Dwell angle and timing are way off - Pontiac GTO Forum
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post #1 of 11 (permalink) Old 06-16-2011, 01:34 PM Thread Starter
 
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Dwell angle and timing are way off

I had lots of trouble getting my 72 Lemans 350 2bbl running. I finally got it running and set the dwell angle to 30 deg and timing at about 10 deg btc. I had the vacuum advance hose off and the port plugged. It ran but it was rough. And it would stall out if I gave it some gas. Didn't matter if I did it slow or fast. So I played around with the points and the timing and now it runs much better and I can rev it up and it runs great. But my concern is that the dwell angle is now down to 23, and the timing is just past the end of the scale so its probably around 16-18 btc. Those numbers are no where near what they should be but the motor runs so much better. Idle is still a little rough. Am I doing something wrong? Are my tools not working right? I have an old Craftsman dwell meter that was given to me and a borrowed timing light thats pretty old. Also I have 87 octane gas in it.
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post #2 of 11 (permalink) Old 06-16-2011, 03:39 PM Thread Starter
 
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I also forgot to mention that I noticed the part of the distributor where the points are mounted rotates back and forth slightly when the motor is running. Is that normal? The distributor hold down bolt is tight and the distributor does not move.
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post #3 of 11 (permalink) Old 06-16-2011, 06:49 PM
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Set your dwell at 30 degrees and your initial timing at 6 or 8 BTDC. Then, hook the vacuum advance up to manifold vacuum, not ported. It whould run much better. The points plate is meant to move when the timing advances. Sometimes they can get worn and sloppy, and move around too much. If your car runs poorly set to specs, and will only run ok with the timing waaay advanced, the distributor may be in wrong. Again, set it back to specs and connect the vacuum advance!!!
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post #4 of 11 (permalink) Old 06-16-2011, 09:16 PM Thread Starter
 
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I did reconnect the vacuum advance hose when I was done. I only had it off while setting the dwell and timing.
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post #5 of 11 (permalink) Old 06-17-2011, 09:24 AM
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Perhaps your vacuum advance unit is blown. Does the RPM increase when you apply vacuum to the unit?
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post #6 of 11 (permalink) Old 06-17-2011, 01:32 PM
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Garage
It's a 72, so unless it has been "trifled with" I'm assuming that it should deal just fine with 87 octane, being a low compression motor.

If the points plate is moving "a lot" then it could be causing your timing to jump around (do you see the timing mark moving around?). Also, you didn't mention age but sometimes the elastomer in the harmonic balancer and age, dry out, and allow the outer ring to slip. When it does, all bets are off as far as timing marks go (not to mention rendering the balancer no longer capable of "balancing" correctly.) If you're not completely sure, then if it were mine I'd start by making sure that when the timing marks say "TDC" that they're telling the truth. For that you need a piston stop that you can insert into a spark plug hole (they can be bought or made - I made mine) and the procedure to follow. You should be able to find it all over the 'net if you look. On a Pontiac though you're going to want to remove the drivers side rocker cover (valve cover) and loosen both rockers on the intake and exhaust valves on #1 cylnder enough to remove the pusrods. Otherwise the valves are likely to hit the piston stop as you move the crank, and something's gotta give when that happens.
If you do find that your balancer is off, I recommend replacing it - AND double checking the new one. I've seen brand new SFI-rated balancers be "off" as much as 5-6 degrees. It's easy enough to fix just by putting on a timing tape, but still you've got to be sure you know where TDC is.

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post #7 of 11 (permalink) Old 06-17-2011, 02:13 PM
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Really good point on the slipped balancer. Bear says what I should have: check the basics first to establish a performance baseline. Find out where your actual TDC is on the balancer and go from there.
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post #8 of 11 (permalink) Old 06-17-2011, 02:30 PM Thread Starter
 
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The timing mark does jump around a little when its running. I used the old "finger over the #1 spark plug hole" method to verify tdc. I know thats not exact but I guess it is pretty close. I'll look into the piston stop thing. Thanks to all!!
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post #9 of 11 (permalink) Old 06-21-2011, 09:16 PM Thread Starter
 
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Guys, I feel like an idiot. I just put a new condenser in. It was the one thing I didn't replace when I gave it a tune up. I'm not sure how I overlooked it. The motor runs great now. I reset the dwell angle back to 30 deg and set the timing at 10 btdc. The timing mark doesn't bounce around at all. Its rock steady. It idles nice and smooth and revs up real nice too. Sorry for wasting everyone's time. I'm happy and embarrassed at the same time.
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post #10 of 11 (permalink) Old 07-02-2011, 12:19 AM
 
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Don't feel bad that is the one thing always looked over on a point car.They make a points and condenser all in one on a plate points. It is called unipoints. That is what I always use.


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