Folks hello,

I've come to the conclusion, come spring that I need the pull the intake on my 390 to fix an internal intake vacuum leak. I would appreciate a go over one more time, to be sure.

At idle the VAc guage bounces from 13-18"Hg. Give here a little gas and she tops out at 20"Hg. I has a noticable loap/lope at idle. Cap/coil/plugs,wires all good. It has a 268 grind cam it has adjustable push rods. I cannot find a vacuum leak anywhere around the normal spots. Hoses carb. ect.. It has a new carb/gas filters gas and so on. Static copmression on all cylinders after warmed up is 153-164. Timing is set aroung 10deg BTCD. The carb is an Ebrock 1406 choke is set up clean and the Idle screws are at about 1.75 -2 turns out.

I did not build the engine. The vehicle has sat for 2 years before I bought it. I do not know if it had the problem when parked or not. I tried to snug the manifold bolts they do not move. I replavcer the exhaust manifold gaskets.

Did I miss something? I did not try spraying carb cleaner at intake area with valve covers off. I did not use a heat gun to check cylinder temps.

Lastly should I change the intake to an ebrock when I do the gaskets? I have 4bbl intake from the 64 t-bird the motor came from.

thanks
bob

 

Well its been awhile since I have run a vacuum test on a motor with a performance cam..But if the Idle from cam lope doesnt stay constant I dont know how you can expect to get a constant vacuum reading...?? and you said it comes right up to 20hg when off idle..sounds normal to me?? JMO..

And I'am alway the wrong one to ask about taking off a 80# Iron intake and putting on a better and lighter intake..the answer is alway yes...

I foret which way it works with the T-bird motors..I used to know..But there's to much ford Junk in my head!! LOL.. If I remember correct the intake on the bird engines sat flat in the frame..therefore had a flat carb pad..and it being installed in anything other than a T-Bird the angle of the carb will be wrong! I think thats the way it worked? LOL.. the guys will correct me if I'am wrong...LOL..

RJ

 

There is an angled carb spacer on the intake. And I cannot find a vac leak there either.

My understanding of this cam was it isn't all that agressive. And yes it vibrates between 14-18"hg. According to century performance what I'm reading is either a vacuum leat or a very nasty cam. I have to have it at about 950rpms in N to get it to idle.

bob

 

How does it run otherwise? What is the rpm idle in D? Do you get backfire?

 

Once I get the rpms over 1200 she runs great till about 4500 and then out of breath. I have 4.10's and off idle it doesn't pull like I think it should. I run 93 oct and that fixed my run on issue. If I set the timing so I don't get runon(diieseling) I can't start it I have a hot start issue. In idle If I advance the rpms will rise till I'm about at 25btdc. But I know that not right.

In drive I idle at about 650-800 and it bounces there. And higher I get runon. lower won't stay running.

I should note that occasionally idle bounce will be better for a few minutes then back to the same.

bob

I wish I had someone nearby to take a listen. I live in chevy country and most won't even talk to me.

 

My 390 idles nearly the same as yours...750 in gear and 900 or so in park.
Do you run a carb spacer? If you don't, you probably should. And if you do, that could be your leak source if it is not mating to the carb and mainfold properly.
Are you using a timing light to set timing? Make sure vac advance is dis connected prior to setting the timing.

Check the link to some vacuum gauge information and tips that may or may not help.
http://www.centuryperformance.com/vacuum.asp

 

Ground out a plug lead one at a time to locate the bad cylinder
and pull plugs looking for a lean plug and cylinder condition.
Are all valves lifting the same amount (cam going flat)?

 

Bryyce, yes to all.

Timed with light Vac sealed all around all ports.
Have spacer new gasket. Unfortunatly I cannot get the old one from the manifold to spacer. Stuck hard but I flooded it with carb cleaner and propane.


bob

 

I've watched all the valve and they appear to working properly. I also did a spin test on the push rods. All check, no excessive looseness. I did the plug test and did not find the offender. For a while I though I had a rich plug but that was a wire issue and fixed now.

bob

 

I would think a valve adjusted just slightly too tight would cause this.

 

Power brake booster leaking if you have power brakes.
You meter your ignition wires and change dizzy cap?
You get the same response adjusting idle ful mix both
sides?
Sprayed carb cleaner around the base of the carb?
All vacuum lines accounted for and tight fitting including
PCV hose and pvc clean and loose inside?

 

Bear, good thought. Best/easiest way to do this? Turn by hand and adjust or while running?

Is this something that could happen overtime? I'm not sure I have the temperment to fix this?

bob

 

I'm certainly no expert, but you might be looking at a leak down test next.
I'd clean off the intake where the old carb gasket is stuck at. I had an old aluminum spacer that was warped and caused a leak. Replaced it with a phonelic 1" and could idle down to <300 rpm. I knew that my vacuum leak was fixed after that.
Check again ALL of the vacuum lines, replace them if they look worn at all. Vacuum hose is cheap & a heck of a lot easier to R & R than an FE intake.
gw

 

Beemer, yes. Sprayed everything twice and propaned it. Hmm I dont think I have a pcv valve. I have a breathers on the valve covers and I have a port on the rear on the manifold that goes to the air cleaner base. And I can see it exhausting/smoking when the engine is running.

I removed the brake booster from the equation 1: I had the issue prior to boosting 2: Pulled and plugged the "T" for booster and c6 tranny. New vac lines. New wires cap coil and rotor x2. Lifetime guarantee items go back when in doubt.

thanks I do appreciate the help.

bob

 

As mentioned above leakdown test with throttle open, listen thru the carb
as well tailpipe.
I'm thinking sticking valve or intake gasket leaking.

As we speak i'm waiting for my heads to get a valve job, while changing
springs and umbrellas found them leaking besides those FelPro intake gaskets failing causing coolant in the oil.
Same boat different ocean.