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Low vacuum and miss-304

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Boris Badanov View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 12:48pm
I looked up that camshaft, it's fairly hot for a stock 304, but not too much at all.
try a condensor and try running the motor with no vacuum advance hooked up.
 
I would expect higher vaccum at 2000 rpm + than idle with any cam, but
even more so with that one.
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ollie09 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ollie09 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 12:50pm

Would an ignition problem result in low vacuum? [/QUOTE]
 
Yes.
 
Low idle vacuum can be the result of bad initial timing
and bad condensor.
At higher engine speeds the combination of mech advance weights and
the vacuum advance will bring the advance up along with the manifold vacuum.
"hot" cam timing will have the same result.
 
I sense the whole problem here is in the ignition system or vacuum plumbing.

[/QUOTE]
There is no condenser, it has the stock electronic ignition. I set the timing for the highest vacuum I could get, 12". It has a 'new' after market ignition module. Unfortunately, I didn't try the old one before I pulled the front cover off. I figured if it runs it must be good.
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Boris Badanov View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 12:51pm
This from a website running a 9.25:1 SBC 350 with that same cam grind
 
Manifold Vacuum:17.5" Hg @ 800 RPM & 18.5" Hg @ 1000 RPM w/ no load.
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Boris Badanov View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 12:59pm
Originally posted by ollie09 ollie09 wrote:


Would an ignition problem result in low vacuum?

 
Yes.
 
Low idle vacuum can be the result of bad initial timing
and bad condensor.
At higher engine speeds the combination of mech advance weights and
the vacuum advance will bring the advance up along with the manifold vacuum.
"hot" cam timing will have the same result.
 
I sense the whole problem here is in the ignition system or vacuum plumbing.

[/QUOTE]
There is no condenser, it has the stock electronic ignition. I set the timing for the highest vacuum I could get, 12". It has a 'new' after market ignition module. Unfortunately, I didn't try the old one before I pulled the front cover off. I figured if it runs it must be good.
[/QUOTE]
 
You are in a tough spot.
I now think you need a drastic distributer re-curve.
That cam and compression combo needs about 16-18 degrees initial
but the distrubiter may have up to 38 degrees in the mechanical advance alone.
 
I think this a job for a guy that knows that distributer better than I.
 
But I will open the circus with this comment.
 
For a test only.
I would try to lock out all advance in the distrubuter and set it for 32 degrees initial.
No mech advance, no vaccum.
 
Run it.
 
Work from there, maybe 15 degrees mech advance in the dist, no vacuum advance till you get the curve correct.
 
In my old AMC rigs I used to run 15-25 degrees initial depending on cam and compression.
Never more than 36 total not counting the vacuum advance.
 
Stock was around "0" degrees initial.
 
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ollie09 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ollie09 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 1:19pm
Originally posted by RAZER RAZER wrote:

What brand spark plugs are in it?


Plugs are Champion 3405 set at .035".
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Boris Badanov View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Boris Badanov Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 1:21pm
Plugs are fine, I now think it's excessive total advance after
setting the engine for max idle vacuum.
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ollie09 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ollie09 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 1:29pm
This is my first AMC V8 rebuild. Done many SBC over the years so this has been a new experience for me. On SBC, we never bothered with initial timing but rather set max timing using a dial type timing light to get 38 degrees total advance at 3500 RPM.

Before I put it back together to try some of the other suggestions, does everyone agree that the cam looks to be installed correctly?

I appreciate everyone's input since I'm new to AMC's. I have a 360 to build after this one, so I hope to learn from my mistakes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rockAMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 2:25pm
A stock 304 is around 5 degrees advanced at curb idle. Since you have the stock distributor, this should be about right. Adding the cam won't change that but upgrading to a higher performance distributor will. I would just start with 5-7 degrees at curb idle and rev her up. Make small changes in timing from there. You will get it. Some recommend getting the engine warm to curb idle then advance the distributor to achieve the highest idle, then retard it just a touch, then drive it and test.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ollie09 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 2:27pm
Not sure if I mentioned this, but if I slow the idle way down (500 RPM), the timing mark comes into view. This would seem to be the advance weight springs, but I've had 2 different Dizzy's in it and both do the same thing. I see one heavy spring and one light spring, does it matter which goes where?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FuzzFace2 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2014 at 2:28pm
To me a motor is a motor and other than where #1 might be, how they number the cly per bank and firing order what works for one should work for them all.
 
At first I thought you did not have enought timing to start with but yo usaid you set it with a vac. gauge to the highest then I dont know what it could be?
 
The other thing that got me is yo usaid you could not use a timing light because the mark did not show up?? You did check the old & new dampers and they were the same so now why no timing mark with the light and no vac or RPM?
 
Did I also read you had this same thing before the rebuild?? If so what are you using that is the same from the old motor to new motor? Being others think timing and the dist might be new or was new to the old motor trying to fix this issue it might not be the dist but what about the IGN box?
Dave ----
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