Quadrajet Choke Issues

[Bonnewagon]

being cranky for the first min when cold in the AM

This is where the vacuum break adjustment comes in. If it wants to die, it's too lean. If it coughs and stumbles, it is too rich. With a cold motor not running, press the gas pedal so the choke closes. Then put a vacuum source like a MityVac to the vacuum break so it opens. Measure the opening of the choke butterfly at the top of the air horn. Adjust that opening by means of the philips head screw on the vacuum break diaphragm. Like I said above, you may need to go find an older model setting for an idea what yours should be. Adjust the opening until it starts and runs perfectly, which will probably be a tad on the rich side. The bad part is you need a cold motor each time to properly make the adjustment.

 

[axisg]

I had a chance at work today to get back at the vacuum pulloff / brake setting you mentioned above ( I've been massaging the throttle for the first 30 seconds to keep it running up until now ). Turns out the vacuum break I had on the car was barely engaging the linkage and I think it was actually popping over the adjustment leg. I took the one off the car and looked at the 2 spare carbs for comparison. The 2 spares each had a metal "tang" on the adjustment leg ( making it a little longer ) whereas mine did not. So I swapped them out. Then the fun began.....

So with the choke break off I took this opportunity to clean up the sides of the carb and the linkage. In doing so I popped the choke housing off to bring it inside and get the choke coil to fit a little better or at least check one of the spares for better fitment. However in the process I knocked off the little bracket inside the carb ( you know the one that attaches to the choke rod ) D'oh !!

I spent the next 30 mins leaning over the fender in the parking lot at work trying to fish the little bugger out. Did it all in 5 minute increments as the position was so awkward. I fished it out with a dab of grease on a wire but then when trying to re-attach it to the choke shaft it popped off again LOLOL
My neighbor seen me working on the car and came over. He promptly put a tiny earth magnet that he had in his truck on the tip of the screwdriver and pulled it out in seconds. All I could do was laugh.

Its all back together now. It was opening a good 3/8" and running rough when first started. I pulled it back to about 1/4" before I noticed the choke coil started opening up so I will be fine tuning this over the next little bit.

The Bonnewagon for the "fine tuning" info. One the weather warms up I will maybe be swapping out Rods.

 

[axisg]

The next issue will be figuring if I need to swap out rods. Per the A/F guage I average ( when fully warmed up )

Idle - mid 15-16 with the occasional 17 blip
Cruise - 14-15
WOT - Low 13's then it drops to way lean when I let off the accelerator

I am OK with the cruise and WOT numbers but not happy at idle running so lean. If I fatten it up at idle then it gets pig rich across the board.

Per the manufacturer it should have
.074 PMJ ( #1974 )
50M PMR #1943
CE Secondary Rod

 

[pontiacgp]

The idle mixture does affect range of the carb. I would go up by two on the main rods. Let me know what you have now cause I have a few spare rods. I also have to order some gaskets for the air horn. They don't sell them separate in Canada but you can get them for a few $$$ from this place...if you want any let me know and I'll add them to my order, save on shipping.

http://www.carburetion.com/quadrajet.asp

 

[axisg]

thx steve, I may take you up on that. By going "up" do you mean numerically to a 52 rod ?
Last rebuild kit I ordered ( probably 5 years ago ) was from these guys in Alberta. Dunno if they are cheaper than the place you listed or not
http://www.carbkitsource.com/HTML/about.html


I believe my orig to the Monte CCC carb has different rod setup so that's no good. And the rods in the spare below are 43p so NFG there. My other spare is buried at home somewhere.

Whilst on the topic of carbs, jets and rods.

Spare at work has a casting # of 17080207
Which I pull up as
Carb # Application Main Jet Main Rod Spring Sec. Rod
17080207 Chev 80 VETTE M/T 71 42 7036019 CH

So how can I tell the main jet size ? I pulled one, cleaned it up and can find zero markings on it.

I had this carb above rebuilt around 1990-1992 IIRC. I see the primary rods are 43p whereas per the info I found above pertaining to the casting number they should be 42's so I would like to know if they changed the jet size as well ?

 

[pontiacgp]

The jets are numbered on top, you might need a magnifying glass to read them. You don't have to change them when changing a rod if you just changing by a few numbers. If you have a 43 in there now I would try a 45 or if you have a 72 or 73 jet you could try one size down with the rod you have now, you seem to be pretty close. The P on the rod means it's a stepped rod.

I looked that link but I could not find just the single gaskets.....

 

[Bonnewagon]

I've seen jets with no numbers. They usually come in carbs from a generic "rebuild" service that builds a one-size-fits-all carb. A set of go-no-go gauges will identify them. Or use a drill bit set and after you find a bit that fits snugly- check it with a micrometer. The size in thousandths of an inch is the GM part # last 2 digits. An old rule of thumb concerning Q-jets is this: you need to change a jet or rod at least 3 sizes to feel a seat-of-the-pants difference. I'm sure if you have sophisticated equipment like Rochester Products has, then 1 size can be significant. But for our use, 1 size is nothing.