Danny76

I've had my 1976 L-82 for about a month now. One of the things I've noticed is some rough idling, especially in 1st gear, sitting at idle. I wanted to start looking around today at some of the vacuum lines and I noticed this. In the picture, the hose coming from the EGR valve has a screw in the end of it, and that screw was then inserted into a smaller hose, which hooks to the carb. Surely a job from bubba. There is no cat and the smog pump was removed by previous owner. Question is, could this be a cause of a vacuum leak? I've seen some threads about these lines being plugged, but being that the smaller hose hooked to the carb is very loose and sloppy, I'm wondering if this could be the culprit of a leak.



Suggestions? Should I get a new hose and run straight without the plug? I'm a novice and know next to nothing about carburetors, so any help/suggestions/explanations would be greatly appreciated!!

CanadaGrant

With your car idling put your finger over the open end of the tube opposite the one with the cut off bolt in it. It will probably smooth out right away as that will be your vacuum leak. It looks like somebody cut the vacuum line and inserted a bolt in each end to block the line but one end has come off. Take the short piece off, remove the bolt and connect the long end back up where you removed the short piece of tubing and see what happens. You might want to trim a 1/4 inch or so off the end of the long line where it has expanded due to the insertion of the bubba bolt.

Danny76

Thanks CanadaGrant. I just tried but I can't even get it to idle long enough without dying. It's idling at like 200-300 rpm. I did get it to stay long enough once to run over, I pulled the end from the EGR and it immediately died. I couldn't get it to stay running at that point. It just kept dying.
??????

CanadaGrant

Insert the bolt back into the short hose blocking both hoses. You can see it was there before because of the thread impressions in the pic. Then start it and it should idle fine because the open end of the hose is probably your vacuum leak.

Danny76

Actually, it is hooked back up. It always has been. I only pulled it apart for the picture. It was hooked together when the idling was low and kept dying. I couldn't get to it to try anything cause it kept dying, but to clarify, I always had it all hooked up.

CanadaGrant

At one time those 2 hoses went to the EGR vacuum control switch which is on the top front of the engine right beside your upper rad hose inlet to the block. The long hose went to the top port of the fitting and the short one which has been cut off goes to the bottom fitting but they have been disconnected and blocked together with the bolt.

Danny76

That makes sense! I saw some pictures showing that switch. Do you think I should do what you originally said? Take the bolt out, cut the end and reconnect? Why did they block it with the bolt to begin with?

CanadaGrant

Not sure as nothing else is visible in the pic. If you think it's a vacuum leak start by removing and plugging ONE hose at a time from the carb and intake manifold ports and checking your idle. Look at your brake booster first to make sure the large hose between it and the intake manifold is still attached as an rpm drop down to 300 is a big vacuum leak. Also remove the hose from the booster, plug it and make sure it's not the booster leaking.

Danny76

Thanks Canada!! I'm gonna look at it in the morning. I'll let you know if I find anything else.

Danny76

So here's what I'm noticing. At cold start up, idle is great, around 800rpm. It's when the engine gets to operating temp that idle drops significantly. I did take the bubba bolt out and hook that hose up directly, though I'm not sure it's supposed to be like that since it normally had a switch before the hose reached the carb?
But while operating, I detached the brake booster hose which had lots of vacuum. I detached the hose I've been dealing with from the EGR and plugged it with my finger and didn't really see any change in idle.
Any ideas why the idle only seems to really drop at operating temp? Oh, btw, I almost always hear a ping when I start the car. Usually only at start up. Not sure if it's related. But I checked the diaphram on the EGR valve which seems to be fine. I thought maybe it was stuck open.
I don't know what to do next. Any suggestions??

SwampeastMike

Presuming your carb/choke are operating properly the engine operates at high idle until it warms thus moving the idle cam to the normal idle position.

Our cars have so many vacuum operated components that they can suffer the death of a thousand tiny cuts. The ends of the vacuum hoses stretch over time and all or nearly all of them can be leaking just a little. Together all of those little leaks become a big leak

Also check the four bolts that secure the carb to the intake manifold are properly torqued. The gasket can compress over time resulting in a leak there.

