‘81 B310 Weird Idle

[averdi]

Hey all,

 

To give a little background, bought an Automatic ‘81 B310 with an A15 a few months ago and have been loving it so far. Started having weird charging issues and low/rough idle so I replaced the alternator and the charge light went away, but the idling was still a bit wonky. Ended up replacing the carb with a Weber 32/36 DGEV and it seems to be happy, but I took it out for a drive yesterday, stopped at the store, and when I got back in it started up funky and started bucking/ shaking a ton at idle. Almost feels like a misfire. 
 

Brought it home, did a quick compression test and everything seems fine, but I also pulled the plug wires and pulling cylinder 3 didn’t seem to make much of a difference. 
 

Thought I’d check in and see if anyone has any recommendations on what I should look for next. No vacuum leaks as far as I can tell and I checked the valve lash and timing a few weeks ago so they should be fine. Maybe the mixture needs to be adjusted more but it was running perfectly all the way to the store, the problem only started once I got back in the car and restarted it when it was already warmed up. 
 

Ps. I removed most of the emissions equipment when I did the Weber swap and blocked everything off, no vacuum leaks from that as far as I can tell. The only thing I left connected was the vacuum advance and electric choke wire.

[datzenmike]

2 hours ago, averdi said:

Ps. I removed most of the emissions equipment when I did the Weber swap and blocked everything off, no vacuum leaks from that as far as I can tell. The only thing I left connected was the vacuum advance and electric choke wire.

 

 

There should be a large hose to the brake booster and on the same fitting on the intake there is a small hose that goes down to the automatic transmission.... better include them in your check.

 

Pull the plugs. One may have fouled (probably #3) Check that the #3 plug wire is secure in the distributor cap, check the inside of the cap.

[averdi]

Okay I’ll check on those lines in a sec.

 

I warmed the car up and then pulled all the plugs to do a compression test. All evenly worn and all hot.
 

Did a compression test and I’m getting pretty low readings but they’re all within 5psi of 115psi (cheaper compression tester so who knows).

 

Swapped the plugs on #2 and #3 and then pulled the wire from #3 while it was running and still didn’t see a change, whereas when I pull 1, 2, or 4 it starts having a bad time.

Went back and double checked the valve lash and it all seems fine, but I tuned it up anyways and it didn’t change anything. 

[datzenmike]

Swap an old wire into the #3 position.

 

115 is very low 150 would be better.

 

 

[averdi]

Any idea what would cause low compression on all 4 cylinders? Doesn’t blow smoke at all from what I’ve seen 

[averdi]

In reference to my original post, the problem seems to be fixed. Honestly a little ashamed that I missed something so small but hoping it’ll help enforce the idea that even the little things need to be checked.

 

Went through and checked the valve lash, spark plugs, wires, choke, everything I could think of. After I finished all that I was just looking around the engine bay and realized that there was no longer a vacuum cap in a spot that I had placed one earlier.

 

Seems that when I took the car out for a drive, the cap that I had put on there had blown off, and checking for vacuum leaks with carb cleaner hadn’t shown anything because it was blowing air out, not sucking air in. After putting a new cap on it seems to be running like a champ and pulling the #3 spark plug wire drops the idle as it should.