hammmy

I just bought a stock 1982 GS today for $900, making me the 2nd owner at 191,405 miles. She's a beaut, excellent condition, other than a good-sized oil leak somewhere between the housings. I did have a couple of problems with her today though that I'd like some thoughts on.

The Engine Temp Overheat light came on for less than a minute when I was cruising slightly above 70mph on the highway. I backed off to right at 70mph, and the light went off. I figured that was probably indicative of a partially clogged catalytic converter, which a search here verified, so nothing unusual there.

However, I've noticed that the 7's motor continues to accelerate when pushed past 6Krpm, after I've pushed in the clutch and lifted throttle to shift. Very noticeable, once going some 800rpms higher than where I lifted at. I tried a search here, but failed to find a set of search keywords that worked. This one has me a bit stumped. I theorized that a clogged cat might be creating some sort of backpressure exhaust backlog that's causing the run-on--I know, I'm reaching, but it's 1:30a.m. and I wanted something to run up the flagpole here. Any thoughts?

Other than that, I had a great day driving her. Probably the best $900 I'll ever spend. Hell, I don't even hate the FB taillights as much now.

Thanks,

Kentetsu

Hmm, as far as overshooting on the revs after engaging the clutch. I would start out by hosing the cabes and linkages with a good penetrating lube. After that check for any kinks or binds. Have someone engage, then release the gas pedal while you watch it working. Does it release right away, or is there a delay? If it releases right away, and you still have an issue, then this is the wrong track (must be something else).

As to the engine overheat warning light, I wouldn't be too quick to dismiss that as a clogged cat. Make sure that your fluids are full, no kinks in the hoses, fan belt not loose, etc. If you have good power, then your cat is probably still flowing ok. If it was clogged, there would be a good reduction in HP.

The oil leak sounds serious. I believe that a leak from between the housings means a rebuild, but I'm not completely sure. Good luck with it...

Kentetsu

BTW, what was your temp gauge reading when the warning light came on? Also, overall how is the car running?

84stock

iTrader: (5)

Temp light, check timeing, can have an impact on exhaust temp, it's free to check and adjust, then check the cats. The carb has a diaphram on the side that holds some throttle pressure when you let off the gas, this helps to match rpms for easier shifting, I pulled it off mine becasue I didn't care for it. Oil leak, see if you can find "Justice Brothers" oild stop leak, this stuff is incredible!

hammmy

Thanks for the replies. Yes, the oil leak indicates a rebuild, but so does 191Kmiles. I have now have a spare 12A in my project '80 that I can swap in if a natural failure occurs.

Overall, the car runs very well. Pulls strong. Smooth idle, smooth acceleration to redline. I'll check the throttle linkages to see if that's causing the run-on. Fluids are full, checked those for contamination before buying. The coolant temp gauge was reading under half when the overheat light came on, and that appears to be its normal operating position--from what I can tell in one day of driving her.

Thanks,

-dave

hammmy

I checked the throttle cable today, and WD-40'd the area. I was alone, so I didn't have somebody to pump the throttle for me while I looked at it. Still, I feel confident that it moves smoothly. In fact, I noticed when driving afterward that the pedal returns normally during the run-on condition.

I'm thinking I'll read the carb manual and look for the diaphragm that 84stock mentioned. I'm also wondering if clutch slipping might cause a problem like this.

Kentetsu: I meant the Exhaust Temp Overheat light in my first post.

Evidently God hates FB lights, because a DUI rear-ended me in a van on Saturday. The lights have been punished.

-dave

Kentetsu

I blelieve that the diaphragm that you are looking for is called the "dash-pot". It's used to keep emissions within limits when coasting or downshifting.

hammmy

See, that's what I thought initially too, but the dashpot only kicks in when the throttle is nearly closed. Judging from the one on the rebuilt '79 carb I have sitting around, there's no way it could be misadjusted far enough to affect full-throttle. Maybe 84stock can clear up what diaphragm he was referring to.

On a trivial note, I was listening to NPR a few days ago, and they were playing some word definition game when "dashpot" came up. It means shock absorber, apparently.

I was thinking today that it might have to do with a sticking vacuum secondary diaphragm. The run-on condition never occurs when revving up slowly, like when only using the primaries. It only happens when I plant the pedal and let it rip to 6K+. I'm thinking the vacuum might build up high enough at that point to cause a defective secondary diaphragm to stick, leaving the secondaries wide open. I'm going to look at my spare carb to see if/when the secondaries are mechanically closed.

-dave

Kentetsu

To test the secondary and eliminate it from the equation, just remove/plug the vacuum line going to the actuator. Car will be down on power, but if problem is fixed then you know what to look at.

hammmy

Ooooh, that's good. Thank you, sir.

ChasRX

The Dashpot dampens the throttle linkage from slamming shut; so that the "shock absorber" term would be appropriate. It does have that little plunger-damper action.
The exhaust temp send-unit could be faulty. I think that is somewhat common after all those years.

Tech_Greek

Would that affect your power at all? I mean, reaction time pedal wise from human to mechanic wise...

- Tech

hammmy

It engages late in the throttle return. If you were to rev your engine and watch the tach, you could probably see the rate of fall decrease when the tach falls to around 1000rpm.

ChasRX

hammmy = correct. It doesn't affect any reaction time. The damping is a one-way action that happens only when the throttle cable / linkage is released, not when there is tension pulling the linkage away from the dashpot's point of contact; such as when you are pressing the gas pedal. It is easy to watch it work once you've identified it on the carb.

hammmy

OK, I disconnected the linking rod from the secondary diaphragm's lever that runs to the secondary throttle shaft, and drove it awhile yesterday. No throttle sticking whatsoever.

I'm going out now to play with the secondary throttle shaft and maybe take off the secondary diaphragm's housing to look at the vacuum lines. I took off the cover of the diaphragm housing yesterday, and it looked decent enough. Couldn't really tell much with it on the carb, though.

Kentetsu

Hammmy, you might as well consider converting to mechanical secondaries while you have it all torn apart. Very simple mod, and the instructions are in the FAQ page. Feels a lot stronger once its done, but you might not like the change in fuel economy...

hammmy

Yeah, I was thinking the same thing today, after I reconnected the diaphragm and it still had the problem. I sprayed a good load of carb cleaner down the throats and around the linkages, but I doubt it's going to clear out whatever is causing this. I tested the secondary linkages on both sides, and they looked fine.

hammmy

It's incredibly irritating to drive a 7 and not be able to wind it up at will.

hammmy

Well, I finally made some progress on this issue today. I swapped the vacuum secondary diaphragm from a '79 carb onto the '82, and while I had it off I blew some compressed air (~40PSI) back through the secondary circuit. I didn't see anything that came out when I opened the throats afterward, but I thought heard something get cleared.

I put it back together and drove her home, and the problem has improved. I can take it to 6KRPM no trouble, and to redline with just a bit of run-on at that point. I'm thinking I may blow the circuit again next weekend, when I can get back to my compressor. I'm loving my new compressor. They're so handy.

Kentetsu

Glad 2 hear it man. Redline = Happiness!