460 w/ motorcraft 4350, EGR, PCV and evap canisters, no cat, no smog pump.
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<ST1PO </ST1installed MSD 6A only modification I can see.

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I Rebuilt the 4350 and got marginally better performance still leaked, flat spots on acceleration, choke pull off non operational, old and tired.

Purchased a used Holley 4160 (list 80452) rebuilt and installed, looks to have power valve blowout protection installed from what I can see of instructions for installing it but not 100% sure as I did not do it. One question would be does factory installed look like the after market kit?



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I ground the edges of the spread bore EGR spacer to allow the 4160 butterflies to operate freely seemed to work well gaskets all aligned fine.

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Big improvement in responsiveness and overall power over 4350 but……….
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15in of steady vacuum at 650 rpm with mixture screws all the way in, turn screws even ¼ turn out immediately starts to run rough and will not idle below 750 rpm.
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Choke and fast idle working properly has a slight hesitation off of idle but runs smooth everywhere else, no pinging starts right up one pump when cold. Ran 20 minutes down the freeway yesterday with ac full on no issues before during or after, temp gauge setting right in the middle like always.
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Here is what I have done / checked;

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Rechecked all settings per rebuild sheet including float levels before install and then again after.

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Checked for vacuum leaks by spraying carb cleaner everywhere and then also removed and inspected each hose and replaced any that were not already new.
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Pulled idle screws shot carb cleaner and then compressed air, both are clear.
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Plugs look good nice color on all cylinders, cleaned and checked gap and reinstalled since they are less than 500 miles old.

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Checked initial timing, was at 14 moved to 12 this put total mechanical advance at 36. I checked this by running idle up to 3000 where timing stopped advancing, all of this done with vac advance disconnected and plugged. Vacuum advance connected as indicated in holley documentation, ported, but I also tried full manifold and one port which seems to have no vacuum, at top of carb angled upward, this might be an indication of mistake in rebuild?

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I am wondering if I may have missed something else? gasket, internal vacuum leak, could the mixtures screws be damaged, they appear fine and have the cork gasket installed to seat. Don’t know what to check next, keep looking for a vacuum leak? also any risk of damage (don’t really see how but thought I would ask) I drive this everyday around the neighborhood and 15-30 minutes on the freeway 3-4 times a week.

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Any thoughts would be appreciated, Thanks!

 

from researching the holley forums sounds like the idle transfer slot could be the issue. Anyone have experience with that?

Thanks

 

Yes make sure you transfer slot is square, showing its as long as its wide below throttle plate. You should really set your idle on the secondaries. Have to pull the carb off to find the screw, and check the transfer slot. Also look down your carb and make sure you have a shot from the accelerator pump as soon as you touch the throttle. Could also need a larger squirter.

 

I am getting a good solid shot form the accelerator pump, hopefully I will have time to pull it off this weekend and check the rest. So the screw adjusts the transfer slot or the idle on the secondaries? or are those both the same thing?

Thanks for the help really appreciate it.

 

If it idles with mixture screws all the way in Your getting fuel from some where else most likly the power valve. Crank it over to fill the fuel bowls then I like to unhook everything and gently lift the carb up and see if it is leaking and where it's coming out at.

 

You adjust you idle screw on the primary side to obtain the correct transfer slot. Then if you idle is too low or high you adjust your idle speed on the secondary idle adjustment, that screw is in the second pic.

And X2 on what Turbo 6.9 said, musta missed that part. Chances are your power valve is passing if it`s pulling fuel and it still runs with the screws in. I`d check that first before worrying about transfer slots, mine ran fine for years before i knew what they did.

 

I put a new powervalve in during re-build then replaced it again since that seemed to be the default problem when idle screws don't work, but no change.

Looks like I have to pull it again anyway so I will try it and see what happens.

Thanks!

 

Thing is Your getting fuel from somewhere be it Your float setting to high or power valve.
If You haven’t had a backfire Power valve really should be okay so check Your float setting.<O</O
Get right on top and look down in the carb when it’s running You shouldn’t see any gas droplets <O</O

 

That makes total sense, getting gas from somewhere it is not supposed to, I have the floats set right at the bottom of the sight plug.

I just don't know that much about the inner workings of carb. I will climb up and take a look to see if anything is weird, I did look to verify the accel. pump was shooting which it was.

One thought as I re-read some earlier research I have not checked fuel pressure, could too much pressure cause these symptons? Something I will check either way.

 

yes, too much fuel pressure is not good for a holley. i've heard less than 6 is good, 4.5 is ideal. i had some similar driveability issues and one of those inline regulators worked great.

 

^ There seems to be a lot of different psi settings people like to use. I've been told to run holleys at 8-9psi. I have mine set at 8 with no troubles.

 

That's funny as I was at the track a few weeks ago and My pressure regulator failed. 15psi is all My gauge can read and it was max out. Car never flooded out LOL

 

When you pull the P/V again, check it for a vacuum leak...suck on it to see if it holds vacuum. Another thing to consider....when you replaced the P/V before, did the gasket come off in two pieces - one half on the valve and the other half on the metering block? If it did, take the 1/2 gasket off the P/V and leave the one on the block and re-install...if the P/V is good. I believe the gasket is too thick causing the P/V not to seat right, and eventually leaking fuel via the gasket. Fixed my problem...

Do you have a pretty stout cam? 15" Hg vacuum at 650 rpm would indicate that you do...requiring you to bump up your initial timing to 16 - 20 degrees. Also, a P/V rating of 6.5 or lower would be good for that amount of vacuum.

Holley carbs can tolerate 6 - 8 psi fuel pressure - stock fuel pumps. Edelbrocks don't cotton to much more than 5.

Agree with the transfer slot (initially) showing a "square" hole beneath the venturi. Leave the secondary idle setting alone for the time being.

EGR working properly and not gummed up?

 

I don't remember on the PV gasket, I will check that.

as far as I know no cam, I believe it to be stock, before I switch the carb I was getting about 18 Hg vacuum but it was very erratic with the old carb leaking everywhere, both gas and vacuum, at least it is steady now.

EGR looks in good shape, if I take it off of the PVS connection and hook it to a manifold vacuum at idle it starts to idle very rough seems like I read this is an indication that it is working?

Trying to get out of here early and take a look at it should have some updates tomorrow or sunday.

Thanks to everyone for all of the input helps just to talk it through sometimes

 

Finally got to work on the truck today. Pulled the carb back off checked idle transfer slot=good
Powervalve = good by sucking on it did not seem to be leaking at the gasket
rechecked settings from re-build kit including secondary idle screw = good

set idle screws at 1.5 turns and re-installed, started perfectly and idled beautifully thought I had it! warmed up idle dropped and I checked vaccum and still needed to run the screws all the way in to get idle at 650 and 15 hg vacuum.

Re-checked the timing moved from 12 to 14 w/out advance ran a little smoother but no change in vacuum.

Idle screws are definatly haveing an affect just cannot open them at all without running the idle at 1000 or so.

Checked fuel pressure, by installing a "t" right before carb and using a vaccuum/ pressure guage, at startup it was 4.5 then as I watched it climbed to 8 throttle action had no affect.

I am not sure what this means but am going to research it tomorrow because tonight I am DONE