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Old 05-06-2010, 12:03 PM
g-bar99's Avatar
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winter project done... need help tuning

Hi guys, wondering if you could give me some ideas here:
I've been helping a buddy freshen up a 305 pontiac small block thats in his '74 Nova. A less than desirable combination- I know, but his baby none the less. It's been in the garage all winter and now it's time to get her back on the road.
First we replaced the old q-jet and stock intake with an Edelbrock performer EPS intake and Edelbrock 600CFM carb. Once back together, she ran great. Seeing as we had the rest of the winter to go- 5 months of it actually, we decided to tear the engine down, clean the block, repaint and dress up the engine (the motor was salvaged from a junkyard, really ugly- to say the least) Installed chrome brackets, polished aluminum water pump, chrome timing chain cover and while it was off replaced the old, stretched timing set with a double roller. With everything back on, fired it up last night and the thing ran like a bag of ****. After playing with the distributor, advancing/ retarding the timing and adjusting the idle screws until smoothed out a bit, but ONLY a bit.
Being that it was a bit late when we got it going, all i had time to check was if there was good spark- didn't get the timing light out just yet. I did notice though that the spark at the plug is quite yellow- definitely not the blue colour I would expect. The distributor is the old Accel HEI that came with the motor. I think I should probably just scrap that Accel p.o.s and get a new MSD. So, I'm just wondering if the yellow/ weak spark would cause such noticeable rough running? The thing I don't understand is that when we originally just replaced the carb and intake- it ran just fine. Now its rough as heck.
What other things could I check to get me pointed in the right direction?
For the record: plugs and wires are new and in the correct firing order. Fuel is fresh also. The new intake and carb were not removed since originally installing them.
Any advice is much appreciated. Thanks

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Old 05-06-2010, 02:21 PM
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Yellow spark means weak spark. All you had to say was Accel, Accel is pure junk that belongs in the garbage.
Being your dealing with a smogger small block, I would set the timing with the vac advance disconnected and plugged to 12 degrees before top dead center. Lock the distributor, reconnect vac advance to a full time manifold vacuum source, one that pulls vacuum full time, even at idle. Recheck timing, it should be around 20-24 degrees. Next is what shape is the valve adjustment in? Also have you checked it for vacuum leaks? Check and make sure the distributor is getting it`s full voltage. HEI types require a full 12 volts to run correctly. They can run on as low as 8 volts, but the side effect is it`ll run like crap. Make sure you check the ignitions power with the engine running.
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