Do I Need a New Carb?

[80Grand_LeMans]

I recently got my LeMans on the road after a while of sitting. I got some work done to it because it ran a little rough when I was driving it. It now has a terrible time starting and I have to pump the gas 4 or 5 times before I start it and even then it still sometimes has difficulty starting. I will have to hold down the gas while I start it or else it will shut off and a lot of white smoke comes out for a few seconds. I have come to accept that even though it is annoying but there is still another problem.

The first 2 or 3 mins I drive the car I can't get past 20mph. It gets up to 20 and the revs start to kinda buck up and down and wont shift (or go past 20, not sure if its trying to shift but it feels like it). Even if I push the throttle harder it doesnt go. It does seem like it starts going if I floor it but even then it sounds rough. A few mins after that and its gone.

The last problem seems to happen right after that goes away. For another 10 or 15 mins my car feels like it wants to shut down when I press on the throttle. It almost seems like when I step on the gas, it isnt getting any. It almost gets to the point of shutting off but then it slowly starts going. I could possibly deal with this except that it almost caused me to crash the other day when I was going to take a left and all of a sudden it almost shut off and I got stuck in the middle of the other lane until it finally got some gas and went.

Could this be my carb? I was thinking of replacing the fuel pump and fuel filter because its been sitting for a while. Also, do you think a full tune up (I just got new spark plugs) would help? Thanks.

 

[bowtie81]

take the fuel line off and turn the motor over and see how much gas comes out. if the pump is shot there wont be much gas shooting out. a tune-up will help

 

[Blackwizard22]

Check your fuel pressure. Pump may be bad. If not you may need to rebuild you carb, maybe clogged boosters or bad needle and seat.

 

[cutlass389]

Is your car stone stock? If it is, I would look very seriously at the EGR valve. I had a '79 Malibu 20 years ago that started doing what you described; on a cold start it would put out quite a smokescreen and run pretty rough for a while but after warming up it would run just fine. Took me a while to figure it out but it was just the EGR valve diaphragm let go. After replacing it she ran perfectly as before. To check it(with the motor off) just take off the vacuum hose, reach your fingers around to the back of the valve and squeeze the diaphragm up then hold a finger tightly over the nipple where the vacuum hose was. It should stay up until you let go of the nipple and then you'll hear a small woosh as the air rushes in and the diaphragm relaxes. If it doesn't hold then it's bad and simply replace. If it's not stock then disregard this entire post.

 

[LS6 Tommy]

If it's a bone stock carb, it sounds like a classic case of a bad choke pull off.

Tommy

 

[80Grand_LeMans]

If it's a bone stock carb, it sounds like a classic case of a bad choke pull off.

Tommy

How do you check and/or fix it?

 

[LS6 Tommy]

If it's a bone stock carb, it sounds like a classic case of a bad choke pull off.

Tommy

How do you check and/or fix it?

The pull off is the little metal vacuum diaphragm attached to the choke linkage. IIRC, 2 screws hold it on & there's a hose & a linkage that has to be popped off. It's easier to do than to explain.

Theses guys have a lot of good stuff:

http://www.carburetor.ca/carbs/tech/Rochester/Quadrajet-index.html

Tommy

 

[Killerdave8813]

Sounds to me like the choke isn't working at all as a pump or two of gas and the choke should be set and it should start right up and go to fast idle,the choke pull off that Tommy mentioned opens the choke blade just a bit after the engine fires and gives it some air so the engine doesn't become flooded untill it heats up and lets the choke off,
I don't like the white smoke as in a gas engine that generally means it's
getting coolant into the combustion chambers,if it was the choke pull off malfunctioning it would be black smoke signifying a rich condition and trying to flood the engine,if you fire the engine and let it sit and warm up for say 10 minutes how does it run? Over the years that I worked on cars for people 99% always blamed the carb but very seldom did I find it to be the problem,there are a lot of vacume operated acessories on you car the could be causing problems IE.EGR valve,vacume advance,heater controls,all kind of little stupid pollution control gizmos the I generally did away with on my own vehicles anyway,drivabillity is hard to diagnose in person sometimes but on the computer is even harder,I'm still wondering about the white smoke? Pull your dipstick and see if there's any discoloration,maybe like a chockolate milkshake,that would be water in the oil,cracked head or blown head gasket,with the engine cool take the radiator cap off and see if the coolant looks normal,green genarally,leave the cap off and start the engine and let it warm up,look for foam or bubbles or anything like that,would also signify a crack or head gasket problem,does it miss or run smooth? I don't know but keep thinking about the white smoke????? one other thing I just thought of,could be a bad modulator valve on the transmission,depending on what trans is in that car there should be a 1/4" steel line coming up out of the trans tunnel that hooks into a fitting on the intake manifold,pull it loose and see if there's any red transmission fluid present as that could cause white smoke as well,that's about all I can think of for now keep up posted and we should be able to figure it out.Later KillerDave