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Discussion Starter · #1 ·
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:
  • 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
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Bill
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Sounds like all carb and fuel pressure problems to me. 8-9 psi is too high. Does that carb have a power valve like a Holley? Check to make sure the distributor weight springs are not broken.
 

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Discussion Starter · #3 ·
I was thinking the pressure seemed a little on the high side as well, but do please correct me if I'm wrong in my thinking; wouldn't too high fuel pressure cause it to push past the needle & seat flooding the carb and causing fuel to Dribble? Wouldn't that have me overly rich opposed to lean? Similar with a blown power valve? But yes it does have a power valve.

I failed to mention that in my post, when I cleaned the points, I also disassembled the weights and springs within to clean and grease the pivot points. Had to remove them for easier access to the points anyway.
 

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Bill
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Have you disassembled the carb for a good cleaning? Maybe needs a power valve or jet change for the off idle bogging. Does it have a sintered filter on the inlet that needs cleaned?
 

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Discussion Starter · #5 ·
I did rebuilt the carb in 2020. I'm considering giving it a tear down again to try cleaning it out as I don't really know where else to go with this... I wouldn't think it would need a change in jets as I'm certain my old man has never changed them in the 8 years he's had the car, and I did have it running great just last year. So I wouldn't think the jets would become a problem now? Short of having trash in them. I checked the fuel filter in the carb inlet, it didn't look concerning. But I may go through it anyway
 

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I would start with a carb disassembly, cleaning and rebuild. All I can think of is sitting for the winter with the crappy ethanol fuel affected something as it evaporated. I have been pretty lucky with my carbs but had a needle and seat issue this spring after winter startup.
 

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Discussion Starter · #10 ·
Pulled the carb tonight to open it up and make sure everything is set right. It is, no adjustments needed. But did find some crud in the fuel filter, so changed that out and blew threw all the carb orifices. Also noticed the 2 week old carb base gasket already starting to split 🤔 so swapped that out with yet another, slapped the carb back on the intake, threw all the vac lines and what have you back on, now she don't want to run without constant throttle input. So I've likely missed something or slipped a gasket and actually do have a vac leak now 🤦🏼 But I'm tired. It's been a hot one today and it's late, I'll look at it fresh tomorrow, get that straightened out and we'll see if anything comes of the rest.
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Are the 2 rubber lines coming up from the left front wheel well part of the EVAP system? If so unhook it and take the gas cap off so the tank is vented you might be creating a vacuum in the tank. You cannot tell if the sintered filter is plugged by looking at it just replace it or take it out just for testing. Check all the rubber lines from tank to the carb, even if they look good they can be collapsed on the inside causing a restriction.
 

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A bad or failing condenser will cause a random misfire and especially when putting a load on the engine (i.e. accelerating).
 

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Most likely you left something off or knocked something off while working on it.I have found that anytime it runs bad after I worked on it then it was something that I probably did.Go back over everything you either worked on or disconnected and then you'll find whats wrong now.
Those 2GC type 2 bbl's have a couple of problems that are part of the way they're made.Number 1 don't over-tighten the air cleaner wing nut as that can cause a slight vacuum leak.
#2 the screws that hold the carb together that are accessed from the bottom of the carb have a tendency to work loose after awhile.
#3 make sure the float setting is as close to perfect as you can get it.
 

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Discussion Starter · #15 ·
Got back into it yesterday, got my hiccup sorted so that it was running again. It was still leaning out so I started isolating vacuum sources 1by1 again but doing test drives between each change. Capping off the trans modulator line, helped it not be so lean on the AFR. So I'm going to take the metal line off, cap one end on the line off, apply vacuum to the other and see if it'll hold it. Otherwise I suppose it could be the modulator itself, though I wouldn't say it shifts concerningly late and it's certainly not smoking like it's burning ATF. The most I could say is that it could shift slightly smoother when its hooked up. I checked the fluid level after a good drive through the gears with the modulator line capped off, it was good.

While I was doing that I seen 396325's comment about the EVAP. Admittedly, I never think about the evap system, so I removed the line (noticed it was wet, not sure if that's normal?)
Anyway that helped it a little more on the AFR gauge. Probably a combination of a clogged filter as + bad lines. I can guarantee the filter hasn't been done in minimum 8 or 9 years and I noticed while disconnecting it that the EVAP lines under the hood were pretty cracked and dried out. I don't imagine the ones going back to the tank will be any better.

Overall it seems to be a step in the right direction. Having the trans mod line capped and the EVAP disconnected, helped the gauge be a little steadier on the richer side and so far seems to have stopped it from leaning maxed out at 18+.
On the AFR it's a full point (1.0) higher than I'd like it to be, and I haven't gotten the 21" back yet, but it's much more drivable now.
 

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Discussion Starter · #18 ·
Most likely you left something off or knocked something off while working on it.I have found that anytime it runs bad after I worked on it then it was something that I probably did.Go back over everything you either worked on or disconnected and then you'll find whats wrong now.
Those 2GC type 2 bbl's have a couple of problems that are part of the way they're made.Number 1 don't over-tighten the air cleaner wing nut as that can cause a slight vacuum leak.
#2 the screws that hold the carb together that are accessed from the bottom of the carb have a tendency to work loose after awhile.
#3 make sure the float setting is as close to perfect as you can get it.
You would be correct, simple little mistake on my part. Sorted that out and carried on. Interesting about the wing nut though, wouldn't have really thought of that. I was worried the baseplate screws may have worked loose, but fortunately they were still pleasantly snug.
 

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That's what I was thinking of, the baseplate screws but couldn't remember the right name of them at the time of my writing. Have you considered switching to a 4bbl intake manifold ? Stock or aftermarket ? If you do PM me I may be able to help you out.
 

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Discussion Starter · #20 ·
That's what I was thinking of, the baseplate screws but couldn't remember the right name of them at the time of my writing. Have you considered switching to a 4bbl intake manifold ? Stock or aftermarket ? If you do PM me I may be able to help you out.
Have I ever... lol.

At this point, admittedly it's just sheer stubbornness making me want to figure this out and get it right... and then throw it all on the shelf and forget about it. Surprisingly it's a numbers matching carb/block for the car, thats the only reason I've put up with it this long. You got someone Canada side with parts?
 
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