L-82 4Speed

Is there a good aftermarket carb that will fit with the stock intake and air cleaner on a '79 L-82 4 speed? My car runs great with the quadrajet but sometimes it floods on hot starts and diesels after turning off. The timing is set at 36 degrees at maximum advance and the idle is set at 900 rpm's. I would like to get a new carb but I don't want to change the intake.

lars

Run-on after shutdown is not a carb issue - it's caused by excessive throttle blade opening at engine shutdown (excessively high rpm). Flooding at hot start is also not likely a carb problem - it's a heat soak problem that can be corrected with a reflective heat shield. Replacing the High Performance 800 CFM L82 Q-Jet is not likely to fix any problems other than provide you with a significant decrease in overall performance.

...But if you do decide to get rid of that Q-Jet, please send it to me - I have people standing in lines waiting for a carb like that..!

Lars

vetteguy75

Lars is the MAN who know carbs!!!! Trust his recommendations! I had a Holley 650 sent to him after many many problems and when I got it back, I installed with and it's been running perfectly...and that was 8-9 years ago!!

L-82 4Speed

Thanks Lars! I'll try the heat shield and see if that helps with the heat soak issue. Is there a particular shield that you recommend? Any advice on fixing the run-on issue?

JoeMinnesota

Your problem may be simple - too much timing and idle too high. Unless you're running a pretty radical cam, turn the idle down to 700/750. That may fix your problem. If it persists, you can also try turning your timing back a degree or two, then readjust idle. It's most likely the idle sitting too high and the motor doesn't want to shut down. 900 with a 4-speed in neutral is quite high.

I'm speaking here to the run-on problem, not flooding. Yes, you should run the heat shield on the intake.

L-82 4Speed

I'll try 700 and see what happens. I set it at 900 because that's what it say's on the emissions label and in the shop manual for the L-82 with manual transmission.

Kevova

Does carburetor have electric idle solenoid?

L-82 4Speed

No,it has the stock air choke.

BKarol

I agree about continuous use of the qjet but to answer your question. Forum member JB78L-82 is using a Holley 4175 with original intake and air cleaner on his 78L82. If I needed to swap this is what I would buy also. My 78 L82 4spd, also calls for 900rpm idle.

https://www.holley.com/blog/post/4165_4175_carburetors/

Kevova

There should be a idle solenoid that would be set for 900 rpm. The base idle screw on carb would be at maybe 500.. When the key is in run the solenoid extends to hold throttle open for idle. When key is turned to off the solenoid retracts and throttle closes slightly to prevent " run on".

jb78L-82

I would go with Lars looking at your OEM Qjet if the issue truly is a carb one (there was no LARS for me to send my OEM Qjet to back in 1985!). I have had my Holley 650 CFM vacuum secondary Qjet replacement on my L-82 since 1985, rebuilt 2X by me in my garage in the last 32 years, and still going. Great carb since it has worked perfectly on the rebuilt/upgraded (2014) L-82 355 with 425+ Gross HP
with minimal effort outside of going up 5 jet sizes after the rebuild from a 63 main jet to a 68...Probs still needs a couple size more jet with the 1 7/8 LTH on the engine now to breath.

stingr69

I might be crazy here. Someone is sure to confirm it....There are anti dieseling solenoids that de-energize when the key shuts off the motor AND air conditioning solenoids that get power only during A/C operation. Depending on the application, the solenoid may be there for A/C. Some cars use a solenoid to bump open the throttle a bit to compensate for the A/C drag once the compressor kicks in.

They look the same but have different functions. Crazy or not?

L-82 4Speed

No idle solenoid on the '79 4 speed.

L-82 4Speed

Sorry,I misread your question. It does not have the idle solenoid.

Jebbysan

Lars already popped in here but I am going to go a step further and suggest checking your float.......condition and setting. Can't hurt and it is free if you break the gasket free without damaging.

Yes....dieseling is caused by throttle plates too far open.
Hot start can be heat also.......try the aforementioned heat shield or a thin phenolic carb base gasket.......many stock Q-jet gaskets are extra thick if you do your research.

Jebby

L-82 4Speed

Does anybody know which heat shield is best for my carb?

Jebbysan

This one is the factory kind...although it is discontinued......
https://paceperformance.com/i-625030...jet-carbs.html

This looks promising.....but you will need the thick base gaskets to go with it....
https://www.ebay.com/itm/ROCHESTER-Q...-/252484955745

Jebby

Bikespace

Here's a possible quick fix. Are you already running high-octane gas? Mine is an L-48 4-speed, so it should run fine on 87. Except that it doesn't.


It ran hot (too lean?) and dieseled at shutdown. I switched to 93 octane and the problem went away.

L-82 4Speed

I do use 93 octane but I just found a station nearby that has ethanol free so I'm going to try that since the boiling point is much higher. I'll fill up tomorrow and see how that works.

JoeMinnesota

The idle adjustment is a quick fix - takes only the amount of time to start the car and open the hood. No need for a 900 rpm idle.