When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a few questions about basic tune ups on these old machines.....I'm such a novice with this side of things, honestly. I follow a lot of interesting people on YouTube who certainly know a lot more than me and I've really enjoyed the various takes on doing a basic tune up on the old girls. I definitely take this kind of advice cautiously but one thing they all seem to agree on is to use the specs in the manual as your starting point. Once the engines get a bit older and things are a bit worn, you often have to tweak the timing a smidge to get things back in line. Sounds reasonable to me but it also seems like it's a little bit of an experience/trained ear type of thing. Do you guys agree? Obviously you have to watch out for detonation.
The other question I have is idle RPM, which I'm quite confused on. Almost everyone I watch doing a basic tune up just kinda sets the RPM's to where it seems fine but to my ear their idle seems quite high compared to mine. In my case, my car calls for an idle RPM of 575 (that would be in-gear, brakes off but with the wheels chocked) and that seems to work out to roughly 675 RPM when in Park.
Now at the same time, all of my tuneup specs ('66 Toronado) are to be adjusted and set at 850 RPM for some reason. I always just use the idle screw to get it up to 850 while I check timing. Just wondering why we have to have the RPM up high like that when checking timing? Does it matter? I assume it does. Seems like the good folk on Youtube......all their cars are idling at 850 already. Seems like you'd have a hard time adjusting the mixture screws with the idle that high? Am I wrong?
The reason the manual shows a specific RPM is the timing increases as the RPM increases, so the factory gives you a specific RPM for a specific number of degrees of timing. This ensures the timing is set properly.
The reason the manual shows a specific RPM is the timing increases as the RPM increases, so the factory gives you a specific RPM for a specific number of degrees of timing. This ensures the timing is set properly.
That definitely makes sense. So, in my case, I do all my timing adjustments at 850 RPM, and then turn the RPM back down to the mid-650's to do my idle mixture screw adjustments?
Just to be clear because I want to make sure I've got this right. The first step is to make sure the dwell is correct. Then turn the idle up to 850 and adjust the timing. Then turn the idle back down and adjust the idle mixture screws and finally make sure the idle speed is 575 with the car in gear and wheels blocked.
575 675 750 850 RPM isn't going to effect the base timing. The centrifugal advance won’t start opening at that low of an RPM.
Centrifugal advance doesn't start opening until 12-1300 RPM more or less.
It all depends on the engine/trans combo and accessories such as AC. Which is why you see different setting specs.
Set the base timing and AF mixture together with a vacuum gauge hooked to a direct intake source (not on the carb).
You can have the vacuum advanced hooked up during this process. You’re not using a timing light for now.
Adjust the timing and AF mix to achieve the highest vac reading possible at 650-750 RPMs.
Give it as much timing as the engine will tolerate without pre-ignition ping/knock. Next test it under load...on the road.
I keep the distributor just loose enough during the road test so I can advance or retard and retest until no spark knock is observed.
Hot and cold weather and elevation will effect this process. It will spark knock easier on hot days.
If it’s not already...hook the vacuum advance canister to a constant vacuum source, not a ported source (which won’t have vacuum at idle).
Make sure the canister holds vacuum. Watch the breaker plate in the distributor move as you apply vacuum by sucking on the line, yes with your pie hole.
Make sure the points are set correctly and the point’s cam/bumper is cleaned and lightly lubricated.
Do not get grease on the points. Clean the feeler gauge and points-set with electronic cleaner.
Do you have a Dwell meter? Get one. 30° Dwell or .016-.017" on the feelers
Pay attention to the centrifugal advance springs and weights under the distributor rotor. They need to be cleaned and lightly lubed. The springs should not be stretched.
Don’t be tempted to install the stupid lighter springs all the "speed shops" sell. Keep the stock springs if they are OK. The weights should not move when static.
The centrifugal advance needs to come in at the right rate and RPM and stop at a specific full advance. This may be beyond your skills at the moment.
Base timing + vacuum advance + centrifugal = the total advance curve or "all in timing."
Do all the above and then we will discuss the distributor super tuning in the next chapter
If you have timing light check to see what the optimum road test results produce for the timing numbers. That is what your engine likes...not some standard spec.
For a stock-ish 66 425 I like 12-14° base timing at 650-750 RPM. 8-10° more with the vacuum advance plugged in and 34-36-38° total before 3000 RPMs
Re adjust the idle to where you like it with and without the AC load.
575 675 750 850 RPM isn't going to effect the base timing. The centrifugal advance won’t start opening at that low of an RPM.
Centrifugal advance doesn't start opening until 12-1300 RPM more or less.
It all depends on the engine/trans combo and accessories such as AC. Which is why you see different setting specs.
Set the base timing and AF mixture together with a vacuum gauge hooked to a direct intake source (not on the carb).
