1985 GMC S15 fast idle

Tiny
PULLMYEFINGER
  • MEMBER
  • 1985 GMC S15
  • 2.8L
  • 6 CYL
  • 4WD
  • 112,000 MILES
Above mentioned truck won't go into fast idle anymore. Takes about 15 minutes to warm up vs 5 minutes before. Nothing changed other than a mechanic changed the float cuz it was wasting gas out the exhaust? Electric choke is getting 11.91v, we repositioned it. Choke plate does move a tiny bit when you start it like it should, but just sits there idling like nothing else is connected. If you try to give it gas it surges and will stall very quickly. I remember running it for 25 minutes and the choke plate never moved past barely open. Any ideas? You are talking to a new enthusiast that knows next to nothing, so if you can send diagram links or explain things in more detail that would help a lot. Carburetor is 17084362 Rochester varajet 2.8L 2bbl. Thank you.
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Saturday, March 8th, 2014 AT 12:04 PM

12 Replies

Tiny
CJ MEDEVAC
  • EXPERT
. AND THE CHOKE FULLY OPENS WHEN IT DOES FINALLY WARM UP?

HAS ANYONE MONKEYED WITH THE HIGH IDLE ADJUSTING SCREWS?

HAD THE CHOKE COVER BEEN ROTATED ANY?

MAYBE YOU DON'T KNOW WHAT THE OTHER FELLER DID. SOMETIMES IT'S A BLUR IF YOU ARE NOT ON TOP OF THINGS

IF YOU HOLD THE THROTTLE OPEN A LITTLE. CAN YOU PUSH THE HIGH IDLE IN PLACE WITH YOUR FINGERS. THEN LET GO OF THE THROTTLE

YOU ARE PROBABLY CHOKED NOW. PUSHING THE THROTTLE AGAIN SHOULD RELEASE THE HIGH IDLE. IS ALL OF THIS OCCURRING?

MAYBE I CAN TALK YOU THRU THE SET UP

DO YOU SORTA SEE HOW THE STEPS MOVE INTO PLACE?

HAVE I TOLD YOU I REALLY LIKE THEM MANUAL CHOKES.I LIKE BEING IN CHARGE. NOT A SPRING!

THE IDLE STEPS STILL WORK WITH A MANUAL CHOKE

I HAVE 5 OR 6 PICS OF MY MANUAL CHOKE, IF YOU WANNA SEE 'EM

THE MEDIC
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Saturday, March 8th, 2014 AT 4:58 PM
Tiny
PULLMYEFINGER
  • MEMBER
15 minutes, and the choke never fully opens. I could try the throttle and the fast idle cam but I don't know how many settings there are and which one is high med run. Is the bottom one closest to the carb base the high setting or what? You have to realize I know NOTHING about this. We did put 12v to the chose to make sure it operated, then positioned it on the grooves and tightened it down. The lever inside is supposed to be at 12:00? Never messed with the fast idle screw or the one on the base of the carb. What does that do (the one on the carb base?).

I would appreciate being walked through the steps, I need this thing working two weeks ago and everyone thinks they are a carb expert. I am still stuck.
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Saturday, March 8th, 2014 AT 5:48 PM
Tiny
PULLMYEFINGER
  • MEMBER
Nobody messed with the idle screws other than a couple years ago the idle on the carb base was turned down because it idled so fast during operation. Forgot about that, but the choke ran fine afterwards for a year or two. Have always gotten lousy mileage with this carb because the other people that worked on it only rebuilt the carb. The previous owners did not know what they were doing so I keep having to pay for their mistakes. Truck is supposed to get 16/21 epa ratings but was getting as low as 8 or 9 around town and max 13 on the highway. Now 13.5 city due to the float being repositioned. Again, I know next to nothing about vehicles, and had to learn on my own due to some very lazy mechanics. Good thing I have a 96 Cadavalier that is fuel injected and doesn't give me problems. Yes, please do walk me though the fix for this.
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Saturday, March 8th, 2014 AT 7:40 PM
Tiny
CJ MEDEVAC
  • EXPERT
OK

JUST LOOK THIS OVER---THE PICS MAY MAKE YOU UNDERSTAND THE BI-METAL SPRING----THIS IS MORE "MANUAL CHOKE RELATED"START AT "JAN 10 2014"

http://www.2carpros.com/questions/1976-ford-f-250-truck-wont-start

THEN READ THIS STUFF

I WILL "ASSUME" THE IDLE STEPS ADJUSTING SCREWS AIN'T BEEN MESSED WITH

'JUST 'MEMBER THIS

IN ORDER FOR THE STEPS TO MOVE (ON OR OFF) THE THROTTLE MUST BE MOVED A LITTLE.....EITHER WITH YOUR FOOT ON THE PEDAL OR ACTUATE THE LEVER ON THE CARB WITH YOUR HAND

