Do you have a numbered distributor cap? You can basically position the vacuum advance anywhere you want depending on what pin on the cap you assign the #1 cylinder (unless you have on of the HEI caps with the cylinder numbers stamped into them- my truck has one). I wouldn't use the vacuum canister position as a guaranteed indicator of something being amiss.
Another thing for your off idle stumble is to make damn sure the little needle & seat under the accelerator pump nozzle is super clean- I've had the Holley tip-in stumble on a lot of stuff and usually cleaning that up helps.
Also worth mentioning is float level - on the Dart I was having a bit of a lean surge on the highway and raising the float level a tiny bit seemed to clean it up. Obviously I didn't set the level way higher than the sight plug, but it was to where I'd loosen the sight plug screw and fuel would come out without rocking the car.
Crap and then Double crap! First I had 2 Paragraphs written and Windows Updated I lost that. then I spent most of an Hour Redoing it and a LOT more and when I hit Post it said PAGE CANNOT BE DISPLAYED and that went away too. so off to the Doctor. and I will Call Later.
SkinnyG Not enough Vacuum and too much Timing/unless you have a BIG Cam,but still too much Timing.
My cam is 231°@050 with 108LSA (285° advertised). It's reasonably snotty. Runs better with more timing at idle for sure. No knock or ping that I can find anywhere, despite 10.9:1 compression (gasp!).
SkinnyG wrote: My cam is 231°@050 with 108LSA (285° advertised). It's reasonably snotty. Runs better with more timing at idle for sure. No knock or ping that I can find anywhere, despite 10.9:1 compression (gasp!).
I dig it. your base shouldn't need to be more than 12- 15 adv.but still Not more than 36 or 38 at 3500,
I have a BBC Boat motor for my Vette with an Old Boat Cam .630 lift and 11.5 comp.making around 600hp that only needs 36 degress total and has 8 to 10 in. of vacuum but I run my Air bleeds at 1.25 turns
A couple small updates: I swapped in a second medium advance spring, but it only made the bog more pronounced, so I'm swapping back - and possibly trying 2x light springs - next time.
I also found another car with both a working tach, and non-COP ignition to test my multimeter/tach, and discovered/confirmed it is labeled wrong - it's actually x100 the display, not x10(nor x80 as I thought it might have been). So at least that piece of the RPM/advance/vacuum puzzle is determined.
In reply to Pete Gossett:
So you weren't reving it to 25,000 rpms after all?
In reply to Ovid_and_Flem:
3200 was as high as I took it. Now that I know what the RPM is I'll take it up a bit higher next time.
GTXVette wrote: I dig it. your base shouldn't need to be more than 12- 15 adv.but still Not more than 36 or 38 at 3500,
For sure. 36° all in at 3000, base is 23°. It works.
I'm looking forward to seeing what known, correct, timing will do for this Vette.
I had worse off-idle hesitation with ported vacuum advance. It was reduced with full manifold vacuum.
SkinnyG wrote: I had worse off-idle hesitation with ported vacuum advance. It was reduced with full manifold vacuum.
From what I've read so far, unless you're running an agreesive cam ported vacuum is preferred. I originally had mine connected to manifold vacuum though, but it still bogged.
In reply to Pete Gossett:
Dayum...you and I share the same sleep patterns. (Or should I say lack of sleep patterns?)
In reply to Ovid_and_Flem:
My sleep patterns are largely set by our sugar gliders - up before dawn, which is their bedtime, feed them in the evening, then get them out to play when they wake up around 8-9pm - and I try to sleep some other time.
No major updates tonight. I double-checked the accelerator pump actuating levers and found they were a bit loose, the secondary one by quite a bit, so I adjusted them until they just barely contacted the pump arm per the manual.
I left both medium advance springs in place, but tried bumping the base timing up a bit again to see if it would still knock with the heavier springs. No knock, so that's good. It reads 29 degrees at idle - which I'm fairly confident isn't correct, but haven't had time to confirm yet.
Lastly, I went ahead and swapped in the 35 accelerator pump nozzles. All together it seems to be a very slight improvement. There's still a bog off-idle, but it's small enough to live with for now.
