Performance
Thread Starter
Intermediate
Joined: Jan 2015
Posts: 25
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Performance
I have a 69 427 390 hp stingray with a rochester carb. Points and condenser replaced. New Cap, rotor, wires, plugs as well as a carb adjustment.
Cars runs great normal driving. As soon as u put your foot in it it boggs down. Didnt have this issue before tunup.
Rechecked wires and such and all all looks good including vacuum hoses.
Any suggestions advice?
Cars runs great normal driving. As soon as u put your foot in it it boggs down. Didnt have this issue before tunup.
Rechecked wires and such and all all looks good including vacuum hoses.
Any suggestions advice?
Last edited by PM427; Apr 28, 2017 at 03:48 PM. Reason: More info
Race Director
Joined: May 2006
Posts: 18,665
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you replaced the points and condenser but make no mention of setting the dwell and checking the timing with the vacuum line to the distributor disconnected, did you perform those two tasks?
on the passenger side of the carburetor, any vacuum hoses accidentally disconnected?
with the engine off can you feel a slight resistance when you press down on the secondary air valve?
on the passenger side of the carburetor, any vacuum hoses accidentally disconnected?
with the engine off can you feel a slight resistance when you press down on the secondary air valve?
Thread Starter
Intermediate
Joined: Jan 2015
Posts: 25
Likes: 2
Thanks guys. Yes the dwell and timing was set. My bad for not adding that. I will check the fuel and i believe as you that a carb rebuild may be in my future. Appreciate the advice and replies guys.
You helped me out a lot.
You helped me out a lot.
Thread Starter
Intermediate
Joined: Jan 2015
Posts: 25
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Le Mans Master
Joined: Dec 2006
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The NAPA kits are good, and have the alcohol resistence accel. Pump.
Melting Slicks
Joined: Dec 2009
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From: Thunder Bay
I'm having a hard time believing this is a carb problem if the problem didn't exist prior to the tune up. That's a helluva coincidence. I'd be rechecking what you did when you did the tune up.
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Le Mans Master
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Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Did you check where the timing was set BEFORE you changed it to factory spec? Factory spec timing is WAY retarded for an engine set up for performance. Move timing up to 12 deg. BTDC with the vacuum advance line pulled and blocked. THEN see how it runs. 
Thread Starter
Intermediate
Joined: Jan 2015
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I moved the timing up a bit and the prob is almost gone. Thank you for the advice.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
GM set VERY mild specifications for stock timing requirements. They did so in order to minimize warranty costs; if the cars didn't get "stressed" to their potential, there would be less engine damage incurred. Worked pretty well....for them.
Most stock engines will perform MUCH better with base timing set to 10 -15 degrees BTDC on the compression stroke. There are detailed procedures to maximize potential by dialing-in the distributor. But, just advancing timing a few degrees will make a substantial improvement in engine performance.
Most stock engines will perform MUCH better with base timing set to 10 -15 degrees BTDC on the compression stroke. There are detailed procedures to maximize potential by dialing-in the distributor. But, just advancing timing a few degrees will make a substantial improvement in engine performance.
Last edited by 7T1vette; Apr 30, 2017 at 02:55 PM.
Racer
Joined: Mar 2011
Posts: 490
Likes: 99
From: The South
Did you relocate your vacuum advance line for the distributor when you did your tune-up? Make sure it is pulling from manifold vacuum and not a ported vacuum port. Also, re-torque your carb mounting bolts (I think it is 10-12 ft lbs. on the quadrajet, IIRC.)
I solved my off idle stumbling problem on my '73 recently just by doing these two things.
I solved my off idle stumbling problem on my '73 recently just by doing these two things.