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rkmjbad67

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Discussion starter · #1 ·
I just replaced my 650DP with a 750 annular main body, but I used the 650 metering blocks, carb runs strong if you ease into it, but on a quick stab of the throttle--it almost dies and when I come to a stop sign, same thing, does that sound like the float level is off, and it real gassy at idle.
 
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#2 ·
The throttle plates are the same for a 650 & 750, so you essentially built a 750DP carb.

It is pretty big for a 327, but it looks like you should have enough gear & converter to make it work.

You likely have to work with your accelerator pumps to carry it through the full throttle transition. You can work with different pump cams & squirters to make it work. Holley sells a cam kit & squirters individually. Read up on tuning of these carbs.... there is a lot of info on the net.

Your idle problem can be caused by a high float level or possibly the primary throttle plates are open too far pulling fuel from the boosters at light throttle.
Opening the secondary plates slightly can allow less opening of the primary idle speed screw.
 
#3 ·
I would add that metering plates do not interchange from one size carb to another. Just because they bolt on doesn't mean it will mix the correct amount of fuel to the air flowing through it.

You can modify one to fit another carb but it is better unless you have a drill press (or the grip of Arnold Schwartzenegger who can hold a metering plate in one hand and drill motor in the other) to just buy an aftermarket metering block for the cfm you have now. As an additional incentive they are also usually anodized to resist the affects of alcohol on your carb. The emulsion tubes and air bleeds need to be reworked to match the increase in carb air flow.

Big Dave
 
#4 ·
A 650 would have been fine and easier to tune with no loss of power. A 600 even better. With the 750 it means bigger venturi so the gas does not mix well at idle. If most of your driving is at high rpm then the 750 would be great but normal street driving the 750 is just too big. Just my opinion though.
 
Discussion starter · #5 ·
carb started out as a 600 DP, baseplate was broken, had the 600 main body machined to match a 650 baseplate. Thought maybe the 750 annular would give throttle response with the annulars and top end with 750 main body, I know the annulars hurt top end some, once I get it adjusted I think it will be good, once I get past the stumble---night and day difference.
 
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#6 ·
Annular boosters will be very forgiving as far as a 650 cfm being upgraded to a 750 cfm on a 350. Usually a street driven 350 would be much happier with a 650 while a track driven 350 wants a 750 to 850 carb depending upon how high you can spin it and still make power. Annular boosters are used on the Dominator series of carbs with their trash can sized throttle bores because once flipped open air flow is a bit weak and the annulars do a better job of atomizing the fuel with poor air flow than the down leg or straight booster.

Big Dave
 
Discussion starter · #8 ·
If I cant get it to run with the annular body, I can always switch it back, lol
 
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#9 ·
rkmjbad67 said:
If I cant get it to run with the annular body, I can always switch it back
Click to expand...
I went through the same thing but with an HP main body and 4778 (700 cfm) metering blocks and base plate. Never could get it to run right - crappy idle, stumble, ect. Messed with different metering blocks and air bleeds - finally gave up and put the 4778 main body back on, put it back to factory calibration and it works perfectly. Best of luck to you!
 
Discussion starter · #11 ·
when I sent my engine specs to pro systems, just to see what they would suggest, they replied back with a 720 cfm annular carb.
 
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Discussion starter · #12 ·
Also had a 575 speed demon carb a few years back, that had annulars, that carb was so snappy, but the engine was a lot milder back then. Thought about installing annulars in the 650 main body, but thought the venturi would be to small with the annulars. Quick Fuel makes a nice 650 cfm annular carb, but its pricey.
 
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Discussion starter · #14 ·
Finally got this annular carb lined out and all I can say is WOW, it pulls and hits so much faster and harder!!! It has both throttle response and top end power.
 
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Discussion starter · #16 ·
Took front float bowl off and pri metering block and was removing the power valve, decided to replace it just to see and the power valve gasket was torn in half and falling apart!!! Replaced power valve and blew everything out, started it back up and let it warm up, float levels were close, maybe just a hint low. I still have to set idle mix with the car in gear, but I like the way it pulls, a lot more top end than before.
 
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bigblockragtop
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