THE BI-METAL SPRING DOES THE REST--WHEN IT GETS HOT OR WHEN IT GETS COLD.....THE SPRING WILL MOVE THE IDLE STEPS AND THE CHOKE PLATE WHEN THE THROTTLE RELEASES THE LINKAGES.....SOMETIMES YOU CAN HEAR 'EM CLICK WHEN YOU PUSH THE PEDAL

IMPORTANT TO KNOWWHEN THE CHOKE PLATE IS FULLY CLOSED---THE HIGHEST IDLE STEP WILL BE IN PLACE....I DON'T KNOW WHAT YOUR SUGGESTED "HIGH IDLE SPEED" SHOULD BE.......ON MY '77 JEEP CJ 5 IT'S SPOTA BE 2000 RPM (TO ME, THAT'S TOO HIGH, SO I HAVE IT AT ABOUT 1500 RPM)

AS IT WARMS UP, AND YOU TAP THE PEDAL FROM TIME TO TIME, THE CHOKE PLATE OPENS GRADUALLY AND YOU DROP ONTO LOWER STEPS......TILL IT AIN'T ON ANY AND IT WILL NOW RUN ON REGULAR OLE IDLE SPEED!

WE WILL ADJUST ALL OF THAT LATER......WE ARE HOPING IT IS STILL ADJUSTED RIGHT

RIGHT NOW, LET'S ADJUST THE CHOKE COVER, THEN SEE IF IT ALL WORKS OUT
.
.
.

WAIT TILL THE ENGINE IS STONE COLD

LOOSEN THE CHOKE COVER'S THREE SCREWS (BLACK COVER [MOST OF THE TIME]...SOME DO NOT HAVE SCREWS, YOU CAN TWIST THE COVER WITH YOUR FINGERS

ACTIVATE THE THROTTLE (EITHER THE PEDAL OR DO IT AT THE CARB) HOLD IT OPEN THE WHOLE TIME

ROTATE THE CHOKE COVER, AS TO FIGURE OUT WHICH DIRECTION OPENS IT OR CLOSES IT

WITH THE THROTTLE HELD STILL OPEN

ROTATE THE COVER TILL THE BUTTERFLY LIGHTLY CLOSES----DO NOT KEEP GOING AND PUT TENSION ON IT!!!! JUST MAKE IT FULLY CLOSE....BUT BARELY!

THEN TIGHTEN THE SCREWS ON THE COVER

WHEN THE BUTTERFLY IS FULLY OPEN THE "STEPS" SHOULD NO LONGER BE IN PLAY----YOU ARE RUNNING ON "NORMAL CURB IDLE" ONLY

.................................DO YOU UNDERSTAND WHAT I MEAN?

NOW THAT YOU ARE ADJUSTED, I'M PRETTY SURE YOUR STEP SETTINGS .......AND CHOKE OPENINGS WILL ONLY CHANGE WHEN:

TEMP RISES.........AND YOU ACTUATE THE PEDAL (THIS TURNS IT LOOSE TO OPEN) TAPPING THE PEDAL FROM TIME TO TIME (WHILE DRIVING) THE CHOKE SHOULD FULLY OPEN AND THE IDLE DECREASES DOWN TO CURB IDLE

WHEN YOU PUT HIM UP FOR THE NIGHT---THEN GO TO AWAKE HIM IN THE MORNING

........................CAREFULLY TAKE THE BREATHER OFF (WITHOUT TOUCHING THE THROTTLE) ......THE BUTTERFLY SHOULD BE OPEN (IF IT'S LIKE I THINK).........IT'S "COLD"........ACTIVATING THE THROTTLE SHOULD LET THE BUTTERFLY "SLAM SHUT" (YOU MAY HEAR THIS, WITHOUT TAKING THE BREATHER OFF, WHILE SITTING IN THE COCKPIT....READY TO GO

YOU PARKED IT YESTERDAY FULLY OPEN---THROTTLE WAS NOT MOVED DURING THE NIGHT

NOW IT'S MORNING--YOU TOUCH THE GAS PEDAL AND THE CHOKE SLAMS CLOSED

.........THE WARM UP PROCESS STARTS ALL OVER

DEPENDING ON THE TEMP, YOU MAY HAVE TO TWEAK THE COVER AND BUTTERFLY CLOSING TO GET IT JUST RIGHT

YOUR TURN

THE MEDIC

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Saturday, March 8th, 2014 AT 7:51 PM
Tiny
PULLMYEFINGER
  • MEMBER
That's fine, but as I said I don't know which notch on the fast idle is the Highest Setting. All this is based on knowing the idle cam steps, right?
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Sunday, March 9th, 2014 AT 1:12 AM
Tiny
HMAC300
  • EXPERT
Check t o see if linkage I s hooked up and clean all of it with choke cleaner. Might not be hooked up or cheoke pulloff is pulling it off to far.
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Sunday, March 9th, 2014 AT 8:20 AM
Tiny
CJ MEDEVAC
  • EXPERT
I'M NO WRITER

