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Quadrajet Carb Talk and Tips / Re: Idle speed solenoid
« Last post by zucchi on May 29, 2026, 05:59:40 AM »
I'm glad to hear you devised a solution. I would like to see photos. I tried using the "Insert Image" button then insert the http address of the image but that didn't work.

Posting a link works…

https://drive.google.com/file/d/1JhEweHVQeCu4oqndJaPeR4skeX9ry-sM/view?usp=sharing

Uploading the image seems to work too.

Albeit some of the parts I listed in the video's description are discontinued, a couple of the TCS valves are reproduced and sold by restoration suppliers. Nevertheless, despite them being discontinued, it doesn't mean they are unobtainable.
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Quadrajet Carb Talk and Tips / Re: Idle speed solenoid
« Last post by Turbo26T on May 28, 2026, 02:15:13 PM »
Zucchi : Thanks for the reply..I had viewed your videos while researching a solution to my idle speed issue.. What I found was that those parts are long since discontinued
 What I came up with is a 12v vacuum solenoid valve ( Omega Enviro Tech P/N 29-40000) that opens to sends manifold vacuum to a carb mounted vacuum dashpot( Guaranteed Parts P/N 779-269 , Rochester 7044055).. The dashpot is strong enough to overcome throttle spring pressure to increase idle speed ...When the AC cycles on 12V is sent to vac switch , that opens and routes manifold vacuum to dashpot increasing idle speed without having to blip the throttle....I had to custom make the dashpot to carb mount plate.
I tried to post pictures of the setup , but I dont know how to do that and could not get them to post
 Stan
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Quadrajet Carb Talk and Tips / Re: My favorite Quadrajet rebuilding tools:
« Last post by novadude on May 26, 2026, 05:03:56 AM »
Quote from: 77cruiser on December 29, 2024, 05:06:39 PM
I'd take a hanger jig if you get enough interest.

I would be interested too.
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Quadrajet Carb Talk and Tips / Re: HEI Distributor mechanical advance curve options
« Last post by Cadman-iac on May 23, 2026, 03:57:08 PM »
  Just got done checking the timing on my truck and it's advancing exactly like the test did, so I've got a 21° mechanical advance, with a 10° initial, and 15°'s of vacuum advance, for a total of 46° @3500 rpm under light load.
 Still have to do a road test to see how it performs, but I'm fairly confident it's going to be fine.

 I did re-jet the carb from 74's to 73's and raised the LIAB's to  .067" from  .066".
 Trying to squeeze as much mileage as I can without doing any damage. The price of gas is killing me at 10 mpg. (Of course keeping my foot out of it might help just a tad bit, or so I've been told).

 Rick
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Quadrajet Carb Talk and Tips / Re: HEI Distributor mechanical advance curve options
« Last post by Cadman-iac on May 23, 2026, 12:45:49 AM »
Quote from: 70GS455 on March 18, 2026, 06:53:07 PM
I've seen some DIY distributor machines and it didn't look all that complicated. Just a support structure, a 12 dc motor, dimmer speed control, degree wheel, tach and timing light

 I incorrectly credited DJD OLDS for the suggestion of using this idea for a tester as at the time I was typing my post and couldn't look back through the thread for who suggested it. My mistake.

 Rick
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Quadrajet Carb Talk and Tips / Re: HEI Distributor mechanical advance curve options
« Last post by Cadman-iac on May 22, 2026, 08:38:32 PM »
  Something else about these center plates, the 422 plate is out of a Cadillac distributor, which explains why it's got a really small amount of advance compared with the others. Not sure what the other plates are from.

  Rick
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Quadrajet Carb Talk and Tips / Re: HEI Distributor mechanical advance curve options
« Last post by Cadman-iac on May 22, 2026, 08:11:58 PM »
More pictures.

 One note here,  most of these results were obtained at 3500 rpm, although I did run all of them up to 4000, and even some as far as 6300, which is what the blower motor I used runs at full power.
 I noticed that a lot of these would begin to loose some of the advance at speeds above the 4000 rpm threshold,  but it was only a small amount,  usually around 2 to 3 degrees.
 I also did these tests using the smallest springs I had, I think they were  .023" in wire diameter with 4 coils per spring.
  I did one test using a bigger set of springs, I think they were the biggest ones I have at  .032" thick wire and 5 coils per spring. These had the advance coming in much slower and not maxing out until over 5000 rpm.

 So what I'm going with in my truck at this time is the 402 center plate and the 139 weights with the small springs.
  I need to test this combo in the truck just to verify that my distributor tester is actually yielding correct results. I'll be doing this tomorrow, and I'll report back with my findings then.

 Rick

 PS: The picture of the timing indicator showing the light took 6 or 7 tries to get a picture that caught it just right.
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Quadrajet Carb Talk and Tips / Re: HEI Distributor mechanical advance curve options
« Last post by Cadman-iac on May 22, 2026, 08:00:28 PM »
Alright,  I couldn't find the reason why my timing was only showing up with about 4 degrees of distributor advance, even though you could clearly see it working like it's supposed to with the distributor cap removed and a remote coil.
 So I've scrapped that method of testing, and I did some research online into building my own distributor machine and found one that looked like it would work for me. I think DJD OLDS mentioned it earlier but it sounded too complicated at the time.

 So after building it and testing everything multiple times, making some improvements as I went along, I've finally got the information I wanted for the parts I've got on hand.

 Here's a few pictures of what I built for a distributor machine, and one of the results of my testing the parts on hand.
 I only tested with the center plates installed numbers up as the factory intended, because I had tried them numbers down during the last round of tests and found that most combinations showed they didn't work nearly as well. There were a couple that looked like they would work upside down, but the time involved in testing each one I felt wasn't worth the effort.
 So I hope this will help someone down the road with making a decision on what to use if you have any of the pieces to choose from that I've tested.

  Rick
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Quadrajet Carb Talk and Tips / Re: My favorite Quadrajet rebuilding tools:
« Last post by zucchi on May 22, 2026, 11:00:41 AM »
I realize this thread is rather old, nevertheless, my favorite Qjet tool is music wire. I find electric guitar strings and piano wire are essential for cleaning out all the small orifices and passages found throughout the carburetor. Since they're made of spring steel, they're resistant to taking a bend making them ideal for probing around curves and gentle angles.
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Diagnose a Quadrajet carburetor problem / Re: marine quadrajet 17082515 on gm 4.3
« Last post by Zyen on May 21, 2026, 06:12:18 AM »
Quote from: Cadman-iac on May 18, 2026, 08:35:34 AM
How did you calculate the LPCP for your engine?
 Rick

Here's how i did it, using my current wot and ignition timing as example:

crank rotation:  60,000 ms / (RPM * 360°) = ms/deg
4600 rpm = 0.0362 ms/deg

~12.8 afr using 87/E0 and ~90% VE (~0.5" hg) = ~1.3ms burn time to peak pressure
~0.3 ms from spark to flame propagation. = 1.6ms
Total burn from start to peak pressure = ~44.2° of rotation.

timing is set to 8° base and hard stop of 10.5° advance @ 3200 = 18.5° TA > 3200 rpm

burn time from ignition to peak pressure - spark advance = lpcp
44.2° burn - 18.5° btdc start = 25.7 atdc lpcp


-Allan

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