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TOPIC: 1988-1994 GM TBI

88-94 GM TBI 14 Jan 2015 20:07 #1

  • Steve Pawlowski
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Hellow out there! Hey when we do the older GM TBI's, do we use the business card on this type? doing my first one, got the IAC filled. ready to groove. wanna make sure. Thanks

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88-94 GM TBI 14 Jan 2015 21:53 #2

  • Tracy Gallaway
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Hey Pete, I just did one. What I did- is I turned the idle speed stop screw in about 1 1/2 turns, this way the Grooves are cut a bit deeper in the bores. This way, if it turns out it needs a bit more throttle opening to support proper idle speed, the Grooves are properly positioned. This is due to filling/recutting the IAC air channels, will restrict IAC flow. This in turn may not provide high enough idle RPM's, (and will possibly result in too-low cold engine fast idle RPM's.)
The idle air channels can be enlarged a bit to increase IAC flow if needed.

IF you leave the throttles in stock as-driven position, do your Grooves, and then need to turn idle speed screw in to maintain good idle RPM, the plates will be "into the Groove" already at idle- not a good idea.

The business card in the bores trick can do the same thing, I usually just do that on drive by wire TB's. Note that opening the throttle plates before Grooving puts Grooves deeper in bores-the Large bit fit w/ about a fingernail of bore material remaining downstream of Grooves. If the idle speed screw is backed out from where I cut Grooves, then the plates will hit the Grooves just a little off idle, which will work great. I figured all this out without the truck present, done by mail, he's doing some custom mods on his Chevy TBI and induction, should be interesting.

Sorry, not the best pics, I'm no photographer! :unsure:

He filled in all vacuum taps, PCV, MAP sensor vac. well, and wanted the IAC flow to enter further away from the Grooves. If it was a stock TBI, I would have put the IAC throttle bore entry "T" cut direct over throttle shafts instead if thru the MAP sensor vac. well wall. You can either make 2 smaller IAC channels in the IAC fill, or one larger center one w/ the "T" cut to the bores, the T single one is faster, is all.

Tracy G
Tracy Gallaway
Carburetor Coach
Mood Elevator
Gadgetman Reno, NV

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Last edit: by Tracy Gallaway. Reason: more info as usual

88-94 GM TBI 14 Jan 2015 22:26 #3

  • Steve Pawlowski
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Thanks for info.. I have always popped the idle screw cap out as general rule. I have a few xtra TBI's and they all have the caps still intact. I was not sure if I should start anew then pop the caps. Thanks for clearing that up.
One more thing ..you used the largest bit?

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88-94 GM TBI 14 Jan 2015 22:37 #4

  • Steve Pawlowski
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See better with my glasses on Da....tired I guess.. Thanks again

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88-94 GM TBI 27 Jan 2015 07:46 #5

  • Ken Bittle
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Darn you Tracy, you've got me re-thinking my groove again. Maybe I could make it better if I re-grooved it, hmm.... 4th times the charm? Seriously though, if I set the idle screw like you mentioned my actual driving at 1500 rpm would be sitting right in the groove. Going to have to give this some serious thought, it might be worth the knuckle bruises from removing all my magnets on that fuel line.


Ken

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