350 tuning issues/vacuum leaks??

Recently rebuilt my 350 and added a few things inside, Ta 284 cam, headers, but nothing totally radical. The car was running and driving alright but didn't have the power I was looking for with the recommended timing from ta so I advanced it a couple degrees (which made a huge difference) But now I cannot get the car to idle smoothly. In gear the engine has a pretty good shake to it which rocks the car, but it hasn't ever stalled on me.

Today I went out determined to make the proper adjustments, hooked up my vacuum gauge and tach but never was getting steady readings in park or in gear. Both needles were bouncing. And I was only readin 12 inches of vacuum in park and only about 6-7 in gear! What gives?! Tried spraying around the base of the carb with carb cleaner to check for vacuum leaks but didn't find any and I'm not hearing any hissing from the engine compartment.

Setup is Buick 350 with Rochester q jet, hei distributor, ta 284 cam.

Any help would be appreciated

 

Did you degree the cam when you installed it?

 

I personally did not, I tore the engine down but it was rebuilt by a very reputable engine builder in my area, so there's not really a doubt in my mind that it would have been done by the shop.

 

So I did have the carb rebuilt when I rebuilt the engine but I did not change the jets so essentially it was a stock rebuild kit.

As for the timing this is what I know. According to ta performance initial timing should be between 12 and 14 degrees btdc total timing 34-36 degrees. I had set initial timing to 14 degrees btdc. But the engine idled better at 12 degrees so I left it there but wasn't getting the power I know the engine is capable of making. So right now it's at right about 15 degrees initial timing. The mechanical advance on my distributor is 22 degrees, so I should be running total timing of 37 degrees but have not checked total timing because I have an original pointer which doesn't go pst 22 degrees and the mark on the balancer disappears after about 24 degrees. I am running vacuum advance on manifold vacuum. But there is really no difference in idle quality between ported or manifold vacuum.

 

Have you plug the vacuum port at the carb and distributor for a test ? Maybe there is to much vacuum at ported vacuum also in idle ?

 

I did unplug the distributor and plug the carb and there was almost no change in idle quality. And the needle on the vacuum gauge won't stay steady as if there is a leak somewhere but I have checked several times and can't find any thing obvious.

Also the ported vacuum at idle is at zero inches.

 

I always wanted to ask the question with a large lift cam , would the vacum gauge still be steady or would it bounce around a bit ?

 

Yes it will fluctuate a bit, say from 11 to 12" or whatever.
It (the needle) should not bounce or pulsate.

 

bouncing or pulsating would indicate a vacum leak ?

 

Ken is a quick drive away for me, guess he'll be getting a visit really soon. Lets hope that fixes it! Thanks for the tip

 

"Usually" a bouncing or pulsating needle on a vacuum gauge indicates a leaking intake valve.
Does the engine idle with a "rumpita rumpita rumpita" OR is it "da da da da"
My description may sound silly, but the sounds an engine makes tell alot

 

I will check today and record a video with the idle sound.
Thanks for your help Mark

 

Mark,
What would be the Cause of a "da da da" Vs a rumpita (haha feels weird typing that) Obviously anything is possible but I had a valve job when the engine was rebuilt so I pray that a leaky valve is not something I have to deal with. I'm still going to look into that spring first before anything else

 

Yep, if your engine is "da da da-ing its more than likely a bad sealing valve.
Can you do a leak down test?
A compression test would reveal a weak cylinder, but it wont tell you where its leaking from like a leak down test.
An engine with a lumpy cam will somewhat mask a "da da da" sound, but if you listen closely, you should hear it if its there.
Geeeez, we sound like a couple of pre-schoolers..... DA DA DA RUMPITA RUMPITA, LOL

 

Ha, i know this "da da da" it must be this one:


Sorry

 

Brilliant! Haven't heard that song in 30+ years. Only to be overshadowed by The Scorpions, Nena, and Kraftwork as far as the German contribution to music.

 

LMAO WTF!!
I liked 99 luft balloons better, or Falco, who did Der Komisar or whatever it was called?