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Old 10-26-2013, 09:54 AM   #1
CF Senior Member
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Location: Englewood FL
Default 1961 Dual Carb Idle Mixture Adjustment

My '61 has dual WCFB carbs - 270 HP. I'm working on adjusting the idle mixture starting with the screws backed out 1 turn. I've shortened a 1/4" barb plug for the next few days until the Paragon 755 comes.

It is a challenge to adjust the back carb given the very limited space. Even my carb adjustment tool can't make the bend to get into it so I'm using a 1/4" open end wrench. Anyone got a recommendation for a tool for this?

But more importantly where do most carbs end up for turns out? My engine has the best vacuum when they are about 1/2 turn out. Is that consistent with other dual four engines? And what is the typical vacuum gauge reading? I also seem to have a slight range where about 1/8 of a turn doesn't make any difference. Should I be on the in, out or middle of this?

And anyone know of a good video for this? I can't find a good one on YouTube or with web searching.
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Old 10-26-2013, 10:56 AM   #2
Frankie the Fink
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Location: Winter Garden Florida

My vacuum at idle on my 270hp dual quad car is a rock steady 18". I have the Duntov 097 cam.

Idle mixture screws are from 1/2 to 3/4 turn out on all four. I am running clone carbs but they are set up just like real deal 270 carbs. Worry less about the number of turns and more about highest vacuum/best idle. When you reach that I always lean the carb idle screws out about 1/16-1/4 turn on each screw. The idle will roughen up then settle down but it prevents over rich idling. I use this tool for the back carbs (I tried a 1/4" box end wrench and those springy flex shaft tools and they suck) - it works but is EXpensive:

You use it withOUT a bit in it and then its a regular 1/4" hex driver. Its well made and includes a ratcheting mechanism and dial indicator so you know EXactly how many turns (or partial turns) you are moving a carb screw...

The incredibly short Philip's head bit for this tool is also perfect for tightening the screw on the back of the turn signal housing using a 1/4" box end wrench to hold it. So - you do get a 'two-for-one' use out of it.

BTW - I run the screws in until the engine acts badly and screw outwards to the highest vacuum point and no farther - so any dead spot is not a factor. I doubt you'll find a YouTube video on these carbs as you are now in an elite cadre of classic car owners with Carter WCFB dual quads - there aren't all that many of us. But the procedure is no different than any other carb.

Last edited by Frankie the Fink; 10-26-2013 at 11:17 AM.
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Old 08-18-2014, 01:48 PM   #3
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I've been fiddling with my idle mixture (on my 2x4 wcfb's) and just about have it right .. I think .. I have found that the idle hunts a little but the rpm is down now closer to 900rpm (varies consistently between 800 and 1000 but much better than the 1600 that I couldn't get below earlier). It also runs a little too hot at idle and on occasion spews out coolant from behind the cap when I turn the engine off. I believe this may be fixed by a little more advance on the timing and screwing out the mixture screws slightly to make the idle mixture a little richer.

I had it running nicely without the air cleaner fitted, as soon as I replaced the air cleaner the engine stalled ... must have leaned off the mixture with the extra restriction of the cleaner and element.

For the stupid ... like myself ... to richen the mixture the mixture screws need to be screwed out (counter clockwise) and to advance the timing the distributor needs to be turned counter clockwise (when looking down at the cap). Richer mixture = cooler idling. Advanced timing at idle = a smoother idle.

Last edited by mickatbp; 08-18-2014 at 01:52 PM.
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Old 08-18-2014, 02:54 PM   #4
Frankie the Fink
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Try securing your advance weights in the dizzy (rubber bands sometimes work) and readjust idle. If it no longer hunts then your high idle is causing the weights interacting prematurely.
The 2x4 air cleaner base has a depression for the choke on one side so make sure its on correctly.
I guess I can post on occasion or answer 10-12 PMs daily.

Last edited by Frankie the Fink; 08-18-2014 at 02:57 PM.
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Old 08-18-2014, 04:13 PM   #5
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Location: Poway Ca

I knew Frankie couldn't resist a good dual quad question!

I think it's highly doubtful that the added restriction of the air cleaner (at idle), is the cause of the engine stalling.

I only have a single quad. Setting it by max vacuum, I ended up both about 3/4 turn out.. However, I had a slight stumble on hard acceleration.. Backing them out another 1/4 turn fixed the hesitation.

But I don't think you could ever notice this at idle. Well, maybe a pro.. but not me.
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Old 08-18-2014, 06:38 PM   #6
59 navy
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Default Duel Quads

I added a vacuum fitting to the Carter closest to the firewall. My 59 283 ran a little rich so thought I could get a reading and set them both a little leaner. No luck. I can't figure out why my meter won't show a reading. For now, I've set them by ear as some on this forum have suggested. (The fitting was from Zip) Still learning. 59 navy
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Old 08-18-2014, 06:38 PM
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