3 carb setup question-Idling WAY too fast - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
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post #1 of 9 (permalink) Old 03-07-2017, 12:44 PM Thread Starter
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3 carb setup question-Idling WAY too fast

Hello all!!
I have had a long hiatus in my hobby, and i seem to still be on the learning curve. i have a 63 comet custom with the 170, for which i purchased the Offenhauser 3x1 intake manifold. I got three Holley 1904's, rebuilt them and now have the engine all back together. my issue is that when i hit the key the car starts and then takes off, going up to what sounds like WOT. I don't leave it on very long to see if it will slow down because i'm nervous i'll spin a bearing with it revving like that. Where is the adjustment for the idle on the 1904's? i only have a mixture screw that i can see.
any help would be greatly appreciated
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post #2 of 9 (permalink) Old 03-07-2017, 02:38 PM
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Re: 3 carb setup question-Idling WAY too fast

In a three carb setup, typically only the middle carb has an idle circuit. The other two typically have different part numbers and have no idle circuits. Otherwise the engine would idle at too high a speed. Could this be your problem?

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post #3 of 9 (permalink) Old 03-07-2017, 06:12 PM Thread Starter
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Re: 3 carb setup question-Idling WAY too fast

Possibly. I actually closed the idle mix screw in the secondaries to see if that made any difference (it did not). I even went so far as to close all three idle mix screws, with no effect. I don't think that i'm even using the idle circuit. According to the Offenhauser instructions, it does seem that all three should be running an idle circuit, since it gives instructions on how to set the mix. Perhaps the loss of vacuum from the two new holes in the intake isn't allowing it to function correctly.
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post #4 of 9 (permalink) Old 03-08-2017, 03:48 AM
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Re: 3 carb setup question-Idling WAY too fast

The way I set up a tri power system is to set up one carb at a time. I start on the center carb and make block off plates for the other two carbs. You block off the outer carbs then make your adjustments on the one center carb. When you get it dialed in as best as you can, remove one of the block off plates and install one outside carb. Typical tri power systems usually only run the idle circuit on the center carb if your running progressive linkage. The outside carbs should have the idle mixture screw turned all the way in. When you add the second carb and it affects the idle you have a vacuum leak at the throttle plate. You would need to adjust the throttle plate in the bore so you cannot see any light between the bore and the plate. This needs to be done on both outer carbs. Takes some time and hard to get perfect. Hope this helps.
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post #5 of 9 (permalink) Old 03-09-2017, 04:20 AM
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Re: 3 carb setup question-Idling WAY too fast

Are the base gaskets somehow holding the throttles open, or is the linkage not allowing it to close?

If the throttles are closed, it's impossible for it to do what you are saying, so I'd be looking down the throat to see what it keeping the plates open even when you back out the screws


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post #6 of 9 (permalink) Old 03-16-2017, 08:41 PM Thread Starter
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Re: 3 carb setup question-Idling WAY too fast

thanks for the info so far everyone.
I have taken your communal advice and i blocked off the outer two carbs, and wow, its a different animal. wouldn't say it purrs, but sure a whole lot better. Going to have to keep at it, will update as it goes along.
thanks again for the input
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post #7 of 9 (permalink) Old 03-18-2017, 11:35 PM
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Re: 3 carb setup question-Idling WAY too fast

MY427Stang my be right. Check to see if the end carbs have the throttle plates closed. To adjust them, back the idle screws on both the front and rear carbs so the butterflys are closed. If the linkage to the front and rear carbs are holding the butterflies open, shorten them till they close. Hope this works for you. Good luck!
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post #8 of 9 (permalink) Old 03-19-2017, 06:28 AM
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Re: 3 carb setup question-Idling WAY too fast

Blocking off the outer carbs and having the idle return to a normal condition tells you the problem is in the throttle plates in the outer carbs. Adjust them so you see as little light between the base and throttle plate then reinstall it (still leaving one outer blocked) and see how it runs. Should make little to no difference in idle speed if you get it right. Takes time, and using worn 50+yr old carbs doesn't help things.
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post #9 of 9 (permalink) Old 03-25-2017, 09:07 PM Thread Starter
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Re: 3 carb setup question-Idling WAY too fast

Whew,
after allot of trials I think I've nailed it:
It seems that Holley 1904's have different versions of the linkage between the accelerator pump cam and the throttle. well, I had the short rod on the long carb, holding the throttle at about half open. Coupled with the others, it sent the engine revving to the moon. A bit of thin rod bending later, its not too shabby.
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