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Discussion Starter #1
My plugs are fouling up bad and have been told its carby problems. I know this is gonna be hard to answer but would like some ideas. I have a 750vc Holley with a Proform main body, Preformer airgap manifold, fuelie heads which are flowed and have big valves, 9.6:1 comp, an Extreme energy XE274H cam 0.49 lift, flat top pistons. any idea what jetting and powervalve I should be using? Not sure whats in there at the moment yet until I pull it apart.
 

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put a vacuum gage on it to see where your vacuum is at idle. try to get the idle speed at or below 1,000 RPM.s set initial timing around 17-18* and [email protected],000 with vac advance not hooked up. I'd start with what comes stock in a 750 vac sec for jetting and PV then fine tune it from there. This will give you a baseline to start from. Before you start the car set the idle mix screws 1 1/2 turns out from the seated position. Once its all tuned and timed fine tune the idle mix screws for best vacuum and RPM. If not experienced with carbs have somebody that knows how to adjust them with ya so you can see how its done. Good luck:D
 

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I agree, set the jetting to stock 750 specs and start there. Also check your powervalve for leakage while it's apart and note what number it is. I bet the basic 6.5 powervalve will work OK with your combo. Use an AC R43 heat range spark plug with those fuelie heads-buy new plugs if they are sooty.
 

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How much fuel pressure? Keep it at 7 psi or less to avoid blowing past the needle and seat. And set the float level after you lower the pressure.
 

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Discussion Starter #5
I know it has 7psi pressure and also has low manifold vacuum and think the PV is around 6.5 but will check everything on the weekend. If the vacuum is too low at idle and the PV number too high will that mean the PV will be open at idle? Had a quick look on the Holley web site and they mentioned to check for a blown PV turn the idle screws all the way in and if the engine stops the PV is OK, I know I can do this and the engine still runs!? Also anyone know what the factory jet sizes and PV are the a 750 vac?
 

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Discussion Starter #7 (Edited)
Ok today I warmed up the engine and check the vacuum and is between 7 and 8", pulled the bowl of the carb and has a 6.5 PV and 75 jets. car runs nice when driving around just when idling mainly. I've put in a 4.5 PV and left the jets, wondering if I should go to a 3.5 PV? anyway ran the motor and set the float levels and readjusted the air screws, not much different. runs and idles nice but just fumy. Can't drive the car at the moment as its in bits doing the body up. It blows smoke when giving it a rev, car has been sitting for about 4 months now dunno if it just needs a good run but checked the plugs after I ran it and some are pretty oily and when I done a compression check last week they were all over the place from 120 up to 155 psi (cranking until I got the highest reading). the plugs were really fouled up before I changed them so not sure if the valves would be gunked up aswell causing the varying compression readings? The engine is new with about 3000mls on it but before it was rebuilt the second time, the first build everything was new but half way through braking the cam in I realised I didn't put water in the radiator....Duh!!! So had to rebuild it again after driving the car around for about 9 months but upon pulling down the engine I found the inlet manifold had been sucking in air/oil in the lifter valley, there was a leak along the bottom of the inlet gaskets. The inlet hadn't been checked to the heads for proper sealing/machining. That said when it was rebuilt the second time all that was check but I'm wondering if its doing it again? OR because its been running rich at idle for the time it's been in the car (3000mls) is that enough to 'fuel wash' oil from the rings causing excessive wear? Your thoughts and comments are much appreciated thanks:eek:
 

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I believe if you are running rich your plugs will have a dry soot like blackness. If its oily I'd suspect leaky valve seals allowing oil to drip onto your plugs causing them to foul.
 

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I don't know anything about the Proform bodies, but I ran 71 or 72 jets in a regular 3310 Holley on my 11 second 406. Might try going down a few jet sizes--but it sounds like you may have other issues.
 

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With that cam I think you should have a little more than 7-8" hg of vacuum at idle. Whats your initial timing set to? Also, will turning the mixture screws all the way in choke the engine?

Dan
 

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sounds like its suffering from body shop rot. Being started and not fully warmed up. That will kill plugs quick. I would keep the 4.5 PV and drop the jet size down to 70. Stock 3310's come out of the box with 72's and a 6.5 PV. set the timing about 18* initial. More than likely you're gonna need to put plugs in it.
 
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