Finally got a chance to hook up the dwell meter today after all the road blocks and saw it read 34°. I backed it down to 30° per CSM, as well as knocked the timing back to 14° from 18°, and balanced the carb screws out a bit better. Well, now it's detonating much sooner than I've ever heard it.

Now, before making an adjustments, I had previously noticed that the distributor seems to have about 14° of mechanical advance.

So..what's next? Ive never had to dig into ignition timing this much, so it's all new to me. I still plan on sending it to the dyno, but Id like to at least make sure it's not detonating before I schedule it in.

 

This is on the '69 442 yes, stock engine? Is it running hot? Fuel fresh and premium?

 

Yes.

Rebuilt engine (.040" overbore, mild cam) premium fuel but it is very hot. Doesn't seem to overheat, but it is stupid hot to the touch.

 

I would start by putting it back where it was and see what happens.

How old is the fuel in the tank ?

 

14 initial + 14 mechanical = 28 total, which seems to be low enough to not cause pinging. Also, the low vacuum (if due to the camshaft duration) should mitigate cylinder pressure and pinging.

 

Fuel is relatively new. I think I filled it up about a month and a half ago but haven't driven it much.

I agree, based on the numbers there's not enough timing in it to allow it to detonate.

 

It's worth using an infrared point and shoot thermometer to know the temp.

 

If you have a vacuum gage, put it on the car and try adjusting the timing until you get the highest vacuum. Tighten it down and go drive it.

 

14° mechanical is one part of the advance curve:

Your in Ohio I'll assume at sea level-ish.

Start w/12-14° initial at warm curb idle, (700-900 RPM). Use a vac gauge on a straight intake manifold port to adjust A/F and timing throughout this tuning session to achieve the highest Hg reading at idle.This is what your engine likes...its happy spot.
Limit vacuum advance to 8-10° at curb idle.
The rest of it "all-in" for a total of 36-37° ± 2° at 3000RPM max..

Specs are for a street car with a good carb & ignition system at sea-ish level, 91+ ethanol free gas, some 108 octane booster, max 11:1 CR, 90°F ambient, engine running temp, no more than 210°F...
Back off on the total as elevation and ambient temp get extreme. Extremes will require richer A/F less advance and cooler plugs,

Cooling and fuel system health, vacuum leaks, point bounce, distributor shaft wobble, negative wire intermittently open, **** china coil, points n condenser, cap rotor wires and plugs, and timing chain slop will cause knock.

 

With no consideration to what that will do to the total timing, yeah real good idea.
Bryan, don’t do what he said.

 

I would say your ignition timing is well within the ball park. I would double check your firing order just to rule it out. Does the balancer look good? It may have slipped, i would pull the number 1 cylinder and verify your at TDC with the mark at zero.

If all that is correct, the next thing I would check for is a flat cam.

 

I wonder if the balancer is indexed correctly? Put the #1 cylinder to TDC and verify the marks on the balancer line up with 0 degrees. Easy enough to do.

 

Balancer mark was verified over the winter when the cam was degreed and new timing set installed.

It ran well a couple weeks ago, only slight detonation (when I heard it I got out of it) but it was dropping into gear hard and hard to start when warm..both signs of being too advanced. I went out today and backed it down the 4°, then adjusted idle/idle mix to try to get vacuum back (went from 9-10 to 7-8). When nothing changed on that front other than how long the car would stay running, I figured it'd be a good time to check the dwell. Once I adjusted the dwell, it seemed to even out a bit (RPM settled out) but it now read 12° initial. I bumped it back to 14° and took a drive.

I dIdnt get the chance to push it heading to my normal turnaround spot, but it did seem to be pushing me (part idle too high, part low vacuum-not great brakes). When I pulled out from my turnaround, I stopped and then floored it from the stop..it cut out, then took off..but as the RPMs climbed, so too did the pinging. My tach in the car doesn't work that well, otherwise I'd have been able to note where it started..but at that point I was just befuddled.

I may go out and back the mix screws off a big and try it. It dawned on me it could just be too lean still

 

Keep in mind those screws affect the idle mixture only, and do nothing once the throttle is opened any at all. The jets, rods, and power piston control the mixture when the throttle is opened.

