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By oldcarmark - 15 Years Ago
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Having trouble getting the fuel level to stabilize on my Holley 390 carb.I have set it dry 3 times and lowered it so its a little lower than specs.Still getting too high fuel level when checking by using the site plugs.Thinking now I may have a bad float.Had a real good backfire through the carb when I set the timing 180 off.I dont see any damage to the float but how can I check without buying a new float?
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By paul2748 - 15 Years Ago
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Take it out and shake it - if you hear something it leaks. Also immerse it in water. If you get bubbles out, it leaks
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By John Mummert - 15 Years Ago
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You didn't mention if the problem occurs at both primary and secondary. I assume this is an early Holley without externally adjustable floats. If only one end has the problem that helps narrow it down. A needle/seat with slight leak could also cause the problem. If you find no other problems you might check fuel pressure.
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By oldcarmark - 15 Years Ago
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Hi John.Its a late one with external adjustment.I have tried lowering the float level a little at a time with no success.Set dry it shouldnt be out by any more than 1/4 turn.Thats why I am thinking the float may have gotten't damaged when it backfired through carb.I changed the needle and seat to the steel ones but even with the original "soft tip" ones it still is too high.I am going to try Pauls suggestion tommorrow.
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By Pete 55Tbird - 15 Years Ago
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Mark I am getting a disconnect from your post. If you check it with the sight plugs then why not set it with the sight plugs? Are you saying it will not stay set or something else. Every time I had a bacfire with an early Holley it blew the powervalve not the float. More info might help. Pete
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By oldcarmark - 15 Years Ago
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Pete! I set it dry initially so I was sure I was starting with a very close to correct setting.Run it for a few minutes so fuel level is stabilized.Check the level via the site plug.Turn the level down gradually.Doesnt have any effect.Shouldnt take more than 1/4 turn at most to set it properly.Another party suggested maybe the float got damaged when it backfired although visually I see none.Its brass float by the way.
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By YellowWing - 15 Years Ago
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Mark, a backfire cannot damage a float. Since yours are brass you would here and feel fuel sloshing around in it if it was leaking. On a Holley each flat on the inlet adjusting nut ( 1/6 turn ) changes the fuel level approximately 1/32" so your 1/4 turn would only change the level 3/64" barely perceptible by eye. Hope this helps. Mike
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By 46yblock - 15 Years Ago
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YellowWing (7/10/2010)
Mark, a backfire cannot damage a float. Since yours are brass you would here and feel fuel sloshing around in it if it was leaking. On a Holley each flat on the inlet adjusting nut ( 1/6 turn ) changes the fuel level approximately 1/32" so your 1/4 turn would only change the level 3/64" barely perceptible by eye. Hope this helps. MikeStuff like this is so valuable, just wish I could remember it!
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By YellowWing - 15 Years Ago
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I can't remember it either. Has gotten worse since I turned fifty. Wife always says, did you google it. Has bailed me out numerous times  mike
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By GREENBIRD56 - 15 Years Ago
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Mark - At the inlet to the bowl on a 4160 type carb, there is a filter element captured under the inlet fitting. Be sure its clear. Wash with rubbing alcohol and a (very) fine brush. Just one more thing to look at...
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By pegleg - 15 Years Ago
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Mark, I realize this may be obvious, but if you set it with the sight glasses, the motor needs to be idling.  The secondaries will not drop until the fuel evaporates, or you gun it enough to use up some of the fuel in the bowl. UNLESS of course it's a four corner idle setup.
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By oldcarmark - 15 Years Ago
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Thanks Frank.I took it apart this morning again.Checked the float-not leaking.The float arm was not straight so I made it straight and reset float dry and after checking it wet after running it appears to be now correct fuel level in the bowl.
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By pegleg - 15 Years Ago
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Good on you. Glad I could help.
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By oldcarmark - 15 Years Ago
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Was still having trouble after "fixing" it.After doing some internet searching I read that Holley carbs dont handle fuel pressure higher than about 5.5 to well.Higher pressures tend to overwhelm the floats.So I bought a regulator and installed it.Set it for 4.5 initially and "bingo" problem solved.No more "stutter"on deacceleration which I assume was excess fuel dumping into the carb.Float level stays where it is set and should be.My question is, what is the relationship between fuel pressure and volume.The pump I have is apparently rated for 6.5-7.5 maximum pressure.With the pressure set at 4.5 it is still providing lots of fuel as there is not a problem even at higher speed.Thanks!
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By Y block Billy - 15 Years Ago
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I currently had a fuel level problem on my ramp truck and chased it for a long time. it turned out the "O" ring that goes around the brass float adjustment and needle was leaking constantly causing a rich flooding condition. finally removed the needle seat and changed that O ring and Bingo, that was the problem.
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