4pistonkiller

iTrader: (3)

so ive got a carter 500 cfm on a racing beat holley intake, i took the muffler off (still stock) just to see if that would help with the cutting out, but it still does it. anything over ~5200 and it cuts out really bad, like its falling on itself, and im stumped as to what the problem could be. at first i thought it was an ignition problem, but my friend brought up the point that the bowls could be running out of fuel because the floats arent letting enough fuel in. i am fairly new to the carb tuning thing, and would appreciate any help that can be offered.

4pistonkiller

iTrader: (3)

its on a stock ported 12a by the way. i just spent the last hour dicking around with the carb, i readjusted the floats, played with the jets, but it still stumbles on itself (WOT) at anything over 5 grand, going up to 5 grand it works great. i think the size of the exhaust might be part of the problem as well, because the pipe gets smaller and smaller as it goes back, it has two reductions, the smallest of which being right before it goes into the stock muffler, and its like less then 2" ID, more like 1 3/4. it might even be smaller then that, but really guys, 30+ views and no one has anything to offer ? i know im new to the 7 scene but im not new to cars.

peejay

You are using a carburetor designed for a plenum intake, on an independent-runner manifold. What is happening is, the engine is running extremely rich to the point of misfiring because the sharp intake flow (booster vacuum signal - this is NOT manifold vacuum) is far higher than the carb is designed for.

You have two options:

The first, ideal, and most expensive, is to ditch the carb and get a Holley from Racing Beat. They extensively modify them to work properly with their intake manifold. It works very well.

The second, less ideal, but far cheaper option, is to either put an open spacer between the carb and manifold, or buy a four-hole spacer and cut a channel between the front and rear rotors, if you want to keep the primary and secondary separate.

I don't know if I'm the first person to figure this out, but I recommended it to somebody who had your exact same problem (except it was the Edelbrock clone of your carb, and the engine was ported) and he reported huge success. He also only cut a channel between the two secondaries, and left the primaries independent. (Well, it's easier to cut than to put metal back, and spacers are cheap enough anyway)

Putting an open spacer under a stock carb has the opposite effect, it runs incredibly lean at the top end...

diabolical1

iTrader: (3)

Peejay's points are valid, and you should take them under advisement, but first and foremost, what fuel pump are you running?

4pistonkiller

iTrader: (3)

im running a holley red fuel pump, and a fuel pressure regulator set at just under 6 psi... this all does make alot of sense, as the car is getting horribly cruddy gas mileage (i just filled up for the second time, and i was getting barely over 12 mpg... i will try the open spacer idea... any chance the exhaust could be part of the problem ... ?

peejay

I made 170whp through a stock 12A midpipe, and my 13B pulled cleanly past 9k, so... no.

4pistonkiller

iTrader: (3)

ok, i got a 1 inch open plenum spacer put on the car today, and it runs so much better now, it pulls hard all the way to the top, and i can already tell that my gas mileage is getting better. it seems to have a slight hesitation at ~6500, but its only intermitent so im not really worried about it, i got my racing beat custom header kit today, so im going to be working on that here pretty soon.

peejay

4pistonkiller

iTrader: (3)

then i took the car racing tonight, broke into the 15's (blek) and my coolant seals are now barely hanging on, so i need someone close to portland that has a good running 12a, or a 13b, but i would prefer a 12a so i wouldnt have to get a whole nother intake and exhaust system.

speedturn

iTrader: (1)

Are you new to rotaries? If so, you need to know that you must not run them hard until the water temperature comes up. If you run them hard when the engine is not warmed up, then you will warp the motor housings, and your water seals will fail. Warm them up thoroughly before racing.

4pistonkiller

iTrader: (3)

yeah im new to rotarys but im not new to cars and i never beat on anything before it warms up.

84stock

iTrader: (5)

Can you tell us what you are using for an air filter? The open spacer is the ideal solution for the edlebrock! An edelbrock or carter is an ideal daily driver/performance carb for a rotary. One more "CRITICAL" question, what did you do about the omp?? Are you premixing?

peejay

The Carter/Edelbrock is a pretty crappy carb IMO. When they work right, they work great, but they aren't as tunable as a Holley. And, compared to a good Holley-pattern carb (Quick Fuel) they are absolutely rubbish...

4pistonkiller

iTrader: (3)

im using a k&n 3inch v8 style air filter... and that is a mighty pretty blower setup

84stock

iTrader: (5)

Good choice on the air filter, and thanks. Speaking from "experience", nothing wrong with a well tuned edelbrock/carter. Get the tuning kit with all the assorted metering rods and add a wideband so you can tune it right in. It is very tunable, you just gotta know what you are doing. Back when I was running the edelbrock on my camden I had a pair of metering rods adjusted on a jewelers lathe to dial the fuel curve in to work right with the blower.

peejay

You can get the fuel curve roughed-in a little more nicely than with a Holley, but there is essentially nothing you can really do for transition, which is super important for drivability. The best you can do is cover over it with excessively rich jetting, which sucks in different ways.

Like I said, when they work, they work great, but when they don't work, there's not much you can do for it. I've driven some that felt like a Q-jet, and I've driven others that had me tearing my hair out trying to get it to not stumble and bog. (Hmm, like a Thermoquad)

84stock

iTrader: (5)

Do you know how to adjust the accelerator pump on an edelbrock? As for the fuel curve, that is dialed in with the use of springs and differing metering rods. They function the same as a power valve on a holley except you have the ability to change jetting and primary fuel curve without opening up the carb and draining fuel. As far as transitioning with the secondaries, the thunder series is completely adjustable with the turn of a screw. With the thunder series you get the best advantages of both mechanical secondaries and holleys vacuum secondaries without opening up a diaphragm and changing springs.

At 47 years of age I've been around the block with them all on everything from big blocks to rotaries. I have a huge range of carbs sitting in my garage. Everything has it benefits and weaknesses. My area of weakness however is with the weber side drafts and down drafts, closest I've been to anything like them was the su's on my 240z a long long time ago before many of you were even born.

4pistonkiller

iTrader: (3)

next blower fuel question, whats the limit of what i could expect to get with a 13b on 92 octane pump gas, as thats the highest we have here, before i go to race gas or methanol. im thinking blower on a bridgeport, i can get bridgeported irons for $300 and go pick them up, i have a good 13b 6 port core motor in the garage, and i have money, so thats not a problem. ive never done any port work or anything, and i really dont know what to expect in terms of the limits of how much power i could make, my aim is 475, but would appreciate any input from people that have experience with something around this combo... thanks...