Overheating and checking for vaccuum leak

[AmadeusCharger500]

I thought my overheating problem was cooling related but after doing several things like having the radiator checked and moving the fan closer, now I am thinking it is vacuum leak. I have a 770 holley carb. I have the vacuum advance plugged off and there is another port in the front that is plugged. The main port in the back of the carb is going to the PVC on the left valve cover. Port on the intake manifold is going to the brake booster.

I see problems that are obvious but I want to ask before I change things just to keep track of progress.
#1 the plugs on the 2 forward ports look cracked and very likely leaking.
#2 I don't have hose clamps on the hose running to the brake booster or the hose running to the PVC.

I guess my question is should I take a vacuum reading now and after I fixing these things? Is this the best way to determine if those were indeed the problems?

Another problem is I am forgetting where to take the reading from.

Any help would be great. I want to have this car ready for Carlisle and at this point it is running at 210 degrees and runon after key is shut off!

[Steve P.]

I would start the motor and let it warm up a bit. Then take some carb cleaner and spray it lightly around the vacuum ports that are suspect first. Move on to the rest afterward. If you get a change in the RPM while spraying a port you have found a leak. Don't stop there. You could have more than one. Keep in mind that most mechanics will change out ALL the vac. lines at one time. Thus leaving them all to fail about the same time..

You said you have your Vac. line to the brake booster coming off the intake. If it is in the center of the manifold that is fine. Some older versions had the booster vac. port coming off the number 8 intake runner. This is bad. Especially if your booster leaks..

Good luck...

[AmadeusCharger500]

Well Steve you may have something there. Give me more info on the booster leaking because I do indeed have the line coming from the #8 runner. Its a Holly street dominator.

So what do I do to change this? Swap lines, PVC and booster?

[Ghoste]

Well, I'm certainly interested to see the results of this question (number 8 SD here as well). 

[firefighter3931]

Heath, Get a vacuum guage on it and start pulling hoses off one by one and isolate the bad hose. Just hold your finger over the nipple of each vacuum source and see if there is any drop in idle vacuum. When you find a bad hose or cap....just replace it. I would attach the vac guage to one of the nipples on the baseplate of the carb. 

In reference to the booster hose location ; the #8 intake runner is fine, inmo.....engine vacuum is engine vacuum. It's not a good idea to run the PCV into any individual intake runner because it can pull too much oil vapour into one individual cylinder and cause oil fouling of the plug on that particular cylinder so you want to spread it out by using the baseplate of the carb....this distributes the vapour to all the cylinders. You have it plumbed right, inmo.

You can also check the diaphram in the booster by connecting a miti vac to it and seeing if it holds pressure (vacuum).




Ron

[Steve P.]

I don't like the single runner vac. port because like Ron said, Sometimes people run the PCV to it. Bad idea as Ron mentioned. The other norm is the power brake booster being run to it. If the booster diaphragm goes to hell and it is sucking on 1 cylinder, that cylinder can go lean. This could be a one in a million but why take a chance..

Quick story.  Years ago I had a repair shop in Rochester, NY. One winter morning a customer leaves his car at my shop to find a skip in the motor. It only happens for a short while when he starts the car.  I open the shop. The car is there and still warm. I start the car and it runs like a champ. Drive it, great.. Let it sit till the afternoon and fire it up again inside the shop. (Too damn cold outside). Still fires right up and runs great. (I am thinking this customer wants to break my chops as I tuned it about 2 months before).  Customer comes in after work and fires it up. Runs perfect.. The next morning he is in front of my shop as I pull in.. Same complaint. Not doing it when I arrive though.. I let it sit outside while I worked on scheduled cars. Around lunch time I went out and sat in the car and fired it up.. Not only did it run like shit, but I could hear a vacuum leak inside the car.. I stepped on the brake and the engine straightened out. I shut off the engine and grabbed a needle nose vise grip and pinched off the vac. booster hose. Started the engine. Perfect.. Open the vise grip and it went back to shit..

When it was very cold inside the car the booster would leak around the rock hard seal. Once it warmed up under the hood and inside the car it would stop leaking.. For shits and giggles I pulled #8 spark plug and it was very white. #6 and #7 where not. The only thing that was different about the tuning was the leaky vac port on #8 intake runner. It did not cause any real damage as the customer lived 7 blocks from work and about 9 blocks from the shop.  The funny thing was that it would start to run perfect just as he was pulling into my shop every time...

So this is the reason I don't like any vacuum being pulled from any one runner..  I never ran into it myself, but was told this was a big problem on the old slant six as well..

[AmadeusCharger500]

haven't attended to this problem since posting last. I replaced the 2 suspect caps. Tightened the manifold bolts and put a hose clamp on the PVC. After driving a few miles car is going up to 210 at stoplights. Timing is 15 BTDC at 850rpms.

I have a question about vaccuum testing but that will wait for now.

I thought I would pull the #8 plug just to see how it looked. Now this is after a 3 mile trip with about 6 stops on the way. The plug looks kinda white to me. So I thought there must be the leak from the booster. Then I decided to just pull #7 plug and well, it looks the same to me. I am on my way to the store to get the vaccuum multi tester but is this problem something else entirely? Is the whole thing running too lean?

I had this car pretty well tuned after rebuilding the engine. Since then I changed the ignition system in 2004, and in the meantime forgot many things about tuning (like am I checking timing correct). It has been running hot every since and within the past year has developed run-on after shutting key off. So the problem is getting worse or I am becoming more aware of it.

[firefighter3931]

Heath....looks like it's running lean based on the plugs.

Have you checked the carb base gasket ? Are the carb bolts tight ?



