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Gunned it and lost all power!

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
Not overheating or anything, just has no power. Feels like it is missing. Starts and idles fine. Do you think I just fouled a spark plug?
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Not overheating or anything, just has no power. Feels like it is missing. Starts and idles fine. Do you think I just fouled a spark plug?
How many miles dose it have on it?? I've seen Timing chains Jump after Romping on it and act like that!!:upthumbs
 

minifridge1138

Well-known member
Joined
Feb 2, 2007
Messages
908
Location
USA
Corvette
1982 Black Fastback
If you just fouled a spark plug, then you'd still have 7 working cylinders. You'd idle and run rough, but you would have some power.

Same thing happened to me and it was my timing chain. Get a timing gun and see what your timing is. I'm not sure about 1981, but correct idle for 1982 was 6* btdc. If your chain slipped, then you're going to be way off (you may not even be able to see the timing mark).

If it turns out that it is the timing chain, then you may want to consider replacing a lot of other parts while your that deep into your engine. I didn't replace the camshaft while I was doing the work, and i wish I had.

Good luck, and let us know if the problem is something other than timing.
 

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
Dropped it off by the shop close to me...they said the accelerator on the carb is shot and carb needs rebuilt. I just had it rebuilt about a year and a half ago. Contemplating trying to drive home (if it doesn't make things worse) and put in garage for a later date...or just saying screw it and put it on a credit card. Don't know much about rebuilding carbs, but don't really have a couple hundred bucks to blow on a red sports car either.
 

minifridge1138

Well-known member
Joined
Feb 2, 2007
Messages
908
Location
USA
Corvette
1982 Black Fastback
I've been told that rebuilding a carb is not too hard (i've never done it). There are plenty of books about rebuilding and tuning carburetors.
Personally, i'd rather spend the money on the book and the parts, than pay the labor to have someone else do it. (depending on the shop, it might be cheaper to buy a new carb and install it than pay a mechanic).

I'm glad it wasn't your timing chain.

Good luck and have fun!
 

wishuwerehere82

Well-known member
Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
It won't hurt anything to drive it home like that. Just don't expect to get any power out of it if it is the accelerator pump. A bad accelerator pump can be seen very easily. Just take off the air cleaner lid and open the throttle. A good pump will squirt gas into the carb throat as you open the throttle plates. A bad one won't.
Before you decide, have them show you the problem. And if it is the accelerator pump, we can walk you through the replacement. It's real easy, and I can't believe they would charge you more than $100.00 to fix it.
But if you decide to have them do it, I can tell you I can do it in about 20 minutes.

HOWEVER, a bad accelerator pump will only exhibit a loss of power for a short period of time after you depress the gas pedal. Eventually, the power will build as RPM increases and regain the power as you back off the throttle. It will not cause continuous missing or loss of power. It does as it is named, Accelerator pump. It pumps extra gas as you accelerate. After you accelerate, it isn't working.
So make sure that it really is the problem before you decide to take it away from the guys you took it to for help.
 

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
Thanks for the information. It exhibits all the symptoms you said, it takes a real long time to get to speed, but not to hard to keep the speed once there. Hopefully I will do the squirt test tomorrow to be sure. I think this mechanic knows what he is doing, However, after 10 years of owning the 81, I have learned to not pay the first mechanic that I take it to and to try it myself if I don't want my car scratched. I did offer to pay him for the inspection, but the fact he wouldn't give me a straight answer "couple hundered bucks" to fix it, I just couldn't do it. I would rather it sit in the garage and look good for now. On top of that it didn't start when I was leaving the mechanic. He said all he did was test drive it and hadn't taken anything apart yet. After checking the battery, he got under the car with a screwdriver and the car started itself without turning the key (that was pretty wild, guess someone wouldn't have a too hard of time stealing it). It would then turn off and on normally with the key and he said it was a bad connection in the steering column. I just got it on the road and headed home. I waited a couple of hours and it is starting fine, so maybe a freak thing on that. I read the repair manual and they stay away from the Q-jets like the plague but I don't mind getting my hands dirty if you guys can stand a couple of dumb questions.
 

wishuwerehere82

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Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
You don't need to rebuild your carb. All you need to do is replace the accelerator pump.
So all you need to do is push the pin for the accelerator pump arm out, remove the top screws on the carb, lift the top of the carb high enough to get the pump piston out, and put a new one in and put it back together.
You will have to buy a whole rebuild kit to get the piston, but it won't take more than an hour to do in your garage. You probably won't even have to put a new top gasket on if it's only a year old.

Here's some photos to help.
http://www.4wheelnoffroad.com/qjet.html
In your case, you won't need to remove the carb from the manifold, just get the top off and replace the pump.
 

