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Old 01-14-2020, 06:27 PM   #1
drolston
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Default Stoplight Stall

59A/B starts easily and runs great, but for some reason takes spells where it will die when stopping. Always re-starts instantly, but it is annoying and kind of a safety hazard.

Engine is 284 with mild street cam, Offy 425 heads and Offy 3 x 2 intake. Speedway 97 carbs with choke and idle circuits only on center carb. The linkage is adjusted so that the secondaries really are closed at idle. Pretty sure I have the float levels right at half an inch.

Adjusted idle rpm to about 750. Adjusted idle jets closed to the point where idle RPM drops, and then open half a turn. Recently re-jetted all carbs from .045 to .047 to reduce overheating, but that did not improve the stalling. Ignition is Pertronix, and I have a nice big blue spark at idle.

So what should I be looking at? Check the center float again? Open the idle jets?
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Old 01-14-2020, 08:43 PM   #2
paul2748
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Default Re: Stoplight Stall

Are the idle mixture screws screwed all the way in on the outer carbs?
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Old 01-14-2020, 08:56 PM   #3
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Default Re: Stoplight Stall

My thought is possibly float setting.
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Old 01-14-2020, 09:16 PM   #4
drolston
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Default Re: Stoplight Stall

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Originally Posted by paul2748 View Post
Are the idle mixture screws screwed all the way in on the outer carbs?
The outer 97's are built as secondaries, with no choke and no idle circuits, and they are on progressive linkage so they do not even start to open until about half throttle. All idle tuning is done on the center carb.
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Old 01-14-2020, 09:17 PM   #5
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Default Re: Stoplight Stall

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Originally Posted by Branded View Post
My thought is possibly float setting.
Do you think too low, or too high? Which would cause stalling when coming to a stop?
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Old 01-14-2020, 09:42 PM   #6
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Default Re: Stoplight Stall

Quote:
Originally Posted by drolston View Post
59A/B starts easily and runs great, but for some reason takes spells where it will die when stopping. Always re-starts instantly, but it is annoying and kind of a safety hazard.

Engine is 284 with mild street cam, Offy 425 heads and Offy 3 x 2 intake. Speedway 97 carbs with choke and idle circuits only on center carb. The linkage is adjusted so that the secondaries really are closed at idle. Pretty sure I have the float levels right at half an inch.

Adjusted idle rpm to about 750. Adjusted idle jets closed to the point where idle RPM drops, and then open half a turn. Recently re-jetted all carbs from .045 to .047 to reduce overheating, but that did not improve the stalling. Ignition is Pertronix, and I have a nice big blue spark at idle.

So what should I be looking at? Check the center float again? Open the idle jets?
FLOAT LEVEL should not be confused with FUEL LEVEL.
Float needs to be set 9/32", measuring down from gasket surface of bowl to the top - adjacent to the hump - on the free end of the float... Just a wee bit lower than level when looking across it. This usually gives the magic 15/32" to 1/2" FUEL LEVEL.
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Old 01-15-2020, 12:40 PM   #7
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Default Re: Stoplight Stall

I will check the float again. The good thing about the Stromberg 97 is that you can pull the top off and actually measure the fuel level in the bowl with the fuel line and pump still hooked up.

Any other suspects for this problem?
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Old 01-15-2020, 12:57 PM   #8
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Default Re: Stoplight Stall

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I will check the float again. The good thing about the Stromberg 97 is that you can pull the top off and actually measure the fuel level in the bowl with the fuel line and pump still hooked up.

Any other suspects for this problem?
The 3 items for combustion. Electrical, fuel and air.
hows the air filters, any difference if you remove air filters, any rpm increase.
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Old 01-15-2020, 01:01 PM   #9
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Default Re: Stoplight Stall

Did you synchronize the carbs?
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Old 01-15-2020, 01:32 PM   #10
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Default Re: Stoplight Stall

Upon re-starting, does it sound, and act rich? Black smoke? These would be symptoms of flooding due to stopping. Make sure your floats are working under fuel pressure, it could be any of the three.
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Old 01-15-2020, 01:43 PM   #11
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Default Re: Stoplight Stall

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Originally Posted by solidaxle View Post
Did you synchronize the carbs?
Not applicable. The two end carbs are completely closed at throttle off and do not even have idle fuel circuits. All idle tuning is on the center carb.
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Old 01-15-2020, 01:45 PM   #12
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Default Re: Stoplight Stall

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Originally Posted by hook00pad View Post
Upon re-starting, does it sound, and act rich? Black smoke? These would be symptoms of flooding due to stopping. Make sure your floats are working under fuel pressure, it could be any of the three.
Starts up and runs fine after a stall. No stumbling or other indications of flooding, such as gas smell or black smoke. Fuel pressure is regulated to 2.5 psi and I have a gauge on the pump output, after the regulator.
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Old 01-15-2020, 06:30 PM   #13
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Default Re: Stoplight Stall

Does it idle slowly,rough,or do anything odd before it dies--or just shut off instantly like you turned the key off?
I'm trying to decide whether it might be something affecting power to the coil or distributor when stopping...like a wire flexing or a switch doing something very weird.


I once fixed a complaint like this in a '60's Chevy when the small spring on the disc in the starter solenoid broke and let that disc touch the starter motor contact and the ignition resistor bypass contact simultaneously when stopping quickly. It grounded the coil to the starter brushes. WEIRD! That's not your problem of course but odd things can happen.


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Old 01-15-2020, 09:10 PM   #14
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Default Re: Stoplight Stall

Checked vacuum?
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Old 01-16-2020, 08:24 AM   #15
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Default Re: Stoplight Stall

You might try to isolate the problem by blocking off and disconnecting the linkage to the end carbs and run it on the center carb.
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Old 01-16-2020, 04:51 PM   #16
drolston
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Default Re: Stoplight Stall

Quote:
Originally Posted by solidaxle View Post
You might try to isolate the problem by blocking off and disconnecting the linkage to the end carbs and run it on the center carb.
The end carbs are on progressive linkage and do not even start to open until about half throttle.
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Old 01-16-2020, 04:55 PM   #17
drolston
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Default Re: Stoplight Stall

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Originally Posted by Randy in ca View Post
Checked vacuum?
That will be my next action. Spray some starting ether around the carb bases and manifold to see if I get any RPM surge.

Is there a better way to check for vacuum leaks?
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Old 01-16-2020, 06:39 PM   #18
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Default Re: Stoplight Stall

Quote:
Originally Posted by drolston View Post
The end carbs are on progressive linkage and do not even start to open until about half throttle.

I assumed you had progressive linkage. By blocking off the end carbs you are narrowing down the search of your problem. You seem knowledgeable, just keep hammering at it. Let us know what you find.
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