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Discussion Starter #1
I just finished installing my re-build 289, Edelbrock Manifold and 4B carb. Idles great but stalls under load when I put it in gear (C4-Automatic). I don't have any exhaust installed yet, only the stock manifolds. Can no back pressure be causing this problem? Timing doesn't seem to help (tried a lot of settings from 6-12 degrees BTDC and disconnected the vacumm advance. Don't believe I have any vacumm leaks. HELP!
 

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What is your idle speed in neutral or park?

What happens if you rap the throttle, then release it? Be specific.

Can you keep the engine running when you put in gear by manipulating the throttle? What's the stall speed of the converter in use?

What is the build state of the engine beyond what you've told us already?

Edelbrock 4V carb, yes?

Get back to us....

BTW, get the exhaust installed...it's not good having the manifolds blowing hot exhaust in the engine compartment...
 
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Idle speed is 580. Engine revs fine with no load applied (in neutral). Hard to keep it running with trans in gear but it will keep running. If I give it gas, in gear, stalls. All lines connected, PCV to throttle body, vacumm advance and trans modulator.

No exhaust pipes connected.

Edelbrock 4Vcarb and performer manifold. I installed a slight Cam from Crane (picked by the machine shop I used).

Complete engine overall, new pistons, heads, lifters, pump, etc.
 
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It's been a long time since I've had a running V-8 under my hood, but my V-6 (minivan) idles at 850 RPM. You might just idle it up a little and try that.
 

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Idle speed sounds a bit low...try 700-800 rpm (turn idle speed screw clockwise 1 turn). Open idle mixture screws 1/2 turn (CCW), noting any change. Examine emissions for smoke (stick trouble light near exhaust manifold outlet).

Can you measure engine vacuum during these tests? If so, measure and report results under free idle, 2000 rpm, and under load at idle, if possible.

Is the car on jack stands to allow drivetrain rotation?

What is current ignition advance setting at 580 rpm? You mentioned a range you tried...

Did you verify TDC mark on damper prior to firing engine? Stock dampers can sometimes slip the outer ring, making timing marks inaccurate.

The only time my D-coder gives me idle troubles is when the points close (due to wear), retarding the timing...the engine runs fine under no load but idles crappy and runs poorly under load.

Get back to us...
 
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I'll bring up the idle speed. You mentioned the points, the dwell is measuring about 23 degrees.

One of my problems is that I have a 66' block w/ 78 302 heads (smaller spark plugs). The pistons were matched for around 8:1 compression. What is the correct spark plug gap and dwell setting?

I didn't check the damper but the car idles great with (at idle) with the dist. turned clockwise about 1/2-3/4 inches. Still sputters and stalls under load.

I also have a vacumm gauge around somewhere ... I'll try it.


Thanks,

Bruce
 

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To be honest Bruce, I haven't used a dwell meter in years (decades more like *G*)...I just set the point gap on the D-coder at .017"-.019" and set the timing so the engine doesn't ping under WOT accleration...that's it..

With stock ignition, I gap the plugs in the D-coder at .035"

The fact that the engine idles good but performs poorly under load leads me in two directions...either the ignition system can't handle the increased cylinder pressures under load and you're getting spark leakage or misfiring; or, the car has fuel delivery problems. IIRC, you said the engine revved fine under no load so I would discount fuel.

Let me review your posts some more and think a bit and I'll get back to you...

Edited to add that I'm thinking either ignition problems or vacuum leak, having reviewed the info....get a vacuum guage and test as noted above and report the readings. That should narrow it down...
 

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Dwell should be in the 26-28* range, spec idle is 575-600 (manual), or 475-500 (automagic), with 6* advance timing. Most of us here run 750 rpm idle, and from 12-16* advance timing for improved performance and gas mileage.
 
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Discussion Starter #9
With timing set to 8 degrees BTDC, Vacumm is steady at 10 @700 RPM. Goes to around 15 @2000 RPM. Disconnecting the trans modulator/dist. advance makes no differenc in vacumm ... doesn't seem to have any leaks there.
I'm told that w/ the CAM I've installed, I should expect lower vacumm.



Some other symptoms:

1. Runs better (idle) with timing set to 12+ degrees BTDC. Vacumm improves to 11-12. Still stumbles with load.
2. Removing the vacumm advance hose really makes it stumble (Yes, I plugged the line). Makes it hard to adjust the timing.
3. Removing the PCV hose and plugging it helps some, doesn't stumble as badly. Actually was able to drive it around the block (wanted to see if the C4 trans actually shifed...it did).

I rechecked all of the valve lifters thinking that I had some either too tight or too loose, all good.


Is it possible that I'm off a tooth on the valve timing? I really believe that I alinged the CAM and Crank gears but now I'm wondering. The Cam gear had 3 choices and I was told to align the 0 (instead of A or R?).

My original question was can no exhaust system make it run bad under load?
 

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Where is your vacuum advance line running to? IME, very little vacuum is generated in this line at idle so it shouldn't affect your idle quality markedly. Distributor advance should be set with vacuum line disconnected.

From experience and other VMF'ers reports, your vacuum readings sound a bit low...

If removing the PCV hose helps that much, I'm starting to wonder if you have a vacuum leak....

When in doubt, I would set the cam straight up as you did...if the timing was off one whole tooth on the chain, the engine would run really lousy, if at all...
It is possible to verify cam timing with the engine together but it does take some tools...

Personally, I don't think not running an exhaust system is affecting your engine markedly, although I'd prefer you run one.

Try starting an update thread on this subject tomorrow with a reference to this thread in it....you now have enough information posted for most of the engine gurus to weigh in (some might be away for the holiday weekend)...

I think we'll figure it out, don't you?? *G*
 
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