You can have the vacuum advanced hooked up during this process. You’re not using a timing light for now.
Adjust the timing and AF mix to achieve the highest vac reading possible at 650-750 RPMs.
Give it as much timing as the engine will tolerate without pre-ignition ping/knock. Next test it under load...on the road.
I keep the distributor just loose enough during the road test so I can advance or retard and retest until no spark knock is observed.
Hot and cold weather and elevation will effect this process. It will spark knock easier on hot days.
If it’s not already...hook the vacuum advance canister to a constant vacuum source, not a ported source (which won’t have vacuum at idle).
Make sure the canister holds vacuum. Watch the breaker plate in the distributor move as you apply vacuum by sucking on the line, yes with your pie hole.
Make sure the points are set correctly and the point’s cam/bumper is cleaned and lightly lubricated.
Do not get grease on the points. Clean the feeler gauge and points-set with electronic cleaner.
Do you have a Dwell meter? Get one. 30° Dwell or .016-.017" on the feelers
Pay attention to the centrifugal advance springs and weights under the distributor rotor. They need to be cleaned and lightly lubed. The springs should not be stretched.
Don’t be tempted to install the stupid lighter springs all the "speed shops" sell. Keep the stock springs if they are OK. The weights should not move when static.
The centrifugal advance needs to come in at the right rate and RPM and stop at a specific full advance. This may be beyond your skills at the moment.
Base timing + vacuum advance + centrifugal = the total advance curve or "all in timing."
Do all the above and then we will discuss the distributor super tuning in the next chapter
If you have timing light check to see what the optimum road test results produce for the timing numbers. That is what your engine likes...not some standard spec.
For a stock-ish 66 425 I like 12-14° base timing at 650-750 RPM. 8-10° more with the vacuum advance plugged in and 34-36-38° total before 3000 RPMs
Re adjust the idle to where you like it with and without the AC load.
Report back on the tire burning results.
Great advice! Just wondering though if 12-14 degrees of base initial timing isn't a bit much for the 91 Octane fuel I run? Spec for mine is 7.5 degrees at 850 RPM
Great advice! Just wondering though if 12-14 degrees of base initial timing isn't a bit much for the 91 Octane fuel I run? Spec for mine is 7.5 degrees at 850 RPM
Thats why I suggest tune for what the engine likes considering the ambient conditions, driving style, and available fuel.
Most muscle era V8 Olds engines seem to like 12-14° on 91+ octane.
I really need to get some proper pictures of it in my driveway. It certainly ain't pretty right now because the paint is toast and needs to be redone. Here is the walkaround I did on it in my garage a couple weeks ago:
I'm running 11:1 at 13°. But its super-tuned. No spark knock.
Nice color combo. Dad had a Deluxe 66 Dubonnet/Plum interior.
Look at your floor pans before you do paint. If they need repair better to yank the interior and have the floors done now rather than trying to work around nice paint.
Same for all metal & mechanical work.
Dont be scared to do paint. You look like you can put your brain out to your hands. Practice on junk. Enamel and Lacquer are easy. BC/CC isnt too bad. Its all in the prep. You could save 10-20K doing it yourself.
Ethanol will cause the flaking you are describing in the original carb. So will any stale gas. Just happens sooner with ethanol.
Look at the 7026250 primary & secondary rods, primary jets, secondary cam and main power piston assemble etc. They should be fatter than the 7036250 carb. Calif carb is likely very lean. Fatter means you can run more timing = better acceleration.
Let the carb guy know you have 702 fatter primary & secondary parts.
You'd be surprised at what a good carb restorer can do. The 702 may be salvageable.
Google:
-Chris's Carbs, he wet test the carb.
-Sparky's
-John Heraald
-Sean Murphy Induction (SMI) (High Perf)
Here's an example of the Dubonnet/Plum to drool over...
Last edited by droldsmorland; May 14th, 2024 at 09:15 PM.
So I was playing around with this today and I have to admit, I don't have the knack for it quite yet.
If I mess with the base timing, the RPMs want to go up and up and up the more advance I give it. It just seems to like more and more advance and I kinda don't know where to stop. I set it where it seemed to be running really nice and I checked the base timing.......yeah, I had it up to 19 degrees! Way too far, I'm sure.
I reset it to 8 degrees to be safe for now which is a touch over the 7.5 spec in the manual. I set the A/F screws to where it seemed happiest and it seems pretty good (in the driveway that is). I'm detecting a slight stumble though when I give it a good shot of pedal in the driveway.
It is normal for the engine speed to increase as you advance the timing. The key is to ensure the total timing (initial + mechanical advance) doesn't get too high. Your present 8º setting is close enough to the factory 7.5º to call it the same thing.
