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Old 06-11-2006, 02:32 PM
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Ratoflic Ratoflic is offline
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blower idle rpm problem

Hi everybody,

my friend just bough a truck with a 6-71 blower. he bough this truck from an old man...the guy never built up this motor and nobody know what this motor is made with. The only thing we know is:

- 396 big block chevy cubic inches, probably bored to 40 thousand.
- hydraulic (sealed power cam) with those spec:
cam number CS 175R
Intake Exaust
duration at 0.50 222 235
duration 306 322
lift 500 505
lobe center 110 120 ???

- 2 vacuum 650 holley carburetor
- 6-71 blower (probably 15 or little more years old)
- a very old point distributor with a accel external coil
- We see oval port head
- And the most bizarre thing, the upper and lower blower pulley have 35 teeth, so it's mean this blower have 1:1 ratio

Our problem is: When we start the blower when the motor is cold or hot..we are not able to let him stay at idle, the rpm goes up from 900 rpm to 1800 at neutral position and he down to 900 and up to 1800 rpm....we where thinking about a vacuum leak problem...so we where replacing all the gasket of this blower....We where setting the initial timming to 20 degre and total at 32 at 3000 rpm.....

WHEN the truck is in drive position and drive it around the street, we are not able to stay the idle at 900 rpm...he always want to die...and he make allot of backfire and after the backfire...the motor dead at 0 rpm....I know it's not a timming problem we set it at 32 degre total...

After this, we where restarting the motor and he made the same problem..the only difference is when we put the rpm more than 1800, the motor goes really weel, no up and down rpm..and the throttle respond very well...but if we dont touch the gaz pedal, the rpm goes up and down again...

What is the problem...we really need help fast....

DO YOU THINK THAT THE POWER VALVE OF BOTH CARBURETOR HAD BLOW???

We really dont know what to do...and we have no blower shop around here where we can asked question (we live in quebec, canada).....

Plz...anybody have comment, advice or trick...or question they can ask to us to solve this problem...

ANOTHER QUESTION, WHAT HAPPEN TO A MOTOR IF THE BLOWER RATIO IS 1:1, DOES IT MEAN THAT THE BLOWER DOESN'T WORK WELL, i MEAN, THE BLOWER GIVE TO THE MOTOR NOT ENOUGHT BOOST OR AIR TO MAKE BIG POWER...WHAT IS UNDERDRIVE???

If I put a 38 lower pulley to make 6 % underdrive, what will be the psi...this motor will be take this psi (if this motor have a stock bottom end)...

Can it be an electrical problem?? I mean not engouh spark....or volt to the spark plug?

Can it be a fuel pump problem..this motor have a mechanical holley fuel pump...can it be the problem at low rpm..i mean the pump dont give enough fuel.....

Another thing, the truck have a th400 transmission with a stock stall...this is good or not??? We have no more information on the cam.....

Can it be a intake gasket problem..i mean if air goes by the intake gasket, is this possible to be the problem....

Heeeeeeeeeellllllllpppppppppppppppppppppp usssssssss

Stephane

nobody can help me???? I really need help and faster as possible.... The guy who have the truck/blower become nervous....

Stephane
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Last edited by Ratoflic; 06-12-2006 at 06:02 AM. Reason: add information
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