Hello everyone,

I’m currently finishing the tuning on my 1966 Toronado which I completely rebuilt recently, and I’m running into a couple of issues. I'm gonna try to give you every detail I can think about.
Before all this happened, the engine was running well overall and idled very nicely. I was mainly trying to dial in the timing because I had some pinging at heavy load, when the primaries are fully open (around 3/4 throttle) but before the secondaries open. At that point manifold vacuum is around 4 inHg.

Here is the setup:
- Original points distributor
- About 8° initial timing
- About 32° total mechanical at 3200 rpm
- Stock vacuum advance can, adding about 20°, starting around 9" of vacuum
- Vacuum advance is connected to full manifold vacuum, as stated in the factory manual
- I replaced the harmonic balancer, but after checking approximate TDC on cylinder #1 it looks like the timing mark may already be slipped by about 5°.

- For the carburetor I’m running a 1967 Toronado Quadrajet (7027130, AIR K19 version).
- the non-AIR version is 7027131. From what I can tell the only calibration difference seems to be the primary rods (45 instead of 44). Jets are 71.
- I use is 98 RON fuel (equivalent to US 93) with about 5% ethanol in it (we can't find fuel with 0% ethanol where I live)..

What happened:
While experimenting with timing to try to eliminate the pinging, I had a big backfire through the air cleaner (big bang in the air filter) at WOT.
Right after that the engine wouldn’t idle properly anymore. I had to turn in the idle speed screw quite a bit just to drive the car back home.
Once home I removed and disassembled the carburetor, checked the float level, passages, power piston, etc., but I couldn’t find anything obviously wrong. Primary well plugs seams to be leaking a bit.

Now the problems:
- The idle mixture screws don’t seem to have much effect (tried between 1 and 5 turns out on each)
- I can’t get a steady idle when backing the idle speed screw down, and engine wants to stall if I back it.
- The idle improves if I partially choke the carb with my hand (which I think means my idle is lean)
- Before the backfire the engine was pulling about 20 inHg of vacuum at idle and idled very well.

So now I’m wondering if the idle circuit might be partially blocked, maybe something got dislodged during the backfire and clogged a passage.

At the same time I’m also still trying to figure out the light pinging issue under load. Should I replace the jets/rod and power piston spring to enrich ? (I was thinking for 72 jets and 46 rods)

Has anyone seen something similar happen on a Quadrajet after a backfire, or have ideas on what I should check next?
Thanks for any ideas or suggestions!

 

Sounds like a vacuum leak somewhere. What is the idle rpm?

 

Now with the current idle speed screw setting, it idles at around 850–900 rpm in Neutral. I can’t really get it lower than that, if I try, the idle becomes rough and the engine starts to shake.

In Drive, with the converter pitch in the high stall position, it drops to around 600–650 rpm. According to the service manual, the idle should be about 550 rpm in Drive, so I’m clearly a bit too high.

I’ve been trying to find a vacuum leak, but so far I haven’t been able to locate anything obvious. I checked all the vacuum lines and sprayed brake cleaner around the base of the carb to see if there was any change in RPM, but nothing changed.

 

With the idle speed high you may be out of the idle circuit in the carb, which would explain the a/f mixture screws having no effect. When you lower the idle speed you get back into the idle circuit but the a/f mixture is not set right and you get the rough running issue. Check all your vacuum connections and hoses. You might try capping all of the vacuum ports including the vac advance canister and then hook them up 1 by 1 if the problem went away.

 

Well, that's all the problem, when I back off the idle speed screw as before the backfire, I can't get it to idle fine. It's really rough and anything between 1 and 5 turns out on the A/F mixture screws doesn't change much, it still badly idles and make very poor vacuum. I tried capping also all the vacuum ports with no change (all accessories, tranny, PCV, brake booster, advance...)

EDIT: Just did a smoke test by blowing smoke in the PCV hose, the only leak I have noticed is the primary axle bushings leaking smoke on both sides of the carb. Could that explain a lean condition ? What I don't get is why could that happen after a backfire

 

Eric has nearly nailed this issue spot-on; yet, in reviewing your issue(s) I've failed to validate you're performing a proper tune-up. I trust you own the 1966 Oldsmobile Toronado Chassis Service Manual (CSM) which demonstrates the correct sequence for performing and engine tune-up. Let's review:

(1) Set the DWELL at the proper RPM - absolutely crucial;
(2) Set TIMING as per the CSM;
(3) It is only then should you be making adjustments to the A/F idle mixture screws.
(4) Set the idle mixture screw.

