Ahoey
Well-Known Member
Takes all the same power valves and jets as a regular Holley sight plug for adjusting fuel level nice feature carb fit and finish really nice and works well easy to tune
Issues with a rebuilt 360
- Thread starter Owen Diaz
- Start date
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Ahoey
Well-Known Member
forgot to mention the electric choke which works well also
750 street demon works great on my 360/426 stroker , even the electric choke works on it . bolted it on and it started right up , took very little adjustment to get it running perfectly . will not use a holley ever again on a street driven car , for a track only car yes they work well . maybe my cam is much smaller than yours and that is the reason the street demon works for me
good luck whatever you decide
good luck whatever you decide
Ahoey
Well-Known Member
But for a street car thee old thermo quad 780 is a tuff carb to beat. Ya it’s not a Holley or a demon but it performs and works well I didn’t use it because the secondary’s wouldn’t clear my wieland intake manifold. But there is a strip kit available with multiple jets and metering rods for tuning non metallic float bowls for cooler gas bonus
Owen Diaz
Well-Known Member
Ahoey
Well-Known Member
Y
Ya the Holley will work fine if you have one. If your driving it on the street and buying new the Holley quick fuel hr750 double pumper with 4 corner idle is a better choice. The old Holley is a good WFO carb kind of lacks on the mid range. The quick fuel has an electric choke nice feature and works well jets power valves interchangeable from old Holleys I had an 800 straight bore on mine when I had the 12 to 1 pistons in it and like I said v good WFO carb experiment they put a 780 thermo quad on it stock
Ahoey
Well-Known Member
The vacuum secondary’s might give you a problem depending on how much vacuum your engine makes. Go mechanical much easier to setup. My cam barely makes enough to operate the power brake.
Ahoey
Well-Known Member
Had to change power valve in quick fuel to a 6.5 as it was a 2 digit number can’t remember what it was exactly but engine over fueling now runs drives idles in gear (727)
Ahoey
Well-Known Member
Ignition timing becomes an issue with higher lift cams be careful total advance no more than 38 degrees at 3000 or BAD things will happen. May need to run off mechanical in disc and crank to get it to idle properly no vacuum advance. So crank will be probably in the high teens
yellow rose
Overnight Sensation
Ok, I have to ask...what did you change? You went from a XX.5 power valve to a 6.5???
Asking for a friend.
Ahoey
Well-Known Member
Ahoey
Well-Known Member
Gon
Ahoey
Well-Known Member
Gone to northern mb hunting 360 miles from no where talk 10 days
mygasser
Well-Known Member
that's not how vacuum secondaries work, they work based on vacuum at wot. your brakes work on idle vacuum which as you say drops off with a 'bigger' cam.
neil.
Ahoey
Well-Known Member
Stand corrected. But mechanical secondary’s are still easier to set up and basically fool proof
Ahoey
Well-Known Member
Yes that is what I did check u vacuum at idle and adjust power valve according to vacuum my valve was opening at idle and over fueling
yellow rose
Overnight Sensation
Just an FYI. Setting power valve opening by using half idle vacuum is not the correct way to do it.
Also, the power valve can be open at idle and it will not affect the A/F ratio. I’ll go and see if I can find the video that proves that.
Ahoey
Well-Known Member
Well changed it and no more black pipes or watering eyes and it will actually idle now below 1300 rpm. So unless I tightened up a loose gasket or jet or something
yellow rose
Overnight Sensation
I looked for that video I mentioned and I can’t find it.
Maybe @Mattax can dig it up and post it.
Setting power valve opening the way you are doing it makes the carb much harder to tune. And if you do correct your power valve opening, you’ll need to fix the other stuff that changes with it. At a minimum you’d need T slot restricters (you most likely need them anyway) and you’ll need to clean up the idle circuit.
@Mattax ??????????
EDIT: 12many did a really great write up about his tuning of power valve opening. It’s in the fuel and air forum. That should be a sticky.
Lets clarify this.
Vacuum secondaries get their vacuum signal from velocity of the air flow. On some carbs this is amplified slightly by a tube with a angled tip in the primary side.
There is a connecting passage into the secondary side. At first this bleeds off the effect on the vacuum diagphram, but once the air is flowing in the secondariy side, it increases the pressure drop.
Much more detail here. Read all the pages. Lots of info in there.
Vacuum Secondary Diaphragm Signal Tube
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You could have. I've had PV gaskets split and also found the wrong ones for the type of PV (window style or holes).
Or it possible the PV opening was effecting idle. It shouldn't but can. One way to picture this is if the IFR is large and the main jet is small. Then the jet will effect flow at idle. But my understanding is it also happens with other combinations of tuning IFRs, jets, throttle position etc the effects the pressures in the wells.
As yellow rose mentioned, Jmarkaudio has a video demonstrating that opening the PV on a decently setup combo normally has zero effect on the idle.
Here: Follow this and if tapatalk popup askes you for anythoing just close the popup.
Effect of an open or closed PV on idle
In this post are two links to more technical explanations.
Need help tuning Quickfuel carb
yellow rose
Overnight Sensation
Still haven't found where we posted Mark's video so it showed up in a FABO post. I know I did that at least once.
edit. Found one
Air/ fuel tuning
You need to take a wood broom handle and go beat the **** outta the guy that built that thing. Then take your money back.
yellow rose
Overnight Sensation
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