1982 Chev S-10 - poor performance question

1982 Chevrolet S-10 "Durango" 2WD pickup; 2.8 V6 engine; remanufactured "VaraJet II/Rochester" 2SE carburetor. Newly rebuilt
Metric 200 automatic transmission (& new torque converter). Aftermarket dual exhaust. No ECM or other electronic or computer components on engine.
I'm having a performance issue with my truck. When the engine is cold: It takes about 15 pumps of the accelerator to start. It idles smoothly and doesn't stall. It hesitates often (big lurch) and occasionally backfires either through the carb or the exhaust. When the engine is hot: Still idles smoothly. Doesn't backfire; hesitates very rarely. Engine is much less powerful when warm than when cold. In particular, in the middle of the throttle range tends to yield even less power than when I release it a little. Pressing the accelerator to the floor will cause a downshift because of that silly GM downshift adjustment cable, but still not much power. Big jerk back when it upshifts again and slugglish acceleration resumes. Also, engine seems less powerful when it is humid outside. It never misses, sputters, or runs roughly.
Experience with this problem: Sounds like an overly lean fuel/air mixture, right? The carb does whistle faintly during idle. I can't find any air leaks, and have disconnected and plugged all vacuum hose fittings -- still no change. The carburetor is new (remanufactured Champion 2SE). I've cleaned the carb -- helps a little, but not very much. The choke is working fine. Both barrels are opening. I did replace the gasket and adapter plate between carb and intake manifold, and tightened the carb down just a little harder than specified in spec. Verified with timing light that timing is OK and distributor advance is working. I've read that low fuel pressure could cause similar symptoms, but I don't have other common lfp symptoms, e.g. the engine isn't overly difficult to start, doesn't EVER stall, and doesn't sputter, idle roughly, or run roughly. Every book or article I've read states there's a mechanical fuel pump on the engine on carbureted models, but mine is different. There's a plate over the outlet for mechanical fuel pump. There's an electric fuel pump in the fuel tank, but not the same one as on the fuel-injected models. (The pump doesn't make a whirring noise when it runs, but instead a constant "tapping" noise as the diaphragm pulses.) I don't know if this is a factory pump or not. The engine temp stays right around 150 F, as in spec. All other vital signs seem fine.
This is driving me crazy! If anyone has any suggestions, I'd be very grateful and will return the favor any way I can. Thanks in advance.
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snipped-for-privacy@charter.net (Bryan Sembello) wrote in message

Several things don't make sense in your post. You say it takes 15 pumps of the accelerator before it starts. Then you say the engine is not overly hard to start. You also say the temp stays at 150, as in spec. Where did you ever hear of an engine running well at 150? They do make electric fuel pumps that use a diaphram, but in tank pumps usually are not that kind. Low fuel demand at idle often allows a bad pump to supply plenty of fuel at that time. Your logic is wrong as are your facts. I suggest you check fuel pressure and VOLUME with a gauge first. (Of course you changed any filters.)
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snipped-for-privacy@yahoo.com (eddy eagle) wrote in message

It goes without saying, but I better say it, if you have to pump 15 times your accelerator pump in the carb is apparently not working. You will get a huge hesitation from that alone. I think that carb rebuild is suspect.
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snipped-for-privacy@yahoo.com (eddy eagle) wrote in message

Well, I should say 4 to 15 -- it varies. And that's when cold, after sitting for at least 8 hours. What I mean is that people with low fuel pressure symptoms sometimes complain that it takes them 3 or 4 minutes to start their engine, and it stalls soon after and must be started again. I don't have symptoms that severe.

What's wrong with that? The factory thermostat is rated at 160, is it not?

I agree with your logic, but I was comparing my symptoms to those reported by some owners with low fuel pressure symptoms. Low fuel pressure doesn't always allow smooth idle -- ask around.

I'd like to do that. Unfortunately I don't have access to such a gauge. Filters have been changed, rubber hoses have been changed, and metal fuel lines have been checked for kinks and weak spots. I was wondering if my particular set of symptoms sounds familiar to you, which becomes even more helpful for someone like myself who hasn't a fuel pressure gauge.

