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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



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.


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.?


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?



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