i have 2 97s and one 81 strombergs with a offenhauser intake can i use the 81 as the middle carb and the two 97s on the outside or do i need three 97s its on sbc
Three 97's - with straight linkage - on an SBC will get you there - barely. 81's don't have a home on SBC's, unless you're running six of 'em.
That's a bit better, instead of 125 cfm something like 170 or 190 i forget which So it should work fine, as long as it aint too big of a SBC Probably be better off with 3 48's like i'm going on my 283, but should still work good
its a stock 305 with Edelbrock PERFORMER PLUS CAM offenhauser intake so i should run straight linkage and not progressive and run the 48 as middle carb? and with straight linkage its very important to sinc carbs?
I've got 3 97's on a 305. The center one is about 80% open before the outers. I'm getting 20mpg. I open the outers once in a while, but it runs mostly on the center just fine. Its not the best for power, but I've had issues getting the idle back down when I open all 3.
Dog Patch..Two things, your return spring is not closing the throttle plates or your you have your air/fuel screws open. Secondaries don't idle, the primary does it..I think it's you throttle plates no closing.. Duane.
I was having a similar conversation tonight with 29Jay about his 318 Poly - the only way he can run those Ford (pre-Holley) 94s progressive is to make the outboards primaries, and the middle the secondary. This comes from an earlier conversation I had with Jon (carbking). My analogy? Nobody likes to drink a Coke through a coffee stirrer. LOL! ~Jason
I'm not talking power - that carb just doesn't let enough air through to idle anything but the 239 it was intended for. It would be like taping your mouth shot and only breathing through one nostril! ~Jason
I have a 350 with a rebuild two years ago to 350HP with about 8 thousand miles ago. First when I got it had a holley 600 it ran good, then an edelbrock 600 ran good and idled better but not quite as strong as the holley. This winter I put on 3 97's with progressive linkage. I have the middle hit 50 percent then the outers bell crank is half the length of the middle so they "cam" over twice as fast and all 3 are WOT at the same time. Know I think it is the fastest it has been. The problem is I believe the cfm is only 140 per carb, so in theory it shouldn't be as fast but the kicker is halving the accelerator pumps on the outer carbs and not waiting for vacuum secondaries to kick in. It rips ass and gets great milieage as well. It is on my 30 sedan
It is the outters not closing all the way. I jump out at a light and shut them by hand and its back to normal idle. I need to hook a spring to just those guys. The linkage for the center is what is trying to close them now and its not working too well.
The 81 was made for 60 hp v8 there is not enough air flow for a sbc so you would be running to rich at lower speeds.
There's really no effective way to "close" the secondary carburetors. Even with the throttle disc closed there's still vacuum under it, and this will still draw fuel from the idle and transition ports. It's probably possible to block these ports, just find where they feed from and insert a piece of lead shot, wire etc. If possible, tap the hole and use a small grub screw like 6-32 etc. so you can get it out.
Both the Edelbrock and the Weiand could be ordered with either the 3 bolt or 4 bolt patterns. The Offy didn't list a 3 bolt intake in my 1961 catalog. Before the nostalgia craze I picked up a 3 bolt 3deuce intake cheap and then just redrilled it for the Rochesters.
smaller carb will give more torque, but lower your peak HP RPM, in otherwords burnouts will be easier, but it wont have the umph at speed
panic, your right, but befor I go blocking or taping a hole I would just try closing the air/fuel mixing screws, that will shut down the idle screws. You can take the idle jets and plug them, then screw them back in..I find just closing the air/fuel mixing screws works just fine. The primary 97 will be the idle. Yes, the secondaries need a return spring, also, put a collar on the inside of the progressive rod and when the primary starts to close it will push the secondaries close also..Does that make sense..OH, also get the Stainless falcrum springs and this will also help. Duane.
You can block the fuel. but the vacuum is another story. Some folks do the valve lapping compound trick, where they put it in the bore of the carb and work the throttle shaft until the butterflies wear into the bore just enough to seal worth a damn. Still, others water down some JP Weld with a common substance (I forget what it is now), and dab the inside of the bore, let it set up a bit, close the butterflies against it, then let up and let it dry, so they seal halfway worth a damn. This is usually done on secondary carbs. Stop the air, and you effectively stop the fuel coming through the idle circuits as there is no suction (negating plugging them). And therein lies the rub. ~Jason
The final test is whether you can get the disc far enough closed that the idle port is no longer below the edge. In some carburetors, it's simply too far down and must be dealt with separately. Some adjusting screws are intentionally made with not enough range (thread length) to bottom out and completely close the passage - because they don't want it done by accident, and to preserve the tapered surfaces. Some throttle shafts have stops built in so that the disc is still at 5° even with the speed screws removed.
LMAO! You make it sound so easy! But yeah, those adjusting screws like that really piss me off. I've also run across the throttle shaft stops, too... with a similar reaction. It's like people just DON'T want me to use their carbs in a multi-configuration! Dicks... ~Jason
We Harley-Davidson owners have seen a useful trick employed on the Linkert M88 carb. Fixed main jet, and they disabled the high-speed adjusting needle by using a dummy. It's threaded, looks normal - but the bottom is a blunt flat end, which simply closes off the passage completely. The actual port is almost always smaller than the needle diameter. If this isn't practical, file off some of the underhead bulk of the needle, remove the spring, etc. so it seats deeper and reaches the bottom of the tapered seat. Alt: find a longer needle.
Hey, rotgg. Start with the linkage connected to center carb only. Fab auxillary springs on end carbs to keep them closed, so that they are assured to be closing off when the center carb is at idle (and above), up to about 1500/1800 rpm where you will be setting the progressive linkage to take effect. Back off all the idle speed screws. Turn all idle mix screws full in, then out 1/2 turn(1/2 might be a bit rich with all screws at that, but it's a start, if it smokes, crank tham all in an equal amount). Crank it up. Adjust idle speed/mix with center carb. Experiment on end carb idle mix screws to tweak for smooth(er) idle. You will find in almost all cases you can get a smoother idle by adjusting idle mix on end carbs somewhat. Never open end carb idle speed screws, leave the butterflys closed at idle. You will find that (whatever) the cfm is, the motor will run great up to a point where the flow in the center carb is max'd out, probably somewhere between 1500 to 2500 rpm. (I'm guessing with your situation in mind). Eyeball the position of the throttle-arm when the motor is accelerated up to a static 1500/1800rpm. Hold it there for a moment and get a good fix on that position. Generally you will be shifting into 2nd gear after comning off a dead stop (Sunday drive-moderate) accelleration. Connect the end carbs to progressive linkage where they start opening(together) just above that point. 1500/1800 rpm is just a starting point, to where on normal-normal accelleration/shifting from a dead stop the end carbs don't come in. That results in a glitch-free sunday drive, but they are laying there ready to open up when you stand on it. For stumbling, stalling/loading up, backfire, etc. etc. , leave the linkage settings alone, those problems are usually attributed to timing/advance, or a combination of, including jetting and accelerator pump function.
I love the M88! I'll always not buying the crate full of those rusty, but salvageable, heavy-ass carbs, for $50 a few years back... I had delusions of running 8 of 'em on a 318 Poly, but talked myself out of it. Not to get this thread too sidetracked! LOL! ~Jason
The Jalopy Journal