When squeezing the accelerator pump lever with the butterfly valve open and the engine off, I can see fuel being squirted into the carb. The same occurs when advancing the throttle by hand. I've thought about this too, so I tried disconnecting the accelerator pump lever assembly to disable it. BIG difference in performance, and you're right, there was a huge hesitation then. With the accel pump connected though, I don't get hesitation when the engine is warm, or if I do it's very seldom and barely noticeable.
Thanks for the criticism -- I agree it's good practice to get the facts straight first. Do you have any suggestions??
Thanks for reading.
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By the way, one reader suggested to me in email that the aftermarket dual exhaust (already on the truck when I bought it) could be causing my performance problems. Apparently this V6 likes a certain amount of backpressure on the exhaust valves in order to operate well, and my dual exhaust (and lack of cats) could be providing too wide of a pathway, thus lower pressure. I think I may pursue this and try reverting to a factory exhaust system. Thank you, Rich!
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Do yourself a favor and ignore Riches advice. The less backpressure your engine has the better it will run. Bob
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What would you suggest?
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What would you suggest?
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What size are the pipes? Rich is partialy right. That truck probably came stock with a 2 1/4 single pipe. Its not that it needs back pressure, but that it needs flow. A pipe that is too large will kill the flow-the velocity of the exaust going through it.(its hard to explain) It might be worth while to research it a little.
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velocity
while
If we were talking about headers Rich could be right.... but we aren't talking about headers. If it has dual 6" pipes all the way back from the converter or even from the manifolds it isn't going to lose power because of it. Bob
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Oh, BTW, forgot to mention that I do not have catalytic converters. The truck would have come factory with one, but I've never seen it. Two 2" pipes all the way from the manifolds to the rear bumper.
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The pipes are 2". Actually, if you want to be precise, one has an inside diameter of 1 7/8", and the other 2 1/8". Nice set, huh? I'll check into it. Can you suggest any sources other than Google?
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Does that carb have a square screen on the top with 2 screws holding it on? I think you can adjust the main jet IIRC. You need a dwell meter and the special "screw driver" to do it correctly. IIRC it will go a little lean and can be adjusted out.
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Yes, that's the one! It's a Rochester 2SE carb, aka VaraJet II, and it has the screen of which you speak. (Later models added electronic crap and called it E2SE, and some models had a Hitachi carb.) All literature I've been able to procure, official or not, says it's an auto-adjusting carb and has no adjustments except the slow idle and the idle mixture screw. Is the main jet adjustment inside the screen? What would I do with the dwell meter? Wouldn't that only help in the case of an electronic feedback carburetor?
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on?
and
Its not a feedback carb on that 82? Yes there is a specal screw driver that fits the main jet inside. I have only adjusted feedback versions IIRC (many years ago). It wouldn't suprize me if you can adjust the pre-feedback versions too. The dwell meter is for feedback carbs yes. As far as the exhaust goes, your pipes are probably too big but that would only hurt your low-end torque a little, it wont make the thing completely gutless. It really sounds like it is running lean. Did you say it runs good with the EGR disconnected? Did you check all the basics like the timing?
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I checked timing with a timing light and adjusted to precision -- 3 deg after TDC or whatever the factory spec was. Also verified that the distributor advance is working (replaced the vacuum advance a while back). The timing was a little off (too advanced), but retarding it to spec didn't have much of a noticeable effect on performance. I did replace plugs and wires after that too. No noticeable effect.
The emissions control system in the 1982 model is much simpler than you're thinking it is. There is no EGR valve. No oxygen sensor, MAP sensor, no air pump, etc. (There really are no sensors, save for a couple of vacuum modulators in the carb. I don't have an ECM nor a "check engine" light, if that tells you anything.) There is the charcoal canister (called something like "evaporative emission control system") that stores unburned gases, but that silly troublesome thing is disconnected and bypassed. The there's the catalytic converter, which is missing. So mine in its present state really doesn't have any emission control. Either 1983 or 1984 added all the extra junk you may be thinking about -- or maybe 1982 with California emissions. You may as well forget this is even a 1980s vehicle.
I would imagine that the main jet would be adjustable on this card too, if it is adjustable on the later feedback version. The E2SE just added feedback sensors, solenoids, etc. to the 2SE. AFAIK, nothing else changed. But I've never adjusted a jet in a carb. What would I use as a guide for adjustment, without the dwell meter? Can you recommend a how-to or FAQ? The Haynes manual details rebuilding of the entire carburetor but mentions nothing about adjustment of the jet, or even that it can be.
Thanks for bearing with me. Your comments are much appreciated.
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I feel your pain. I've got a 83 s10 2.8v6. I had similar problems. I can tell you 4 sure that your truck did not come with an intank fuel pump. I installed a new electric fuel pump ($40), removed the origianal mechanical pump, advanced the timing 1deg and now it runs like a champ.
Looks like crap, but runs like a champ.
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Hi! Thanks for your message. So it looks like you concluded that your old fuel pump was the problem -- low fuel pressure or low fuel volume. What kind of fuel pump did you get -- could you share any details? I really hope my solution can be this easy. I did also try advancing the timing slightly, and there was a discernable difference, although only marginal, so I set it back to factory spec.0

Hey, at least I've got 1 out of 2! ;-)
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