cbolt Posted November 1, 2022 Share Posted November 1, 2022 Went for a drive today and after 10 miles or so the car started having difficulty idling, really running rough at idle to the point I had to keep a foot on the gas at red lights to prevent it from stalling. Got home and did a quick physical inspection which revealed nothing out of the ordinary. I then tweaked the mixture screws (Carter AFB) and idle speed screw to get the car to run a bit better, but it is still off. Vacuum check has it around 13 psi and it wanders a bit an inch or so either way, but not a regular type of wandering which would be a valve, ring, or other such issue. My plan is to add some fuel additive (My last fuel stop was on my way home from the eastern meet... I have been busy and not had time to enjoy the car), check and replace the fuel filter, inspect the spark plugs, and reseal the vacuum riser on the back of the manifold that provides the a/c canister with vacuum. My question is... what else do I need to check/inspect/replace? My thoughts are the low vacuum is indicative of a leak, maybe just a small one, but the low vacuum indication may also be a result of the car just running rough due to bad gas. Any input from you engine gurus would be welcome. Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted November 1, 2022 Share Posted November 1, 2022 I'm no guru but I'd start by checking all the vacuum lines and hoses. Could be something as simple at a cracked hose or hose or line that came off. 1 Quote Link to comment Share on other sites More sharing options...
Dtret Posted November 1, 2022 Share Posted November 1, 2022 As stated above but possibly the fuel filter. You may be sucking up moisture from the bottom of the tank. 3 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted November 1, 2022 Share Posted November 1, 2022 I agree with Dennis. Check the fuel filter. 1 Quote Link to comment Share on other sites More sharing options...
DragCat Posted November 1, 2022 Share Posted November 1, 2022 Just throwing something else out, possible fouled plugs. Don't think you have headers, and don't know how it would work on exhaust manifolds, but I got one of this laser temp guns from HF. I had a fouled plug, rough running, the temp gun on the header tubes showed me exactly where the problem was. 2 Quote Link to comment Share on other sites More sharing options...
dejh22 Posted November 2, 2022 Share Posted November 2, 2022 Is this a stock engine? If it is 13:" is pretty low. My first check, as others have said, check vacuum lines. I take a can of carb cleaner and spray a small amount on Vacuum lines, base of carb and vacuum fittings. If that all checks out, check plug wires. Are you running a HEI distributor or the stock cap rotor and points? If you are running points you may need to check the dwell. Quote Link to comment Share on other sites More sharing options...
cbolt Posted November 2, 2022 Author Share Posted November 2, 2022 Not stock. I have the aluminum Edelbrock heads, intake, cam, Carter AFB, .060 flat top pistons, etc, etc..... Vacuum lines was my first thought as well but they all seem okay so today I am moving on to the plugs and fuel filter as those were my thoughts as well. 2 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted November 2, 2022 Share Posted November 2, 2022 Does the exhaust smell of raw fuel ? When Montelishi arrived, I had a similar issue, which turned out to be the air/fuel mixture. I wound up leaning out the jetting and backing out the air screws to correct the problem, after having replaced most of the vacuum lines and having no results. The plugs were the next step.... And that helped as well. Quote Link to comment Share on other sites More sharing options...
cbolt Posted November 2, 2022 Author Share Posted November 2, 2022 No raw fuel smell. Fuel filter is clean as a whistle and the plugs aren't fouled either. Ugh. Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted November 2, 2022 Share Posted November 2, 2022 If you have the plugs out still you could do a compression test, if there back in maybe pull the wires off one at a time see if there's any difference and check the spark. 1 Quote Link to comment Share on other sites More sharing options...
Rob Peters Posted November 2, 2022 Share Posted November 2, 2022 Jim, maybe a stupid question but I will ask it anyhow. Is this rough running only at idle or is it also at higher RPM's. If only at Idle I would think the primary thing to check is what others have suggested above, maybe a cracked or loose vacuum line. The first thing I thought of when reading your post was that maybe the anti-dieseling solenoid, also known as the idle solenoid. If that solenoid is not working or if it is not getting the proper 12 Volts it would drop the idle down lower than it should be. Just something else to consider. I tend to first look at the easiest thing to check. rob Quote Link to comment Share on other sites More sharing options...
cbolt Posted November 3, 2022 Author Share Posted November 3, 2022 Rob, its only at idle and I dont have an anti-dieseling solenoid. I agree about it acting like a vacuum leak but I have not been able to find a leak in any of the hoses. I capped them all to test it but no change. I did the plugs one at a time, pulled them, inspected them, cleaned them, and reinstalled them. I may try pulling a plug wire at a time, that's a good idea. Quote Link to comment Share on other sites More sharing options...
