Best and easiest Carburetor for tunability???
Thread Starter
Drifting
Joined: Aug 2001
Posts: 1,606
Likes: 14
From: Vacaville, CA
Best and easiest Carburetor for tunability???
Engine guys, what is your opinion on the best Carb for tunability?
Have a 383 with a Holley 650 and mechanical secondaries. When you step on it the car stumbles, hesitates then rumbles ahead.
Was considering upgrading to a QFT 680.
Link;
https://www.summitracing.com/parts/qft-ss-680-vs
Any thoughts?
Have a 383 with a Holley 650 and mechanical secondaries. When you step on it the car stumbles, hesitates then rumbles ahead.
Was considering upgrading to a QFT 680.
Link;
https://www.summitracing.com/parts/qft-ss-680-vs
Any thoughts?
Advanced
Joined: Dec 2011
Posts: 65
Likes: 10
From: FL
Hard to say without more info, it could be a variety of things that aren't properly tuned on your current carb. Possibly the accelerator pump out of adjustment, clogged fuel filter/ lack of fuel pressure, floats not adjusted properly/ needles not clean or seating properly/ bad O-rings/ vacuum leaks.
I have the quickfuel carb you have posted in that link and I love it. I have a custom built 350 unlike your 383, but it is still a great fit for the motor around 400hp. I'm more of a vacuum secondary fan versus the mech. secondary which that carb is equipped with. As for tunability, the quickfuel comes preset out of the box to get the motor running and you can get it pretty dialed in relatively quick. You can also get a variety of vacuum secondary diaphragms to adjust your secondaries opening speed.
Some guys are strictly Holley style carb fans, but I've also had good luck being able to fine tune the Edelbrock 1405/1406 series carbs I have on another 350 motor. They can be fine tuned with various spring sets rather than float adjustments like a Holley would be.
I have the quickfuel carb you have posted in that link and I love it. I have a custom built 350 unlike your 383, but it is still a great fit for the motor around 400hp. I'm more of a vacuum secondary fan versus the mech. secondary which that carb is equipped with. As for tunability, the quickfuel comes preset out of the box to get the motor running and you can get it pretty dialed in relatively quick. You can also get a variety of vacuum secondary diaphragms to adjust your secondaries opening speed.
Some guys are strictly Holley style carb fans, but I've also had good luck being able to fine tune the Edelbrock 1405/1406 series carbs I have on another 350 motor. They can be fine tuned with various spring sets rather than float adjustments like a Holley would be.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
650 and 383 should be instant on. It should be very easy to adjust following any manual like "how to adjust Holley carbs"
I'm not going to type out..................... because it is all on the internet
I'm not going to type out..................... because it is all on the internet
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Save your money and tune your 650. I have the same carb and tuned out my hesitation by increasing the squirter size on the primary. But before you start to tune a carb, make sure your ignition and timing is spot on or you'll just be wasting your time fiddling with the carb.
Instructor
Joined: Jun 2015
Posts: 193
Likes: 34
From: Ohio
I could not for the life of me get rid of a cruising speed lean condition on my new 650 Edelbrock. Messed with many different combinations of springs, jets, and metering rods. Took it back to Summit for a full refund and got their 600 cfm Holley knock-off and it ran great out of the box. This was on my ATK 357 crate motor.
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Pro
Joined: Jan 2016
Posts: 502
Likes: 103
From: Reno Nevada
Your question was what carb is easiest to tune. Hands down the Holley is the easiest to tune IMO. Note that this is a double edge sword though. Easy tenability, means it needs to be tuned all the time. A holley will run great if you spend the time to tune it, and they are easy to tune. However if you are after a carb that you don't have to tune depending on the weather conditions or time of year, then an Edelbrock or honestly the original Qjet is tough to beat. All of these have to be tuned initially.
Don't think you can get something out of the box, slap it on and have it perfect right out of the box. It is possible this could work, but unlikely.
Save your $$ and tune your holley that you already have.
Don't think you can get something out of the box, slap it on and have it perfect right out of the box. It is possible this could work, but unlikely.
Save your $$ and tune your holley that you already have.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Your question was what carb is easiest to tune. Hands down the Holley is the easiest to tune IMO. Note that this is a double edge sword though. Easy tenability, means it needs to be tuned all the time. A holley will run great if you spend the time to tune it, and they are easy to tune. However if you are after a carb that you don't have to tune depending on the weather conditions or time of year, then an Edelbrock or honestly the original Qjet is tough to beat. All of these have to be tuned initially.
Don't think you can get something out of the box, slap it on and have it perfect right out of the box. It is possible this could work, but unlikely.
Save your $$ and tune your holley that you already have.
Don't think you can get something out of the box, slap it on and have it perfect right out of the box. It is possible this could work, but unlikely.
Save your $$ and tune your holley that you already have.
Holley is as easy as it gets. That is why it is so popular with racers. You could change jets between passes.(At least when I was a kid).
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
Save your money and tune your 650. I have the same carb and tuned out my hesitation by increasing the squirter size on the primary. But before you start to tune a carb, make sure your ignition and timing is spot on or you'll just be wasting your time fiddling with the carb.
I would add that your problem could very well be with the accelerator pump diaphram. They wear out over time and when they do you won't get a full shot from the pump. These are cheap and easy to replace. I replace them every year because the new fuel degrades them quickly these days. I'd do this before changing the squirter or anything else on the carb. This year for the first time I spent a little more on the type I've linked below. These green ones are designed to stand up to the alcohol in our fuel these days and they should last longer. The old black ones were designed before alcohol was blended into our fuel.
https://www.summitracing.com/parts/hly-135-10/overview/
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
Holleys are easy to tune, but I have rarely ran into one than was tuned properly.
The most common mistake I find is the power valve is set to open to late (small number) making a lean spot between cruise and wide open, the crossover between where you cruise and start asking to make power. Most of the time people cover it up with larger main jets making the cruise too rich or larger nozzles for the accelerator pump or both. Either is just plain wrong.
Holley is to blame for most of this because of their instructions to use half the idle vacuum as the power valve number. They tell people to do this because it is easier than trying to explain how to do it properly. If you use a wide band and a vacuum guage it is easy to see that is not how to tune it.
Mike
Mike
The most common mistake I find is the power valve is set to open to late (small number) making a lean spot between cruise and wide open, the crossover between where you cruise and start asking to make power. Most of the time people cover it up with larger main jets making the cruise too rich or larger nozzles for the accelerator pump or both. Either is just plain wrong.
Holley is to blame for most of this because of their instructions to use half the idle vacuum as the power valve number. They tell people to do this because it is easier than trying to explain how to do it properly. If you use a wide band and a vacuum guage it is easy to see that is not how to tune it.
Mike
Mike
Le Mans Master
Joined: Oct 2007
Posts: 7,462
Likes: 985
From: RI, Now Franklin/Nashville TN
Holley by far...there is no such thing as a carb that does not need to be adjusted based on weather conditions, I don't care what it is...That is why they have fuel injection...
Le Mans Master
Joined: Mar 2001
Posts: 5,741
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From: Lincoln, CA