Flat spot on 77 quadrajet when cold

[OxonCounty77]

Hi
I have just fitted the electric choke conversion that I bought from CarbJunkys as the old hot air choke was useless.
(To my 77 GMC C15 truck, 350 V8/Quadrajet)
It works brilliantly-It now starts better,I now have fast idle,& it returns to normal idle in 3 minutes.
I was hoping this would also cure the following issue,but it's still there.
The engine still cuts if I breathe on the throttle on a cold morning until the engine is warmed thru,when it then pulls/drives beautifully.The accelerator pump jets seem to be squirting fine,the throttle spindles dont seem too worn,& the engine seems in great shape having done 100k miles.It retains the standard air filter & I have replaced the hot-air trunking to the exhaust manifold.All the vac hoses look fine & the carb looks immaculate.
If you increase the revs very,very gradually the engine will rev,but press the pedal normally & it dies.As I said,after a couple of minutes warming thru,everything is perfect.
Does it sound like any adjustment/tweak would help the problem?

Best regards,Andrew. Oxfordshire,England,UK.

[GM-power]

Do let it sit in your driveway and warm up or just crank it and go? Its normal for it to sputter while still cold, also I would never sit and rev a cold engine its just not good. I see your new so welcome and post some pics of your rig!
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[geezer#99]

Sounds normal, no adjustments needed.

[OxonCounty77]

Thanks folks for speedy replies!
I would have expected it to start & drive straight off (the 76 camaro I just sold would). Unless you let the truck warm thru for a minute or so its undrivable because as you go to move off it cuts as soon as you touch the throttle. I realise you dont want to rev a cold engine as it wears most during warm up etc. it seems as though its either not momentarily got enough fuel being dragged in or else getting a big slug of air. If there is not a known quick-fix, I'll have to have another good look at what the choke flap is doing when someone opens the throttle.
Thanks for the welcome!

[OxonCounty77]

PS/ Perhaps she's got a grump on as I took her from a lovely quiet life in sunny Mississippi to the rain and frosty mornings of England........!

[geezer#99]

Burn us off a pic of your motor!
Do you have a factory air cleaner set up?

[OxonCounty77]

Yep, All factory. Thats why I imported her; standard all round & never mucked about with.

[bnoon]

If the accelerator pump isn't working properly it will not squirt enough fuel and bog when cold. It can still bog when warm but not be as noticeable. That's what mine was doing and I got a rebuilt carb to put on there and now no bog cold or warm.

Nice looking truck by the way!

[OxonCounty77]

Thanks; is the accelerator pump adjustable?

[Boog]

Yes. There should be two holes in the accelerator pump lever. I think you want it in the hole closest to the pump rod for max squirter shot.
Nice looking truck.

[OxonCounty77]

Thanks for that. I'll get and have a look.
She's a beauty!
Cheers.

[INSIDIOUS '86]

The quadrabog being from Mississippi had all its Jets and rods tuned for that elevation and weather. Being that your in England you prob need to have it tuned again.
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[OxonCounty77]

You may well be right.
I have asked the guys at Carb Junkys http://www.carbjunkys.com/
the same question. The excellent Melissa there has just replied with:
The Quadrajet got a bad name because people always go for that side curb idle screw first and it totally messes up the synchronization of the carburetor. It should not be what you use to adjust the idle. Find that factory setting and then use the front air fuel mixture screws. I'm not kidding, that is the problem about 80% of the time.

Never, ever, never adjust your carburetor without a vacuum gauge. EVER. Promise me.

I suspect I need to reset the base setting & go from there. The truck easily passed it's UK emissions test (the testers were taken aback as to how well/lean it was running),so I expect theres plenty of scope to tweak her a bit.
PS/ if anyone is having coldstart difficulties, I can wholeheartedly recommend the electric choke conversion that I got via CarbJunkys ebay shop. Their service to the UK was 1st class too.
Thanks again people for your thoughts & compliments about the truck

[geezer#99]

I'd still like to see some more pics of your truck. Motor, inside etc.

[INSIDIOUS '86]

Yes a bog comes from a lean condition your carb is Definitly lean once you tune it for winter you will have to tune it for summer again otherwise it will be on the rich side
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[OxonCounty77]

Hi Geezer99
Havent got any good shots of the inside yet-but have a couple from the ad the guy posted when I bought it
Plus one with the new tonneau just fitted
(and one with my son's C1500....!)

[geezer#99]

Since I read you hooked up the heat tube does the valve in the air cleaner snout close when you first start it?
What's your initial timing set at?

[OxonCounty77]

Good point. I was hoping that replacing the choke would sort all the issues,so havent actually checked that the valve in the nose is working as it should...
I realise of course that the carb is the last link in the chain,after compressions/timing etc. The engine runs sweet with no coughing back thru the carb or exhaust,& runs lovely on all 8. I will recheck the timing (I have just had a workshop manual arrive so now have the settings available).
The fact that it drives perfect when warm just lead me to think it must be the carb.Again I realise that any issue present will be magnified from a cold start.
I'll have a tinker with some of the suggestions when I get a mo & report back.
Thanks geezer

[OxonCounty77]

Incidentally,I assume most of the trucks of this age on here are still running with these quadrajets-or do most poeple chuck them away & fit a Holley or similar?

[geezer#99]

A lot of people pull them off and turf them and put on a Holley or Edelbrock thinking a new carb will cure all their little tuning problems. Problem with that is if they can't get their quad working then the won't have a clue how to get the new carb running either.
And for what it's worth a lot of perceived carb problems are timing related.
To me your carb sounds like it's working right. I wouldn't tinker with it.

[Boog]

Originally Posted by OxonCounty77

Hi Geezer99
Havent got any good shots of the inside yet-but have a couple from the ad the guy posted when I bought it
Plus one with the new tonneau just fitted
(and one with my son's C1500....!)

Nascar fan eh? Ol Jimmie isn't doing so well right now at Phoenix. He hit the wall and went a number of laps down.

[OxonCounty77]

Just been watching it; carnage again!!!
Looks like no Mr Six-Pack for Jim...
Team mate No.24 in hot water tho!!!!!

[GM-power]

Originally Posted by geezer#99

A lot of people pull them off and turf them and put on a Holley or Edelbrock thinking a new carb will cure all their little tuning problems. Problem with that is if they can't get their quad working then the won't have a clue how to get the new carb running either.
And for what it's worth a lot of perceived carb problems are timing related.
To me your carb sounds like it's working right. I wouldn't tinker with it.

I have q-jet on my truck and I love it. I agree that that your carb is working fine.
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[86c20]

the qjet that i have on my 350 is great the choke hasnt worked in 7 years and always starts no matter how cold unlike my edl. the choke is wired open pump 2 times and start her up hold the idle at about 12-1500 rpm for a good minute to 2 and good to go. still takes a little more pedle to go but i have a sm 465 and 5k of steel to move lol. if it is running good worm then i would just readjust for you climit and alt. and call it good. some motors are just cold harted. you should see my 454 even with choke its ten min before she can move

[INSIDIOUS '86]

Originally Posted by GM-power

I have q-jet on my truck and I love it. I agree that that your carb is working fine.
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It isn't. A bog is from a lean condition even his emissions testers said it was lean. It runs better when warm because warm air is less dense and the mixture richness slightly. Either way it needs tuned. But yes you do need to check your timing first and verify its at 10-12*btdc before any carb work
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