K10 Project

[JoeliusZ28]

It lives!

Bypassed the ESC tonight and it wasnt even a full rotation of the crank before it lit right off and purred like a kitten. The timing is most definitely too far advanced, but even as it is right now its the best its ever run for me. Everything is quiet smooth and responsive. What a relief im so glad i can finally get some enjoyment out of this thing. Thanks to everyone that helped even in the slightest way

[MP81]

Surprising that the timing is too advanced without ESC - though it does have the vac advance as well (still don't understand how both of those work together - mine just has electronic control).

Base timing shouldn't have it sitting super advanced - is it idling high as a result (my theory of my high idle is a lot of advance at idle).

[JoeliusZ28]

Its idling high (not out of control high, id guess 1000-1100 rpm) and the throttle response from idle is more aggressive than it used to be so im assuming its timing. Feels like its making more vacuum. Exhaust also smells like its burning a little hot but thats not exactly scientific lol. I think it will be fine if i turn the distributor back a couple degrees.

[JoeliusZ28]

Well the trucks been running great. Idle is still a little rougher than id like but i dont know that it means theres a problem, it drives great. i got a tach installed too which is very helpful but i forgot to take a pic. I also finally got around to powerwashing the wheel wells out. Apparently theyd never been cleaned, there was some very tough grime... Multiple passes with the powerwasher and brushing with simple green was needed. But i found something cool under the protective layer of dirt!

[JoeliusZ28]

First recorded fill-up since i bought the truck: 14.4 mpg.

also have a question for those familiar with old school carbs/distributors. Ever since i got it back together it seems like the engine bay is hotter than it should be... IE the hood/fenders have heatsoak and even the filter lid is nearly too hot to hold my hand to, and the engine bay smells of hot grease/gunk after driving it. That said, the engine seems to run great and engine temp is normal. Ive got good torque in the low rpm and i dont hear any spark knock. But maybe this is how its supposed to run? Im wondering if my timing might be too aggressive. Base timing is set at 12 degrees. Another thing i want to figure out is my idle isnt as smooth as id like it to be. It isnt what id call "rough" i just remember the 350s in my last two trucks idling smoother than this 305. Might also be nature of a carb however my last two trucks were tbi and mpfi.

[birdie2000]

Might want to try asking on Motown Muscle if you don't get much response here. There are a couple guys there who really know their way around a distributor and carb if I remember correctly.

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[JoeliusZ28]

[MENTION=558]9T8W66[/MENTION] - any ideas?

The other odd thing i remember i noticed was i have no (or very little) vacuum at idle. Vacuum jumps when i blip the throttle, i thought the opposite should be true??

My chilton manual also says it recommends 4 degrees btdc initial timing for this year/engine.

[MP81]

You should have full vacuum at idle - less as you rev.

[JoeliusZ28]

I just talked to a coworker. He thinks my hot engine bay is normal. Also for my vacuum gauge i used the feed for the distributor. He thinks my truck might use a "timed" vacuum port on the carburetor for vacuum advance which will read differently than a normal vacuum feed. He thinks it may run better if i put a direct vacuum feed to the distributor instead of this timed feed, as the timed feed was developed for emission control rather than best driveability.

[9T8W66]

Zero vacuum from the distributor port is correct Joel.
If you were pulling vacuum from that port at idle and you pulled the hose off the the cannister the idle would change.

[JoeliusZ28]

Sorry not 100% clear what you mean... I wasnt measuring from the distributor, but from the line for the distributor. I didnt pay attention to where it was routed i just assumed it was a vacuum line since it is a "vacuum advance" distributor.

[JoeliusZ28]

Relevant:
http://www.thirdgen.org/forums/carbu...m-vs-full.html

Specifically:
"Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it."

[9T8W66]

The timed port doesn't draw vacuum at idle.
What I meant was if the distributor was pulling vacuum the idle would be higher because it would be advancing the timing. Check your vacuum from a different source. As far as the timing 12* is a good start. I would bump it up in 2* increments until it knocks under load. Then back it off 2*.

[JoeliusZ28]

I'm thinking about trying to change it to a full vacuum source. Idle quality and hot engine bay were my two concerns and it sounds like retarded timing at idle can cause exactly that.

[9T8W66]

If you put it on a different source it will draw vacuum at idle and raise the idle speed all by itself. The distributor vacuum advance port is not supposed to draw vacuum at idle. Everything you have explained to me sounds like it not so it's good to go. If your idle is still a bit rough it is most likely carb related.