New guy, 1969 GMC 1500, NW FL

[PanhandleShantyman]

Hey all, I've been lurking since the summer and figured it was time to sign up. Many thanks to all the members who've shared their expertise! I've learned a ton just searching the old threads.

I'm working on a 1969 GMC 1500 stepside, inline 250, 3 speed manual, heater only. I've been low-key looking for something like this for a decade, and finally found one for sale on the side of the road that's just like the one my granddad used to drive me around in, and I figured it was a sign so I bought it.

This was basically just a good ol' "gettin around truck" that I'm told spent 3 generations on the farm in AL, then spent 5 years with a couple different owners who didn't do much to it but keep it running. When I bought it, it was drivable, but had definitely had some jury-rigging done to it. The choke was busted and held midway open with baling wire, and the throttle plate was stuck kinda open so it idled real high. I'm not experienced with these old trucks at all, so the first thing I did was just put a rebuilt Rochester MV carb in it, thinking that might be an easy way to solve all the issues. Well after that, it still idled at like 1700 RPM, so I checked timing and that was way advanced to +32. Backed it off to the recommended +4 but that made it idle real rough, diesel on shutoff, run real hot (idiot light would come on after 15-20 minutes idle), and backfire through the carb on start and shutoff. Seemed like it was running too lean, but the idle adjustment screw made no difference at all, so I put a vacuum gauge on it and it read just 5, and I couldn't find any bad vacuum hoses or connectors, so I figured I must have a manifold gasket leak? Of course I snapped a couple bolts/studs off in the process of getting the manifolds off, then I snapped an extractor off in one of them, and cussed my way through the drilling and tapping process so I could get everything put back together. I finally finished getting the manifolds back on with a new gasket today. Tomorrow I'll fire it up and see how she runs.

The problem list I've figured out for this truck so far includes:
1. Rough/hot/fast idle with vacuum leak (I'll find out tomorrow if the new manifold gasket fixed any of this).
2. Brakes seem a little soft and when I hit the brakes the truck pulls pretty hard to the left.
3. Heater fan doesn't go even if directly jumped off 12v power.
4. Heater cables are pretty sticky and I snapped one of the pot metal heater control arms off fiddling with it, which I've learned from this forum is one of the classic blunders.
5. Windshield washer pump doesn't work.
6. Horn no beep.
7. Battery drains over the course of a couple days parked, if I don't disconnect the positive lead when I park it.
8. Turn signals don't flash. (I can signal a turn by manually moving the turn signal arm back and forth though--anybody know what problem would cause this peculiarity?)

My goal for this truck is basically just to get it running reliably, and then clean the interior up enough that my wife will consent to ride in it. (I kind of love the exterior just the way it is, patina and all.) The interior is pretty beat up. I replaced that cracked out dash pad first thing, then I shucked two layers of after market vinyl upholstery off the back of the bench seat and found that the bottom most layer looks like probably the original upholstery and is actually in pretty good shape. Can anybody tell me if they recognize this as OEM upholstery? What did the bottom upholstery look like? (I don't have any hope that the original bench seat bottom is under there in passable condition, since the replacement vinyl is so worn out I can see through to the foam!). I'll put in some carpet and floor mats when I find something I like that feels like it fits the vibe.

Anyway, happy to be here, and thanks again to all the wise men of this forum; the expertise you've all shared here has been incredibly helpful to me so far!

[D.B]

Welcome aboard!! Thats a fine-looking truck and a nice one to start with. Keep us posted on what you do and be sure to include photos. As you know we all like to see photos.

[PanhandleShantyman]

Progress report: after getting the manifolds back on she fired up no problem, with no more dieseling or backfiring after I reset the initial timing to spec at +4. Once I adjusted the idle mix screw for max vacuum, I was super happy to see the vacuum gauge reading steady at 18 inches Hg on manifold vacuum, way better Than the 5 I'd seen before. Then I put in new spark plugs and wires and that really smoothed out the idle even more.

She sounded great idling in the driveway, so I decided to take her out on the road for basically the first time since bringing the truck home. Then I hit a new issue in that the truck was really stumbling under any significant amount of throttle. I limped to my destination, had a beer and a sandwich and thought about it, then went home and decided there must be a failure of the timing advance at speed, so I put the timing light back on and found that that the mechanical advance was at least doing something and could get me up to about an additional 20 degrees advance at 2500 RPM, with ported vacuum not hooked up to the vac advance. Hooking the vacuum advance back up however gave me no additional advance at steady 2500 RPM, so I figured either that linkage is just frozen up or the diaphragm is shot, and as a result my total timing must still be too retarded at speed. I was running out of daylight so I didn't dig into the distributor at that time. I just decided to advance the timing to +13 to make up for it and see how she ran, and that worked great. Truck idles a little higher, at 650-750, but the stumbling on acceleration is gone, and the truck fires up first try and turns off with no dieseling or backfiring.

Next steps I guess are to figure out why the vacuum advance is not doing anything and fix that, and also make sure my mechanical advance is reasonably close to factory curve. Then maybe I could get her back to running smooth at recommended initial timing. Although, I've read expert opinions on this forum about how the low +0 to +4 recommended timing advance on these trucks was primarily just for emissions control measure designed to make the exhaust run hot for better smog combustion with the A.I.R. injection system, which my truck doesn't have. (I see a bracket for holding the A.I.R. pump, but there's nothing on it, I guess maybe the previous owner just got rid of it?). Should I just forget about factory recommended initial timing in that case and give my engine the extra advance it seems to want? Any downsides to that approach longterm if I just keep the initial advance a little high like that?

Anyway I am super happy to finally have this truck performing well enough to drive around my local area and run an errand or two! Maybe tomorrow I'll drive it down to the Christmas tree lot put it to use hauling a Christmas tree back home.

[D.B]

Good job, keep plugging away and you will have the truck running like a sewing machine.

[PanhandleShantyman]

made it to the tree lot