BUT THE SITE DOES MESS ME UP SOMETIMES. CRAMMING WORDS TOGETHER. TAKING OUT MY HYPHENS. ADDS SPACING BETWEEN MY WORDS

ABOVE, IN THE OTHER ANSWER, I WROTE THIS

"IMPORTANT TO KNOW----WHEN THE CHOKE PLATE IS FULLY CLOSED---THE HIGHEST IDLE STEP WILL BE IN PLACE"

. MEANING. THIS STEP WILL GIVE YOU THE MOSTus RPMSs THAN THE OTHER STEPS. AS THE PLATE OPENS GRADUALLY. YOU GET LESS AND LESS RPMs OUT OF THE STEPS

THE MEDIC
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Sunday, March 9th, 2014 AT 8:54 AM
Tiny
PULLMYEFINGER
  • MEMBER
Ok, I understand but I was looking for a straightforward answer. You wrote it backwards but I get it now. I was looking for "top, middle or bottom notch when you look at the left side of the idle cam".

So, if I set the fast idle on the correct notch/step and the choke plate is closed. I start the truck cold by pushing the accelerator in based on the temperature outside and start the engine, the choke plate should move " out towards full open. IF the truck won't go into fast idle then, what do I do? I have already flooded a set of plugs and replaced them. Again, what it is doing now is just running pretty much at curb idle and wants to stall if I give it ANY gas. After 15 minutes, the engine finally warms up enough to drive it without much hesitation. It gets continually better the longer I drive.
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Sunday, March 9th, 2014 AT 10:12 AM
Tiny
HMAC300
  • EXPERT
Unfortunately you have one of the crappiest carbs that ever bore a gm name to it. It's a varijet and a real pain the a. To work on. We dont' have any pics of this carb so best to gonline an dlook for them. If it looks like half of a Rochester 4 barrel it is an e4me carb if not is an e2se carb varijet and it should show most adjustments for it.
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Sunday, March 9th, 2014 AT 11:02 AM
Tiny
PULLMYEFINGER
  • MEMBER
That may very well be the case, but this thread has no real use to me so I will delete it. Where do you get off telling someone their vehicles are a piece of crap?
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Sunday, March 9th, 2014 AT 11:17 AM
Tiny
HMAC300
  • EXPERT
I didn't say you vehicle was a piece of crap I said the carb was one of the worst ones ever produced by gm. Not your fault that is what it was made with.
https://www.2carpros.com/images/external/79VarajetAdj0002_jpg.jpg
go to this link it shows where everything is and will be the best help I think that you will be able to find you wold want your truck to idle at about 1600 rpm but I think factory says 2100 but tha tis kind of fast. use choke cleaner to clean the cam so it moves freely up and down. also you can set the idle while engine is warm it won't hurt anything and set electric coke in about middle of notchs. Make sure all the llinkage there is connected as well as ther may be a clip broken off so look for that first then all you should have to do is rehook the linkage back up as I kind of think that is what has happened.
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Sunday, March 9th, 2014 AT 11:36 AM
Tiny
CJ MEDEVAC
  • EXPERT
VERY GOOD Hmac!

I SPENT WELL OVER AN HOUR LOOKING FOR A "HOW TO DIAGRAM" FOR HIM BEFORE I GAVE UP AND TRIED TO SHOW HIM HOW THE JEEP LINKAGES TO THE IDLE STEPS WORK. I EVEN BROKE OUT THE OLE CARTER BBD AND TOOK SOME PICS (MY HOLLEY 390 IS TOO HIDDEN TO GET PICS, UNLESS I SNATCH IT OFF, . AND WE AIN'T GONNA DO THAT!). MAYBE WITH YOUR LINK, I WON'T SPEND HOURS IN MICROSOFT PAINT MAKING MY OWN EXPLANATIONS

SOMETIMES JUST ACTUATING IT AND WATCHING AND BEING OPEN MINDED ON HOW THE STUFF WORKS IS THE BEST "CLASS" YOU CAN GET!

KEEP US POSTED AS TO WHAT YOU FIND OUT. AND MAY THE FORCE BE WITH YOU!

DID I MENTION THAT I REALLY LOVE MANUAL CHOKES?

THE MEDIC
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Sunday, March 9th, 2014 AT 12:38 PM

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