Quadrajet V8 carb problem

[craigvk]

Having a problem with my carb when cold. The car when starting takes about 6 turns as it keeps starting up and then conking out. My motor is having trouble burning the fuel when cold. And when taking off, it either conks out or stuggles majorly for the first couple of k's. When I run it on gas it is fine. Gas doesn't need to evaporate like petrol and burns fine at any temperature.

I have fiddled a bit with the automatic choke making it leaner or richer but nothing seems to be working properly. My old carb worked ok but I replaced it because it was warped. I have pulled it apart before I installed it to check out the gaskets and they are pretty good.

All I want is for my car to start, idle high on choke and be able to drive off without chugging or struggle. Maybe I still need to look at the choke a bit more but how do you explain the struggling take-offs? I know the choke is ok. The choke valve closes when cold, when you press the pedal. I know this carb is a good one. It's in very good condition and I am sure it just needs some tweaking. The base gasket on the manifold is good too.

Thank you for reading.

[Tree cutter]

Sounds like it is a bit lean. You might need to open the idle mixture screws a bit. Also start it with the air cleaner off when cold to see if the choke is actually working

[craigvk]

I will adjust the carb tomorrow to make it a bit richer and see what happens. The mixture screws, are you talking about the ones that aren't supposed to be adjusted from the factory, but people have drilled and made them adjustable? The things I am talking about are at the base of the carb where the primary throttle valves are. They are just above it. Or are you talking about something else?

Cheers.

[Cane_It]

the idle mixture screws are in the front of the baseplate, check that the fast idle solenoid engages on the throttle linkage when cold. it can be adjusted by screwing the end in or out, just do go stupid with it. I'll email you a very informative document on q-jet tuning. an old friend had a few v8s and they all struggle when cold on petrol so it maybe that you've had the good life driving it cold on gas like i have.

[Tree cutter]

The idle mixture screws i was talking about are the ones that are not supposed to be adjusted from factory. The fuel we use now is a lot different to when cars were made with that carb, so it needs to be adjusted to compensate. There are other adjustments that can be made to richen it up which Cane_It should be able to help you with. There are two air bleed holes that can be plugged to give you more fuel on the primary barrels.

[hispeedvp]

im not a quadrajet man im a holley man, had simillar problems once turned out the accelerator pump diaphrame was split. if any on the internal gaskets arent sealing you'll get a vacume leak internally causing the fuel flow inside the carby to be all wrong. the first thing i would do, (if not already done) is put a minor kit through the carby to eleviate any physical problems if it doesnt help you know its just tuning. if its tuning sounds like its not getting enough fuel but i dont know enough about the quads to lend any advice on tuning

[craigvk]

Cheers. I will need to look at it again tomorrow. Today was party day, so no keen interest in tinkering with the VK I will note and read everything said and I will let you know how I go. Thanks again.

[Ragnarok]

check your jets... if you have ever had a gas backfire. it melts the damn quadrajet... had it happen on my old girl running dual and seen on another i bought just for the engine. thats why i went straight gas with gas research. a couple of backfires and your carby is useless for petrol

[craigvk]

I have had a few backfires with gas but not for ages. Petrol is fine when the car is warm, so the carb is likely fine. I seem to be having insufficent choke at the moment.

I adjusted it richer the other day and it went like a barge. The starting was the same, ran like a barge but what was worse was the idle went up and felt too rich.

[hispeedvp]

if quadrajets are the same as most holleys they should have check balls to protect the main diaphrames (powervalve, accel pump, ect..) from being damaged by a backfire, dont know about the jets though. when you say your richening the chocke mixture are you adjusting the butterfly on the top of the carby or are you adjusting a mixture screw, all idle and chocke mixture screws do is meter the amount of atomized fuel (already mixted with air) that enters the carby on the idle or choke cercuit. they dont acutally change the amount of fuel to air, just the amount of pre mixed fuel that can enter so i would return them to factory settings and adjust the choke plate at the top of the carby witch should almost close on start up. again i know sweet fvck all about quadrajets so this could be completely useless to you.

[craigvk]

The mixture screws were set when I first put the carb on. I have been adjusting the auto choke on the side of the carb. Turn it one way to richen it or the other way to make it leaner. The thing is, the choke valve closes when cold as it should but it runs like a barge until it's warm. It's like it can't evaporate the petrol quick enough as when I run it on gas, so when it's hot it can evaporate it no problem obviously because the heat makes the petrol go into vapour a lot quicker than burning cold petrol.

[craigvk]

Pretty much the auto choke isn't working at all I think.

[atrail308]

is your metal line from the manifold heating up your thermocoil in the choke??? Check for a blockage in that line, undo it from your choke housing with a 1/2" spanner and pull it out from the plate on the intake mani, if thats all go, we'll go from there...

[craigvk]

I just went and checked my car now. I took off the choke pipe you were talking about and it's clean and not clogged. I took the carb hat off and started it up. The choke valve closed as it should but after a minute, the dang choke valve was fully open even though the engine wasn't warm enough. The choke valve is opening too early.

[hispeedvp]

from what i've read im asuming the choke isnt electronic, what travels through that pipe? is it coolant or is it just air? i'de say what evers inside the choke mechanism that senses the temperature needs replacing. you may be able to uprgrade the entire chocke mechanism for an electronic choke wich is definatley the way to go in my opinion

[craigvk]

The choke asm is an in and out job. One pipe goes to the in and the other to the out.

[atrail308]

try another heat coil in the choke housing, is there enough tension on it when cold???

[craigvk]

Ok. I have two spare carbs here. I will try another one (coil) now.

[craigvk]

Dang it. I changed it and it still is crap.

[Tree cutter]

I think your problem could be a blocked vacuum port that is at the top of your choke housing. Take the springy thing off again and then ondo the bolts that hold the choke housing onto the carby body. Next pull the choke housing off to the side and see if you can blow air through the little vacuum hole at the top of the housing. If that is clear try the port in the carby it could be corroded and blocked if it has been sitting around for a while. Once you have that sorted it should be just a matter of turning the springy thing around so the choke stays on long enough. The little vacuum port needs to be open so the choke butterfly opens a bit when you put your foot down on the throttle.