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79' GMC C15 - Spruce Caboose

79 GMC 1500
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I don't know how accurate that technique is, however I did the same thing with a truck 20 years ago that was having problems. It pegged the 8 lb. gauge quickly. I installed a regulator in the feed line and it made a big difference. I ran it for years at 4.5 psi with good results.

If your truck is flooding, can you see this happening by looking down the carburetor after you shut the engine off ?
 
6872xtc said:
I don't know how accurate that technique is, however I did the same thing with a truck 20 years ago that was having problems. It pegged the 8 lb. gauge quickly. I installed a regulator in the feed line and it made a big difference. I ran it for years at 4.5 psi with good results.

If your truck is flooding, can you see this happening by looking down the carburetor after you shut the engine off ?
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Okay yea, most of the ac delco pumps or carter ones on rockauto dont specify what they pump (psi) ive read lots of people in forums, saying they are pumping 8-9 when tested and most people suggesting 4.5-5.5 for a qjet. I just dont wanna spend the money on a regulator if i dont need one. Most of the ones ive seen id have to mount somewhere, or support with AN fittings and what not.. for an engine i dont plan on really keeping, but if i knew it would fix it i would hah...

I havent looked down the carb after it runs, thats a good idea. ive just been going out to an empty float bowl, wet gasket and some fuel down near the base plate ( which could be from well plugs or flooding) so ill def give that a go and see what i find. Thanks!

Round 4 of the carb install should happen tomorrow or this weekend so ill know more then. Going to give the pressure gauge a try on the outlet before i hook it up and see what i get for PSI
 
bix said:
https://www.summitracing.com/parts/mrg-9710

something like this would be easy enough to install.
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Yes sir! I had one like that which I found locally back then.

I know that if you have a smart-butt friend turn it all the way down, it will only get enough fuel for most of the primaries.... secondary action was fall flat after a tiny shot of ummph.
 
So I tossed the carb back on, took awhile to run with so much of the fuel line empty, but she runs decent. Definitely needs a tune up and what not, but I'll get to that if I can keep gas in the carb first. Mixture screws are just set at the 4 turns out benchmark


I looked down the carb after I shut it off, didn't see any fuel going down it as far as I know, looked down the vent of the bowl which I hadn't thought to do before, and the bowl looks super full. Not 100% sure what part of the float I'm looking at, regarding the slope of it from the needle valve outwards. But fuel pressure could be my problem. I tried to check the fuel pressure with my gauge but I was alone and unsuccessful. Probably could have taken the plugs out n turned it by hand but I didn't hah.. I'll get my ladies help next time and check it soon if the float empties again.

Also don't want to pay 50 bucks for shipping on a 50 dollar part from summit, so I'm gonna see if a local store I have a discount at, will order one. It seems almost necessary ragrdless because almost all the fuel pumps I see for sale, vary enough to potentially cause a qjet to run poorly, if they pump more or less than 4.5 -5.5.
 
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Oreilly's has a crappy Mr Gasket regulator that will work if for nothing else testing the theory.
 
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max 02 said:
Just get a regulator from Lordco
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Yea that's exactly what I was thinking. I get 30% off so it sometimes compares to online ( not with 50 shipping from summit though )

centexk5 said:
Oreilly's has a crappy Mr Gasket regulator that will work if for nothing else testing the theory.
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I'm all the way in Canuck land. No o'riellys up here, but yea you're right. I figure if I spend 45 bucks on one, it's definitely not going to be anything special, but if it works at all, it'll be worth the squeeze.
 
Went out this morning and looked down the vent first thing. There was still some fuel in the bowl so that was a good sign. She took a couple pumps of the pedal and some cranking but she fired up, ran a little rough like it wanted to die until it warmed up after 15-20 seconds. I feel like this is some progress. Ill re adjust the choke to see if that's what maybe caused the rough start, also adjusted the high idle cam a bit more as it wasn't kicking it into much of a high idle. Not sure what the rpm recommendation is for the high idle cam. Maybe like 1000 rpm maybe. Anyway , I'm not sure if was resealing the well plugs, tightening the two fuel lines that were wet at the ends , another fuel filter with a new check valve in it or what , but I feel like this is a step in the right direction so hopefully im making progress.
 
