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Old 01-19-2018, 01:59 PM   #1
johnwaynejeep
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How do you tune a Q-jet

All,

I'm re-assembling my Q-jet today and re-installing it. I'm trying to find out how to get a basic tune of the mixture screws.

I've seen two methods described. 1) adjust the mixture screws out to reach the highest manifold vacuum. 2) adjust the mixture screws in to reach the highest RPM.

Which one is more accurate? and is there more to these procedures?

Thanks all
Robert
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1975 C10 - Huckleberry
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Old 01-19-2018, 02:17 PM   #2
jwilson645
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Re: How do you tune a Q-jet

Gently turn the right one in until the engine starts to bog, then back out 1/4 turn, then do the left one the same way.......................HOWEVER, There is a lot more to tuning one than just adjusting the idle mixture screws.

Did you use one of the kits from Cliff's High Performance? He supplies the best parts and they're ethanol resistant. The cheap part store kits don't do the job. Trust me, I tried many before finding Cliff. He also sells a book that he wrote on building/tuning them that was priceless to me.


Forum: https://cliffshighperformance.com/simplemachinesforum/

Parts: https://cliffshighperformance.com/
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Old 01-19-2018, 04:11 PM   #3
Tiger Joe
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Re: How do you tune a Q-jet

start doing some googling and find the tuning papers from Lars about how to tune a q jet. there is more in the papers than you can believe
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Old 01-19-2018, 07:11 PM   #4
geezer#99
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Re: How do you tune a Q-jet

Read this carefully.
There will be a test. LOL!!
http://www.digitalcorvettes.com/foru...ad.php?t=88376
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Old 01-19-2018, 07:39 PM   #5
Dead Parrot
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Re: How do you tune a Q-jet

IF all you are wanting is the basic idle tune, then what jwilson645 said works well. For a fresh carb, lightly turn the screws in until they just start to seat, then back out 2 turns, then start your adjustment on a warmed up motor. Make sure your choke is fully open.

Before you start, get your timing and idle speed set. You can't adjust idle mixture if you are running on any part of the carb other then the idle mixture.

You want to wind up a little lean on your idle mix to avoid unburnt gas washing the oil off cool cylinders. Idle mix has little to do with the running down the road setup.

If you are wanting to setup the rest of it, you already have 3 suggestions for 'how to' information.
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Old 01-20-2018, 03:41 AM   #6
johnwaynejeep
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Re: How do you tune a Q-jet

Thanks all.

I do have Cliff Ruggles book and I followed it the best I could during the rebuild. I used a rebuild kit from quadrajetparts.com and I ordered a few other parts that I knew were lacking from the basic kit.

I chose not to mess with any of the metering rods because it ran ok before and I don't know enough about these carbs to do that without messing something up.

I did find Lars writeup and I'm excited to read it, but I really need some time to absorb it.

Thanks for the info.
Robert
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