Quadrajet sputtering

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
2,338
Reaction score
3,568
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
Start with the basics. Remove the air cleaner. With the engine completely cold, floor the throttle. Make sure the choke fully closes. Start the engine, the choke plate should open just a little as soon as it starts. If not, you may have defective choke pull off, or it may need adjusted. As the engine warms, the choke plate should open more, until it’s eventually open all the way. Fast idle speed should be around 1200-1400 rpm. Once the engine is warmed up, a tap on the throttle should disengage the fast idle.
 
Last edited:

Eighty5ov

Full Access Member
Joined
Dec 30, 2021
Posts
69
Reaction score
23
Location
Canada
First Name
Ov
Truck Year
1985
Truck Model
c15
Engine Size
5.7
Well if it's only sputtering when it's cold maybe it's in the choke. So I guess I need that answered doe it only sputter cold?

If that's the case then we need to be looking at the choke, is it fully closed before cold start up?
It's an 85 so it's got an electric choke which will open up pretty fast, you can adjust it to stay closed a little longer though, how long did it take for the sputtering to disappear after starting it?
Is it running the factory air cleaner housing as is the thermac at least hooked up?
Is the heat riser the weighted mechanical type or vacuum operated, it's probably vacuum given the year. Make sure the vacuum hose is hooked up to the heat riser.
If that's all hooked up we can troubleshoot that stuff, but I had previously thought it was sputtering all the time, not cold only.

Since that wasn't mentioned earlier I had you check the ignition system which wasn't really needed, but on the other hand on an old engine it's good to check the timing anyway.

Yeah only when it’s cold. Once it was warm it was fine. Rev’d up nice had that q-jet screaming. The choke wasn’t closed all the way so I think that needs adjusted but it opened quick yeah.
It stopped sputtering after about 10-15 minutes. All lines are hooked up for vacuum. I’ll try again today and try to get video.
 

Eighty5ov

Full Access Member
Joined
Dec 30, 2021
Posts
69
Reaction score
23
Location
Canada
First Name
Ov
Truck Year
1985
Truck Model
c15
Engine Size
5.7
Start with the basics. Remove the sit cleaner. With the engine completely cold, floor the throttle. Make sure the choke fully closes. Start the engine, the choke plate should open just a little as soon as it starts. If not, you may have defective choke pull off, or it may need adjusted. As the engine warms, the choke plate should open more, until it’s eventually open all the way. Fast idle speed should be around 1200-1400 rpm. Once the engine is warmed up, a tap on the throttle should disengage the fast idle.
I’ve monitored this and on that kick down it’ll break up or sputter
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,698
Reaction score
11,148
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Yeah only when it’s cold. Once it was warm it was fine. Rev’d up nice had that q-jet screaming. The choke wasn’t closed all the way so I think that needs adjusted but it opened quick yeah.
It stopped sputtering after about 10-15 minutes. All lines are hooked up for vacuum. I’ll try again today and try to get video.
Adjust it so it's fully closed when cold and I'd bet that solves your problem or at least improves it a ton.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,121
Reaction score
6,037
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
Adjust it so it's fully closed when cold and I'd bet that solves your problem or at least improves it a ton.
does he have intact other emissions that could affect cold driveability or should he just look at carb

if just at carb
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
 

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
2,338
Reaction score
3,568
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
does he have intact other emissions that could affect cold driveability or should he just look at carb

if just at carb
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
Years ago I found the fancy Kent Moore tool set for adjusting the choke flap in a swap meet. It wasn’t dirty, all the manuals were there, all the special tools and accessories were all in there place. It was a very old tool kit, it was in a metal box (long before the Kent Moore tools started coming in plastic boxes!!). I thought about buying it, for just a couple seconds. The 400 asking price was pretty step for something that I would probably never use.
 

Latest posts

Forum statistics

Threads
41,847
Posts
903,380
Members
33,361
Latest member
iiixtremeiii
Top