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Old 06-24-2008, 06:05 PM
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Finish Tuning

Having some issues with a new setup. SBC, flat tops, 882 heads, ~9:1, 500 lift/300dur, lo-rise intake, Holley 650 carb. Plenty of fire, all MSD. Engine seams to be running rich , can't get that clean crisp strong idle. Sluggish from a start like its loading up and also at cruising speeds with throttle just cracked. Runs decent when I get on it. A little help please?!?!

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Old 06-24-2008, 06:24 PM
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This is just a guess, because I'm certainly no carb guru. The long duration of the cam is causing low manifold vacuum. The power valve is seeing the low vacuum and mis-interpreting it as the motor being under load, opening up the circuit and adding fuel. Maybe you could install the lowest calibration power valve (1" hg) and try it.
http://www.jegs.com/webapp/wcs/store...-1&showValue=1
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Old 06-24-2008, 10:32 PM
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where are you mixture screws at, you may need to reduce the diameter of the IFR's
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Old 06-24-2008, 10:59 PM
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Assuming your timing is all where it should be, the next thing to do is put a vacuum gauge on it. Measure manifold vacuum off the carb or manifold. As mentioned already, make sure your powervalve isn't open at normal cruise or idle vacuum. Set your idle to maximum vacuum. That should be a starting point.

How do you know it's rich and not lean off a start?

Oh, thought of another early thing to check: make sure the float level isn't too high and dumping excess fuel into the venturis.

A 02 will make things a lot easier.
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Old 06-24-2008, 11:12 PM
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Quote:
Originally Posted by dh79
As mentioned already, make sure your powervalve isn't open at normal cruise or idle vacuum. Set your idle to maximum vacuum.
the powervalve feeds the main metering system, it doesnt affect the idle at all
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Old 06-24-2008, 11:16 PM
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Quote:
Originally Posted by darkostoj
the powervalve feeds the main metering system, it doesnt affect the idle at all
Yeah, but if you're idle vacuum is 4" and the powervalve opens below 9.5", then it'll be open at idle (and probably all the time).
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Old 06-24-2008, 11:59 PM
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Quote:
Originally Posted by dh79
Yeah, but if you're idle vacuum is 4" and the powervalve opens below 9.5", then it'll be open at idle (and probably all the time).
ah, i thought you were saying that an improper powervalve would give you an overly rich idle.

In you scenario the pv will be open at all times, but it will not feed fuel to the idle circuit.
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Old 06-25-2008, 01:16 AM
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If it's open at idle and feeding fuel into the motor, then the idle circuit has nothing to do with it. The motor will be rich regardless and you won't be able to get a clean idle. That was where I was coming from.

" i thought you were saying that an improper powervalve would give you an overly rich idle."

Yes it will, just won't be through the idle circuit.

Forget the idle circuit. That's not where the problem is the way I see it.
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Old 06-25-2008, 06:40 AM
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Quote:
Originally Posted by dh79
Assuming your timing is all where it should be, the next thing to do is put a vacuum gauge on it. Measure manifold vacuum off the carb or manifold. As mentioned already, make sure your powervalve isn't open at normal cruise or idle vacuum. Set your idle to maximum vacuum. That should be a starting point.

How do you know it's rich and not lean off a start?

Oh, thought of another early thing to check: make sure the float level isn't too high and dumping excess fuel into the venturis.

A 02 will make things a lot easier.
Call it old school or just my opinion....It's rich @ idle! I go to the exhuast, cup my hand and it smells like raw fuel. And cruising down the road at low RPMs it smells very strong of fuel.

After your responces and reading some of the other threads I relly believe there is a Vacuum issue for starters.
I also believe that the "match" of the components is wrong.
82 350 4bolt .040 over w/ eagle crank and rods, hyp flat tops
882 heads 1.94/1.50 valves 160? cc runners 76cc chamber basicly stock
Crane 100112 cam 500 lift 302 adv dur
Wiend intake http://www.holley.com/8004.asp
Holley 650 DP vac advance
All parts are new or rebuilt

I am looking for a decent set of aluminum heads with ~64cc chambers and bigger runners and a more aggressive intake. Should bring it to life.

Thank you very much for all your help guys!!
Take a look please......
http://s279.photobucket.com/albums/k...t=e9853e33.pbr
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Old 06-25-2008, 07:02 AM
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Have a set 461 castings, yes the old double humps...again! lol that I can pick up from an older gentleman that came out of a mid 60s 327 vette orig. Been sitting in his shed for 20 yrs. 100 bucks plus shipping yes 2.02s

or
something loke this:

New set of Aluminim Small Block Chevy Pro Comp Motorsport Heads (2 heads)
Produce 500 HP Out Of Box With Advanced Port Design
Just do a nice bowl blend
210cc Intake Runners
64cc Chambers
Straight Plug Design for easy header clearance (ANGLE PLUG AVAILABLE ON REQUEST FOR SAME PRICE)
Bronze Valve Guides
Premium Hardened Seats
2.02 and 1.60 valve seat size
for 420 bucks bare

economy went to hell so $$$ is tight now, unless Im going to get 50+ more hp off the alum heads screw it I'll be a camel jockey. sorry if I offended anyone.
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Old 06-25-2008, 09:57 AM
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Quote:
Originally Posted by techinspector1
If it's open at idle and feeding fuel into the motor, then the idle circuit has nothing to do with it. The motor will be rich regardless and you won't be able to get a clean idle. That was where I was coming from.

" i thought you were saying that an improper powervalve would give you an overly rich idle."

Yes it will, just won't be through the idle circuit.

Forget the idle circuit. That's not where the problem is the way I see it.
he said that its rich and loading up with just the throttle cracked. That means hes running off the transition slots, which get fuel from the idle circuit. To me it seems like he needs to work on the idle first to get it in the ballpark.

to the original poster. Your combo is fine it just needs some tuning to run properly. How much vacuum are you getting at idle? Where are your idle mixture screws set at? Did you set your transition slots in the carb properly?
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Old 06-26-2008, 12:27 PM
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One of the local shops recommended that I block off the power valve and increase the primary jet size by 2-3. Also, not running any vac lines off the carb at all. No PCV at all just vents, and the brakes and trans is off the intake with a T. Whats your take on this?
Steve
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Old 06-26-2008, 12:38 PM
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Quote:
Originally Posted by sick7
One of the local shops recommended that I block off the power valve and increase the primary jet size by 2-3. Also, not running any vac lines off the carb at all. No PCV at all just vents, and the brakes and trans is off the intake with a T. Whats your take on this?
Steve
i wish every car(minus track only cars) had an electric gadget on it that automatically shocked anyone that was about to replace the primary power valve with a plug. That is such a bad idea. The power valve is there for a reason to only open up and enrich the carb when vacuum drops below the pv rating to give the carb more fuel when there is load on the motor, when you are in the mains and there is no load on the motor (ex. cruising on the highway at 3,000rpm) your pv is closed and running off the front main jets giving you a leaner mixture and saving you gas mileage
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Old 06-26-2008, 03:42 PM
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I agree, DO NOT block off your powervalve. In fact, don't go back to the shop that recommended this to you. Anybody who would recommend that for a street car has no business tuning carbs. It's not terribly difficult to do things the correct way. With a little knowledge and some trial and error you can tune the carb to work perfectly.

The only time to consider losing the powervalve would be for a race only engine that is only WOT or idle.
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Old 06-26-2008, 03:44 PM
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Oh, forgot to add. You need a pcv to have some negative pressure in the crankcase. This will help the rings stay seated which helps power and efficiency.
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