Ron

[AmadeusCharger500]

Just checked and, no they were not.

I guess I should take it for a spin now?

Quick question though.

I hooked up vacuum guage and its reading 13 Hg. Both idle mixture screws were turned out 3/4 from base. So I tried turning out 1/2 turn sequences and got no change in vacuum. Does that mean the 3/4 turn was correct?

[firefighter3931]

What carb are you running Heath ?

I usually close the idle mixture screws until the idle quality starts to degrade.  Using the vacuum guage you can simply close the idle mixture until vacuum starts to drop....then do the other side. Just one screw at a time.

You might need to jet up if the plugs are looking whiteish/light grey. Try taking it out for a short cruise and stay out of the secondaries....run it just on the front barrels....then do a plug reading. This will tell you if it needs more jet on the primaries.


Here's some good reading on a 383 tuning exercise ;

http://1970chargerregistry.com/70messageboard/viewtopic.php?t=1207




Ron

[Todd Wilson]

I had a bad vacuum brake booster years ago on my ol 74 truck. I couldnt get the 440 to idle good. I just took off the hose from the booster and plugged it with my hand and saw a noticable difference in the way the engine ran and I knew right away what the problem was. If you take a hose off and plug it with your finger and you do not see or hear a change in how the motor is running thats not your problem. Remember it will change when you first unplug it but as soon as you put your finger back on it to plug it it should return to how it was when the hose was hooked up. Just because you have a vacuum leak doesnt mean its a rubber hose. Could be a in the carb or base of carb to intake or intake to head. Might even have to snug up some bolts.


Todd

[AmadeusCharger500]

I pulled the hose off the manifold (going to booster) and there was no change. I pulled off PVC and there was a change. Only from 13 to 12 but that is something right?

[Steve P.]

The PCV is a calculated LEAK. It is to make sure the engine stays in a vacuum and not under pressure. In 99 of 100 cases you will see a change with the hose disconnected.

Pics. on the computer do lie, but I'm with Firefighter . They look lean to me as well..

With the motor running and the air cleaner off,  sort of cup your hands around the top of the carb and slowly close off the air flow. SLOWLY!!!!! And not totally.  If you get an increase in rpm it needs more gas. This could be due to a vacuum leak or a mis-tuned carb.

[AmadeusCharger500]

I will try that Steve. I went ahead and changed the PCV and its grommett. The grommett was cracked anyway. I took it for a drive and it got up to 210 again, with the runon. So no luck yet finding the problem.

[Steve P.]

How much time does it take to get hot??   Does your motor ping?? How long , (if ever) , has it been since your motor was rebuilt??

[AmadeusCharger500]

It takes a little to get it hot. but once it gets up there it will not come back to the 180 stat that I have without a mile or 2 of nonstop driving.
The engine was built in 2002 and this is approximately 7,000 miles. I'd have to check but no more than 10k.
Motor runs really nice, no pinging or hesitation.

I tried the cupped hands, not much change. I am going by ear because my outside tach went kaput so maybe thats not so reliable.

I bought this vacuum pump tool that works as a gauge and a pump. I thought I would check the booster. Although I don't see a change when I take the hose off and plug it with my finger. Anyway, I tried pumping up the booster and it does not hold anything. Is this the right tool for this and am I doing something wrong?

I had upped the jets from the original 72 to 76 when I was originally tuning it in 2002. I was just reading about this and the guy says only make adjustments by one jet size each time?  My problem with jetting is, no place to get a good drive in except major highway plus I am not adept at reading the plugs. Although at the time I was satisfied they were tan.

[AmadeusCharger500]

I planned on taking this car to Carlisle next friday. I know it will be okay if not heavy traffic but. Is there anything I should just throw at this problem to cut off all the options, becuase it might take some time.

Should I order gaskets for the carb?

Should I get a new valley pan gasket, or maybe take it off clean up and put new soft gaskets on either side(I have a set)?

If this is not a vacuum leak then I am at a loss. I have the clutch fan with a spacer and shroud. 3 row rad was flushed cleaned and checked a few months ago.

[Steve P.]

And this problem just recently started happening??  Has the T-Stat been checked?? Flow look good when the stat opens?? Was anything done to the motor just before this trouble started?? Maybe a bad water pump??

Have you tried a new stat?? 160* - 180*. No higher unless you are trying to pass emissions..

[AmadeusCharger500]

It started a little over a year ago. I had just changed from FBO to MSD ignition. That is the only change.
I checked flow in the radiator. it moves past the top pretty strong.

[Steve P.]

Well, strong and good flow takes the water pump off the hit list.

Have you checked the TDC line on the balancer to make sure it IS TOP DEAD CENTER??   The run on can also be conducive of retarded timing.   Still I think you need to fatten up your carb.  Are the plugs as white as they look to us?? I am one of those guys that likes it a bit rich..

[Purple440]

#2 I don't have hose clamps on the hose running to the brake booster or the hose running to the PVC.

Try clamping the brake booster hose.  My #1 plug was almost black and my #7 was pure white until I put a clamp on the brake booster hose, at the housing and the manifold.  That fixed it for me.

[firefighter3931]

Heath, pull a few more plugs to see if they're all the same.

First thing i'd do is jet up.

Also it might be worthwhile to run a cooling system pressure test. If there is a leak somewhere and it's not holding pressure then it will have to be sorted out.


Ron

[AmadeusCharger500]

Would you suggest just one jet size or can I go 2 or 3?

[firefighter3931]

Would you suggest just one jet size or can I go 2 or 3?

Those plugs look pretty lean...start off with 2 jet sizes.


Ron

[AmadeusCharger500]

I will do the jets but I forget what pressure do I pump the water system up to?