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Discussion Starter · #1 · (Edited)
Holley 390 IFR resizing

I'm helping someone with his 200L6 tuning. This engine has the Classic Inlines aluminum head, headers, four barrel intake, and 274/274 - 112* cam, and Holley 390CFM 4160 carb.

He has had a bad time getting this thing to idle worth anything. I spent the day over there and brought my wideband O2 meter with me. My meter showed that it was way lean at idle even with the mixture screws out past four turns. AFR was at 18-19:1. I think that it is having trouble with the low vacuum and long intake runners.

I'm thinking about opening up the IFRs in the primary side one size. I didn't have my pin drill bits with me so we had to stop.

Also, does anyone know if the Quick Fuel metering blocks will work on this carb? I like the idea of changing it out to one that is adjustable.

Quick Fuel 34-8 - Quick Fuel Billet Carburetor Metering Blocks - Overview - SummitRacing.com

I may just drill and tap the IFR and air bleeds so I can use set screws as blanks.
 

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Discussion Starter · #2 · (Edited)
Re: Holley 390 IFR resizing

I just called Quick Fuel and they said that their blocks will not fit a 390 because the wells are too large. They did say that they could custom make me a set of adjustable cast blocks for about ~$50 each.
 

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Discussion Starter · #4 · (Edited)
Re: Holley 390 IFR resizing

It cruises at a reasonable 14-15:1 AFR. I didn't get into WOT yet. It's only the idle circuit that isn't right. The mixture screws are set to best vacuum. The idle has to be set high at ~1200 RPM to keep this thing running due to the lack of fuel.
 

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Discussion Starter · #6 ·
274 * at what spec. ? type of cam ? degreed in ? cam will give the same problem . long runners would aid the idle
Cam is installed straight up. I was told that is was checked with a degree wheel when the engine was built. This is a cam from Classic Inlines. I don't know much about this cam. It's a hydraulic flat tappet.
 

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Discussion Starter · #7 ·
I found more about the cam.

Adv Dur = 274/274
@.050 = 224/224
lift = .450/.450
lobe center 112 (I think)
RPM range 2800-6700


I have the initial timing set at 15* BTDC and have the vacuum advance disconnected and plugged.
 

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Discussion Starter · #11 ·
It's a new carb. Well it's about one year old.

The distributor is a Ford Duraspark 2 with a CD ignition box.

I'll try more initial timing. What are your thoughts on total timing? Will more initial timing help with the lean idle?
 

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You don't say what rpm or vacuum when cruising. If you have enough fuel on transfer for cruise then you have it for idle. May need less idle air bleed.
 

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Discussion Starter · #13 ·
You don't say what rpm or vacuum when cruising. If you have enough fuel on transfer for cruise then you have it for idle. May need less idle air bleed.
I don't have that info. I wasn't the one driving. The owner said that it felt than it has been but that doesn't mean a lot.

I'd like to hook up my Innovative LMA-3 so that we could datalog throttle, MAP, RPM, and AFR.

I could certainly drill and tap the IABs to make them adjustable.
 

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It's a new carb. Well it's about one year old.

The distributor is a Ford Duraspark 2 with a CD ignition box.

I'll try more initial timing. What are your thoughts on total timing? Will more initial timing help with the lean idle?

Total timing 34 to 36 ish. Do you know how to modify Ford advance plate slots? Do know how to se the advance slot numbers through the hole in the base plat. LIKE 15R one slot 18R opposite the slot with the post in it is the one being used.


Befiore you start drilling the IFR and or air bleeds. Order some nylon / plastic idle screw seals the cork ones dry out even new ones in todays fuel start shrinking up in a week or so. The seals can be purchased from Quick Fuel. Leaking ones can suck air into the emulsion feeding through the idle mixture screws.
 

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Discussion Starter · #15 ·
Do you know how to modify Ford advance plate slots? Do know how to se the advance slot numbers through the hole in the base plat. LIKE 15R one slot 18R opposite the slot with the post in it is the one being used.
I do on the V8 stuff. Is the six different? My old DS2 on my Falcon was a 10L for 20 degrees of advance. I'll likely need to mod the advance plate on this one to get the timing down to 16-18 mechanical.
 

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The idle transfer slot is very long / tall on the 390 carbs. They will run at quite a high speed before transfering into the main curcuit compaird to most 4bbl Holleys. Unless its geared low.
Get a vacuum test gage were the driver can see it. What was vacuum at idle?
 
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