Idle Problems /Suggestions Wanted - The 1947 - Present Chevrolet & GMC Truck Message Board Network

flashed · 03-30-2014, 02:06 PM

I just put a rebuilt carb (1 bbl) on my 74 stepper w/a 250 inline six and cant get it to idle right .I replaced all the rotten vacuum lines and everything seems to be in the right place as before .The truck runs and drives much better than before other than the really high idle ,any suggestions ?

**MikeB** · 03-30-2014, 06:21 PM

I don't see a way to delete this duplicate post. Am I missing something?

**MikeB** · 03-30-2014, 06:22 PM

I am not familiar with that carb, but let's start with the basics. What happens if you try to reduce the idle speed using the idle speed adjustment screw? This is the screw that adjusts the throttle linkage, not the idle mixture screw which will be low on the base of the carb (and may be sealed).

flashed · 03-30-2014, 08:03 PM

There is no idle adjustment screw that I could find ,never dealt with a 1 bbl carb before though .I did get it to idle lower ,just not as low as I would like it to but I can live with it until I find out more to try . Thanks for your reply .

SkinnyG · 03-30-2014, 09:55 PM

Did you loosen or remove the throttle plate at all? If it was moved or reinstalled slightly out of place, the throttle plate could be catching on the body before it hits the idle speed screw.

No open ports left unplugged or disconnected?

flashed · 03-30-2014, 10:15 PM

I dont know what the throttle plate is and didnt see a idle speed screw .

Straight six · 03-30-2014, 10:21 PM

Is it a monojet? If so there's a idle stop solenoid around the back side wrench it in or out to lower idle or you could just unscrew it out and put a same size bolt in there does the same thing...

flashed · 03-30-2014, 10:35 PM

I did screw that out and got the idle down ,may do it some more ,and yes it is a monojet . This is my first experience with one .I knew my truck needed a new carb badly as it sat for 20 years before I bought it but never imagined it would run this good afterward . It runs so smoth now ,thanks for all the suggestions ,it will get better soon.

**MikeB** · 03-31-2014, 07:25 PM

In found this picture of a 76-77 Monojet carb, but don't see an idle speed screw. That's really strange, since even my emission control-laden 1982 2 bbl carb has an accessible idle speed adjustment screw. Is this what your carb looks like?

flashed · 03-31-2014, 08:19 PM

No ,mine is nothing like that one ,but I looked all over my new one before I installed it and no idle screw .

Straight six · 04-03-2014, 03:36 PM

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Is this what yours looks like? And that's the idle stop solenoid is the back left which can be removed and replaced with a bolt with same size thread. Hope this helps..

Straight six · 04-03-2014, 03:41 PM

Sorry about the twisted pic..

03-30-2014, 02:06 PM	#1
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Idle Problems /Suggestions Wanted I just put a rebuilt carb (1 bbl) on my 74 stepper w/a 250 inline six and cant get it to idle right .I replaced all the rotten vacuum lines and everything seems to be in the right place as before .The truck runs and drives much better than before other than the really high idle ,any suggestions ?

03-30-2014, 06:21 PM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Re: Idle Problems /Suggestions Wanted I don't see a way to delete this duplicate post. Am I missing something? __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 03-30-2014 at 06:25 PM. Reason: duplicate post

03-30-2014, 06:22 PM	#3
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Re: Idle Problems /Suggestions Wanted I am not familiar with that carb, but let's start with the basics. What happens if you try to reduce the idle speed using the idle speed adjustment screw? This is the screw that adjusts the throttle linkage, not the idle mixture screw which will be low on the base of the carb (and may be sealed). __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

03-30-2014, 08:03 PM	#4
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Re: Idle Problems /Suggestions Wanted There is no idle adjustment screw that I could find ,never dealt with a 1 bbl carb before though .I did get it to idle lower ,just not as low as I would like it to but I can live with it until I find out more to try . Thanks for your reply .

03-30-2014, 09:55 PM	#5
SkinnyG Registered User Join Date: Feb 2012 Location: Beautiful BC, Canada, eh?! Posts: 2,265	Re: Idle Problems /Suggestions Wanted Did you loosen or remove the throttle plate at all? If it was moved or reinstalled slightly out of place, the throttle plate could be catching on the body before it hits the idle speed screw. No open ports left unplugged or disconnected? __________________ 1961 Apache: "Grabber Orange" Shortboxed, pancake, step-notch, air-ride, turbo, LS 1977 Silverado: Shortboxed & dropped, potato-potato V8 Pontiac Firefly (Chevy Sprint): The ultimate engine swap: 5.7L in a 1.0L bag Lotus Super 7 Replica: Scratch-built street-legal rollerskate

03-30-2014, 10:15 PM	#6
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Re: Idle Problems /Suggestions Wanted I dont know what the throttle plate is and didnt see a idle speed screw .

03-30-2014, 10:21 PM	#7
Straight six Registered User Join Date: Aug 2012 Location: Newington ct Posts: 177	Re: Idle Problems /Suggestions Wanted Is it a monojet? If so there's a idle stop solenoid around the back side wrench it in or out to lower idle or you could just unscrew it out and put a same size bolt in there does the same thing... __________________ 1978 GMC C15 4.1 250 Twitter: StraightSix78 Instagram: StraightSix78

03-30-2014, 10:35 PM	#8
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Re: Idle Problems /Suggestions Wanted I did screw that out and got the idle down ,may do it some more ,and yes it is a monojet . This is my first experience with one .I knew my truck needed a new carb badly as it sat for 20 years before I bought it but never imagined it would run this good afterward . It runs so smoth now ,thanks for all the suggestions ,it will get better soon.

03-31-2014, 07:25 PM	#9
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,597	Re: Idle Problems /Suggestions Wanted In found this picture of a 76-77 Monojet carb, but don't see an idle speed screw. That's really strange, since even my emission control-laden 1982 2 bbl carb has an accessible idle speed adjustment screw. Is this what your carb looks like? __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

03-31-2014, 08:19 PM	#10
flashed Registered User Join Date: Oct 2009 Location: canton ga Posts: 12,724	Re: Idle Problems /Suggestions Wanted No ,mine is nothing like that one ,but I looked all over my new one before I installed it and no idle screw .

04-03-2014, 03:36 PM	#11
Straight six Registered User Join Date: Aug 2012 Location: Newington ct Posts: 177	Re: Idle Problems /Suggestions Wanted Is this what yours looks like? And that's the idle stop solenoid is the back left which can be removed and replaced with a bolt with same size thread. Hope this helps.. __________________ 1978 GMC C15 4.1 250 Twitter: StraightSix78 Instagram: StraightSix78

04-03-2014, 03:41 PM	#12
Straight six Registered User Join Date: Aug 2012 Location: Newington ct Posts: 177	Re: Idle Problems /Suggestions Wanted Sorry about the twisted pic.. __________________ 1978 GMC C15 4.1 250 Twitter: StraightSix78 Instagram: StraightSix78



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