Cold start problem - JeepForum.com

 
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post #1 of 11 Old 04-26-2013, 10:47 AM Thread Starter
bluedaffy
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1989 YJ Wrangler 
 
Join Date: Oct 2011
Location: Stevens Point
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Cold start problem

So I'm having a little trouble with my cold start. It's a 4.2L with a weber 32/36 (electric choke) carb.

Let me start by saying this, after she warms up and the choke is out of the picture, she runs very smooth. As far as I can tell when warm she's running at a satisfactory air/fuel ratio because the acceleration is smooth and there are no pops or hesitations or backfires and right after a cruise I can check the plugs and they look great (mostly white but with a touch of tan).

The problem is when I cold start, I will:

1. Turn the key to on
2. Pump the gas one time to prime the carb and close the choke.
3. Start her up

She starts immediately, sounds great, and the cold idle works good holding the idle about 500-700rpm higher than the regular warm curb idle (not exactly sure on the rpm because I am skeptical my tach is working properly). BUT, after about 5 seconds of great cold start action she starts to buck and does not run smooth at all. She will keep running but it seems that she it too rich because if I open the choke by hand during this period she smooths out and sounds great, also she is coughing black smoke out the exhaust during this time, but after she's warm the exhaust is white and barely noticeable.

Could this be a choke setting problem because of the fact that she runs perfect when warm? or might this be a problem of too much fuel delivery? Because the choke seems to be operating fine (closing fully at cold start and slowly opening over a few minutes of running)

I apologize for the lengthy explanation, but I thought it would be beneficial to get all the info out there right away. I would really appreciate some help or input on this. Thanks

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post #2 of 11 Old 04-26-2013, 11:16 AM
Rproject
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Quote:
Originally Posted by bluedaffy View Post
2. Pump the gas one time to prime the carb and close the choke.


Could this be a choke setting problem because of the fact that she runs perfect when warm? or might this be a problem of too much fuel delivery? Because the choke seems to be operating fine (closing fully at cold start and slowly opening over a few minutes of running)

I apologize for the lengthy explanation, but I thought it would be beneficial to get all the info out there right away. I would really appreciate some help or input on this. Thanks
I think you have that backwards. The choke should be full open when cold, then close as it warms up. It sounds like your choke is closing too quickly.

1996 White ZJ
1987 Maroon YJ (sideways build)
1996 Forest Green XJ

The "sideways" build thread: http://www.jeepforum.com/forum/f22/r...hread-2164793/
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post #3 of 11 Old 04-26-2013, 11:51 AM
dancytron
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Quote:
Originally Posted by Rproject View Post
I think you have that backwards. The choke should be full open when cold, then close as it warms up. It sounds like your choke is closing too quickly.
No. The choke should be closed when cold and open up slowly as the engine warms up. Sounds like it is opening too quickly.
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post #4 of 11 Old 04-26-2013, 11:56 AM Thread Starter
bluedaffy
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So when the engine is cold and she's started the choke butterfly is restricting air coming in from the air filter, when warm the choke butterfly is vertical allowing all air to move through the air filter and into the intake. When the choke is restricting air intake is this referred to as "closed"? I may have the terms confused. Thanks
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post #5 of 11 Old 04-26-2013, 11:57 AM Thread Starter
bluedaffy
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Thanks dancytron, but I thought that too, and I checked what it does upon start up and the choke stays closed when the bucking starts, it doesn't even being to open until after about a minute or so of running.
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post #6 of 11 Old 04-26-2013, 11:59 AM
Mark05059
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think of the choke as a door for air... when closed air cant get through it. This door is closed when the engine is cold (richening the mixture). It sounds like your choke isnt opening soon enough hence the black smoke.

1998 ZJ 5.2 Auto

1989 Wrangler Black Bone Stock 2.5l 5spd
/l , [____],
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post #7 of 11 Old 04-26-2013, 12:09 PM
Rproject
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Quote:
Originally Posted by Mark05059 View Post
think of the choke as a door for air... when closed air cant get through it. This door is closed when the engine is cold (richening the mixture). It sounds like your choke isnt opening soon enough hence the black smoke.
That helps me to understand. Thanks. Apparently I was the one who was backwards.

1996 White ZJ
1987 Maroon YJ (sideways build)
1996 Forest Green XJ

The "sideways" build thread: http://www.jeepforum.com/forum/f22/r...hread-2164793/
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post #8 of 11 Old 04-26-2013, 12:33 PM
dancytron
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I agree. Not opening fast enough.
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post #9 of 11 Old 04-26-2013, 12:54 PM Thread Starter
bluedaffy
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alright, sounds easy enough. How would I go about adjusting how fast it opens?
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post #10 of 11 Old 04-26-2013, 06:05 PM
Old4X
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You have eliminated your hot air stove and associated plumbing, and your cold engine operation is what suffers when you do this.

From the factory all carbed motors had a heat stove on the exhaust manifold to feed hot air to the air cleaner to improve cold engine and choked running characteristics.

By adjusting your choke coil over a period of several days to a week, you will find the sweet spot for how you are now equipped.

418 miles on 19 gallons of gas. Can't beat the BBD !
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post #11 of 11 Old 04-26-2013, 06:08 PM
Old4X
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Quote:
Originally Posted by bluedaffy View Post
alright, sounds easy enough. How would I go about adjusting how fast it opens?
This is done by turning the choke coil cap (black thing 2" in diameter).

Loostening the 3 screws and twisting the cap to close the choke more will slow choke opening (reverse makes it quicker)

418 miles on 19 gallons of gas. Can't beat the BBD !
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