Help, please!! Our '74 has had intermittent problems with running rough. Usually runs fine cold, but sometimes when it gets hot, it'll run rough and stall out when stopped. Thought we had figured out the problem (loose spark plug wires) and it ran fine. Took it to a mechanic to check the timing and the tach - the timing was fine, but it started running rough again. Found another loose spark plug cable (think the mechanic knocked this one loose). Ran GREAT for the past 3 weeks or so, even on longer trips of a couple of hours. Took it to Firestone Friday for an oil change (cheaper than we could do it!) - yup, started running rough again. Decided to replace the plugs and wires, and found a bad spot on one wire. Not the problem. Checked all the vacuum hoses, t-connectors, etc. - no leaks. Choke is working fine. Air filter is clean. When it's running fine, the idle is around 700-800 RPMs, but when it's running rough, the idle drops below 500 and it has backfired a couple of times. Any suggestions??? Is there maybe a vacuum cap hidden somewhere that maybe we missed?

UPDATED TODAY, 10/14 - SEE POST #22

 

I just fixed a problem on my 81 and it was the spacer between the bottom of the carb and the intake manifold had a big piece of it blown out. Created a hell of a vacuum leak and it would not idle but this was all the time it would run terrible.
New spacer and it runs great again Yeee Hawww

 

Glad yours is running good again, Yeller81USNRet! Pretty sure it's not the spacer since it happens only once in awhile. For example, yesterday it ran fine on our way to an event, but from there to the restaurant and then back home again, it ran really ragged. Tried to stall out at every stop we made. After we changed the plugs and wires, it still ran rough. Today we couldn't MAKE it happen. Really hard to troubleshoot!!

Anybody else have any ideas??? Thanks!

 

Has anyone looked at the fuel filter and carburetor lately? It sounds like an intermittently sticking float.

 

Interesting you should mention the fuel filter - just said to my hubby tonight that maybe we should change it just in case it was gunked up. The carburetor is fairly new - the last owners had replaced it, but the car sat more than it was driven. Would sitting like that cause it to stick? If so, what do we need to do to fix it?

 

Let us know what the problems ends up being. My 81 is doing the same type thing. Not a consistent miss

 

Could be a cracked distributor cap...is it damp out when it starts to run rough?

 

No, the distributor cap is fine - we had checked it thinking that might be the problem. Also checked for moisture - there was none. Thanks for the suggestion, though!

 

OK, check the float level, one or both May not be seating tight, lets in too much fuel and the engine will want to crap out and die. Check the floats, the old style cork types can get soggy and start sinking, same thing..cant stop the fuel from filling the bowls, and engine wont run right. Reset the float level while your in there..then if alls well then you can rule out float bowl problems and move on..Youll find the problem eventually and have a complete tune up done too

 

Lars always says that 90% of carb issues turn out to be ignition related. Have you checked that the coil is ok?

 

Thanks for the info! Unfortunately, we know very little about carbs. I've done some online research, though, and found a couple of sites that may help. If we can't figure it out, guess I'll be asking more questions!

 

Nope, but we will - thanks for the tip!

<Edit> Duh! What was I thinking?? That was the FIRST thing we replaced!!

 

Might want to also replace the coolant sensors and wires if you have them. I had the same exact problem. Also check your intake you may have a small water leak and catching an air bubble around the sensor

 

Sounds like it is running fine when cold. I would double check the choke operation and make sure it's fully opened when warmed up and that the linkage is not binding (because of insufficient lube or linkage making contact with filter housing, etc.) causing intermittent problems.

 

We did find a leak and fixed it, but it wasn't causing our problem . . . . . . It's amazing the little problems we've found and fixed while trying to figure this out!!

Thanks!

 

I checked the choke yesterday after doing some reading up, and it was working fine. But then, yesterday, it ran fine all day!! I guess we'll have to wait until it acts up again and check it then.

Thanks!

 

i would still chech into the coolant plugs and wires. After i went through and changed all the stated above distributor wires plugs even had the crossfire totally rebuilt I still had the problem. After talking to another mechanic buddy he told me to check the sensors and told me where they were. As soon as i grabbed the wire connectors they fell apart in my hand. So i traced the wires back to the point were they where not scorched clipped them and replaced the connectors and the sensors themself and i haven't had the problem sense.

 

What sensors are you speaking of?

 

[QUOTE=Bob Onit;1562133970]What sensors are you speaking of?[/QUOTE

These sensors I'm speaking of, one is located toward the front of the enigine block on the right hand side just under the head and the other is on the left hand toward the rear of the block in around the same as the other. Both having a single lead wire. But as I said in one of my first response if you have them that would be the area to check. Being that there Vette is almost 10 years older then mine.

 

Don't think my '74 has these sensors?? But I didn't have time to check last night - will definitely look for them tonight. Thanks!