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| low idle vacuum, normal >1400 rpm vac, engine dies in gea https://slantsix.org/forum/viewtopic.php?t=59268 |
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| Author: | marineviper [ Wed Mar 09, 2016 2:27 pm ] |
| Post subject: | low idle vacuum, normal >1400 rpm vac, engine dies in gea |
Long time non poster, finally got around to fixing my parked 80 Aspen, I advanced my mp 244 cam 4 degrees, and pulled the motor to reseal all my oil pan leaks. Got it back running and i solved my mid range power band issue but I still have the same issue of the car wanting to stall in gear at idle so I was checking my vacuum. I have a steady 13in at idle, and thats the best i can do adjusting idle mixture screws, if I rev the motor to 1100 rpm I get 16" and after 1400 rpm I have a steady 18". I have final timing at 32 degrees with 12 degree initial. Carb is a holley 390 with the smallest jets I could find, head was shaved .050 5 years ago, over sized valves. no vacuum leaks, and choke is open, (granted when closing choke it rev the engine for 3 seconds before it dies. Any more info needed I'll let you know tomorrow. Thanks in advanced for any ideas. |
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| Author: | drgonzo [ Thu Mar 10, 2016 10:34 am ] |
| Post subject: | |
Quote: Carb is a holley 390 with the smallest jets I could find, head was shaved .050 5 years ago, over sized valves.
Those jets could be a large part of the problem. Since closing the choke speeds up the engine momentarily, you are probably jetted way too lean. I'd put the original jets back in it and see how she runs.
no vacuum leaks, and choke is open, (granted when closing choke it rev the engine for 3 seconds before it dies. |
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| Author: | DusterIdiot [ Thu Mar 10, 2016 5:29 pm ] |
| Post subject: | x2 |
Quote: I'd put the original jets back in it and see how she runs.
Yes, these should be #50 or #51's.... I ran a set of #48's, that was wayyyyy too lean....
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| Author: | wjajr [ Fri Mar 11, 2016 6:14 am ] |
| Post subject: | |
My engine build: 225; Engbuilder over sized valves; ported head shaved to give 9.5:1 compression; 0.030" over bore; recurved distributor; Holley 390, Clifford shorty headers; 2" duels to rear bumper; 2600 rpm stall converter; 3.55 8 3/4 Suregrip; 24.5" tall tires. I'm running 53 jets with 390 Holley at sea level. I found that with 52 jets there was a slight bit of hitch in the getty-up when tipping to throttle. I have tried 49 jets along with every other in between, and those were too lean. Another thing to consider is your gearing and torque converter stall. You may need a few more rpm at idle, and at low speeds to make that cam play well, and develop more vacuum. I have a 2600 stall & 3.55 rear gear, and idle in park around 1000 rpm. Below 1000 rpm there is not enough vacuum signal to carburetor for it to operate correctly. Below 2000 rpm the engine is low on torque, so-so to 3000 rpm, and pulls like a V8 in 4500 to 6000 rpm range. That's how my machine runs, and every one is different when using after market parts. |
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