Warm starting/choke problem
 

First the requisite details: 86 c10 4.3 v6 automatic with 90k original miles, rebuilt 4-barrel quadrajet put on last year with electric choke. Truck otherwise runs good.

I've had a warm engine starting problem crop up in recent weeks that I seem to have narrowed down to a problem with my choke.

If I drive till the engine is good and warm, then park the truck, wait maybe 20 minutes or so and come back sometimes it just won't start. When the problem happens, it turns over just fine and even "fires" for just a split second and dies. After that, no amount of cranking will do.

Last night I got it to happen in the driveway. I looked at the carb and noticed the choke was closed completely. I had my wife crank it while I held the choke open and she fired right up. Just for kicks, I repeated the process a few times (e.g. waiting 15-20 minutes before a restart) and it wouldn't start again unless I opened the choke.

If I try to restart right away after running the engine, it's fine. But if I come back between 20 minutes and an hour or even more later it won't start because the choke is closed. Four + hours later it starts fine.

It's been really cold here lately (not really been above freezing all month) so I suspect that thiis maybe causing the choke temp sensor to cool off quicker than the engine itself. Does that make sense? If so, how can I fix it? Is it an adjustment issue or is it a faulty part?

I've tried reading some related threads here but didn't seem to find the exact same issue.

Thanks in advance,

TimQ

Re: Warm starting/choke problem
 

Maybe a dumb question but, is the choke electronic?

Re: Warm starting/choke problem
 

Yes it is an electronic choke. Has a single wire going to what I believe is the controller for the choke on the passenger side of the carb. Here's a pic when I was putting it in last year.


Attachment 670786

Re: Warm starting/choke problem
 

Sounds like you need to lean your choke a bit. The 3 screws holding the black cap need to be loosened and the cap turned clockwise a couple notches. Should be some marks on it at the top and a mark on the choke housing for referencing it. You should see rich to the left and lean to the right.

Re: Warm starting/choke problem
 

Thanks...that's a lot simpler set of instructions than anything I could find searching online and in my stack of manuals here.

I'll head out and give it a shot and see what happens.

Re: Warm starting/choke problem
 

Do you have a pic of the drivers side of the carb ?

Sounds like the choke pull-off is faulty or not adjusted properly.

Once you start cranking that builds enough engine vacuum for the pull-off to open the choke a little, This keeps the engine from flooding before it cranks.

Re: Warm starting/choke problem
 

Sure...here's a pic of the driver's side.

Attachment 670815

Re: Warm starting/choke problem
 

OK, Your model carb doesn't have a choke pull-off. All you can do for now is try leaning the adjustment like geezer#99 explained.

That would put less closing spring pressure on the butterfly....

Re: Warm starting/choke problem
 

He does have a choke pull off. It's on the other side. The amount of opening is controlled by the screw on the top.

Re: Warm starting/choke problem
 

OK, so on the passenger side of the carb (photo in post 3 above) there are two flying saucer looking things that I assume are the two choke pull offs. If I'm following correctly some other posts I've read, I guess one is tied to the primary (smaller plate???)and the other the secondaries (larger plate???). Which gets adjusted for this warm start issue? It looks to me like the back one controls the smaller place but before I mess with it I want to make sure I have it right.

Thanks again for all the great info.

Re: Warm starting/choke problem
 

Your right, I'm getting my pull-offs mixed up. You need to make sure the pull-off on the back is opening the choke butterfly slightly during cranking or right at start-up.

Put a longer piece of hose on it and see if you can suck on it and have it open the butterfly slightly.

Re: Warm starting/choke problem
 

Now you got it restorob. Front one is for the secondary lockout. Back one pulls the choke plate open just after it starts. How much the choke plate opens is contolled by that little screw on top.
Here's a couple links.
http://www.florida4x4.com/tech/quadrajet/
http://www.vetteprojects.com/kstyer/quadrajet.htm

The second link is one found in the first link.

Re: Warm starting/choke problem
 

You might try adding a phenolic spacer between the carb and engine. Heat could be dissipating your fuel, and without a manual choke to override the lack of fuel, I can't imagine what cranking hell it must be with an electric choke and mechanical fuel pump. I have the same problem with my truck (no spacer yet) even with an electric fuel pump. Heat soak ain't fun.

Re: Warm starting/choke problem
 

I had a similar problem on my computer qjet in my 86 Firebird. Had to replace the choke pulloff and adjust the set screw on it. The diaphram inside is probably leaking vacuum. You might want to remove it and see if it holds a vacuum. First with the engine off, push the pulloff rod all the way in and see if the choke linkage moves just a tiny bit. That may be out of adjustment. The pulloff is the front vacuum can between the choke thermostat and the MCS connctor.

Re: Warm starting/choke problem
 

Thanks all.

Had it happen again tonight. This time on the road while picking some stuff up at the store. I just took off the air cleaner cover and had someone crank it for me while I operated the choke and throttle from under the hood. She fired right up. I'm convinced its just an issue of the choke not opening at all when the engine is just a little warm. When it is HOT, it starts just fine - so if I shut it down and restart it within 5 minutes or so it works fine. It's the semi-warm start that gets me (say after 10+ minutes to more than an hour).

Anyhow, I'm going to try and mess some with the pull off and see if that is the issue. Hoping it's just out of adjustment.