i just installed the Slayer 600 on my 390 powered truck and had very similar results.  I had to jet down to 66 from the installed 68's (nice that they provide a printout of the intalled parts) and the choke was a bit stiff for the altitude in Denver so I have backed it off as well - these are pretty minor adjustments for altitude for an out of the box carb.  I am very pleased.  I have backed out the vacuum adjustment a turn or two and after I get brakes back on it I am going to do as they suggest which is to continue to back out until a bog is felt and then turn it back in for optimum opening.  It does use the "purple" spring inside and I found that with a relatively light car and a big motor lke you have it may work better (more HP less mileage) with a lighter spring.  But, if it is running great as is, I'd leave it alone.  Quick Fuel seems to make a good product and appears so far to be miles ahead of the competition.  I'm putting the 650 double pumper on my Mustang just because I have never had a double pumper before.

MustangSteve wrote:

After running the 670 Holley on the 427 in my 66, I decided I would try a little bigger carb.  While the Holley ran well (and got 19MPG on the bash trip) it just did not have the punch that the old MSD EFI system had. But at least it did not die out all the time.

I bought the Quick Fuel 750 CFM vacuum secondary Slayer carb and installed it.  It fired right up and idled.  The electric choke was properly set up and functioned flawlessly.  I DID NOT HAVE TO ADJUST ANYTHING.  The carb has huge glass sights for the float level, so I could verify that was set properly.  The choke came off fast idle properly and the carb idled very well.  This was without having to do so much as even reset the idle speed.  After it warmed up, I did reduce the idle setting about 100 RPM to get it right for my engine.

Drove the car and WOW it picked up a bunch of HP.  Really pulls alot harder.  I am  experiencing a slight stumble when accelerating in 4th and 5th gears.  Probably needs a little stronger squirt from the accelerator pump to get it over the initial acceleration.  Otherwise runs good, cruises without any surge.

I'll fiddle with it a bit.  Doesn't look like the accelerator pump lever arm spring needs tightening any, so maybe a slightly larger squirter will do it, or a different pump cam setting.

The main thing I like about this carb over the Holley is the adjustable vacuum advance setting.  Rather than having to change out springs like a Holley, they use a very light spring but vary the rate of opening with a tapered needle screw that just increases or decreases the rate of vacuum it receives.  Very easy to adjust, but it seems to be perfect for my engine right out of the box.

the slayers are killer for the money . . holley still wants $500.00 for a carb they designed over 50 years ago.

just in case you don't know, it stutters/burbles when you hit the gas it is getting too much gas . . if it simply seems like it is out of gas then accelerates it is lean.

also unless you had your engine dyno tuned or properly set the timing yourself, you could be down on hp . . i would guess that you might need at least 28 degrees total at around 2800 rpm with that engine.

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I bought a Quick Fuel 650 http://www.summitracing.com/parts/qft-hr-650/overview/  for the 68 Coupe (5.0, AFR heads, and so on) a couple years ago, and it has been a great performance carb, I love the way the mechanical secondaries hit. The only issue I have had, and I do not claim to be a carb expert in anyway, is it is not that uncommon here in Kentucky to get a 20-40 degree temp swing in a 24-48 hour period (this week is a prime example), and the Quick fuel does not deal with those type of swings too well and requires some adjusting to get it back where I want it, seems as if I am always adjusting the idle 100 rpm's one direction or another.
On a side not, don't laugh, but on my 79 F100 with a 351w, and small cam. I bought a Summit 600, and it has been a great street day to day carb. It reminds me a lot of the Autolite 4100, there are no seals below the fuel level, it cant leak, and it is very resonably priced.
http://www.summitracing.com/parts/sum-m08600vs/overview/




 

slow-poke wrote:

I replaced my Holley 750 DP with a Quickfuel 750, best carb I have used in 35 years.
N/A Street car runs high 10's granny shifting

How bout more details on the engine/drive train!
6sally6