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Any carburetor experts


86 2dr.ltd

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I recently rebuilt the Stromberg for my old GMC and it runs great,however it is completely gut-less.I suspect it has something to do with the adjustment of the 2 jets at the front of the carburetor.What is it these do? add air or gas?What is the best way to adjust and balance them?One friend of mine has some old meter "thing" you can set dwell and other stuff with.It also gives very precise RPM readings. He told me if I set one screw to its absolute highest idle RPM then adjust idle back down and adjust other screw to highest idle RPM then adjust idle back down and I should have it. Can anyone verify this or have any other "do it me-self" methods.Much appreciated!

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The screws you refer to are the idle air adjustment screws. Your friend is right in that with the meter you can adjust each screw for the maximum rpm, and this should be good. I have found that the best way is to have the car idling very slow, as you will not be able to tell much of a difference if the engine is running above ~750 rpm when you do the adjustment. I usually idle the engine down until it is about to shut off, then come back up slightly. This way, you can "hear' the difference in rpm without a machine. A good starting point is to (without the engine running) turn each screw all the way in LIGHTLY (do not bottom out hard, as the screws have a taper to a point, and you can cut a groove in them if you apply too much force on them on the seat), and then back each out 1 1/2 turns. This should be close enough to start the engine and make the adjustments with it running. If the screws do not make a difference, you either have a vacuum leak, or float height set wrong, or some other internal problem. <P>Apologize for the long post, but took this much to explain.<P>------------------<BR>Boyd Shuler<BR>Orangeburg, S.C.<BR>65 Riviera

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Float height should be good.Would float height cause power loss but still run smooth?I'll tell you what is does.It pulls as good at low throttle but when you push it down it just makes more noise.The only thing that changed was I rebuilt the carb.In other words it had power now it doesnt.<P>478 V6 GMC

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i'm no carb expert, but maybe try looking at the power valve & accellerator pump. Sounds like it could be either one of those, or maybe it's just set to rich (the idle-mix screws are to far out) and it's flooding itself on WOT.<P>Best way I know of to adjust idle-mix is with a vacuum gauge hooked up to manifold vac source. Do what Nail-Head said, set the idlemix screws in lightly seated, back out 1 1/2 turn, start car. If it refuses to start, bump up the idle speed a bit until it starts. Then slowly back down idle speed until it wants to die. Then start the idle mix settings. Turn each screw out slowly until vacuum gauge reading doesn't go any higher, turn in 1/4 turn or so. Do this seperatly for each screw. Then it should be 'lean-best-idle'. Reset RPM to spec and your good to go.<P>If it's idling rough, I tend to play with the timing a lil, just remember playing with timing also changes idle RPM.<P>thats all from here. hope ya get it fixed<P>Still-A-Newbie<BR>

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Although the Idle Air Screws do need to be adjusted they have no affect on the way the engine runs on anything above an idle.(example: the outer carbs on a GM Tri-Power do not have Idle mix. screws only the center does). As for your power problem, do the easy things first. Check linkage to be sure you truly have full throttle when depressed. Make sure the "butterflies" in the carb are opening all the way and that the Choke is not staying closed. If all is OK then its probably time to get back into the carb.Check float level as previously suggested. Make sure you used the EXACT same Primary Venturi gasket/s. (at anything above an idle all carbs run off the Venturi, look at an exploded view in your carb kit instructions to identify this part). Make sure there are no extra balls or springs left over (obvious I know, but check anyway).Kit instructions are usually VERY generalized so you have to be very careful when building a carb to get everything back where it belongs. Last resort: buy a remanfactured carb. thru an auto parts store.<BR>Sorry couldn't be more help!<BR>Good luck <BR>Dale.

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