The headlights, climate control, cruise control (if you have it), fuel EVAP system, vacuum advance, transmission modulator (automatics) and brake booster are all vacuum operated and potential sources of leaks.

Many hoses can be trimming a 1/2" or so at each end but others to not have sufficient slack. Dr. Rebuild (look it up) offers excellent quality vacuum hose replacement kits with great diagrams.

Replacing all of the vacuum hoses in my '79 L82 was the best thing I've done to the car performance wise! Combined with the previous regular tune-up things (plugs, wires, rotor, etc.) and generous use of carb/choke cleaner mine now starts, idles and runs like new.

Danny76

Thanks for that Mike. I was kind of thinking about that, changing all of the vacuum hoses. I'll take a look at Dr. Rebuild.

From your experience, does this "sound" like something that might be a vacuum leak? I know there are many things that could be the issue, but everything seems to be working properly. Also, from my picture, would me removing that bubba bolt and running the EGR directly to the carb cause any problems since the TVS valve is not there?

Thanks so much for the help guys!

SwampeastMike

My experience with C3s is limited to the one I own and it's the only carbureted car I've owned for decades. That said, it does sound like you have some serious vacuum leakage.

While mine never had much problem with stalling at idle it would happen on occasion when warm. The idle speed adjustment was so far advanced however that it was beyond the position for the solenoid "bumps up" the idle speed with the A/C running. The first vacuum hoses I replaced were all of those involved with the headlamps. The idle speed went up noticeably and I had to adjust it down. I replaced all* of the remaining hoses at once and the idle speed went WAY up.

*My HVAC system was leak free so I didn't replace those hoses. I also neglected to replace the little 1" or so vacuum line at the transmission modulator valve and it failed during my first shake-down cruise with the "new" car! Fortunately it failed less than a mile from home so I was able to limp back in first gear.

I had previously tested many of the hoses themselves for vacuum leaks and found none. The problem was that the ends of all of them were stretched out. During the big replacement though I found that the EVAP system vapor hoses were utterly toast. While the vacuum control hose for the EVAP system didn't seem any worse that the rest of the hoses the system was obviously not functioning. Since the EVAP system is connected to the PCV system I believe it was preventing the PCV from working properly as well.

Danny76

I just found something else. Bubba put another bolt somewhere. This is looking towards the front of the car, on the drivers side. There are 3 vacuum hoses here...one goes to the vacuum tank, the other goes to a "T" between the headlight actuators, and then there is this one with a both in it. Any idea where it goes?

stumpshot

What carb are you running? Is your vacuum advance hooked up? Have you turned the curb idle screw in so the car will warm idle long enough for you to do some vacuum checking?
You can check the leaks best by plugging each hose source at the engine, thereby taking the hoses out of service one at a time and see if anything changes.
A vacuum gage is a great tool to have for this work.
​​​​​​​Good luck!

Danny76

Thanks stumpshot! It's got the original Rochester carb. Vacuum advance is hooked up. I actually had just played with the idle screw when you mentioned it. That screw was basically backed all the way out, so I think that might have a little to do with it right there.

I just ordered a vacuum gauge so I'll start there and also I think I'll try to get the mixture correct. The smell is so horrible when I run it in my garage. I hope I can get it running a little less harsh as far as smell.
BTW, the rubber plug on the front of the carb was toast. That was probably a little leak there as well. I'm getting there, slowly.

Thanks for your help as always everybody! If anybody can pinpoint that Bubba bolt in my second picture, I'd appreciate it!

stumpshot

Danny- I'd run the warm idle up to 5 or 600 rpm. Don't know about the Rochester carbs but they probably have an idle air screw on each side. Turn the screw in slowly till the engine starts to labor then back it out a little till the engine runs free again. Do the other side the same way. That will probably hold you till the vacuum gage comes aboard. If the RPM's come up after you set the air screws just back it down with the curb idle.
Good luck!

Danny76

That sounds like a plan. I'll give it a shot this week. This carb stuff is starting to make sense to me! It's amazing how much I've learned in the month I've had this car. Thanks to folks like you!

Thanks again. I'll update this week.