I have an '86 Trans Am, carbureted, and I suspect the carburetor is the source of some problems I have starting the engine from cold.

The engine cranks, but doesn't turn over for a few seconds. Giving it a push on the gas pedal before I start helps - eventually it catches. If I don't do anything after that, it'll just stall. If I give it some gas when the RPM starts to drop, I can stop it stalling. After that, sometimes it 'hunts', or just idles way too high (1500rpm) rather than the usual ~500rpm. The noise from the engine also sounds a bit 'bubbly'... less of a purr and more of a slight gurgle.

After the engine's been running for a few minutes, the whole thing works perfectly, and I can get it running from a warm start easily.

My knowledge of cars and engines is pretty feeble, but I believe the carburetor could have something to do with this. I've attached a video of what the carb operates like when the engine's completely cold. The butterfly thing that's higher is the primary, right? It's meant to be completely closed when the engine's cold, but it isn't. Is this the source of my problems? Do I just need to adjust the choke?

Thanks!

 

The choke is probably not functioning correctly. It needs to be adjusted so when cold the front primary choke plate is almost closed which will increase the idle to around 1500 rpm , which you said it does sometimes.The choke spring housing is on the passenger side of carb with 3 screws holding the spring load in place.Loosen the screws and turn the inner plate so the choke plate is about 1/2 to 3/4 closed .With you being in L.A. , do it in the morning or night when it is cool outside.You will have to play with adjustment and may have to adjust the choke high idle screw below choke housing.If it is an electric choke it should heat up in about two-three minutes and drop idle to normal.

 

Did this problem just start or has it been a chronic issue?

Before you start twisting screws you need to do some visual inspection and review your start-up procedure. We'll assume no one has messed with the carb it yet.

Drive the car around and get it up to operating temperature. Now park it overnight.

With the engine cold, remove just the air cleaner lid. Note how much the choke plate is opened (the choke plate is the one to the left in your video). It should be opened full.

Get in the driver seat (leave the keys in your pocket) and press the accelerator to the floor ONCE.

Get out and look at the choke plate. It should now be fully closed. If it's not, the carb isn't able to provide a rich start-up mixture. You need to find out why. Either the choke stove is bad or the linkage is hung up.

If the choke plate is fully closed, take the keys out and start the engine without touching the accelerator pedal.

Once the engine is running (however badly it might be) get out and look at the choke plate. The plate should be opened slightly. If it is not, the choke pull-off diaphragm is bad and not opening (slightly) the choke plate essentially flooding the engine.

Check these two things 1) choke fully closed before starting, 2) choke slightly opened after immediately starting and report back.

 

Ok, so I did as advised. The choke plate closes completely when I press the accelerator once from a cold start, and then opens up slightly when I turn the engine over. I guess the choke plate is not the problem?

This is an issue that's slowly come to be over many months - when I bought the car 10 months ago, it was fine, and it slowly got to this point where it's a pain in the **** to start it up from a cold start.

 

Likely cause is, the plugs in the bottom of the metering wells leaking, allowing all the fuel to drain out of the carb as it sits; then it has to crank for awhile to pump enough fuel back up into it for it to run.

Easy enough to tell: next time it has sat overnight (or however long it sits to generate the problem), before you actually try to start it, pop the air cleaner off and work the throttle by hand and see how much fuel the accelerator pump delivers. If the pump shot is weak or non-existent, then you've found the problem.

 

It seems like choke is basically operating properly. You may want to remove air cleaner prior to a cold start and after starting engine immediately manually open and/or close the choke plate small increments from the almost closed position and see if it affects idle quality.If it does, there is an adjustment to help adjust air/ fuel cold idle mixture.I'm assuming the cold engine idle quality is the issue as well as a long crank time before firing.Also, fouled spark plugs can affect the cold idle.Since as you stated, it has been a gradual worsening issue,you may want to tune engine if it hasn't been done lately or check condition of plugs.

 

I am having the exact same problems to a T as the original poster!!! Was there ever a solution?? Any new info on this problem?? I also have an 86 T/A 305 4bbl.

 

Sadly not, I'm still living with the inconvenience of the car being kind of shitty when it first starts up. The information given by others in this thread require rather more car engine knowledge than I have, so I'm probably going to take it in to my local mechanic before too long.

 

I'm also considering the same. Here is a typical start up from cold for me.......pump gas 5-6 times.....turn key.....car will start....run for about 4 seconds then die....pump 3 more times.....start up again, but this time will usually stay running....but sometimes will die again after a few seconds. If I try to start it supposedly the right way.....1-2 pumps....turn key with foot off gas.....won't start at all. Runs great after warmed up the whole day with never touching the gas pedal?

 

What happened when you actually acted on the suggestions above? Any improvement?

 

When car has been sitting for at least a day.....choke plate is completely open......push gas pedal completely to floor.....choke plate closes (but not completely and is a little loose).....Choke pull-off is good (holds vacuum when pushing in). After I start it... closing (by finger) the choke plate more definitely keeps the car running at a much higher idle and it doesn't die. If I pump the gas pedal enough times, it will start and stay running at high idol like it's supposed too. I think I may have this problem: "Likely cause is, the plugs in the bottom of the metering wells leaking, allowing all the fuel to drain out of the carb as it sits; then it has to crank for awhile to pump enough fuel back up into it for it to run".