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Original Message

Carb jetting help!

By bprewit - 03/06/2004 12:18:52 AM; IP 209.240.162.167

I am having some problems getting my jetting correct on my engine. The engine is as follows:
390 .060 overbore
10:1 compression
236/236 .571/.571 cam
Single plane intake w/1" open spacer
Holley 750 vacuum secondary
3.70 gears C6 tranny 2500rpm stall
Ok I currently have a 10hg power valve in primary metering block and a 6.5hg power valve in the secondary metering block. #72 jets primary and #74 jets secondary. I stepped up from #70 primary and #72 secondary since the engine would surge at cruise speed. With the larger jets the surge is gone but it still seems to lean out over 5K rpm. I have changed the secondary springs going lighter until a bog was felt then back to previous stiffer spring and ended up with purple secondary spring. Finding jets in this small town is not possible so using a index chart I am drilling out my jets to the size needed so I dont want to go too big as there is no way to go back after drilling. The plugs are still very white in color so I know its lean and also notice a temp increase (10-20 degrees) with higher rpm's. Should I keep the primary size and only increase the secondary size? Or should i increase both primary and secondary one step larger? I pull about 12hg vacuum at cruise rpm so the primary power valve is right on the money but not sure about sizing the secondary power valve. Any help/ideas/suggestions is greatly appreciated.

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Collapse <b>Carb jetting help!</b> -- <font color=#0000ff>bprewit, <i>03/06/2004</i></font>

Carb jetting help! -- bprewit, 03/06/2004

Collapse <a href=../ForumFE/reply.aspx?ID=20545&Reply=20542><img src=../images/reply.png width=30 height=10></a> <a href="#" id="anchor20545" onclick="return false;">RE: Carb jetting help!</a> -- <font color=#0000ff>bprewit, <i>03/06/2004</i></font><script type="text/javascript">
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RE: Carb jetting help! -- bprewit, 03/06/2004

Collapse <a href=../ForumFE/reply.aspx?ID=20546&Reply=20542><img src=../images/reply.png width=30 height=10></a> <a href="#" id="anchor20546" onclick="return false;">RE: Carb jetting help!</a> -- <font color=#0000ff>greg, <i>03/06/2004</i></font><script type="text/javascript">
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RE: Carb jetting help! -- greg, 03/06/2004

Collapse <a href=../ForumFE/reply.aspx?ID=20556&Reply=20542><img src=../images/reply.png width=30 height=10></a> <a href="#" id="anchor20556" onclick="return false;">Power valve</a> -- <font color=#0000ff>Royce, <i>03/07/2004</i></font><script type="text/javascript">
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Power valve -- Royce, 03/07/2004

Collapse <a href=../ForumFE/reply.aspx?ID=20569&Reply=20542><img src=../images/reply.png width=30 height=10></a> <a href="#" id="anchor20569" onclick="return false;">RE: Power valve</a> -- <font color=#0000ff>bprewit, <i>03/08/2004</i></font><script type="text/javascript">
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RE: Power valve -- bprewit, 03/08/2004

Collapse <a href=../ForumFE/reply.aspx?ID=20570&Reply=20542><img src=../images/reply.png width=30 height=10></a> <a href="#" id="anchor20570" onclick="return false;">Stock size is 6.5</a> -- <font color=#0000ff>Royce P, <i>03/08/2004</i></font><script type="text/javascript">
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Stock size is 6.5 -- Royce P, 03/08/2004

RE: Stock size is 6.5 -- bprewit, 03/09/2004