 

yeah, I realized that while I was out tinkering. I reset everything to what the factory calls for (yes, I know this isn't a completely stock engine but figured it'd be a good jumping off point). It was idling okay, then started to pick up RPM on its own..I bumped the throttle a couple times and it settled back down. When it idles around 850-950 (I say around for a reason) it idles rough. It idles well the higher up you go, but then it slams into gear and has a hard time stopping. I got back to the house after no change in testing, and shut it down..and it had a good amount of run-on. So I backed the fuel back down and the throttle screw back down to where I had them at the start of the day and had a heck of a time to get the thing started/running.

For grins and giggles I compared my two dial back timing lights..one read 11°, the other 14° (this is the one used to set everything).

If it weren't detonating and the issue was solely the rough running, I'd think my issue was the timing light being off..but that doesn't explain the detonation.

Plugs definitely got hot, but there's a bunch of carbon build up around them (see not so great picture)

I'm simply just trying to get the thing running decent for a starting point for the dyno. I only get 2 hours so I'd like to have it as close as possible, but I feel like no matter what I research & do, I'm only going backwards.

 

I would check the cam at this point. Pull the covers and crank it over. See what they look like. I'm not thinking you have an ignition timing issue at this point.

 

Sorry but not true.
The idle circuit typically flows at least some fuel 100% of the time. In fact if there’s enough vacuum at wot it can even pull fuel from the accelerator pump nozzle.
Bryan, I’m guessing you never bought a wideband?
Even though the plugs show rich, if you have lean spots that’ll induce detonation if your timing is on the edge, and/or you have cooling or circulation issues. Process of elimination, get the O2 if you haven’t already.

 

No, thats the primary reason Im going to send it to the dyno. I just need to get it to where it'll make it on/off the trailer and then where it isn't immediate detonation.

 

I didn’t realize the running quality was that bad.

 

it wasn't until recently

 

Off the wall but check anyway. QuadraJet, right?

Engine off, stick a small screwdriver in the airhorn bowl vent and make sure the power piston is traveling freely against its spring. If it's stuck down the primary metering rods won't raise in the jets under acceleration and you'll have a lean condition.

Also check the secondary metering rods to make sure the cam raises them full travel.

QJets can be bad about bleed tubes falling out of the airhorn too, which will make them do stupid stuff.

 

Yes, fresh rebuild/restore Qjet from OldsMotion. It had a Jet Qjet on it and I practically had the idle mix screws closed and it was still rich..but when I swapped carbs thats when my rough running started. Ive thought about swapping them back for troubleshooting purposes, but at the same time I don't understand how it ran fine after assembly, ran fine when I put it on the car initially, and the 2nd time I drive with it on..it starts acting up.

 

Oldsmotion does excellent work. Are you sure it's definitely suffering from detonation? I'm not an expert by any means but it's not very often you hear about issues with Qjets causing the engine to detonate......that's usually ignition related isn't it?

 

agreed, that's why I can't immediately assume its carb (even though that's when the headaches started)

It sounds like someone has a jar of change and is rattling it around. I figured ignition based on A. I knew it was high to start and B. It acted too advanced even before swapping carbs, but that was the payoff for vacuum issues.

The detonation did get substantially WORSE when I set dwell where it needed to be, which to my understanding of how dwell works..that makes sense. But it shouldn't have gotten worse after lowering the initial 4°.

 

If you changed the tires on your car and all of a sudden you had a vibration, what would you be looking at ?? Just saying.

 

I don't disagree with that, however I will say when I've had a car set up to run with a carburetor dumping too much fuel, switching to a carburetor that isn't dumping that much would tell me I need to back everything else up to match it back up. The inconsistency as far as the idle goes is a bit concerning, but then again even with the old carb there were plenty of inconsistencies.

 

Quit chasing your tail Bryan, buy the wideband. At the very least that’ll be something you can cross off the list as a potential problem.
John’s(Oldsmotion) carbs normally work as originally designed, BUT are not necessarily jetted correctly for anything other than a totally stock build. Buy the wideband.