Note the sequence of events (above). You must perform the tune-up in the stated sequence. You are far outside the idle circuit and there's no amount of adjusting the A/F mixture screws which will bring you back into the idle circuit. Follow the exact sequence of tune-up specifications as outlined in the CSM: DWELL>TIMING>A/F mixture.

As noted in your 1st statements:
next;
Additionally, the carburetor is expected to be set/adjusted correctly. This is well established in the CSM. You should be able to achieve a rock solid STEADY vacuum reading of ~17"Hg - 21"Hg. Again, you're far outside the idle circuit. Look at the topic at the bottom of this page "Tuneup Checklist" for a stock 1966 Oldsmobile Toronado.

Perform the very 1st upper left-hand test in this guide (below). You should pass w/o fail.

 

Are you using the points style distributor still? Definitely have a look at your timing to make sure you're still in the ballpark of where it should be.

A couple threads I had going on my '66 Toro:

https://classicoldsmobile.com/forums...p-talk-179351/

https://classicoldsmobile.com/forums...cklist-186301/

 

The backfire may have blown a gasket in the carb, under the carb, the intake, the vacuum advance etc. It may have also damaged the exhaust system internally. Check the idle vacuum. Yes smoke leaking at the carb shaft is an issue but I doubt that happened from a backfire, that's just long term wear.

 

I suspect if the backfire was as strong as 2800 tons of Ammonium Nitrate (think Beirut, Lebanon) the timing chain may have jumped several teeth?

 

Dwell is set without any RPM specs.

 

You're correct. I could/should have worded my response better & I should have stated to set the dwell at curb idle - suggesting the high idle cam (full choke) wasn't engaged/sticking.

 

Dwell can be set at curb idle or any RPM, 650 RPM, 1,000 RPM, 2,000 RPM, etc. Dwell is dwell. Some people use a feeler gauge to set point gap at 0 RPM's, which can be measured as dwell.

Dwell also has nothing to do with high idle cam, choke, or anything else. Dwell is dwell.

Dwell should be set before engine timing is set.

 

I think I already said you are correct; but, I’ll say it again you’re correct.

 

Then why suggest "I could/should have worded my response better........" ? This contained misinformation.

 

It is not misinformation. OP appears to be negotiating perhaps some difficulty, establishing DWELL at curb idle provides a better opportunity to ensure fast idle cam is not engaged esp. w/ A/F mixture screws dialed in per carb specs.

 

Point out to me where he says he having trouble establishing dwell at curb idle. Also refer back to Post #12 and read my comments.

Yes, the OP has some difficulty people are trying to help with, setting dwell is NOT one of them.

 

Ok, enough arguing. I believe the point has been well covered regarding dwell, there is no use dwelling on the subject anymore.

 

 

Thank you everyone for your answers. Regarding the dwell, it was already set correctly at 30°, that was of course the first thing I checked when I started the car after rebuilding it. I initially had some dwell variation caused by a bad set of points, which I replaced, and everything was fine afterward.

After spending a few hours on the car this weekend, I noticed that my new balancer had actually slipped about 10 (not 5) degrees from TDC. I used a dial indicator to determine the true TDC and took the midpoint between the two readings.

So while I was chasing a pinging noise that I didn’t have before, the initial timing was in fact set about 10° too retarded compared to spec. And I think the noise was coming from "dieseling" more than spark knock. I'll still have to confirm that by taking the car for a ride again. But the retarded timing turned out to be the cause of the backfire.

As for the idle issue after the backfire, one of the Q-Jet idle pickup tubes got clogged during the backfire. 4 out of the 8 cylinders were running on the passenger side idle circuit, while the other four were not because the idle pickup tube was blocked. I cleaned all the carb internals and now it runs like new again, pulling 20 inHg of vacuum at idle at 630 rpm.
Thank you again everyone, hope that can help if it happens to someone.

 

Great news ! Thank you for posting a follow up.

If the harmonic balancer is slipping, it will continue slipping. It might be time for a a rebuilt one.

 

Thanks following up! Good feedback.

 

Great news, great work!

 

Great find! Glad you got it worked out. Could you clean the tubes without pulling them or did you yank em out?