Low vacuum

[Randra]

Ok guys I'm no expert and never claimed to be. But I've been trying to tune my superbee 383 fresh stock build. With an edelbrock 650 (1805). I hooked up a vacuum gauge to manifold. I've got about 5 lbs of vacuum at idle but the needle bounces back and forth wildly about a couple pounds. It ldles a little rough and smells rich. I know almost nothing about tuning but I know this isn't right. Any thoughts to push me in the right direction?

 

[BeeKool]

You could have a vacumn leak. Check all vacumn lines and connections. Make sure carburetor gasket is good and carb is tight.

 

[Randra]

You could have a vacumn leak. Check all vacumn lines and connections. Make sure carburetor gasket is good and carb is tight.

That was my thought. But I sprayed carb cleaner and couldn't find a thing.

 

[snakeoil24]

a stuck valve lifter or the brake booster is leaking at booster. Timing is set way to retarded, check with timing light. Last thing are hte butterflies completely closed on carb while idling?? If open then your operating outside of idle circuit..

 

[Motor_Head]

You said it's a fresh build, right? Could also be the intake manifold gasket didn't seal properly

 

[Lionized]

You say it's running rich? Bring the engine up to temperature and lean the mixture up, using the vacuum gauge, until you see the vacuum gauge needle climb. May be best to gently tighten both idle mixture screws until seated, then back them out 1 1/4 turns each and start there.
I'm experiencing the same problem with my 383 with an Edelbrock1405. I'm pulling about 10"Hg at idle at 900rpm. and my vacuum gauge will fluctuate around 1 or 2" intermittently. I'm thinking either I'm still a bit rich or I've got a bad plug gap with one cylinder. Hopefully not a sticking valve.

 

[Billy T.]

This chart has helped me out in the past. It might be some assistance to you as well.

 

[Bruzilla]

If you have power brakes, be sure to check the multi-port connector on the booster. I looked everywhere for a leak and couldn't find anything, then I turned the connector around while doing something else and saw the port on the bottom side was open.

 

[lewtot184]

5 inches of vacuum is going to let the metering rods jump up and down instead of being stable. this will create a rich condition. i have to wonder if it's too much cam for 8:1 pistons,...? a lot a stuff to look at here.

 

[PurpleBeeper]

On a STOCK rebuild, 5" Hg vacuum means you have a vacuum leak I'd say & a pretty big one at that. I'm going to ballpark guess that you should be around 15" or maybe a little more with a stock cam & stock motor.

 

[BeeKool]

View attachment 415144

This chart has helped me out in the past. It might be some assistance to you as well.

I took a screen shot of that chart. It will no doubt help me in the future.

 

[Randra]

I too agree that it must have a vacuum leak. But finding nothing with carburetor cleaner kind of discouraged me . But I do know it could be leaking underneath the intake . It doesn't have power brakes. And it doesn't have a big cam. My first thought was to replace the intake gasket with one that sandwiches the Valley Pan and see what happens. Cross my fingers

 

[lewtot184]

using paper gaskets with the valley pan and not machining the intake to compensate for the additional .060" on each side can create issues.

 

[Randra]

using paper gaskets with the valley pan and not machining the intake to compensate for the additional .060" on each side can create issues.

Oh yeah, crap I forgot about that. Well I'm gonna start with a new Valley pan I gues . Any recommendations on sealer so I don't have to do this again.

 

[moparwacko]

Do not use the paper gaskets unless you've made up the difference in machining - listen to Lewlot! You will not get the manifold on.
I've only used the pan with aviation sealer, never had a problem.
Except the one time I tried the paper, and pan.....long time ago and never forgot.

 

[PurpleBeeper]

Yeah... the paper gaskets don't usually fit. FelPro "used" to include a little tube of blue sealer & a tiny brush, but I'm not sure if their valley pan still comes with it. If you're really concerned about a leak, you can use a tiny smear of RTV silicone, but keep in mind any excess might squeeze into the intake port & reduce your air flow...but it will be sealed for sure.

 

[Lionized]

I too agree that it must have a vacuum leak. But finding nothing with carburetor cleaner kind of discouraged me . But I do know it could be leaking underneath the intake . It doesn't have power brakes. And it doesn't have a big cam. My first thought was to replace the intake gasket with one that sandwiches the Valley Pan and see what happens. Cross my fingers

Would you happen to have the cam specs?
I just found out that anything less than 112°c/l and you're never going to get it to run properly. My cam is 106°...so guess who's going cam shopping!

 

[coloradodave]

Would you mind sharing all the cam specs? BTW, my intake lobe centerline is 104* and the lobe center separation angle is 108*. 13" of vacuum at idle and the engine runs great...

 

[lewtot184]

Would you happen to have the cam specs?
I just found out that anything less than 112°c/l and you're never going to get it to run properly. My cam is 106°...so guess who's going cam shopping!

before you buy another cam let us know the spes of what you have.

 

[Lionized]

before you buy another cam let us know the spes of what you have.

I won't hijack this thread but I'm bringing the Bee to my local engine builder.
I've had about enough of trying to tune it...I'm at my wits end.