I am running three 97s. On the two secondaries, the idle screws are plugged on the outside, but the rest of the circuit is untouched. I think I need to plug it internally?? And how is the best way?? I can't get it to idle under 1200 or so and I think this is the problem. Thanks, GW
If you just plug the idle mix screw holes on the outside then the tiny holes where the mix screw tips are supposed to be located are wide open. You will have a very rich mix. Just put the screws back in and screw them all the way in.
You can cover the idle passage holes - in the base & the carb - with a small piece of 3-M tape. The gasket will help seal it. If you want to get carried away, you can also bend over the ends of the idle jets with needlenoses and create "plugs".
All this advise is good, but you should be able to get it to idle properly w/o blocking up the carburetors. I'm not a big fan of making Strombergs into "secondaries" or "dumpers". Build them they way they were designed to be run and you should be fine. I just set up 8 on a car and it idles around 800 RPM.
Remember you have TWO circuits of potential tuning use down there. The actual idle circuit can be blocked by simply tightening the screws if you are running progressive linkage with end carbs closed.. The upper hole feeds off-idle and is actually in use beyond 1,000 RPM because jets cannot deliver significant amounts of fuel until there is enough air moving through venturis. Block those off non-destructively...you may find the engine needs them if you have a lean stumble at low speeds. The holes there are bigger than holes in idle jets, so they can be tuned up or down by altering those. No one has looked at fast idle problem...that would seem MUCH more likely to relate to air than fuel. Those holes cannot even feed if air is properly cut off...either you have a leak in manifold/gaskets/hoses (What engine? This stuff is pretty bulletproof on a flathead) or more likely your throttles are not properly sealing. You SLIGHTLY loosen throttle screws, which can be done without trashing the staking, hold throttle bodies up to light, and shake-rattle-roll until you cut off all possible light coming around the butterflies. Gronk screws back down, make a pointy anvil like a punch in a vise, and tighten up the staking a bit with someone to help hold stuff...this is a 3 or 4 handed operation without a custom anvil staking fixture. You cannot make a progressive setup worj right if air is getting in without gas.
And consider this...fiddling with linkage is pretty easy. You might consider checking out the possibility that straight linkage has its points...one of which is that you use all your carb circuits, allowing fairly normal progression of carb function. You still need to address the throttles on all three for this, as you will be looking at TINY openings at idle and any leakage will render the idle system FUBAR.
The engine is a 327. The butterflies are damn good, I did loosen the screws to let them center themselves. No light whatsoever. The shafts on secondaries have very slight movement, but I even sucked on the bodies with my mouth and they seem very airtight. The primary shaft is a little looser, but it seems that it would'nt matter as much, if the air is coming in thru the butterflies or at the shaft. I can seal the top of the rear carb with my hand and the idle does slow down. I have no vacuum lines to leak, But I have used the same gaskets over because I have torn them down a thousand times. I surfaced the surfaces on a glass plate and they all fit tight, but I guess it could stiil have a leak at a the gasket. Right now I can not test to see if the tape did anything, because I had to pull a head off. The head shop did not pressure check and one new valve seat is leaking water.
A 327 has a big displacement advantage that will make it pick up with either straight or progressive much more easily than a 260 flathead! On the other hand, it has a much more complex manifold sealing problem. Rear carb sounds like it somehow has a bad air problem, air with no gas added getting through somehow. Need more coffee. What is going through where back there?? An engine that big might well be a good candidate for straight linkage. Shafts can be temporarily sealed for test purposes with heavy grease to stop air.
I'll try new gaskets and see if that helps. If I do try straight linkage, I will have to remove the lead plugs at the idle screws. Drill and easy out or what?? Gregg
Ditto.....running 4 97's progressive on a SBC and none of 'em are modified for secondary use.....all idle screws are set the same and idles fine at 600.... Set all your linkage up with just the bases mounted to the manifold, that way you can set the butterflies "just right" and ensure everything moves smoothly....then bolt the bodies on.
Get the best idle you can on the center carb with the mixture screws on both ends all the way in. Slow down the speed, then open each end mixture screw 1/8 turn until the motor idles well, and wont stumble at just off idle while pulling the car. Usually 1/8 is all they need. I like to set the float level on each one individually with the top off the carb, and the motor running with the fan not turning. Have a helper stand by with a fire blanket.
You do your melt with ONLY the throttle body...actually, I'd play it safe and just run a small drill through lead and pick out the rest with dental tool. We're dealing with finished parts here. I really think on an engine this big straight is the way to go. Don't EVER let the zinc stuff into a fire...you will definitely not like what you learn about the melting point of that stuff, which is about at the grilled cheese sandwich level.
The Jalopy Journal