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
OK, I tried the squirt test and I couldn't see any gas squirting in the carb, so I think accelerator pump is where the problem is. I am going to try and remove it this weekend. Thanks for the photos, that should help a lot. I have been reading thru the photos I see the accelerator pump mentioned a lot, but I still haven't identified exactly what that is.
 

wishuwerehere82

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Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
See the green colored lever that moves like a see-saw when you open the throttle? The rod that it pushes down on is the top of the accelerator pump piston. It's right in front of the choke plate on the drivers side.
vc-585f.jpg

..................................(^)

You will need to disconnect the choke linkage and push the accelerator pump linkage pin out in order to get the top of the carb off. Otherwise they will prevent you from pulling the top of the carb straight up and off. The accelerator pump rod will stick out of a hole in the top gasket, so you will need to pull the gasket up to get it out. Usually the spring force pops that corner of the gasket up anyway. Hopefully the gasket will still be in one piece, but you will have a new one if it isn't.
And flip the carb top upside down while you work on the pump, so the brass tubes won't get damaged.

One helpful trick to getting the carb re-aligned when you put it back together is to insert a couple of the corner screws into the top as guides for aligning the top plate to the main body. It is important that it comes out straight up and goes back straight down, so that the chance of bending the brass tubes is minimized.
 

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
Thanks for the help, now it all makes sense. Hopefully I will be up and going again by late tomorrow.
 

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
Got accelerator pump out. The kit I have has a couple of gaskets, but not a whole new piston. Looking at the pump, there doesn't seem to be anything wrong with it. The springs are in good shape. There is a blue cup/gasket thing on it that my kit also has in it. The cup is installed with the open end down (with a ring of spring inside of the cup that my kit also has), but it would seem from a more airtight/pump application that this should be installed up (like a cup) with the closed end down. Is the cup not getting a good seal? Is there something I can't see in the piston that causes it to be faulty? I pushed down on the piston once the whole thing was apart and it squirted some gas out of a jet. Putting the top back on does not seem as easy as taking it off (isn't that always the case?).
 

SIXFOOTER

Well-known member
Joined
Jul 15, 2007
Messages
117
Location
Boca Raton Fl
Corvette
1981 L81 Tan Coupe
The cup gets installed open side down, just loke what you had. Change the cup and spring out for the new parts and put it back together
 

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
still no power

Replaced the cup and spring on the accelerator pump piston, assembled, but still the same problem. There is a little bit of smoke when I started it and drove it, but it could be because I just reassembled carb. Any ideas what else I should look for?
 

wishuwerehere82

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Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
One other thing that could result in no squirting of the accelerator pump when it is working and new could be a popped fuel pump.

What you need to do now is isolate the problem.
Is it lack of fuel? Check your carb throat for fuel flow.
Is it timing? Check your timing. Insure that your vacuum advance is working.
Is it spark? Check for a bright blue spark at the spark plugs. A yellow or orange spark might indicate a weak coil.

Your starting problem at the mechanic might not be just a coincidence.
You might have a bad connection at the starter or in the battery wires that would cause a low voltage to the coil that would make for low power at acceleration. Check your battery voltage and alternator output. It should be charging at 13.7 Volts at idle and keep that voltage while running.
 

Evolution1980

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Administrator
Joined
Feb 25, 2002
Messages
4,302
Location
Cleveland, Ohio
Corvette
ZZ4, 700R4, Steeroids rack & pinion, VB&P Brakes
Replaced the cup and spring on the accelerator pump piston, assembled, but still the same problem.
Prior to replacing the accelerator pump, you said that pressing it down didn't squirt out any gas.

After replacing the pump pieces, did it still not squirt out any gas at all?
 

LanceB

Well-known member
Joined
Jul 18, 2003
Messages
455
Location
Louisville
Corvette
1981
Well I had my brother looking when I pumped the gas and he could not see any gas spraying. I had him pump the gas while I looked and I do see a little bit of gas spraying down in the primaries (I don't know how much I am supposed to be seeing, but there is some spraying in there), so I think I was barking up the wrong tree. The carb was rebuilt a little over a year ago and has been running great, so I really don't think that is where the problem is. I am going to start inspecting the ignition system starting with the coil. I have found I can do anything on this car so long as someone can diagnose my problem first, but finding out the exact problem is 75% of it, so I guess I only like the fun part which is taking things apart and putting them back together.;)
 

Evolution1980

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Administrator
Joined
Feb 25, 2002
Messages
4,302
Location
Cleveland, Ohio
Corvette
ZZ4, 700R4, Steeroids rack & pinion, VB&P Brakes
...I do see a little bit of gas spraying down in the primaries (I don't know how much I am supposed to be seeing, but there is some spraying in there)
I just tried to go out and take a video to post online for ya, but I needed a third hand and didn't have it, so....here's what I saw.

With the car off, pressing down on the accelerator pump will give you a single solid stream of gas for about .5 second or less. (As long as there is existing fuel in the line, as there is no fuel pump.)
With the car on, and the choke on, the accelerator pump will be essentially locked if you just try try to push on it.
With the choke off, grab ahold of the throttle linkage and blip it as if you had given a quick blip on the pedal. You should see a significant spray shoot out for maybe just shy of 1 full second ("One-One-Thousand"). The spray pattern should be nice a airerated (sp?) or atomized funnel of sorts.

I don't know if that description is really gonna help you, and quite frankly, I don't know if anyone without a trained eye will notice. Me personally, I didn't see the difference between my bad pump and the new one. Both "shots of gas" looked just about the same to me from what I could recall, but my mechanic (and the engine!) definitely noticed a difference! In fact, it made all the difference in the world!
 

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