1969 C/10 won't stay running

[Stephen717]

Hi, I know that this has already been covered before but I don't know where else to turn. Three days before my eighteenth birthday I bought my first truck, a 1969 Chevy C/10. It has a 250 inline 6 from a 1979 and a rochester monojet from a 1973 pontiac, along with a muffler from a kia so it is surprisingly quiet. When I bought the truck for $700 I thought that I was getting a steal since I thought all it needed was a fuel pump to be a running project. It has a 3 speed column shifter that is original to the truck but it originally had a v8 in it (I am thinking a 307). Anyway to get back on topic I put the new fuel pump on and checked the points only to find that they were brand new and already set right. it had a slight miss to it but my father and I advanced the timing and rebuilt the old single barrel carb and that took care of that. Then I turned the manual choke (opening thing?) around so that to choke it I pull the choke rod out instead of push it in. Then I replaced the dimmer switch and sprayed some pb blaster in the original horn a few times and rapped on it a couple times with a rubber mallet to get it working again. Anyway I know that I keep getting off topic but my mind keeps reminding me of what I have done and what I still need to do, Like get new side marker lights and replace the interior roof sheet metal. But we got the truck running good and it ran fine for about a half an hour. then I was to to rev it up and see if it would come back to idle. Well I did just that and it did come back to idle but ever since then it has blown a greyish smoke from the exhaust and shuts off when ever it gets to it's running temperature of about 190. its holding oil and the exhaust doesn't smell of burnt oil when the exhaust starts blowing out its smoke but I don't know what this could be and as I said at the begining of this I don't know where else to turn or what else to do. If anyone can help me out with this that would be great.

Thanks,
Stephen

[geezer#99]

Could be a cracked block or head letting coolant into the combustion chamber. It'll only leak when it gets up to temp and the crack widens.
Are you loosing coolant?

[Stephen717]

Yesterday when I checked it everything seemed fine. the block has a bit of oil on it but it was missing a valve cover bolt. I was lucky that I had the chrome valve cover hold downs from my dad's old Camaro. But every time I have started it since it started doing this it will run for about 5-15 minutes and shut off. Also since it started acting up it we can't get it to run past half choke.

[geezer#99]

Ran it with the rad cap off and watch for bubbles in the coolant.

[Baddflash]

Sounds like coolant is getting in the engine, either from a crack in the head or cylinder or if you're really lucky it's the head gasket starting to let go. Is there any residue sort of a white foam on the valve cover cap or dipstick? any loss of coolant?

[Stephen717]

As previously stated when checked yesterday before it ran and after it shut off and cooled down the fluids all looked the same. have a block in the fuel line that showed up this morning and will blow it out tomorrow. will watch the coolant then. thanks for the info. also the head looks like it was replaced so it might be a head gasket. the truck came with a new one so i will change it tomorrow. and will get the stuff to do an oil change to

[Baddflash]

Also want to mention make sure the rad is not filled to the top, there is a mark facing the engine showing the level when cold. If the cap is not working it could cause excessive pressure in the cooling system.

[Stephen717]

if there was a crack or bad gasket and coolant was leaking in the engine wouldn't my oil by a milky color instead of the golden brown color that it is.

[Baddflash]

Not always, the leak would have to allow the coolant to get to an unpressurized part of the oil system, a bad head gasket has potential to allow this as does a crack I suppose. However the crack or leak could just be allowing a small amount of coolant into the cylinder and causing the smoke you refer to as it's being vaporized in the cylinder. This can also cause the stalling as the coolant can prevent the mixture from igniting.

[Stephen717]

it smells more like oil than rad coolant burning through the exhaust and making the smoke though.

[Baddflash]

Maybe re-state your issues to be clear what you are asking. Sounds like it could be rings maybe? Valve stem seals? Combination of the two? Could just be a really worn out abused engine? maybe the Kia muffler you are using is to restrictive and causing excessive crank case pressure?

[Stephen717]

OK first off, I'm still new to all of this. I only got the truck about a month ago and I am still finding problems with it. Second, the kia muffler was on there when i got it so it and the truck has supposedly had that muffler on there and ran fine until the fuel pump went on it before I bought it. And third I would like to put a 307 back into it since that's what I am almost certain that it came from the factory with so if. I thank you for the information and if anyone would like to trade a 307 for a project 250 I am more than happy to do so. I just wish I knew a bit more about this stuff. I don't mean to go off and rant but I didn't smell oil until this morning and when I came on here and explained it I guess your answer just made me feel like a kid.

[garyd1961]

I'm probably the only guy on here who is a big fan of the 307 but I wouldn't waste my time on one unless I could get a nice running one cheap. A 350 just offers so much more for the same price.
Don't give up too fast on the 250, at least keep at it until you figure out the problem. It may be something simple but if it isn't you will have learned something you can use latter on. When it comes to mechanics the best education you can have you get by getting your hands dirty.

[Baddflash]

Maybe work on the fuel issue first and see if you can get it to run without stalling. Than work on your next big issue, just take things one problem at a time and you'll get there. I would maybe go for something like a 327 or 350 myself, the 350 was optional in 69. I'm not biased cause I swapped a 350 into my 69, really.

[Stephen717]

Thanks for the info. I kind of like the 250 because it is a pretty good motor with all the hills in my area. Drove a friends truck with a 250 before I got mine and liked how much torque it had. Plus my dad had one in his 69 GMC. I like the 350 but since it's a 2wd I would like to eventually put a 427 in it baked by a Muncie 4 speed. that's a long way down the road though. as for the possibility of a cracked head. I was told that before I bought it the guy put a new head on the motor. He also threw in a set of manifold and exhaust gaskets and a head gasket. So once the fuel problem is figured out I might just spend a day changing gaskets. I am also going to take off the kia muffler and see about getting a cheap thrush muffler to get me by. Also while I am thinking about it if I change my shift linkage for the 3 speed to put it on the floor of my truck will I have to cut a second hole later on when I change the 3 speed to a 4 speed? Again thanks for the help.

