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Discussion Starter · #1 ·
I posted a while back about a lean issue I was having with a 750DP, the latest version with the 4 corner idle adjustments, specifically when it's running on the main circuit of the primaries before the secondaries start opening. Thanks again for the advice, which I followed, upped the jets from the stock 71 to 74, changed the power valve to a 6.5 from the 5.5, took out the wire I had used in the idle feed restrictions to lean out the idle. So I take my time, set the idle, have vacuum gauge this time and manage to set it so it has 12 inches and idles about 900 rpm. So I'm checking how it runs at speeds from 2500 to 3500, 100 rpm at a time, slowly increasing to each next RPM. Now I have a new problem. When I get to 3100, it has a major hole, sounds like it just flat runs out of fuel, and then recovers, and runs like s*** in the next 500 rpms, and then there is no more throttle without the secondaries opening. WTF? Timing, checked, still locked at 36, fuel pressure is 6 psi on the gauge even when that happens, I shut it off, checked the level in the bowl, and it's right at the bottom of the sight screw. Put in a set of new plugs just to rule that out since I had them. Vacuum is 15 inches at 2500 and stays there as the rpms are increased, up until the point it falls on its face and then it only drops momentarily and goes back to 15 inches once past the hole, even though it's running crappy. If this was happening when I hammered it I would think it just needs more accelerator pump, but it happens at a slow increase, probably when it drops the power valve opens and lets some much needed fuel in which lets it continue, but at such a slow increase in throttle the power valve shouldn't even come into the mix. If I mash the throttle it revs like it should, but that's two accelerator pumps just covering up this problem. It seems it just wont make a good transition to the mains in the primaries for some reason and even after it does it seems I have a problem. Where do I look? I wouldn't think an increase of only 3 jet sizes would cause anything other than maybe it runs too rich, but I don't think thats really the issue here. Metering block Fubared? Demonic possesion? I took it apart and checked the passaged in the body and base plate, all look clean as far as I can tell, cant see internally in the metering block, so not sure about that but all the small holes seem to be open. At this point my irritation level is reaching it's limit so on goes a 650DP that I ran on my boat for years, starts, idles, runs smooth throughout the same range of RPM,s no holes, no miss. I've never had so much trouble with a Holley. Is it a paperweight? Again any advice or help is greatly appreciated. Sorry if the post is lengthy, just want to get as much info as I have out there.

Greg
 

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Cantard
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I think you feel like me last week. Does this (pos:D) have mid airbleads that you can change? For me it would do that but it was actually a suden rich missfire....pop...sputter....wanted to burn the thing right after it was retuned with a large hammer. Had to open them up to .004 to get them right. Going up on the float level would make it worse but got me where I needed in the top.
 

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Discussion Starter · #3 ·
No, it's not a version with changeable air bleeds. It's the standard 4779-9. Looks good on the shelf right now.
 

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Discussion Starter · #5 ·
Well, I started by having both the primary and secondary fully closed, of course it won't idle that way, so I gave each one an 1/8 of a turn at a time until it would idle so that they are both open the same amount. (I did put one of those easily adjustable screws on the secondary side). I can close the secondary side but then I have to open the primary more and it starts getting too far into the transfer slot so that the primary idle mixture screws don't do anything.
 

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Cantard
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Well, I started by having both the primary and secondary fully closed, of course it won't idle that way, so I gave each one an 1/8 of a turn at a time until it would idle so that they are both open the same amount. (I did put one of those easily adjustable screws on the secondary side). I can close the secondary side but then I have to open the primary more and it starts getting too far into the transfer slot so that the primary idle mixture screws don't do anything.
Not suprised.. you need to drill the throttle plates. Start at 1/8 hole but you will probably end up at 3/16 holes. Lets you run back off the idle circuit and still have the air to idle.
 
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