help with 17082224

[bruno]

So I finally got back to working on the car. I’m not sure if I should continue this post, or start a new one, so If i should start a new ine, let me know and i will. otherwise, currently I think I still need more idle fuel. there is a major bog when i crack the throttle open from idle. the accelerator pump seems to have a good shot of fuel, so I don’t believe it is that. although I’m not 100% sure. it sprays across both primaries do the whole stroke, so i’m assuming that’s is good. the idle exhaust still burns the eyes a touch, but not near as bad as before i shrunk the LIAB. I currently don’t have anything to measure them except drill bits, and there is a gap right where i need it! my timing is set at 6 degrees with VA disconnected and plugged. Rpm at 650. 17” vacuum. with VA plugged in to manifold, idle is 750. idles great. just bogs when i whack the throttle, with the odd pop through the carb. adjusting the idle screws will kill the car if i turn all the way in, so pretty sure i’ve got the throttle angle good. from 2.5 turns out and further, there is no noticeable difference. It will still bog just as bad, maybe worse with the vacuum advance disconnected, so i don’t believe it’s a manifold vs ported VA issue.
My current thoughts are that i need to make the LIAB smaller yet, or increase the i’ll tubes or DCR. they are .038 now, so from my reading here, that should be lots. not sure if I will be able to shrink the LIAB down further. I would like cliffs opinion on using brass set screws in the and drilling those. or any other suggestions. also going to double check float height, as i assume that would have an effect if it was too low. am i on the right track for now? thx.

[lightning boy]

I think the cam you have is what Comp called the High Energy. They sold alot of them. With rebuilder pistons and thick head gaskets will need 12 to 14* on the crank to start with. You can figure out the vacuum adv later when you drive it. Get the timing light and plot the timing curve at every 500 rpm until it stops advancing. Report back.
Is the bog immediate or on the secondary side?

[bruno]

will plot the timing curve tomorrow hopefully, but the bog is immediate. right off idle, while in park. haven’t really driven the car yet, just from the garage to my shop all of 200’ away.

[bruno]

I tried to plot the timing. it was pretty awkward by myself, as the idle speed adjustment screw would not increase the rpm much past 1500. anyway here are the numbers i came up with. these are with the VA disconnected.
RPM - BTDC
650 - 6
950 - 8
1100 - 14
1250 - 18
1900 - 23
2200 - 26
2800 - 29
3600 - 32
it was hard to look at both a tach and the timing light, and hold the throttle steady. what do you think of those numbers?

I’m more concerned right now that i think im still lean at idle, and trying to figure out where to make an adjustment there. if im wrong, please let me know ow and ill move on. but I think i need to shrink the LIAB more, but not sure how to do that. i’ve already peened it down as much as i think i can. It was mentioned to install a brass set screw and drill that, but I’ve only heard that once, so would like some clarification before i ruin the body. thx.

[bruno]

I tried setting the base timing to 12, and the bog is much better. still there, and I think i’m still lean at idle. once it cools off, I will try to peen the LIAB a touch more. any other suggestions welcomed!!

[lightning boy]

I think it will run best at 36*-38* of total timing, it may need more than that but it would be a good place to start. Set it at 38* total and see were the base timing is. If you are lucky it will be around 14* at idle. Then you can start playing with the vacuum adv. Do you have full control of both mixture screws now?

[novadude]

I've got a nearly identical engine  - 396, 063 heads, factory exhaust manifolds, 204/214 @ 0.050 cam, Weiand 8123 intake, SMAB Q-jet (I think mine started as an Edelbrock 1904), TH400, 3.08 gears.  Bad quench with cast "rebuilder" pistons, un-decked block, blue 0.039 fel-pro head gaskets.   It's in a '70 Chevelle.  I can tell you what has worked for me. 

Ignition

My mechanical curve is close to yours - 36 deg at 3500 rpm, with 10 deg intital.  I run ported vacuum  with about 15 deg.  I can't guarantee it is optimal, but it seems to run well with this timing set-up.

Carburetor

Single main air bleed q-jet (like your 17082224)

UIAB = 0.067
LIAB = 0.059
IDCR = 0.052
Idle tube = 0.035
Idle bypass air = 0.086
idle screw orifice = 0.086
main air bleed = 0.046
main jet = 0.073
primary rods = 50M
secondary POE = 0.052
secondary POE well fill holes = 0.036
secondary bleed tubes = 0.033
secondary rods = DA
secondary hanger = F
air door opening (per method in cliffs book) = 1.36
accel pump nozzle = 0.026
float = 10/32
Float needle seat = 0.128

All-in-all, it runs pretty good.  Responsive, no hesitations or bogs, good economy (about 16 mpg running 70 mph on the highway).

Hope this helps!

[bruno]

it does!! thx. it confirms my thoughts on the LIAB needing to be smaller.

[bruno]

I think i am getting there! I was able to shrink the LIAB down to about .063”, and due to operator error in measuring, I opened up my DCR to .060”!! I didn’t notice the error right away, so i installed it back on the car, and now it doesn’t seem lean anymore. I have lost a touch of control with the mixture screws, although seating them both will definitely affect it. right now I have them set a 2 turns from seated. Idles is 800 for now, with VA connected to manifold. I think i need to limit the VA some, as I have adjusted the base timing to 12, centrifugal adds 30, and va i think adds another 15-17. I may need to adjust the centrifugal as well, or lower the base timing to 8/10.
the bog was still there, but different than before. there is very little change when covering the primaries, until they’re almost completely covered. pulling a manifold vacuum line off and the rpm’s come up about 100 rpm. I think this means i am very close, possibly a bit rich. I decided to disconnect the accel pump, and it still had a bog, although different again. I reinstalled it on the outer hole this time, and the bog is gone!! so….

1. will leaving the DCR at 060” hurt anything else?
2. the engine needs to come out again, as it developed a rear main seal leak. I’m quite positive it’s not the valve cover or manifold, as i can see them pretty clearly with a mirror. I will attempt to measure the cam better when th engine is out.
3. I guess the next step is to drive it and see how does? unfortunately there is still lots of snow here, so that will be a few weeks away.
4. thanks everyone for the help so far, I’m sure I will have more questions shortly!!

[bruno]

I think the whole issue was th LIAB, just like cliff said. I may have to back up a bit and replace the DCR but will see.