But can you put it up against the Torque and spin the tire (singular/Plural) Cars and coffee this morning at work(Larry Kizer's) He just bought a 1970 GTO Judge, so heading over to get it outside Pretty Nice white w/ Blue Interior Ram air 4 speed
In reply to GTXVette:
Oh it spins the tires quite easily. They're 10-year old Hoosiers though, so I'm not sure it's much of an accomplishment.
Pete Gossett wrote: In reply to GTXVette: Oh it spins the tires quite easily. They're 10-year old Hoosiers though, so I'm not sure it's much of an accomplishment.
You tease us with this yet you still haven't given us a burnout video.
In reply to Stampie:
I've not done any all-out burnouts, but the first vid did show me getting a bit sideways.
I took the Vette out for a bit longer drive tonight, probably about 12-miles round-trip. Unlike previous evenings where I'd been running/tuning/test-driving, I'd not touched it tonight. I let it idle about a minute, drove to the end of the street & pulled out onto the highway somewhat slowly. I was met with it damn near stalling out for an instant - way worse than it had bogged when hot and I was accelerating more briskly. I also noticed that when I pulled away from a stop at a more normal/legal pace it would always bog about the same RPM, regardless of throttle position.
Given that it seems to be RPM-dependent I'm thinking it's more than likely ignition not fuel, correct? Especially considering I've made drastic changes to the timing and advance curve, but it's only made moderate changes to the bog.
So I ordered a new set of plugs tonight. I know the ones in it didn't look great when I'd been fooling with getting it running, so it seemed like something cheap & easy to try. I can also check/confirm TDC vs. the timing mark while the plugs are out.
Time to throw away the timing light, disconnect and plug the vacuum advance, and keep advancing the base timing until:
1 the starter won't crank it when its hot;
2 it runs worse than the last run; or
3 it pings
I just swapped the plugs out, anyone have any insight on reading them? The left side is 1/3/5/7 top to bottom, and right is 2/4/6/8. 1 & 3 were very wet. They look oily, but smell more like gas. The electrodes & grounds on all plugs were whitish in color.
Here's #1 up close.
Edit:
After it finally finished storming today I took the Vette for a spin. The new plugs made no difference. I was able to hook up the multimeter/tach so I could run it into the cabin, and on a subsequent drive I confirmed the miss is occurring from 1800-2100rpm consistently - it first comes on at 1800rpm and is completely goon by 2000rpm. Is there anything specific that would be occurring in that RPM range that could be related?
Lastly, I attempted to find TDC using the zip-tie technique while the plugs were out. I found the stopping point going forward easily, but I turned the crank backwards 4-times/2-cycles and never could find it while going counter-clockwise.
Bump for the weekday crew, any input appreciated!
they are pretty wet looking maybe just a little oily find a compression gauge do the cyls. for a comparison if you are not going to drive it for a couple days let it sit with the plugs out then Do NOT give it gas Spin it over while you Hold some paper against the sides over the plug holes.... see what Spits out then do the compression test. I know the Guide seals are new,but the oil is coming from somewhere very low comp. COULD mean rings high but even comp. COULD mean Seals. don't worry though do the check first May just need a hotter plug.
In reply to GTXVette:
Any suggestions on why the miss is occurring consistently between 1800-2100rpm and whether that sounds ignition or fuel related?
Is it really a "miss" or does the power seem to go flat.... If the power drops off, could be fuel tuning. The carb should have a true idle circuit, with adjustment screws, then a idle circuit of some type, then the main jets. I don't know anything about the type carb you have, but the idle circuit could be a tad lean. You could have some oil fouling and maybe the mains are to rich, causing the plugs to also turn black. But that could also be related to the timing experimenting. Now that it has run some, put in a fresh set of plugs, run it a little more and pull a few out and see how they look. After only a little running they should be fairly clean to light tan.
In reply to TED_fiestaHP:
If I'm in a steady cruise below 1800rpm, and very gradually accelerate until I'm between 1800-2000, there's a very noticeable sputter/miss/bog the entire time I'm within that RPM range. When I accelerate more quickly it feels more like a brief hesitation, especially if I accelerate hard enough to downshift.
Sounds like once you get into the main jets it might be OK, there is a idle or mid range fuel circuit that needs tuning.... I mostly deal with webers or similar stuff, but all carbs are somewhat similar. Or the timing at that range could use some adjustment.... If you play with the timing and it does the same thing, then its fuel. But it's fairly simple, only a couple things that could be off.
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