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Old 01-25-2002, 09:23 AM   #1
KJL
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Default When Cold, Car starts but then dies on first try, why?

When I try to start my 72-L48, I pump the gas a few times then start it. It fires up and RPMs increase to about 1500 then within seconds the RPM drop off and the car stalls. I pump gas again a couple of times, start it again and it is ok. The carb is a Q-Jet with divorced choke. I am not sure it is the cooler weather. The car usually is only run once a week or less. Could it be the fuel has evaporated out of the carb bowls?
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Old 01-25-2002, 09:33 AM   #2
woodworkr
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Default Re: When Cold, Car starts but then dies on first try, why? (KJL)

Fuel evaporating in the float bowls sounds like a possibality. The fuel pump has to get the gas to the carb to fill the bowls to bring up the float level. If I remember right the Q-Jet for 77 has a vacuum activated choke could be that the diaphram in the choke assembly could be weak. I am really grasping at straws here with that one. Also what about the filter in the carb when was the last time that was changed?
Just a couple if ideas,
JoeB
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Old 01-25-2002, 12:51 PM   #3
Drache
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Default Re: When Cold, Car starts but then dies on first try, why? (KJL)

Quote:
It fires up and RPMs increase to about 1500 then within seconds the RPM drop off and the car stalls. I pump gas again a couple of times, start it again and it is ok.
Mine does EXACTLY the same thing, with the same carb. I haven't got far enough to figure out what it is yet. I know it is a problem with the choke, but I don't know what.

Right after it starts on the second try, does it run a little roughly for a couple of minutes? Right after you start it, if you pull off the vacuum line from the intake manifold (the one connected to the headlights), and leave it unplugged (open to the air) does the engine speed up and run better while it's cold?
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Old 01-25-2002, 01:11 PM   #4
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Default Re: When Cold, Car starts but then dies on first try, why? (KJL)

Mine used to do exactly that when it didn't have a choke.

sounds like your choke may not be functioning at all...
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Old 01-25-2002, 02:34 PM   #5
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Default Re: When Cold, Car starts but then dies on first try, why? (71 BHG 454)

When the car does start it goes to about 1800 RPM. I let it stay there for about 30 seconds, then I tap the gas and it drops to about 1000 -1200 RPM. I let it warm up for about 4 minutes, then it will drop into the idle circut when I tap the gas again. It takes a little longer to warm up because when I installed the headers, I removed the exhaust flow diverter valve. If the choke was not functioning at all the engine would go to idle after start up and would most likely want to continue to stall unless you kept your foot on the gas to maintain a high enough rpm to prevent it until it warmed up. A year ago I had the carb re-built by the cab shop then again by Lars. I may have put 600 miles on it sence. I don't think it sounds/feels unexpectedly rough for a cold carbed engine after it starts. It smooths out in a couple of minutes. Trouble is that my point of reference for how an engine should sound has been dominated be fuel injected computer controlled engines. There will be a difference.
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Old 01-25-2002, 02:57 PM   #6
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Default Re: When Cold, Car starts but then dies on first try, why? (KJL)

I have the same problem. Q-jet carb. When I start it it will run up to 1500-2000 rpms then slowly start to cut out. I have noticed that I have to feather the gas to keep it going. I would think the choke is on because of the high idle at startup, then when it warms up the idle will come back to 1000. It almost seems like there isn't enough fuel or air comming into the engine. I was going to take it to my mechanic to adjust the choke. But I haven't yet. so I dont' know what the problem is.
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Old 01-25-2002, 03:51 PM   #7
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Default Re: When Cold, Car starts but then dies on first try, why? (flood)

All of the problems described sound like minor adjustments. Checking it stone cold, pull off the air cleaner and set the choke(pump it twice, or what ever you normally do). It should be closed all the way. If not, adjust it 'till it is just closed. Q-jets use a couple of different designs to "pull off" the choke after it starts (either a vacuum pot or an arm on the linkage). Have a helper fire it up as you watch the choke (without touching the throttle). if it opens too far, it will rev up to 1500-1800 RPM, then die. If it doesn't "pull off" far enough, it will start to load up and run rough (black smoke from the exhaust) for a period of a few minutes until the choke gets hot and releases completely. Thats an over-simplified version, but it will give you an idea if it's rich or lean. Only adjust the choke itself COLD.

Hans

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Old 01-25-2002, 05:06 PM   #8
KJL
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Default Re: When Cold, Car starts but then dies on first try, why? (Wrencher)

Hans,

Thanks for the insight in what may be the problem. I believe my choke may be opening to far when started. I am still not sure as to why the second time it starts fine. How is the choke adjusted if it does open to far? My Q-jet has the vacuum pot type.
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Old 01-25-2002, 05:44 PM   #9
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Default Re: When Cold, Car starts but then dies on first try, why? (KJL)

I found this for you:

Problem: Engine starts, then dies within a few seconds.

1) Choke not closing properly. 1) Adjust choke if necessary.

2) Big vacuum leak on engine somewhere. 2) Use vacuum gauge to check. Fix the leak. You may have put the base gasket on wrong or it is the wrong one for this carb & engine combination.

3) Choke pull off setting incorrect. 3) Adjust to factory specs. Carb can get bumped in shipping or transportation and can accidentally change the setting.

4) Fast idle RPM set too slow. 4) Adjust to recommended RPM.

5)Low fuel delivery. 5) Correct delivery to carb. Usually it is a plugged up filter.

6) Electrical or compression problems on the engine. 6) Do complete tune up & diagnosis. Fix the problems found.

7) Float level set very low. 7) Check & adjust the float level to factory specs.

