I'm having an issue where I will idle, after about 30 seconds it revs up then slowly come back down, and then the engine stalls, upon restart, it idles really low then dies, tried again with a little gas, it revs up, works its way down and slowly dies out again. I've tried adjusting the idle speed, replaced pretty much all of the vacuum lines, and I'm still having an issue. When I parked it, it ran great, but the idle screw just wouldn't stay where it needed to be, I cruised around quite a bit with no issues but every few weeks the idle needed adjustment or it would slowly get lower and lower. I left it parked for a couple months, and now i'm having this issue and i'm stumped. I also replaced the Cap and Rotor as well as all the plug wires in an attempt to fix the issues, but all it seemed to do was net me another 30 seconds at idle. I'm pondering on replacing the fuel pump and fuel lines to see if there might be a clog somewhere, and maybe trying to see if I can clean the strainer in the tank. does anybody have any other opinions as to any other possible causes? thank you in advanced!
first check if all the screws holding the carburetor together, and the nuts holding it on, are tight. Also check the manifold bolts to make sure they're tight. Then check the ignition system....
manifold bolts are tight, carb is aswell, it was just recently replaced. I did go over it again today, and Just in-case I'm going to go and try spraying it a little and see if anything happens, I was also curious if maybe the butterfly valve on the exhaust / intake where they meet could cause this? I know the flange where the exhaust is attached is bent so it technically has an exhaust leak between the headers and pipes, I've been waiting to redo the entire exhaust before I fixed that though, I don't think that would cause an issue, would it? I also noticed just the first time I started it there appeared to be a small amount of smoke in the carb (i pulled the air filter off), which I had attributed to the butterfly valve directly below it though. It didn't appear to be a recurring issue when I tried again
There wasn't the last time I checked, are you thinking bad fuel pump? Sent from my iPhone using Tapatalk
I'll try and get to the truck in the morning and see what I can find Sent from my iPhone using Tapatalk
All the lines are brand new, those for my first places to check, but unless they cut them somewhere with a razor knife there's no leaks. Tomorrow I'm planning on spraying everything and seeing if I can find a leak anywhere Sent from my iPhone using Tapatalk
Good point, I know the base plate has gasket maker in addition to the gaskets, thanks for all the ideas! Sent from my iPhone using Tapatalk
It ran fine for a few months, it's intake, gasket with sealant, adapter, gasket with sealant, holly 2 barrel Sent from my iPhone using Tapatalk
It doesn't appear to have gas in the oil, I shortened all the vacuum lines and it ran for a good few minutes with the same rev issues, up and down and it would slowly slow down, if it hit the gas a little it would rev up and slowly work its way back down, at any RPM's except idle it runs great, Revs normal, but if it drops low to typical idle it would start slowing down again and die. I put a spark tester on each cylinder and all the plugs are getting spark, and they are pretty new, replaced at the beginning of this year, They are NGK's, the wires and rotor and cap are all brand new duralast gold. Would it be possible for he butterfly valve connecting the intake and the exhaust to cause issues?? I've also noticed I lost one of the metal clamps that extends between the intake and exhaust manifolds that held them in. The rest are all tight. I also noticed the check valve in the PCV valve rattles around when you shake it, more so than normal. I'm thinking of replacing that aswell. Sent from my iPhone using Tapatalk
The exhaust heat valve will not cause a slow idle. All it does is direct heat up under the carb to help keep the fuel vaporized. Is it stuck closed or open? Closed is directing all exhaust up, open the exhaust exits the manifold as normal. If it ran before setting, assume the gaskets in the carb have shrunk or dried out, todays fuels will do that. Fuel pressure is also a possibility, but it would have to be pretty low or not at all. Pull the line and crank the engine to see how much fuel flows in to bucket after a few revolutions. Check the distributor mechanical advance, make sure it is not stuck, then check the vacuum advance to make sure it holds vacuum. Joe
How would I check the mechanical and vacuum advance? I could see that helping as shortening all the vacuum lines seemed to help tremendously Sent from my iPhone using Tapatalk
I'm also trying to figure out how to check between an open or closed emissions / vacuum system for which PCV valve I need, they look identical and I want to replace mine Also, all the gaskets and whatnot on the carb and intake : exhaust manifold are brand new this year Sent from my iPhone using Tapatalk
I would really get that clamp on there before you start changing everything else. Should be pretty easy to find at a local yard. If not PM me and I'll see if I have one laying around.
I'm trying to find one, going through local parts channels and what not right now, but the PCV Valve was nasty when I pulled it so I'll be replacing it anyways Sent from my iPhone using Tapatalk
And the exhaust valve isn't stuck as far as I know, I'm just curious of it could have an effect, because it's different, most vehicles don't have that Sent from my iPhone using Tapatalk
Stock distributor? Points or HEI? Check for excessive side play in the distributor shaft. It's not uncommon for these engines after they get some mileage on them. With enough wear the point dwell can get erratic and the problem gets really noticeable at idle speeds. Not sure if HEI is quite as sensitive. And as already mentioned, make sure the mechanical and vacuum advance are working properly.
My C10 with a 250 I6 was stalling and it turned out to be the hose from the valve cover to the air cleaner was cracked.
Mine doesn't route to the air cleaner, carb, to a T that splits to the valve cover and intake manifold Sent from my iPhone using Tapatalk
Large heavy duty washer might work for a temporary manifold hold down. Could just be a simple vacuum leak. To check mechanical advance, pull the distributor cap and see if the rotor will turn and snap back. Vacuum advance can be checked by pulling the hose off at the distributor, move the vacuum arm and plate, then hold your thumb over the inlet where the hose goes. If the plate and arm doesn't move all the way back till you remove your thumb, then its good. You can always suck on the hose and see if it will move, but thats kinda nasty and tastes bad.
Your description of the vacuum hose routing and the rubber oil fill cap have got me a little concerned. Do you have a PCV valve somewhere in the system, and where is the crankcase vented to atmospheric pressure? Or is that chrome thing on the side of the valve cover some kind of a vent?
The PCV valve is on the back of the valve cover, where the hose attaches, and the chrome thing is the only breather filter with the correct size to fit the hole I could find. It used to be plugged when I got the truck, and I was told on here that I was at risk of blowing seals if I didn't remove the plug and install a breather Sent from my iPhone using Tapatalk
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