and spray the base of the carb first then the
gasket along the intake manifold to head joint with the engine running.
If the idle stumbles or changes, there is a leak. Loose carbs and
intake gaskets are more common than one might think. Lots of times they
can just be tightened, sometimes they need a new gasket.
I then pinch all the vacuum tubes closed as close to the carb as I can
reach. If pinching one changes the idle, I check it more and see what
it is hooked up to. That would be a leak either in that line or the
part it is putting vacuum on.
The vacuum advance system itself is easy enough but it sounds like you
want to cover the entire vacuum system; a little more complex but
doable. A handheld vacuum pump and guage are going to help a lot for
checking the whole system.
As others have mentioned, carb cleaner or other flammable substances are
useful for finding vacuum leaks (keep an extinquisher handy!)
Unfortunately this won't help for a leaking vacuum device (ruptured
diaphagm inside) or systems that operate from ported vacuum or portions
that are downstream of a switch that isn't energized. Use the vacuum
pump to operate the vacuum devices to see if they move and/or hold
vacuum, put the pump on one side of a switch and the guage on the other
and make sure it only passes vacuum when it should, use this same
technique to test hoses, should hold vacuum with the guage on one end
and the pump on the other.
There is a nice piece of equipment called a "smoke machine" that pumps
out smoke at 1 PSI or so that is great in a shop environment but at
$1000-2000 US it's a bit pricey for home use!
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