I set mine to around 36º total, which translates to 18º initial because the distributor has 18º mechanical advance. My original points distributor had 24º mechanical advance, so I would set the initial to 12º to achieve 36º total (the factory spec was 10º initial for 34º total).
Took it out for a drive today and it seems to cruise ok but there's a horrible flat spot when accelerating away from a stop sign. Falls on its face and then comes right back to life. The dwell is rock solid at 30 degrees, base timing is at 8 degrees, and the A/F screws are both set about a turn and a half out. Looks like a solid stream from the accelerator pump too.......I did tweak the A/F screws a 1/4 turn out a couple times and it got a little better but still fell on its face on initial acceleration especially from a stop and trying to accelerate to regular side street speeds.
You really need to use a vacuum gauge to dial in the idle mixture screws - one at a time, adjust each one (one at a time) until you achieve the highest Hg" vacuum. You should easily be able to pass the 1st test in upper LH corner and your reading should be rock steady.
You really need to use a vacuum gauge to dial in the idle mixture screws - one at a time, adjust each one (one at a time) until you achieve the highest Hg" vacuum. You should easily be able to pass the 1st test in upper LH corner and your reading should be rock steady.
Oh I did do this. I followed your advice from before.
I did notice that the vacuum read isn't rock solid but it's pretty solid. There's a slight bounce on the gauge. It's not an inch of Hg but it's got a slight bit of shaking. If I rev it up a bit it seems to be very steady.
Hmmm. That really sounds like an air - fuel issue (bog). I doubt it’s a timing issue.
My car has a couple oddball items in the mix. There's a thermostatic switch on the vacuum advance. I could test that pretty easy.
Could a malfunction with that switch causing no vacuum advance.possibly cause this? Maybe I'll try hooking it to manifold to see if it gets any better.
I also have the AIR system (K19) on it. I wonder if it's doing something that's working against me.
I do not think a timing issue would present as you said. The vacuum advance should go to zero when the throttle is opened, so the distributor vacuum switch should not matter.
The A.I.R system injects air into the exhaust to reduce emissions, so it shouldn’t have any effect on the induction system.
I do not think a timing issue would present as you said. The vacuum advance should go to zero when the throttle is opened, so the distributor vacuum switch should not matter.
The A.I.R system injects air into the exhaust to reduce emissions, so it shouldn’t have any effect on the induction system.
Ok thanks....the bog seems to be at part throttle, accelerating slightly, under load. Just like a regular acceleration away from a stop sign.
Confirm that the APT piston is not stuck. Could present a similar hickup on acceleration.
Not sure if that model Quad has an adjustable APT.
If it does it would have another access hole between idle mixture screws in the base plate.
Might be worth it to get access to it, but that requires work to be done on it off car.
And can be tricky if screw is frozen. Cliff does make an externally adjustable screw kit.
I had the carb apart a while back, here's some pictures of it. It does not have APT adjustment as it's a very early style Qjet that has none of that stuff that came later.
With that description my first thought would be insufficient accelerator pump discharge. What happens when you go full throttle?
Originally Posted by ourkid2000
I'll give it a test today. Maybe I'll make a video, hopefully it will show it better than I can explain. Thanks for your help by the way!
OK. I don't know the exact conditions under which the rear (outer) hole of the accelerator pump is &/or can be used most efficiently. There's various conditions among various groups of people who use the rear (outer) hole (e.g. altitude, non-stock modifications, etc.). The hole isn't there because Rochester had nothing better to do than drill an additional hole in the accelerator pump arm. It takes all of thirty seconds to change the location of the accelerator linkage to fit into the rear (outer) accelerator pump arm. If you have an extra thirty seconds it might be something to try.
I took some time today to make a couple videos of the issue. I made one showing the vacuum gauge while I did a few throttle snaps. I also made one where I took the car for a short drive. Hopefully you can hear the engine trying to cut out when I give it gas.
Would love your opinions on what could be going on. If you have any questions, I can always make another video if you're not getting what you need. May have to turn the volume right up on the drive video as the phone was banging around making a bit of noise.
Your vacuum gauge needle is bouncing around - it may not demonstrate +/- 4Hg"-5Hg" but that is not a steady vacuum.
You said in the 1st video your timing is set to 8° BTDC initial? Try between 10°-12° BTDC.
Norm, I think that outer hole would cause a shorter pump stroke, so less air/fuel enrichment.
Kenneth - Yeah, like I said I'm not exactly certain if it would have an affect. With that said (before I listened/saw the videos) I'm still suspicious of a vacuum leak &/or misconfiguration of the vacuum hoses (after viewing the videos).
Your vacuum gauge needle is bouncing around - it may not demonstrate +/- 4Hg"-5Hg" but that is not a steady vacuum.
You said in the 1st video your timing is set to 8° BTDC initial? Try between 10°-12° BTDC.
May 13th, 2024, 01:54 PM