1970mcss Posted November 3, 2022 Share Posted November 3, 2022 Did the timing get screwed up?? Quote Link to comment Share on other sites More sharing options...
Scott S. Posted November 3, 2022 Share Posted November 3, 2022 Gum in the jets from bad fuel ??? Had that happen on a '77 Silverado with a Q-jet a long time ago...... Especially notable in cold weather. Quote Link to comment Share on other sites More sharing options...
cbolt Posted November 3, 2022 Author Share Posted November 3, 2022 lol Scott. We don't get cold weather. I removed the idle mixture screws and shot some carb cleaner in each side but that didn't make a difference. Paul, I checked the timing and it is spot on, so that isn't it. What is baffling to me is the idle started misbehaving mid-drive, on my way over to a friends house to finish hooking up the electric fan. So it ran fine for about 15 minutes and suddenly it started idling rough. To me, that is something that is broken and not a fuel issue but I really cannot count anything out. My next step is to drain the fuel tank and put all new, fresh fuel in it to see what happens. Because space is very limited in my garage it takes a contortionist to perform tasks like removing spark plugs as the passenger side is very close to the work bench, and I have to duck under cabinets just to raise the hood. Forget about opening the passenger door. Ugh. The cramped quarters make working on anything more time consuming than it should be, thus the slow and methodical progress. Anyway, after the fuel change I guess the compression test will be next, or maybe pop the carb off and give it a good cleaning. Fun! 2 Quote Link to comment Share on other sites More sharing options...
1970mcss Posted November 3, 2022 Share Posted November 3, 2022 I was thinking bad fuel also Quote Link to comment Share on other sites More sharing options...
cbolt Posted November 3, 2022 Author Share Posted November 3, 2022 Yep, could be. Smells okay, like fuel should smell, but you never know. Quote Link to comment Share on other sites More sharing options...
dejh22 Posted November 3, 2022 Share Posted November 3, 2022 Weak coil? Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted November 4, 2022 Share Posted November 4, 2022 Yea I don't have a lot of room in my garage either it's a real pain to do some stuff for sure. I put up a wall years age between the 2 car garage to convert one side into an office but that wall has to come back out now just need to find the time to do that. Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted November 4, 2022 Share Posted November 4, 2022 Wait!? What?! You guys have garages!?!? Sooooooo lucky! 2 Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted November 4, 2022 Share Posted November 4, 2022 4 minutes ago, MC1of80 said: Wait!? What?! You guys have garages!?!? Sooooooo lucky! Yes 2 car garage but barely enough room to work with all the other stuff in the way. I'm in the process of cleaning out but it takes time. Plus I gotta replace one garage door that I sealed off when that was an office. Garage doors have gotten crazy expensive 😳 and hard to get. Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted November 4, 2022 Share Posted November 4, 2022 2 garages with doors too!!! OMG!!! Sweet!!!! 2 Quote Link to comment Share on other sites More sharing options...
Dtret Posted November 4, 2022 Share Posted November 4, 2022 Can anyone say basement. Lol. Garage ha. 2 2 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted November 4, 2022 Share Posted November 4, 2022 21 hours ago, cbolt said: lol Scott. We don't get cold weather. I removed the idle mixture screws and shot some carb cleaner in each side but that didn't make a difference. Paul, I checked the timing and it is spot on, so that isn't it. What is baffling to me is the idle started misbehaving mid-drive, on my way over to a friends house to finish hooking up the electric fan. So it ran fine for about 15 minutes and suddenly it started idling rough. To me, that is something that is broken and not a fuel issue but I really cannot count anything out. My next step is to drain the fuel tank and put all new, fresh fuel in it to see what happens. Because space is very limited in my garage it takes a contortionist to perform tasks like removing spark plugs as the passenger side is very close to the work bench, and I have to duck under cabinets just to raise the hood. Forget about opening the passenger door. Ugh. The cramped quarters make working on anything more time consuming than it should be, thus the slow and methodical progress. Anyway, after the fuel change I guess the compression test will be next, or maybe pop the carb off and give it a good cleaning. Fun! Garages AND no cold weather ??? Now that's what I call "spoiled"... lol 3 Quote Link to comment Share on other sites More sharing options...
ripleydale Posted November 5, 2022 Share Posted November 5, 2022 One way to prove a vacuum leak exists is to cup your hand over the carb when it's running, not choking it off, leaving enough air to run. If the idle goes up, there's a leak somewhere. 1 Quote Link to comment Share on other sites More sharing options...
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