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 Intake / Carb and Fuel Delivery Tech
 Sooty plugs, hesistation at mid rpm range
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Bensjammin66
Tribal Scout

USA
6 Posts

Posted - 08 Jul 2015 :  10:05:55 AM  Show Profile  Reply with Quote
Looking for some help on a mid range rpm stumble / carbon fouling lots of plugs.

Motor info:
-.060 over 455 forged TRWs with Moly rings, eagle rods, stock turned and polished crank, main studs. 60psi pump.

-KRE 295cfm heads from SD performance, springs matched to his roller "stump puller" cam shaft.

-Edelbrock performer RPM manifold, dougs 1 3/4" headers to 2.5" out to the bumper, AED850 in stock configuration not sure of jetting. 4 Idle screws are about 1.25 turns out to achieve max 11" of vaccuum. Fuel level is 2/3 up the sight window on the primary and 1/2 way up on the secondary per AEDs instructions. Open element clean 14" KN filter on top.

-3/8 fuel line with 7psi at idle but sees 8 psi sometimes on the gauge, Holley mechanical 90gph pump. Free revving the engine the gauge sometimes drops to 5.5 - 6psi.

-HEI ignition with 12 initial and 36 total all in by 3000, vac adjust can set to add an additional 12 degrees. Using R5671A-11 cold NGK plugs recommended by Kaufmann. I will admit the plug wires are old but they appear to be fine and all cylinders fire evenly according to the universally sooty plugs. Could this be my issue?

-TKO 5 speed manual transmission and 3.73 rear gearing.

-The motor does use just under a quart of oil every 1000-1500 miles but after the rebuild and some break in miles the COLD engine leak down only tested to 5%-8% leakage. Also using a moroso PCV inline oil separator before it is sucked into the carb base which after 200 miles has not collected an ounce of oil yet.



Now the issue, with new plugs the car runs GREAT. But, after 150 miles or so the plugs are black and sooty and i have some popping noises in the exhaust and hesitation around 3000-4500 rpm in second and third gear, then it cleans up a little on the way to 5500rpm but not all the way. Motor free revs perfectly in neutral. AED told me lean out the idle mixture and try a smaller rear squiter so that is on the agenda. Anything else I should try? Jet change recommendations?

Bill Boyle
Horse Feathers (Charter Member)

USA
4794 Posts

Posted - 08 Jul 2015 :  10:32:44 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Why did KRE recommend cold plugs? Everyday street use right vs. strip action? Hotter plugs may clean up that soot. That may be part of the problem though. Overly rich mixture may be the other, however, take on one area at a time.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Bensjammin66
Tribal Scout

USA
6 Posts

Posted - 08 Jul 2015 :  10:48:42 AM  Show Profile  Reply with Quote
Thats what I thought too. That plug is just what their website recommended. Car is 100% street driven. They offer the R5671A-11 all the way "up" to a R5671A-7 being the hottest. Think I need a hotter plug? Try a -10 or -9 first?

Edited by - Bensjammin66 on 08 Jul 2015 10:49:49 AM
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Blued and Painted
Chief PONTIAC

USA
3406 Posts

Posted - 08 Jul 2015 :  12:01:22 PM  Show Profile  Reply with Quote
Try moving you float levels down to the bottom of the sight glass. Double check for correct power valve for engine vacuum at idle.

Valve spring retainer could be coming into contact with valve stem seal. Seal Bashing.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 08 Jul 2015 12:09:20 PM
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Bill Boyle
Horse Feathers (Charter Member)

USA
4794 Posts

Posted - 08 Jul 2015 :  12:38:18 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Give the hottest plug a try.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Chicagogoat
Cochise

USA
823 Posts

Posted - 08 Jul 2015 :  2:12:01 PM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
I agree with Bill & Blue regarding trying hotter plugs first & I've also had to lower the fuel level on the bowls until fuel is slightly visible in the glass and it does run and start better. I also have KRE D's and I do run the same plugs with -9 cold range and they're tan to dark. That's a good place to start before opening up the bowls and jetting down.

Pure Pontiac: learn it, live it, love it!
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Bensjammin66
Tribal Scout

USA
6 Posts

Posted - 08 Jul 2015 :  2:33:36 PM  Show Profile  Reply with Quote
Jeff Kaufmann replied this to me in email a few moments ago. I ran to the part store and grabbed some 9s, think i should take his advice and go right to 7s?

Ben,
Yep that?s way too cold of a plug for a street car. I would either go straight to a NGK R5671A-7 or NGK FR-5. Most street setups I?ve been using the FR-5

Thanks,
Jeff
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Bensjammin66
Tribal Scout

USA
6 Posts

Posted - 09 Jul 2015 :  09:29:49 AM  Show Profile  Reply with Quote
No brainer! Car responded to the -7s great last night! All the power is back, but the true test will be after driving 500 miles then pulling a plug.
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bluebird
Cochise

USA
292 Posts

Posted - 15 Sep 2015 :  3:35:03 PM  Show Profile  Reply with Quote
did it solve your problems after 500 miles?

"Experience is the best teacher, unfortunately, it's the costliest!"
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