258 4barrel
Printed From: TheAMCForum.com
Category: The Garage
Forum Name: AMC 6 Cylinder Engine Repair and Modifications
Forum Description: AMC-made I-6 engine mechanical, ignition and fuel from basic repair to high-perf modifications
URL: https://theamcforum.com/forum/forum_posts.asp?TID=94382
Printed Date: Apr/18/2024 at 11:37pm
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com
Topic: 258 4barrel
Posted By: 5spdwagon
Subject: 258 4barrel
Date Posted: May/27/2018 at 8:31am
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Has anyone had any luck using a holley 390 carb on a stock 258? I have one on my car but I have a dead spot in the carb off idle. I can not seem to get rid of the dead spot. I can adjust it and get it to move in the rpm rage but can’t get rid of it. ------------- Real hot rods have 3 pedals |
Replies:
Posted By: Greyhounds_AMX
Date Posted: May/28/2018 at 8:09pm
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I'd expect that you need a larger accelerator pump squirter. ------------- 1968 AMX 390 w/T5 |
Posted By: 5spdwagon
Date Posted: May/30/2018 at 2:35am
I may try that. That’s the only thing that I can think of that is the issue. It ran fine on a 231 Buick a few years ago so I figured both the Buick and my 258 were about the same power so I thought it may work. So far nothing I have tried has done any good. ------------- Real hot rods have 3 pedals |
Greyhounds_AMX wrote:Posted By: Trader
Date Posted: May/30/2018 at 6:03am
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An I6 has longer intake runners and a more pronounced vacuum signal then a V8 or V6. It's likely getting too much air/fuel and bogging until it reaches an RPM that vacuum signal to the carburetor steadies more. Try jetting the carburetor down and see how it performs. |
Posted By: 5spdwagon
Date Posted: May/30/2018 at 1:08pm
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I have tried up and down 2 sizes on jets did not make it any better the larger ones made it worse ------------- Real hot rods have 3 pedals |
Posted By: tyrodtom
Date Posted: May/30/2018 at 3:20pm
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Which intake do you have the 390 mounted on ? ------------- 66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va. |
Posted By: Greyhounds_AMX
Date Posted: May/30/2018 at 3:22pm
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Off idle would be pump shot thougb, main jets are later. Every 258 I've built with a 4 bbl Holley needed more pump shot. Most needed the high volume accelerator pump conversion. ------------- 1968 AMX 390 w/T5 |
Posted By: 5spdwagon
Date Posted: May/31/2018 at 2:03am
Clifford intake ------------- Real hot rods have 3 pedals |
Posted By: Greyhounds_AMX
Date Posted: May/31/2018 at 12:47pm
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I would start with a 31 squirter and a blue pump cam on position 2. Also run as much initial timing as you can get away with as that will help. ------------- 1968 AMX 390 w/T5 |
Posted By: 5spdwagon
Date Posted: Jun/01/2018 at 12:22pm
Timing is as high as the motor will take it and still crank good. ------------- Real hot rods have 3 pedals |
Posted By: Greyhounds_AMX
Date Posted: Jun/01/2018 at 12:35pm
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Ok, then the pump shot is the next step. Do you have the Holley pump cam kit? If not, you should order one of those. https://www.amazon.com/Holley-20-12-Accelerator-Camshaft-Assortment/dp/B00029JE1U" rel="nofollow - https://www.amazon.com/Holley-20-12-Accelerator-Camshaft-Assortment/dp/B00029JE1U For the squirter itself you can order a larger one or get a pin vise hand drill and 0.031, 0.033, 0.037, etc drill bits, something like this: https://www.ebay.com/i/172076133863?chn=ps" rel="nofollow - https://www.ebay.com/i/172076133863?chn=ps The plop in the blue cam on position 2 and readjust the pump arm, drill the squirter to 0.031 and see what happens. It wouldn't hurt to have a spare squirter or two so you can keep enlarging until you go too far. ------------- 1968 AMX 390 w/T5 |
Posted By: 5spdwagon
Date Posted: Jun/03/2018 at 1:14pm
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Drilled my squirter up to a 40 and got rid of my dead spot. ------------- Real hot rods have 3 pedals |