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GMC V6 and V12 Engines Engine repair and rebuilding

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  #11  
Old February 20th, 2016, 03:00 AM
Clarke Clarke is offline
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Default Re: Too much timing?

TJ, wild and crazy stuff!
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  #12  
Old February 20th, 2016, 06:40 AM
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Default Re: Too much timing?

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Originally Posted by Clarke View Post
TJ, wild and crazy stuff!
For sure. lol I'm gonna go out in the morning if the weather is better and do some checking.
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  #13  
Old February 21st, 2016, 04:58 PM
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Default Re: Too much timing?

Ok folks, so I have an update. Turns out my new distributor's vacuum advance pump has a hole in it or something as I can blow air through it. So I took the pump off of my 292's dizzy and I now have advance. On my edelbrock there's two vacuum ports...one is timed vacuum and the other is full constant vacuum...I tired the 2nd port first which put the idle advance at around 16 and Man....you talk about that motor really becoming smooth and quiet...it always had a cool lope to it, but once the timing advanced that far the motor was super smooth and quiet. Took it for a test run and it was much peppier and pulled a bit better( I need to get my manifold machined for that 4 barrel because the 4 down to 2 ain't doing it no more.) I then tried it on the 1st port and the engine seemed to like that best. The 1st port offers No vacuum advance at idle, but once you rev it the advance comes in....so I bumped the timing up to 10 degrees and ran it....seemed to be happier. I will be uploading a video that I'll post this afternoon guys. See ya.
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  #14  
Old February 22nd, 2016, 04:29 AM
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Default Re: Too much timing?

Here's the video guys, still doing tuning:

https://www.youtube.com/watch?v=vUX6qsNt2dA
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  #15  
Old February 23rd, 2016, 06:57 PM
Clarke Clarke is offline
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Default Re: Too much timing?

Thanks for sharing TJ. Mine idles a little rough too and I don't have any vacuum advance at idle, so this will motivate me to fix it.
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  #16  
Old February 23rd, 2016, 07:42 PM
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Default Re: Too much timing?

Quote:
Originally Posted by Clarke View Post
Thanks for sharing TJ. Mine idles a little rough too and I don't have any vacuum advance at idle, so this will motivate me to fix it.
Be sure to post your findings!
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  #17  
Old March 9th, 2016, 02:24 AM
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Default Re: Too much timing?

Quote:
Originally Posted by TJ's GMC View Post
Be sure to post your findings!
Update: I mentioned before that ever since I've had this truck, it doesn't matter if I disconnect the hard vacuum line to my vacuum advance; the timing remains the same and so does the idle.

Thanks to TJ, I decided to investigate instead of ignore it. Anyway, I disconnected the hard line from the back of the carb and hooked up my vacuum pump to the hard line. I tested the vacuum advance several times and obtained consistent readings. At 5 psi, I noticed the rod in the slot starting to move, and it would hold vacuum. At 14 psi, the rod would stop moving, and it would hold vacuum. I could pump it up a little higher, but the rod quit moving after 14 psi.

So I removed the reducer fitting from the back of the carb to inspect and it was clear. I also looked in the hole in the back of the carb with my inspection mirror and there were no obstructions.

Do my test results seem normal? Any suggestions on additional inspections? Maybe I need to dig a little deeper into the distributor? The mechanical advance weights/springs on the top side (under the rotor) are clean and move easily.
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  #18  
Old March 9th, 2016, 03:04 AM
George Bongert George Bongert is offline
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Default Re: Too much timing?

Quote:
Originally Posted by Clarke View Post
Update: I mentioned before that ever since I've had this truck, it doesn't matter if I disconnect the hard vacuum line to my vacuum advance; the timing remains the same and so does the idle.

Thanks to TJ, I decided to investigate instead of ignore it. Anyway, I disconnected the hard line from the back of the carb and hooked up my vacuum pump to the hard line. I tested the vacuum advance several times and obtained consistent readings. At 5 psi, I noticed the rod in the slot starting to move, and it would hold vacuum. At 14 psi, the rod would stop moving, and it would hold vacuum. I could pump it up a little higher, but the rod quit moving after 14 psi.

So I removed the reducer fitting from the back of the carb to inspect and it was clear. I also looked in the hole in the back of the carb with my inspection mirror and there were no obstructions.

Do my test results seem normal? Any suggestions on additional inspections? Maybe I need to dig a little deeper into the distributor? The mechanical advance weights/springs on the top side (under the rotor) are clean and move easily.
Greetings Clarke!

There's no need to dig into the distributor. That's not where your problem is. The fact that your vacuum pump causes the vacuum advance to move, and that it holds vacuum tells you that your vacuum advance is OK and not your problem. If you connect a vacuum guage to the fitting at the back of the carb, dimes to donuts you will not get a vacuum reading when the engine is running. Check the gasket between the carb and the intake manifold to see if the area in that gasket to that fitting is blocked off. Without being there and not being able to see things firsthand, that would be my suggestion at this point, because there is something that is stopping you from having vacuum to that fitting. Hope this helps!
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  #19  
Old March 9th, 2016, 04:16 AM
Clarke Clarke is offline
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Default Re: Too much timing?

Thanks for the feedback George.

I'll hook my vacuum gauge to the port on the back of the carb to see if there's anything at all. If not, I'll pull the carb off and check the base as you suggested.

I had the carb rebuilt two years ago, so I would have thought it would have been addressed at that time, but no difference.

New base gaskets were installed at that time. I will check the oreintation of the gaskets in comparison to the bottom of the carb. If I have any questions, I'll post them.


Thanks again,

Clarke
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  #20  
Old March 9th, 2016, 07:57 PM
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Default Re: Too much timing?

Clarke:
That does sound normal. I didn't have a gauge on mine, but mine does the same. Give it a bit of throttle and the advance arms starts to move....give it more and to a point it stops. And since I'm running a 4 barrel that was on Ported Vacuum. I do need to get another video up. lol Been sick and busy so I haven't gotten around to it.
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