Exactly....TY!

 

He claimed 12 mechanical in the post I was replying to, though looking back, the distributor card is showing 22 mechanical, which would definitely be too much.

 

ah, okay..chalk another one up in the "previous info was incorrect" column. I'll back it out anyway though..as when it was at the most recent shop to be degreed, he commented how he'd let it idle and it wouldn't load up. So I probably had them correct, then started turning on them (fortunately I know how much)

 

I'm just not getting a warm fuzzy good feeling w/ regards to your fiddling w/ the A/F mixture. Spot-on get an O2 sensor installed in the exhaust when you head in for a dyno - absolutely the best approach. But, until then, I'm just not comfortable with your adjustments on the carburetor.

As Eric pointed out, once you're out of the idle circuit fiddling w/ the A/F mixture is meaningless.

Until some other time arrives, I hope when you're establishing the near best idle circuit scenario you're doing it this way:
(1) Turn one A/F mixture screw until you achieve the highest RPM setting; next,
(2) Turn the other A/F mixture screw until you achieve the highest RPM.

Establish the HIGHEST RPM you can achieve @ idle and leave them alone.

 

Lets disregard all of the past posts and start over, drop your rpm's and see what your initial is and note, then raise your rpms and see where it starts to advance and note, then see what your total is and at what rpm it stops advancing and note . All done without the vacuum can connected. We'll worry about the vacuum advance when you get the mechanical situated.

 

Yeah, I'm gonna reset the mix screws to where they were. Since it came back I'd only put 1/2 turn in, so I know where I need to go with it.. then go back to the drawing board with the timing. I'll set if I can get my hands on a tach that'll allow me to monitor the RPMs while checking timing.

 

Remember, we are not adjusting, just verifying your current settings to make sure the spec sheet is right. Once we've established where you are at and the associated math, we can go from there.

 

Alright, so I reset the mix screws this morning before headed to work just that way I didn't forget, and brought my light/dist wrench/screwdriver with me with the goal of addressing this after work (at least the baseline aspect mentioned above)

For some reason, I looked down at the tach when I parked it and noticed it's at 1250rpm. Got to thinking, and every time I read the 900-1000 rpm..that was after I pulled it out of the garage. It wouldn't make sense that the fast idle is slower than the curb (off choke) idle, but then again that would explain why it felt the choke was kicking off sooner than it should. I didn't think to check the RPM in gear, but it doesn't clunk hard when being put in gear, so I can't imagine it's too far off.

To that point though, based on the above..that would explain why it runs better with the choke still somewhat on, correct?

 

Sounds like the lower piston spring isn’t correct for the engine ? That can cause an off idle stumble

did you order that Q jet with a custom power piston spring that works with your 8” idle vac in gear?

you are on the right track giving it lots of initial timing.

 

Carb was an off the shelf buy, nothing different for my combo.

I went out and dropped the idle down to factory spec, and just for giggles drove it around the parking lot. It died whenever you give it a quick throttle blip, so safe to say that's too low.

I'll run out after work when I have more time and work on gathering the vacuum advance info based on factory spec RPM, but then return it to where it was for the drive home. I wish I would've brought my vacuum gauge, because I'm curious at this point if everything is off..how far is the vacuum off from where it had been?

 

I don't much care about the vacuum advance at this point in time. Just the specific timing setting under the conditions set in post#85

 

Alright, so I went out and followed the procedure per post 85 and it's just raised more questions..

At idle (850 RPM) with vacuum advance disconnected and plugged, timing read 18°. I turned the throttle screw until the marker stopped moving, checked RPM and it read 2200 RPM and added 14° giving me 32° total (initial plus mechanical)

The questions arose after hooking the vacuum canister back up and returning the idle back to where it was when I got to work..it stumbled immediately, every time I went to get on the throttle from a stop. Which brings me back to the idea that it's heat related.

 

Did you run the RPM higher than that? Your distributor card says you should have roughly 14 degrees more advance at 2000 RPM, as you measured, but it keeps climbing all the way up to 4000 RPM. Either your distributor card is entirely wrong or you didn't get the RPM high enough to see the timing actually stop advancing.

My guess with your stumble is that you're running lean. You said it runs better on the choke, which is just richening your mixture. As soon as that is gone, you're left with a lean mixture and opening the throttle doesn't help anything. Your low vacuum may be causing issues with proper signal to the carb, as CANADIANOLDS alluded to.

 

This made me wonder if those distributor specs are in crankshaft RPM or distributor RPM.

 

The dist vs crank RPM isn't a bad thought, honestly. Though, I would've expected it be consistent or even notated.

As far as the RPM only going as far as I did..I went until it stopped advancing, screwed the throttle screw in to hold it there, then stuck my head in the car and got the number.

When this first started happening/I first started noticing..I thought lean as well. I was going to live with it until the exhaust/dyno appointment..but I can't ever leave well enough alone.

 

That would be really bad in distributor degrees because then you would need to multiply everything by 2. Since the timing column on the sheet is labeled BTDC I'm going to assume it's crank degrees.
Brothergood, reread post #85 and note what you get per each operation I suggested.

