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Hey all, I apologize in advance for the long winded post!.. I've been chasing my tail a bit and need help getting this set straight for my old man's car!
Bone stock driver, 72 350 SBC (hydraulic flat tappet, 882 heads) / 2 barrel 2GV Rochester carb / automatic trans th350 / 195 t stat, doesn't overheat
Points style ignition, stock fuel system - mechanical fuel pump, no regulator or return system
Only "add ons" are temp gauge, oil press gauge, & afr gauge
12 initial / 36 total + don't remember vac advance amount
20psi oil when fully hot, climbs no problem with throttle input
Problem:
- Very inconsistent in how it runs. Just sitting idling it can go from running nice, stand a nickel on it smooth (literally) to feeling it stumble/miss sometimes just slightly and sometimes it's enough to feel it throughout the car, AFR leans when this happens, but leave it alone for a moment, look back at the AFR gauge it's now reading 14.7 and the rpm changes again. Yet vacuum gauge seems to hold a steady 20" during these events
- Noticeably down on power across the board - on the street, on the highway etc
- Bogging / stalling on off idle part-heavy throttle acceleration
- Vacuum is "usually" solid steady, but the number it hangs steadily at can occasionally change. As in, generally it's at 20" lately. But a couple blips of the throttle, sometimes it only comes back to a steady 19, and only once, I seen it drop to 17 and search 17-20 but then goose the throttle again a couple times and it'll come back to 20 steady again.
Genesis:
I pulled the engine last Summer, cleaned it up, gave it new filters, seals & gaskets, replaced the old crank sprocket, nylon cam gear & standard timing chain with a roller set. As well as the old balancer, I 100% made sure the balancer and timing marks were the same. Nothing done to heads, they weren't touched. Pulled the lifters and push rods to check, made sure they all went back where they were pulled from, checked the cam with a borescope. Rebuilt the carburetor. Put it back together, had it running great and consistent for a few months before putting it away for the Winter. Constant 21" of vacuum from the 18 it had prior to pulling it, AFR of 12.7 at idle, 15.0 cruising, don't recall WOT. It had a nice tire spinnin' up and go to it versus how flat it is now. Popped an intake end gasket (used the rubber end seal, my bad!) resealed it with RightStuff, all good again. Put it away for Winter, with the occasional starts once or twice a month allowing it to warm up and heat soak as usual.
Went to pull it out in the Spring and it just wasn't right, has all the aforementioned problems and nothing I do will bring the vacuum back to 21" Best I can ever get is 20". AFR was 12.7 before putting it away but lately it's usually 13.7 - 14 when it's running "decent" with the rare time of it going back in the high 12's. Even with mix screws backed ridiculously out. When it's running more noticeably rough, the AFR is usually maxed out lean. Yet the vacuum gauge stays at a solid 20" when this happens. A wot press of the pedal will get AFR down to 17's and then it shoots back up when you come off.. A few days ago, started it up left it idling, everything was reading okay and consistently (20" vac, 13.7-14AFR) for 60-90min while I did other things and kept a watch on it, all I did was pull it out the door to go for a drive since it seemed to be holding up, got out to close the door behind me, came back and it completely leaned out on the AFR, idle changed, threw a vac gauge back on, still showing steady 20". Not the first time that has happened.
Things I've tested/changed:
I don't understand how I can have all vacuum add on's isolated, spray around the intake/carb gaskets which were changed anyway, and find no leaks, yet nothing will bring it back up to 21" of vacuum
I don't get why the vacuum sometimes changes where it hangs at if I blip the throttle a couple times, yet will return back to 20 if you just hit the throttle a couple more times
I also don't see why it'd be leaning out so hard on the AFR and changing it's run quality (stumbling, missing, varying idle) without any visible changes to vacuum or fuel
The falling on it's face on off-idle acceleration & the loss of power I'm assuming is a result of whatever the problem is
![Hood Motor vehicle Gas Auto part Automotive exterior]()
Bone stock driver, 72 350 SBC (hydraulic flat tappet, 882 heads) / 2 barrel 2GV Rochester carb / automatic trans th350 / 195 t stat, doesn't overheat
Points style ignition, stock fuel system - mechanical fuel pump, no regulator or return system
Only "add ons" are temp gauge, oil press gauge, & afr gauge
12 initial / 36 total + don't remember vac advance amount
20psi oil when fully hot, climbs no problem with throttle input
Problem:
- Very inconsistent in how it runs. Just sitting idling it can go from running nice, stand a nickel on it smooth (literally) to feeling it stumble/miss sometimes just slightly and sometimes it's enough to feel it throughout the car, AFR leans when this happens, but leave it alone for a moment, look back at the AFR gauge it's now reading 14.7 and the rpm changes again. Yet vacuum gauge seems to hold a steady 20" during these events
- Noticeably down on power across the board - on the street, on the highway etc
- Bogging / stalling on off idle part-heavy throttle acceleration
- Vacuum is "usually" solid steady, but the number it hangs steadily at can occasionally change. As in, generally it's at 20" lately. But a couple blips of the throttle, sometimes it only comes back to a steady 19, and only once, I seen it drop to 17 and search 17-20 but then goose the throttle again a couple times and it'll come back to 20 steady again.
