350 Tuning Issue

[cebra]

My plan is to check:
1. secondary butterflies/high idle
2. floats/boosters for drizzle
3. hose her down with starting fluid yet again but focus around carb throttle shaft

That is about all I can think of I have not checked. The transition slots I don’t get, could this be related to a different intake manifold? Mine has one big hole all 4 barrels feed. Will report back, thanks again.

[geezer#99]

The transition slots are explained in here.

http://www.crankshaftcoalition.com/w...EI_distributor

Generally if you get the primary throttle closed nearly all the way the transfer slots will be covered adequately.

[Coley]

What sort of intake manifold is on the truck?
Stock? Aftermarket? edelbrock or?.....hopefully not single plane because that won't help your situation.

Ok...get that timing up and then get the vacuum gauge on it and we can go from there.
Post up a few pics if you have a chance....because 'seeing is believing', at least with guys.

All good
Coley

[cebra]

I understand the transfer slot thing now. This appears to be my issue (butterflies too open when throttle is “closed”). I have the carb pulled, how do I measure the “square” to make sure it is .020”? Is there a mini feeler gauge for this I can get at the auto store? Thanks

[geezer#99]

It’s just an ‘eyeball’ measurement.
If it looks square, it’s close.
Like in the link.

[cebra]

Here are some pics. I am trying to adjust the transfer slot setting. I read you do this by adjusting the idle screw? If so, wouldn't this just get jacked up once you try to set the idle? I also noticed the primaries shut but then you can pull back to shut them more. In the picture with the screwdriver, this "tab" was dragging on the metal piece behind it which caused this issue. I bent it to "catch" on the metal piece behind it but then my butterflies would come nowhere near closing (the pic where they are open more), I can get it set correctly with the idle screw if I bend this tab out so it does not "catch". It seems like something is amiss with this mechanism. Also, my secondaries are completely closed, do I need to adjust them as well? If so, how do I do this? Thanks.

[cebra]

Here is a picture of the secondary controlled by the vacuum thing. Also, a pic of the engine to see what I am working with here.

[Boog]

Looks like that old Holley has been around for a long while.
It's pretty neat and clean under hood too.

[geezer#99]

Couple things come to mind.
With your choke link (the part thecable hooks to) all the way back, the high idle screw should be on the cam. Yours is 1/2 inch away. Which suggests that something is holding it down. The wire spring by the big philips screw doesn’t look right.
You’re right about the transfer slot not staying square if the idle screw is adjusted excessively. One cure for that is more timing. More timing makes your idle increase and let’s you close the throttle back down. Another cure is to open the secondaries a bit (there’san Adjustment screw right beside the vac pot linkage.

[68 P.O.S.]

Any progress?

[cebra]

Yes, a lot of progress...I threw on a new Edelbrock carb. Mine just was not functioning properly and I don't have the carb knowledge to sort out what was making the primaries stick and what parts were missing or had been assembled incorrectly (per Geezers post). Once I put the new carb on, it started and idled normally which is a win since I couldn't get it under 1,400. It did stall out dropping into gear but I hope this is timing related at 6 advance. I plan to set the timing, idle, idle ratio this weekend and will report back. I will add pics as well.

[cebra]

It took me a bit to update as I wanted to make sure I could get the truck started with a new carb and I had to cut the throttle bracket a bit, work out a return spring setup, get longer hoses. I do have a question does the 350 C10 (1971) have "full vacuum advance" (old carb had vacuum sucking at idle when vac advanced pulled) or "timed vacuum advance" (no sucking effect with vac advance hose pulled at idle)? I did not check this before I pulled the old carb as per the Edelbrock manual so I may have the vacuum lines reversed. thanks.

[68 P.O.S.]

Very nice, congrats on the new carb and getting it running. So what RPM does it idle at now and how does it drive? Yes, timing could be why it stalled out. Factory timing specs are 8 degrees initial; these engines perform better with more advanced timing.

Vacuum advance is a hotly debated subject...such as Holley carbs vs. Edelbrock. Manifold vacuum is the way to go (the one that sucks at idle). Read this article, its a little lengthy, but it was written by a GM engineer who helped develop it and explains it very well (I researched him, he's legit). I'll believe the guy who helped develop it over anyone else. https://www.google.com/url?sa=t&sour...qW-jLv2NSpbyTi

[cebra]

I got the timing set to 12 advance and I set the idle to 925’ish. Any lower and it would would sputter and bounce between 450-500 and stall when put into gear. I think this is due to the .480 cam? At 925, it drops to about 550 in gear and can idle fine. I have the idle air screws about 2 full turns out to try and feed it a bit more fuel for the cam/headers/open’ish exhaust setup. It idles and goes into gear ok with this setup but open to input. I can’t “tell what the motor likes” as I don’t know what that sounds/feels like but i could tell when i was overly rich by the exhaust smell.

[geezer#99]

More timing.
Try 16.
If it smells rich you need to limit your fuel pressure to 5 psi.

[68 P.O.S.]

Agreed, sounds like you need some more timing. Have you tried 14, or 16 as Geezer suggested? You want your vacuum advance set to manifold vacuum. How is the rest of your HEI setup? You’ll also want to setup your transition slots again on the new carb.
Edelbrock carbs are finicky with fuel pressure. In general they don’t like more than 6 psi. Edelbrock recommends a regulator set at 5.5 psi, or their Performer RPM fuel pump which puts out the correct pressure. Some people have no problems with Edelbrock carbs using a stock pump which pushes out 7-9 psi. I’m in the crowd that did have flooding issues. I went the Edelbrock fuel pump route because I needed a new fuel pump anyway.