Author Topic: Quadrajet causing ignition timing problems?  (Read 4010 times)

Offline jeffb

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Quadrajet causing ignition timing problems?
« on: August 11, 2011, 09:46:06 AM »
Hello, have a  part number 17057253 Q jet on my 68 Firebird. I bought an APT gasket and upper horn gasket last spring from Cliff. When I had it apart, from what I can read, here is what is in it:
primary rods- A66 or AA3
Front small jets- 27 or 47
large metering rods-33797
Would these be optimum in my combo as detailed below?
I can't get my initial ignition timing set, someone suggested a lean condition?? as I will state below, thanks for any advice:

Here is where my build is at for the 68 Firebird:
455 .030 over,
factory cut crank (my weak link)
balanced bottom end
ATI super damper
1971#96 d ports that are decked, polished, not ported, Ferrea stainless stock height valves, 3 angle valve job, Comp cams +.050 retainers, 10 degree locks
Ultradyne valve springs
Crane Cams Energizer 1.65 true roller rockers
ultradyne cam, .231-.239@.050, .538/.558 lift with 1.65's, degreed in at 107 degrees
Jegs noisy gear drive
holley street dominator
Holley blue fuel pump and external regulator set to 5 PSI
800 cfm quadrajet
Eagle forged h beam rods
TRW forged flat tops
10.1:1 compression ratio
1 7/8" to 3 1/2 "Hedman headers
new stock (I think piece of sh&&) distributor from Ebay
Accel 8.8MM wires
Autolite #85 plugs
TH350 with 2800 stall converter,
3.42 gears.

THE PROBLEM:
I cannot get the ignition timing right and running hot at idle (205 degrees). I tried Zedo's method (from my ignition timing post) with a vacuum gauge. I have 14-16" of vacuum at idle, depending on how far I have my idle screw turned in to keep it running. I advanced the timing until I get the max vacum reading (in the travel available in this position it will NOT ping), retarded it 3 " of vacum, and I am at 25 degrees BTDC. At this point, the car will barely rev, is very sluggish. The closest I can get the initial timing with vac. advance plugged is about 25 degrees BTDC, any closer the car will not idle, idle goes too low, even with carb adj. screw turned way up, and stalls. I think there a problem with how my cam is degreed, although I degreed it.
With this combo, it has a mild cam. I built it more to be a solid combo than a really nasty street car. There should be no reason at all that I can't put a timing light on it, adjust my initial timing from 12-14 degrees BTDC right through 0 degrees without screwing with my idle adj. screw. What is wrong? Could the gear drive be machined wrong, but isn't that what degreeing the cam is for?
I tried to set the timing by ear until it sounded good, locked the dist. down, and took it for a ride. Before all this, last fall it had a stock 1973 455 with junk 4X heads. if you tapped the gas, then, it would burn the tires off. Now, it is very sluggish with no power and will not get out of its own way. I will address the running hot at idle problem once this problem is corrected, but with a brand new stock 3 row radiator, fan shroud, 7 blade clutch fan, stock water pump, there is no reason that this shouldn't run at 170-180 degrees at idle all day like when a little old lady bought a '71 Bonneville and drove it for 100,000 miles back in the early 70's. Ideas?

Offline Cliff Ruggles

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Re: Quadrajet causing ignition timing problems?
« Reply #1 on: August 14, 2011, 02:14:38 AM »
The 17057253 is an excellent carburetor for what you are doing.  It is emission calibrated, and will need some help.  Did you modify the idle system per our book?

Wanting that much timing to idle well tells us that the carburetor is quite lean on the idle curcuit, assuming the camshaft is degree'd correctly.

That carburetor is also pretty lean on the primary side, I would install larger jets and our tapered primary rods to add some fuel, which will help it run cooler as well.....Cliff

Offline 77cruiser

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Re: Quadrajet causing ignition timing problems?
« Reply #2 on: August 20, 2011, 06:07:07 PM »
Have you verified the timing mark @ TDC?
Jim

Offline jeffb

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Re: Quadrajet causing ignition timing problems?
« Reply #3 on: August 31, 2011, 04:56:31 AM »
Hello, thanks for the replies to my problem. I figured out my issue, at top dead center, I had my cam gear installed at 12:00 instead of at 6:00; now I got it to time at 15 degrees btdc. Cliff, I will have to order one of your kits and whatever jets and metering rods you recomend. The car runs good and feels strong now, but sometimes after I shut it off and try to re-start it, it won't start unless I floor the gas.  I bought a Jiffy kit last year locally, and a power piston assembly gasket from you, but I think maybe I set the float wrong? In the near future, I will give you a call to order these from you. Thoughts on the starting problem for now?? Thanks again, Jeff

Offline Cliff Ruggles

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Re: Quadrajet causing ignition timing problems?
« Reply #4 on: August 31, 2011, 07:24:28 AM »
I would get one of our kits, add the secondary cam/spring, power piston spring (included in the HP kit), custom quick release choke pull-off, primary jets, primary metering rods, and secondary metering rods.  We will send the correct parts to set the carb up exactly for the applications....thanks....Cliff