 

Well, like I was saying I'm trying to get it to at least run decent to get it to the dyno..but with that being said I've reached out to a friend who tunes for a lot of the local racers around here. He set me up with the parts list for my SBM Dad and I built years ago, and it ran great..especially when it finally had the right converter behind it. If he's willing to (and comfortable working on it) then I'll go ahead and buy a wideband kit and go that route. I'm not overly confident in my tuning abilities past what I've done thus far. While there's no better way to learn, I'd rather learn on something I don't already have 11k in..ha

 

Obviously a wideband will at least let you know if it is a carburetor problem but I think you have more than that going on. Can you post your camshaft specs ?
Is the vacuum advance working properly on the distributor ? Do you have it hooked to manifold or ported vacuum ?

I am just thinking out loud but unless your camshaft is some outrageous one I dont think you should be having these issues. Yes the carb will need to be tuned but it shouldnt be as far out as it sounds like it is.

 

Cam specs below:

vacuum advance is hooked up in the factory location but I have not verified the advance is working properly..but at the same time I figure it wouldve had this problem before if it were the advance The vacuum issue has been a constant since the engine was built. It has gotten better since degreeing the cam, but still not where it should be. I wouldn't imagine overbore creating a drastic drop in vacuum, so I don't even really consider that a culprit. I had done a compression test prior to the cam being degreed and it came in between 145-155...so consistent (though shouldn't have that much gap between for being a new engine) but lower than expected. I have not done one since degreeing the cam.

 

That's a bit of a cam; more than I'd want for my poor old G-motor. You might consider backing off on it a wee bit.

However, I don’t think it's the root problem -- it's not so radical that it should be causing the dismal vacuum reading you're getting, or even the lackluster cylinder pressures.

Maybe a wideband is the only way to solve the mystery, or at least point you in the right direction.

 

That is a pretty good size cam especially with it being on a 108 ls. I think you would do yourself a huge favor by getting the vacuum advance working and hooking it up to manifold vacuum. It is virtually impossible to have a proper timing curve without it. That would be my first step.

 

b,
Try this just as an experiment. Bump your base timing up to around 20 degrees and see what happens to your vacuum reading. You probably don't want to drive it like that but it might give a clue which way you need to proceed.

 

18° helped vacuum out tremendously, but was kicking back. With that being said though, it was 18° when it had it's first bout of detonation

 

Post #13, 7-10Hg vac signal, there is part or most of the problem. Call John (Oldsmotion) and give his that cam and Hg data.

The carb needs to be set up for all of this. Cliff Ruggles could help with suggestions and the right parts as well.

The wide band O2 is a great tool. No guessing which side of stoich you are running, then tune accordingly. I'll bet you are well above 14.7 AFR.

Get an assortment of Qjet parts to dial in the carb before the dyno. You will need an assortment of primary and secondary rods, primary jets, power piston springs, and possibly a different secondary hanger and cam.

 

Thats because it is actually too much but ...... if you had the vacuum advance working you would only have the 8 or so initial while starting but once the engine starts the vacuum advance will pull the timing up to maybe 20 or so. When you get the car under load the vacuum cam will retard the timing and help with the detonation. Thats with the vacuum hooked up to direct manifold vacuum. All of this stuff has to work together and also affects the carburetor so its a juggling act.

 

I've been texting back and forth with John while at work, he said it sounds to him like its either a fuel starvation issue or is sucking air (at the very least regarding the idle/running issue, not sure if he's also looking at the detonation issue).

I think for troubleshooting sake, I'm going to swap the Jet carb back on it. As he pointed out, if the new carb is off..its halfway to being shipped for him to look it over.

 

Alright, so I got off work and threw the Jet Qjet back on. It idled better (especially once I found a vacuum port I forgot to put a plug on), vacuum was between 9-10, and most importantly it didn't detonate. It actually pulled HARD, which it'd never done.

John had suggested to swap them and if the situation was resolved, to ship it back..so I'm reaching out to him. Hopefully its something simple (maybe something that got knocked out of adjustment in shipping) but we'll see.

 

But the Jet carb ran rich at idle correct?
I’m just going to point out the obvious, NOBODY can guarantee that the carb they give you, no matter what it is, will be right for YOUR combination.
I’m getting really tired of beating that dead horse.

 

Yes, mix screws are practically bottomed out. Im not saying the Jet is the answer, nor am I saying I expected the new one to have been perfect OOTB..I just didn't expect this many issues and in talking with him he didn't either. He's going to get it back to ensure there's not an internal problem.