 

Yeah, I did that. I did however realize this morning that I had a brain fart while typing this that yesterday I typed what my initial was set to, not what it read at the lower RPM..so I just went back and fixed it.

Now, this was done with the factory tach as the RPM reference. The only time I've had reason to question it, is occasionally it gets stuck above 3k (every once in a while I get on it) and every once in a while it seems lazy. Though not consistent enough to deem it faulty

 

According to the distributor spec sheet you have 22* of mechanical advance that should come all in at 4000rpm. It should start advancing at 1000 rpm, you need to drop the idle speed down as low as you can get it and see what the timing is. Using a defective tach is not helping you.

 

While I don't disagree, I had the idle down as low as it'd go-to the point where it'd die if I gave it a quick throttle blip in gear..and ran the RPM up until the marker stopped advancing and the math still came out to 14 degrees mechanical. I focused on the marker, the RPM was secondary at that point.

Regardless however, I still don't understand why whenever the engine builds heat it runs decent until you go to accelerate from a stop. My initial thought for a while (even before this thread) was it was lean when warm (which is why when the choke was still active it was okay) but the excessive heat on the intake (vs. the exhaust manifolds) was concerning.

 

Running an engine lean and with the wrong timing will generate a lot of heat. You keep focusing on a symptom, thinking it is the cause. It likely isn't. Its likely a result of a bad tune. You need to get your tune dialed in - timing and fuel.

You've got a number of issues and you're going to need to methodically start working through them. If you really are only getting 14 degrees of mechanical advance, your distributor is defective, at least according to your card. Advance curves don't typically max out at 2000 RPM, which would further support the theory it is defective. Otherwise, something has gone wrong with your measurements. Personally, I'd actually rev the thing to 4000 RPM and check the timing to verify it really stayed at 14. When I see measurements that don't line up with expectations, I double and triple check, try different methods of measuring if I can, and figure out if my measurement is wrong, or the thing I'm measuring is wrong. You can also take off the cap and make sure your advance weights are actually moving freely, and not getting hung up or catching somewhere in their travel.

For your fuel mixture, you can take out your plugs and try to read them. Personally I think most of plug reading is BS, since I've never found resources that actually agree with one another on what each thing means, but you can generally get an idea if its way out of whack that way. I can already tell you based on Jet's recommended camshaft specs, yours is more aggressive than what they tuned that carb for. You could also try tuning the carb yourself. Cliff Ruggles book is pretty useful in understanding how they work. Would be better to have that than to stab in the dark or rely on shops to do your work for you. Same with the distributor - may want to start looking into the how and why of timing.

 

Agreed. I had already accepted that the tune isn't correct-I'd felt it was lean enough to cause the stumble with the choke off but not enough to detonate. The goal is to have it tuned on the dyno once the exhaust is replaced (after OCA Nat's). I just thought it was odd that the top end was so hot-to the point where the thread was started.

Right now, my priority is shifted primarily to the transmission leak..but hopefully I can have that fixed by Sunday and utilize Sunday afternoon to try a couple more things if anything just comes to me that may be of benefit. I'm hesitant to do much of anything, really though..as again it runs well until you're in stop-go mode.

 

One thing you'll need to make sure of is whether your dyno place has parts for your carburetor. Some places require you to bring your own tuning parts...

 

For sure. The rate is for 2 hours, so I plan on getting what would be necessary to tune the carb, as well as possibly one of those adjustable vacuum canisters (just in case). I've already got a set of new plugs aside for it as well, and will be putting a bung in the exhaust for the wideband that way they don't need to do it.

I'd much rather they spend the 2 hours fine tuning, than waste time on tracking down parts/fixing my boneheaded oversight first.

 

Interjecting my thoughts...not my expert knowledge...ensure you know the correct (best) position/placement for installation of your bung to provide the best/optimum reading/performance. I run wide band sensors on my motorcycle and narrow band on my truck - my truck is a turbo. I run a programmable high performance tuner on the wide band on the motorcycle. Anyways, I don't know where the best placement is for your exhaust/engine application, just ensure you know the best placement of the bung. Good Luck.

 

I'm not the one doing it.. the exhaust shop will be.

 

I'd suggest you ensure you're on the same page as the exhaust shop relative to correct placement.

 

That's fair. I suppose at that point, maybe I should just let them do it while at the dyno.

 

Call your Dyno folks and ask what they'd prefer. Based on wide-band manufacturer, your exhaust system, controller, location(s), etc. your Dyno folks might have the best suggestions.

 

that's not a bad idea..ill have to remember that.

 

Even though the distributor is supposed to be dialed in, I would bring an advance curve kit with multiple springs, just in case.

 

Gonna revisit this with a tad bit of new info.

I picked up a new timing light that has a built-in tach so I could at least get some sort of an idea as to whether or not my dash tach was accurate. I got home and hooked it up, and it's off approx 300 RPM. So, while the dash reads 1150ish, the gun read 850ish (both had around 50rpm fluctuations I'm assuming is due to cam). In gear, it drops to around 900 on the dash and about 600 on the gun.

When I get some more time (I literally was pulling the car in as I needed to get to church, then realized Id might as well check the tach while it was warmed up) I'll reset it to at least factory spec per the gun and see what that gets me...both with driveability, timing/advance, and vacuum.