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Old 08-30-2010, 05:11 PM
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Need help selecting a carb

Hi, I have a 1986 Monte ss witch has a 1978 gm good wrench 350 block in it for what the casting number tell me. I have on it a Stage 2 rochester pass carb q-jet from jet performance.

http://www.jetchip.com/Shop/shopdisp...pp=10&catID=36

I recently put
edelbrock performer rmp heads,
# Thumpr Hydraulic Flat Tappet CamAdv/Dur: 279/297
# RPM Range: 1800 to 5600
# Intake/Exhaust Lift: .498/.483
lobe separation is 107

Also has a edlebrock performer intake

and it seems the carb may not be right for the application any more. seems like its running too rich at idle and to lean at wot or just goin to the road. the carb seems too complicated to re work to get it right. any one have any ideas? maybe just change the jets in it if its possible to do.

Thnaks!

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Old 08-30-2010, 06:01 PM
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If I were you, I'd be on the phone to Jet....
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Old 08-30-2010, 06:24 PM
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alright i was gonna do that any ways, but i feel like it would be just be better to choose a different carb that's easier to change the jets and what not.
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Old 08-30-2010, 06:44 PM
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Quote:
Originally Posted by PiperDavid14
alright i was gonna do that any ways, but i feel like it would be just be better to choose a different carb that's easier to change the jets and what not.
Don't be silly. You already have over $400 tied up in the Jet carb, now you want to spend another $300+ for another carb? Pull your head out and get on the phone.
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Old 08-30-2010, 08:16 PM
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Quote:
Originally Posted by PiperDavid14
Hi, I have a 1986 Monte ss witch has a 1978 gm good wrench 350 block in it for what the casting number tell me. I have on it a Stage 2 rochester pass carb q-jet from jet performance.

http://www.jetchip.com/Shop/shopdisp...pp=10&catID=36

I recently put
edelbrock performer rmp heads,
# Thumpr Hydraulic Flat Tappet CamAdv/Dur: 279/297
# RPM Range: 1800 to 5600
# Intake/Exhaust Lift: .498/.483
lobe separation is 107

Also has a edlebrock performer intake

and it seems the carb may not be right for the application any more. seems like its running too rich at idle and to lean at wot or just goin to the road. the carb seems too complicated to re work to get it right. any one have any ideas? maybe just change the jets in it if its possible to do.

Thnaks!
A lot of the driveability issues will cease when you dial in the timing curve, IMO.

You'll likely need around 16-18 of initial, no more than 34-36 total all in by at least 3000 rpm and the vacuum advance adding 10 or so, connected to a manifold vacuum source.

This is ballpark, you may find that you need to modify the mechanical advance to limit the amount it adds. or you may need to limit the amount the vacuum advance adds.

The ACCEL #31035 is an adjustable vacuum advance can for GM HEI that allows infinite adjustment to BOTH the amount and rate of advance. Comes w/instructions and tool.

To limit the amount of advance w/an OEM vacuum advance can, you will need to physically limit the vac can's travel w/a VACUUM ADVANCE LIMITER PLATE- Crane #99619-1, #99619-1 INSTRUCTIONS.

DETERMINING TDC will allow you to be sure the timing tab and damper are correct for TDC.

MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light.

You will find that the idle speed will increase using manifold vacuum- if you were using ported vacuum before. The increase in idle speed will increase the vacuum at idle, but you will still want to lower the idle speed using the curb idle screw if it's too high.

Once the timing and curb idle speed is dialed in, go back and readjust the idle mixture screws to get the best idle vacuum.

If the cam has too low of idle vacuum, the power piston spring may need to be swapped out for a lighter spring to keep the rods from enrichening the fuel/air mixture before it's needed. This is the probable cause for the idle to be too rich, if all else is as it should be- like the float level (~1/4"), the jetting should be close as well as secondary opening rate, but if not this is changed easily enough.

You might want to go through and readjust the APT setting on the power piston as a final tweak.

If you'd rather have an Edelbrock 600, I know someone who'll be happy to trade you even up.
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