Today I went and hunted down a guy who had a 79 for parts. Grabbed a grille off it. Got some whiskey dents in it but atleast it's complete and the correct grille.. unlike the bowtie one I got in there. I knabbed a power brake booster and the rod, the master was pretty shot looking, but I figured the brake booster probably doesn't fail very often? And I also picked up another mirror , since I needed one to have a matching set of the newer style ones for this truck.

IMG_20200405_183434.jpg

A mint grille is like a unicorn around here. Atleast for these round eyes out here.

I'm in the market for a master cylinder and I know the brake code jb3 and jb5 are for power brakes, the truck I grabbed this from was a 4x4 and a full floater rear. From what I've read the jb5 brake code was for the larger brake pads and drums, and is a dual diaphragm booster and slightly bigger? If this is the booster I got , can I run a jb3 code master on it since I don't have the big brakes , or do I need a jb5 master? I've read that it's all interchangeable. Just wondering if anyone could confirm that?

Donor truck had no rpo codes.

I ordered new rotors and wheel bearings for the front, as I still have some bad shakes while braking at certain applications. Ordered new brake lines for the front, Shoes, brake stuff for the rear. Some pretty decent kyb shocks all around.. The ones on here might be original so anything is better. Picked up a new check valve and filter for the brake booster.

I still have one tire that leaks bad, a motor that had a mysterious / obvious crappy idle,
A "tuned" carburetor that runs like crap, and rust.... Buuut one thing I now have that I've never had before!
IMG_20200405_114823.jpg IMG_20200405_114254.jpg
Just a bit of dust...
IMG_20200405_173750.jpg
 
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The booster also looks a bit rough. But I'm hoping it works good. I Figure I'll hook it up to manifold vacuum to double check it functions before installing and then being fubar.
 
I guess this answers my question. If I got one of these 4 brake code boosters then it should work. Im a bit bummed they don't have any other brands, lots of talk about bad brands on the internet in terms of MC. Has anyone ever used these?
Screenshot_20200406-084858.png

Sometimes rock auto is so cheap it makes me wonder about the quality haha.
 
Truckman4life said:
Cardone is not bad from what I've seen.
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Yea I'm sure it's not great but for now it'll be fine hopefully . Money's kinda tight and there's a bunch of stuff to do to this thing so the MC is getting the shaft. Eventually I'll do SS lines from inline tube and all that. If it isn't holding up well by then I'll source out another one.

Ordered the master cylinder, a long with some new spark plug wires, and a coil. Ohming out my current one was giving me some iffy results so I figured while I'm just throwing money at the truck why not haha. Going to source a T fitting and plumb the booster into the PCV vacuum, unless anyone sees an issue with that? Got a new check valve and filter for it as well.

I hooked up my vacuum gauge and dialed in the fuel mixture screws. Since it idles kinda shitty I might take another crack at it.

I also ordered up some thick airhorn gaskets from quadrajetparts, because mine is quite warped, and I'm wondering if my idle issue is related to that. If the gaskets do fix it, I'll take the air horn off and try to straighten / file it to within .030 tolerance ( regular gasket thickness ). The engine is pulling 20 " HG pretty steady, so im thinking the shitty idle is carb related or ignition at this point.
 
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20" vacuum is damn respectable, should be able to work with that
 
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Bent77 said:
20" vacuum is damn respectable, should be able to work with that
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Yea i was happy to see that, as this motor is a mystery to me really. Its got some steady smoke from the pcv valve, but doesnt seem to be burning much oil, so im gonna take those valve covers off and look at potential gunk in there, as i have some new gaskets as well. I still need to do a compression test until i know any more numbers for sure, but im starting to lean away from motor being crappy, and just the things attached to it that are crappy. Id hope with 186k km on it, it should have lots of life left mechanically, and once its warmed up itll fire the first turn everytime, so thats been good to see also.

Hopefully ill figure it out this weekend! Unless its the warped air horn, thatll have to wait until those gaskets show up. They said you can double them up if need be to diagnose your problem, but straightening the air horn should be attempted. The kit came with two gaskets at .047 thick so with two of them i should be able to close that gap for sure. I didnt measure the gap but when i take it off again i will.
This is a bad photo but its for sure warped more than the .030 gasket, im sure with the proper torque sequence ( inside out ) it does go back down a bit but i dunno if itll flex that much. AND the damn thing aint level either...:whistle:


IMG_20200327_101809.jpg
 
It’s a Qjet, it’s warped

20” means the rings are probably good. Probably sucking oil through the pcv into the intake
 
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