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Old 08-11-2016, 02:43 AM
Roberto_Lux Roberto_Lux is offline
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383 stroker low vacuum

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Hi,
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Ive bought 64 corvettes which has a 383 stroker engine. But Im facing some problems when it comes to acceleration in "cruising mode" low rpm. I notice serious backfire, happening in the exhaust system and hesitations.
[COLOR=#000000] [/COLOR]Some initial data:
- Engine chevy 383 stroker
- Quick fuel carb Q Serie 750cfm Drag Race
- Aluminium heads
- MSD Distributor (Vacuum advance)
- Procomp ignition system (PC-2017_6AL & PC-2041D)
- CompCam Part # 12-433-8 (see attached cam card)

Here the tests I already did:
- Checked my camshaft and it matches the spec
- Set the ignition to:
total timing 34 BTDC and
initial timing 18 BTDC
- Compression test: all cylinders between 165 and 172 psi
- Spark plugs: all have black top ends (rich mixture) see pics
- Vacuum test: ONLY!! 5 inch Mercury (slightly vibrating between 4-6)
- Leak test on the intake: Couldnt find any leak. Even not with smoke ... it came out of the carburator top.

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Is my camshaft THAT SHARP, that such low vacuum can be expected?
Why are the plug showing a rich mixture when the vacuum test is indication a manifold leak, this should result in a lean mixture shouldn't it.?

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Ill perform a second test where I will take of the carb and blind the connection flange, set the crankshaft to 45 BTDC (no overlap on any cylinder) so no smoke can go through the engine.


[COLOR=#000000] [/COLOR]Does anyone of you have some other ideas what I should look at?

Thanks

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Bob
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