At 05:58 AM 4/2/99 -0800, nikolai jaremka asked:
>
>what should the manifold vacuum at idle be?
>
Hoo boy, its been a long time since I've done any serious troublshooting
with my old vacuum gauge. So, I refreshed myself with the checks from my
old 1979 Chilton's manual. (If anyone wants to chime in with actual
measurements from their working Spitfire, go ahead.)
Best way to check vacuum is to connect a tee into the port on the ZS carb
(goes to the flame trap, then the EGR and distributor)
NORMAL:
17-22 inches of Mercury and steady
LATE IGNITION TIMING OR LOW COMPRESSION:
Low (10-15 In. hg.) and steady
VACUUM LEAK:
Very Low (4-9 In. hg.)
NEEDLE FLUCTUATES AS ENGINE SPEED INCREASES:
Ignition miss; blown head gasket, burned leaking valve, weak valve spring
GRADUAL DROP IN READING AT IDLE:
Starts high, say 22 in, then falls lower than 10: Excessive exhaust back
pressure
INTERMITTANT FLUCTUATION AT IDLE:
Ignition miss, sticking valve
DRIFTING NEEDLE
Corresponding variation in engine revs: improper idle mixture, minor intake
leak, or, if a dual-carb car, improperly synchronised carbs
HIGH AND STEADY:
22 & higher in. hg: early ignition timing
Hope this helps.
+++++++++++++++++++++
Getting back to Glenn's original problem:
An additional cause of lean mixture could be the hoses in the crankcase
breather system.
The original-type hoses are a non-reinforced, shrinky-type rubber which
does not require clamps to stay tight. When these hoses crack, they are
often replaced with coolant-type hoses which are not nearly as vacuum-tight.
If that's what you are running Glenn, make sure that each end has some kind
of clamp on it! I'm talking about the hose at the valve cover, and the
large port on the forward side of the ZS carb, and the connections to the
charcoal cannisters.
Happy troubleshooting,
Atwell Haines
'79 Spitfire
"I'd give my right arm to be ambidexterous!"
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