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Good article explaining carburetor idle screw adjustment.


acem
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This is a link to a holley article explaining how to adjust the idle mixture on their carburetor but is pretty much the same for any make. 

Sadly new 'automotive technicians' are not taught these skills.

I just thought it might be useful to someone here.

https://www.holley.com/blog/post/here_is_the_correct_procedure_for_setting_an_optimized_idle_mixture_and_speed/

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I had really good luck with thermoquad carburetors back in the day. However all of mine eventually warped the plastic center housing. They were good for 20 odd years for me. 

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Thx acem your timing is impeccable I just bought a Quickfuel double pumper yesterday and it's been a looong time since I played with this stuff

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Really don't get the hate I sometimes see for the holley. One of the easiest carbs I know of to work on. A guy once said the Quadra junk you could feel every stage as they went thru the range of positions of all the linkage and brick a brack, where as the holley was more smooth. This was either an old gm mechanic that I had rebuild the factory holley off a 390 mustang or a tech school teacher I had later can't recall for sure.

Thanks for the article ace.

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I was about 14 working after school pumping gas when the shop mechanic was having a good laugh. It seems a do it yourself guy was checking for leaks and loose screws and tightened the mixture screw in the carburetor. Needles to say it wouldn't idle.

The idle mixture screws on the Amal Concentric carbs on my Norton are actually air screws rather than fuel screws, so out is lean, in rich.

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I had many issues with a Holly 600 CFM standard on a 413 Dodge M300 chassis Motor Home in 73. The float bowels leaked fuel back into the manifold causing hot start issues. I believe it was due to the RV sitting a lot with little use and the cork gaskets dried out.

I had a 66, 425 HP 427  Corvette with a 780 CFM, few issues with it.  Most  the HP options in most brands of vehicles in the 60's ran the Holley 750 CFM. if big cubes. 

Pontiac used the Carter AFB on the 326/389 engines, no issue that I recall. 

Prior to the smog introduction in Ca in 66, Carburetors were not the boogy-man that most remember. 

Operators today, who have never OWNED  a vehicle with a carb keep telling me about carbs.

We currently run an Eldelbrock 750 on a 440 Mopar, in a Dart. I keep thinking that I will go to a Holley BUT today's high cost and the no issue AFB meet our needs. I did put an overhaul kit in it earlier this year,  accelerator pump was the failure.  I did go to an electric fuel pump  years ago, makes starting much quicker.

I often wonder who at Carter thought a plastic throttle body would be a great idea on a hot intake manifold, great bit of marketing, cheap, lousy, engineering!

 

 

 

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16 hours ago, New Englander said:

I was about 14 working after school pumping gas when the shop mechanic was having a good laugh. It seems a do it yourself guy was checking for leaks and loose screws and tightened the mixture screw in the carburetor. Needles to say it wouldn't idle.

The idle mixture screws on the Amal Concentric carbs on my Norton are actually air screws rather than fuel screws, so out is lean, in rich.

Reckon the chances of getting a couple of  SU's tuned?

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7 hours ago, Ian Beale said:

couple of  SU's

I always though of the SU as a good carburetor and not all that hard to adjust/sync. I always got a kick out of people pumping the throttle on a cold day start.

 My MG TF has a pair.

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33 minutes ago, New Englander said:

I always though of the SU as a good carburetor and not all that hard to adjust/sync. I always got a kick out of people pumping the throttle on a cold day start.

 My MG TF has a pair.

I agree - so long as you know how to handle an SU.  I've retrieved some horribly botched attempts.

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Always wanted to try one on the Panhead, beautiful art piece, some liked and some bashed but I don't think they knew about their quirks

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22 hours ago, hardtail said:

beautiful art piece, some liked and some bashed

Yes, they polish up nicely. The bashers don't bother to learn how they work. There's no choke as such and no accelerator pump, just a single jet and no idle jet so it's a mystery to some. Tuned properly they provide the same mixture across the RPMs.

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7 minutes ago, New Englander said:

Yes, they polish up nicely. The bashers don't bother to learn how they work. There's no choke as such and no accelerator pump, just a single jet and no idle jet so it's a mystery to some. Tuned properly they provide the same mixture across the RPMs.

I saw a comment years ago that a good SU man with a jeweler's lathe could give you any performance profile you wanted.

I won't vouch for the truth

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The guys that understood their differences loved them

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