8) No electricity up to idle solenoid, or no ground. 8) Check for power & ground. Correct the problem.

9) Defective idle solenoid. 9) Replace it.
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Old 01-25-2002, 07:08 PM   #10
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Default Re: When Cold, Car starts but then dies on first try, why? (The Dude)

This is exactly the way mine starts as well. Actually if my car sits for a few days, I have to crank it over a few times. It starts..runs around 1800, slows down and stalls. It will start right up again and run at around 1500-1800 until it comes off fast idle which takes quite sometime now as I removed my heat riser valve when I installed the right side pipe. I thought that this was the way most quads started up as my other 77 did the same thing from the day it was new.


[Modified by Binnie77, 7:09 PM 1/25/2002]
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Old 01-28-2002, 09:22 AM   #11
KJL
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Default Re: When Cold, Car starts but then dies on first try, why? (Binnie77)

I started it up yesterday and watched the choke. The air valve pulled the choke off and openned the valve about 1/4". The car then shortly lost rpm and stalled. I let the car cool down a few hours then started it again, as the rpm began to drop, I closed the valve a small bit and this seemed to pick up the rpm again. The engine did not stall, but it was not stone cold when I started it either. I removed the pull off rod and gently bent it so it would not open the valve as far. I am also not going to pump the gas as many times as not to drain the bowls. Tonight I will try to start and let yall know what happened. If this has no impact, I may try to bend rod in other direction. I may have to put out an APB to Lars.
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Old 01-28-2002, 01:36 PM   #12
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Default Re: When Cold, Car starts but then dies on first try, why? (KJL)

This was sent to me from Lars. Thanks Lars!!!
From: Grimsrud, Lars [lars.grimsrud@lmco.com]
Sent: Monday, January 28, 2002 11:33 AM
To: Lavallee, Keith J.
Subject: RE: Carb question

Keith -
I can't post to the Forum from my work terminal (firewall issues don't give
me access), so perhaps you can cut and paste this e-mail into your post with
a note that it's from me:

A common problem with older Q-Jets is balky cold-starting. Over the years,
so many people have tweaked and adjusted these carbs, that most of them have
choke systems that are way out of spec and configuration. Here are the
basic steps to correctly adjusting the choke pulloff system and fast idle:

First, check out your choke pulloff (also known as the Vacuum Break
Diaphragm) to assure that it is operational and not leaking. To do this,
simply pull the short vacuum hose off it, put a long one on it, and suck on
it. When you suck on it, the pulloff should retract completely, and it
should hold a vacuum. If it either does not work or if it leaks, you need
to replace it. New units are available from NAPA in the Echlin product line.
If you need a part number, simply send me your carb number and I will
provide you with the correct Echlin pulloff part number.

Next, you need to adjust how far the pulloff opens the choke. To do this,
leave the long test hose attached to the pulloff. Crack the throttle open a
little, and manually close the choke by pushing up on the choke linkage -
just like the divorced choke would do when the engine is cold (if you have
an integral hot air stove choke or an electric choke, you need to manually
move the linkage just like the choke would do when cold). While maintaining
light pressure on the linkage in this manner, suck on the hose to fully
retract the choke pulloff. The pulloff should hit the choke linkage and
force the choke open a crack (don't restrain the linkage too much - allow
the pulloff to pull the choke open). In this configuration, lightly push
the choke plate towards its "open" position (there is a bit of slop in the
linkage - air flowing across the choke plate will push it towards the "open"
position, so simulate this with a light touch of the finger). Once in this
position, the distance between the forward (lower) edge of the choke plate
and the forward wall of the air horn should be exactly 1/4". Measure it by
sticking a 1/4" drill bit down between the choke and the air horn. Adjust
it by bending the linkage where the choke pulloff contacts the choke
intermediate linkage, or by adjusting the pulloff screw on the intergral
choke models.

Once this is set, you can do an initial adjustment of your fast idle screw
as follows: Back your regular idle screw out exactly 3 turns from its
current position so that the throttle blades will close completely. Back
the fast idle screw out (located on the passenger side down below the choke
linkage)until the fast idle cam/counterweight can be lifted all the way up
to its fully raised position without cracking the throttle. Slowly screw
the fast idle screw in until it JUST BARELY starts to drag on the high step
of the fast idle cam as you move the fast idle cam up and down. From this
point, screw the fast idle screw in 2 more full turns. Screw your regular
idle screw back in the 3 turns that it was backed out. This will give you a
very close setting for your fast idle speed.

These adjustments will normally make your Q-Jet run very well when
cold-starting. Have fun adjusting, and copntact me with any questions.

Lars
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Old 01-28-2002, 03:26 PM   #13
paul 74
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Default Re: When Cold, Car starts but then dies on first try, why? (KJL)

Sounds OK to me. But I only put the pedal to the floor once to set the choke. I find any more than that squirts too much fuel into the engine.
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Old 01-29-2002, 09:26 AM   #14
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Default Re: When Cold, Car starts but then dies on first try, why? (paul79)

I set up the car per Lar's recomendation and it started right up. It was not very cold last night here in Atlanta..bout 50 degrees. I am interested to see how it does when it is colder. One thing I noticed was my fast idle speed was at about 1600 RPM. It was about 2000 which seemed to high. This high fast idle speed seems to be a common thread for all of us having this problem. I noticed the screw turned quite easily and I bet that over time it turned from it's set position. I hope others who are having this problem try this and let me know how it goes. It took me about 15 minutes to make the adjustments.

Good Luck
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Old 01-29-2002, 09:26 AM
 
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1997, 73, car, cold, corvette, couple, dies, fuel, problem, rev, rise, rpms, sarts, seconds, stalls, start, starts


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