[Baddflash]

Yes the 3-spd hole is different than a 4-spd and I would say not worth it anyway cause it's still a 3-spd and now the shifter is in the way for having girl slide over. If you're going to change the head gasket I recommend having a torque wrench and all the specs handy, do not mix up the pushrods make sure they go back where they came from.

[dflarsen77]

Black smoke is oil, white smoke is coolant, but from what you describe, not being too sever, it shouldn't cause it to shut off. The back pressure from that Kia muffler should be pretty high, and that could make it stall. I wonder if enough back pressure could cause ring and valve seal problems. If you can, unbolt the exhaust from the manifold or header, let it run and see how it behaves. I can't imagine you'd want to keep that muffler for long even if it isn't causing problems.

[Stephen717]

Update, blew out the fuel line and put a bit of gas in carburetor, it drew fuel from the tank the first couple of times and then stopped so i don't know whats wrong there. took a hack saw and a hammer and cut off the kia muffler. Learning from the previous owners mistakes a 1" muffler should never be welded to a 2" exhaust. no longer seeing smoke when it starts but like stated above now its not drawing fuel from the tank. also met a guy who said it could be the coil causing it to stall when it gets to running temp.

[Stephen717]

So I went to see a guy named George who has an awesome shop with a lot of cool old toys. he has a 64 long bed behind his shop that I might ask about when I get some more money and a 69 swb gmc. anyway he told me to check the sending unit in the fuel tank and the rubber line that connects the two hard lines for the fuel (which I now know needs replaced), and he said that its either the ignition coil or the condenser that's causing the truck to stall when it gets to running temp. anyway that's all for now. also how hard would it be to take out the 12 bolt rear and put in a 14 bolt from a 1 ton truck. I have been toying with the idea of a work/show truck because I have always liked the usefulness of a utility bed and I wanted something unique which got me to thinking, Hey you never see a 69 c10 show truck with a utility bed. and the extra weight would help with the WV winters

[cleszkie]

Based on the color of the smoke, my money is on unburnt fuel, not oil, exiting your exhaust. Water makes white smoke, oil makes blue smoke, and fuel makes gray/black smoke. That would explain why the truck runs when cold and not when hot. When cold, the excess fuel is acting like a choke, and the engine can deal with that. When it gets hot, and the excess fuel is still acting like a choke, the motor dies.

Maybe a stuck needle valve is causing float bowl to flood. Maybe a leaking accelerator pump. Just something to consider.

[bw46]

Sounds to me like the choke is stuck on. In your first post you mention you reversed the linkage and that has me suspecting it.
Double checking the choke seems too obvious to mention, but hey, we've all ran out of gas before and scratched our head for a while.

[Stephen717]

got a fuel line today but have to exchange it for 5/16 line tomorrow since i got 1/4" today also when you put seafoam in your gas and then spill it on your face when taking off the fuel line, it burns. yes I did reverse the linkage for the choke but it has been working better than before I reversed it. hasn't stuck once on me. I also replaced the condenser and ignition coil because my local backyard mechanic has told me that the truck could have been dying when it got to running temp from either of those going bad. I recently rebuilt the carb and triple checked to make sure that everything worked in it before it was put back on but I've been told that single barrel carbs are finicky anyway. is previously stated I spent a good chunk of the morning with a hack saw and a hammer getting the 1" kia muffler unwelded from the 2" exhaust pipe. I'm going to save up and get the pipe to finish running it back so it doesn't end under the cab of the truck. also apparently I got a hell of a deal on the truck since there is barely any rust in the cab (one small spot above the windshield) and the frame and undercarriage look like someone has done a lot of work to them. the entire bed needs replaced though which is why I am going to put an older fisher utility bed on it and make it a work/show truck. I am also going to get a new sending unit for the tank next time I get paid as the truck sat for about 2 years before I bought it. the only things that should need replaced now are the emergency brake, the starter since its still the original one on there and I fear it will go soon, and the battery. oh and the fuel line that I am getting tomorrow. also an advance auto is opening in my area tomorrow and I am so excited because now there will be deals from both autozone and advance auto since they are right down the street from each other

[garyd1961]

Although the old one barrel carbs are pretty simple, rebuilding one is not something a beginner should attempt alone. Carburetors take a long time to master and there are not a lot of good carburetor guys left since fuel injection became popular. I would find someone who knows carburetors and go back through it.
I'm not saying you are stupid or anything just that you may have missed something being inexperienced.

[Stephen717]

thanks for the info. watched a lot of videos and followed the instructions along with an older closed forum about rebuilding the carb that's on my truck (I will see if I can find it again) but like you said I could have missed something. there is an older guy down below me with a bunch of older gm vehicles, 2 64 long beds, 1 63 2 door suburban, a 69 swb gmc c10 and a k10 frame that he's working on now. I might take it down and have him help me if I get time to take it back off but I don't think because when I was still getting fuel to the engine before I accidentally blew a hole in the rubber line underneath the cab that connects the 2 hard lines by trying to get a clog out of the line, it ran great for about 30 or 45 minutes until I gave revved it up. then it blew a greyish smoke and shut off. since I cut off the muffler today it has stopped doing that as far as I know. tomorrow I am going to trade the 14" fuel line i got for the 5/16" line I should have got. then I will jump it with my dads 97 k2500 and see if it will run better with the muffler off of it. I know it sounds better now though. and the slight miss in the motor seems to have disappeared. So that should be good.