Car is an '81 with the computer still in place. Rebuilt engine with about 1000 miles on it now. Still chasing down the lack of performance "feel" that I have along with an oil leak.

Found oil leak to be both valve covers loose.....easy fix there.
In looking around under the car, happened to grab the #8 plug wire and found that I could turn #8 plug with fingers.......not good. Removed #8 plug and found it black with carbon. Did a compression check and got 135 psi. Went to #6 plug and it was only sightly tight...removed plug to find same carbon build-up. Did compression check and got about 130 psi.
Ended up removing all plugs and found them all to be black with carbon and all not as tight as I think they should have been.l

Now I know my engine is running rich....but come on now...????....it still runs....do get alot of black smoke on start-up, but it goes away very quicly.

Timing is at about 10-12 BTDC at idle with computer unplugged....get full 36 advance all in by 2500 rpm.....

Cleaned all plugs and installed a new Bosch O2 sensor as I could not get a GM one locally. Have not started car yet.

I rebuilt the carb and have rechecked the float level and solenoid travel several times. Only odd thing is that turing the idle air bleed valve is not very sensitive as the Service Manual says it is and even the idle mixture screws have little effect.

How can I tell if the jet seats are leaking? Would I be able to see fuel on the butterflys with the engine off?

I have all emissoins equipment off or plugged at this time.

Any hnts as to where I should start checking?
Should I just get a rebuilt carb and go from there?
No error codes.

Thanks for any hints in advance that anyone can offer.

LannyL81


UPDATE:
Drove car and of course it was running very nicely....gee...it should with all that carbon removed from the plugs and all the cylinders actually sealing....
Got home and then hooked-up the dwell meter to set the idle air bleed valve once again. Turned the idle mixture screws in and out to the recommended setting of 3 1/3 turns and then started adjusting the idle air bleed valve.....and what do I find??? The setting is very, very sensitive...just like it is supposed to be according to the Service Manual!!!!...very small adjustements to get the dwell at 30....very touchy...

I thought I had changed the O2 sensor, but turned out not. Looks like this may be the solution. Going to drive it for couple of tanks of fuel and then pull the plugs and see what they look like.

 

The lack of replies is probably due to the fact that there are only of couple of rocket scientist in here that can make an '81 with a 'puter run worth a crap, and do it with power. They are around, so be patient.......

In the mean time, want a lot of opinions? Trash the 'puter, smog, cat, and make some mod's!!

 

on my 82 the throttle body butterfly shaft was worn.it was letting in more air .the o2 sensor then called for more fuel .it would load up the plugs .i changed to a new coil and a new throttle body[off e-bay] problem gone ,better idle more responsive.

 

I have heard about the throttle shaft getting worn and letting in air on the QJets as well. May be just another reason to get one that has been rebuilt along with a new bushing installed on the throttle shaft.

LannyL81

 

mine was so bad you could move the linkage by hand ,with the motor running it would whisle .i would also check for other vac leakes .do your head lights work good ?

 

When I was searching for a vacuum leak, I plugged the vacuum source on the intake for the headlights in order to eliminate them completely. In fact the only vacuum line I left alone was the one for the PCV valve.
If I do have a leak around the throttle shaft of the carb, it must be small as I cannot hear or feel anything. I slowly covered the airhorn with a shop rag and the engine began to stumble, which pretty much eliminated any leaks of the throttle shaft.

Its running really good right now, so I may have fixed my problem. Have to keep driving it and then check the plugs after two tank fulls.

LannyL81

 

You might try a little carb cleaner around the base of the carb and throttle shafts with the engine idling, if the idle changes you have a small leak there. I am about to do all the stuff you did on my 81 and am keeping the computer and am interested in how it turns out. Sounds like you found the bugs, let us know. I have seen posts in here from Lars and others talking about new bushings and shafts for throttles so it should not be a huge deal if it is required.

 

When you are ready to do anything to your L81 engine in that '81 and have a question....just ask me. I think I found all the problems that were possible!

One thing I learned for sure: SBC aftermarket parts do not necessarily fit with all SBC aftermarket parts...just because it fits on the block, does not mean that the next aftermaket part is going to fit due to the previous aftermarket part.

Oh and SBC engine bolt kits are worthless....most of the bolts are to short.

LannyL81

 

Lanny,
The throttle shaft bushing installation is simple (just remember that there are 2 screws that are hard to spot when taking the carb apart!). There's a place that sells kits that include 2 reamers (but I don't know who it is). One is used to open out the holes in the carb so that the bushes can be pressed in & the other is for running through the bushes once they're fitted (I didn't need to do this as the shaft was a real nice fit). A forum member sent me some bushes & I bought the reamer here. It may be worth buying the complete kit (not doing what I did & just getting the bushes thinking that picking up a reamer locally would be the best idea) as the reamer is a 32nd or 64th size & is MUCH more expensive than more common ones. The reamer alone cost me more than an entire kit!
I was able to tell mine was worn by the fact that idle would be at different speeds after letting off the throttle. It was only over a range of about 100rpm, but with my idle set at 600rpm it would sometimes idle at 700rpm, others at 650, etc. Blipping the throttle would change the idle speed, pointing to the butterflies not seating/closing correctly & letting in some air. There's other symptoms & tests for it, but that's how I found mine.
Have you still got the charcoal cannister fitted? I found both valves on mine had air leaks that the computer hadn't detected (not enough air getting past them in closed loop to be of any consequence) & I wasn't aware of any problem. I only found them while fiddling with the cannister when it was off the car & after fixing the leaks the idle is much more regular (not that there was anything wrong with it to start with). It's these fiddly little stupid problems that all add up to make an engine run below what it should.
Good luck with checking the plugs next time.