Genesis:
I pulled the engine last Summer, cleaned it up, gave it new filters, seals & gaskets, replaced the old crank sprocket, nylon cam gear & standard timing chain with a roller set. As well as the old balancer, I 100% made sure the balancer and timing marks were the same. Nothing done to heads, they weren't touched. Pulled the lifters and push rods to check, made sure they all went back where they were pulled from, checked the cam with a borescope. Rebuilt the carburetor. Put it back together, had it running great and consistent for a few months before putting it away for the Winter. Constant 21" of vacuum from the 18 it had prior to pulling it, AFR of 12.7 at idle, 15.0 cruising, don't recall WOT. It had a nice tire spinnin' up and go to it versus how flat it is now. Popped an intake end gasket (used the rubber end seal, my bad!) resealed it with RightStuff, all good again. Put it away for Winter, with the occasional starts once or twice a month allowing it to warm up and heat soak as usual.
Went to pull it out in the Spring and it just wasn't right, has all the aforementioned problems and nothing I do will bring the vacuum back to 21" Best I can ever get is 20". AFR was 12.7 before putting it away but lately it's usually 13.7 - 14 when it's running "decent" with the rare time of it going back in the high 12's. Even with mix screws backed ridiculously out. When it's running more noticeably rough, the AFR is usually maxed out lean. Yet the vacuum gauge stays at a solid 20" when this happens. A wot press of the pedal will get AFR down to 17's and then it shoots back up when you come off.. A few days ago, started it up left it idling, everything was reading okay and consistently (20" vac, 13.7-14AFR) for 60-90min while I did other things and kept a watch on it, all I did was pull it out the door to go for a drive since it seemed to be holding up, got out to close the door behind me, came back and it completely leaned out on the AFR, idle changed, threw a vac gauge back on, still showing steady 20". Not the first time that has happened.
Things I've tested/changed:
- Set transfer slot to .20"
- Throttle shaft on carb had some play, sent it out to be bushed in May. They said it ran well on their engine
- Re did the intake seals 2 weeks ago (measured for flatness on intake & heads, most variance I found was .002)
- Replaced the carb base gasket 2 weeks ago as well. The "new" one I put on after reinstalling the engine last year, had already split.
- Capped all vacuum sources and slowly added them back 1 by 1 (power brakes, trans mod, full manifold vac port on carb attached to vac gauge, PCV, no vac on ported port)
- Replaced vac lines
- Smoke tested for leaks
- Sprayed around intake, carb gasket, and vac lines many, oh so many times, looking for leaks while watching a tach and listening
- Muffling carb with hand doesn't affect idle - doesn't raise or smooth out. Idle is "usually" around 740rpm right now but can vary with how its running at the time...
- Had a fuel pressure gauge on it for a good week, cold readings are 8-9psi and when fully heat soaked 5-7psi. Rev it up and hold it, readings don't drop
- The winter gas is long gone, it's on it's 2nd tank of fresh fuel trying to figure this out
- Pulled plug wire one a time when its running rough to look for a variation, but each had an equal effect.
- Plug wires were new but tested them with the multi meter anyway, all are fine
- Resistance tested + checked distributor cap, rotor, and ignition coil (also swapped them each out individually with tested new ones I already had on hand. I usually try to keep some maintenance items like these around for the old man)
- Cleaned points, set dwell to 30 degrees with dwell meter
- Cleaned distributor, checked for shaft wobble and greased mech. plates, vac advance works with vacuum tester
- New plugs (NGK YR5, gap set to .35 same as what was in it before)
- Did a compression test last year before pulling the engine, they were 150-160. No significant blow by through valve cover tube
I don't understand how I can have all vacuum add on's isolated, spray around the intake/carb gaskets which were changed anyway, and find no leaks, yet nothing will bring it back up to 21" of vacuum
I don't get why the vacuum sometimes changes where it hangs at if I blip the throttle a couple times, yet will return back to 20 if you just hit the throttle a couple more times
I also don't see why it'd be leaning out so hard on the AFR and changing it's run quality (stumbling, missing, varying idle) without any visible changes to vacuum or fuel
The falling on it's face on off-idle acceleration & the loss of power I'm assuming is a result of whatever the problem is
