68 auto stalls off idle acceleration, need help.

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68BlueStraight6
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68 auto stalls off idle acceleration, need help.

Post #1 by 68BlueStraight6 » Thu Oct 06, 2016 8:18 pm

I have a 68 mustang with a straight 6(obviously) and an auto Trans. Everything that unbolts has been replaced or rebuilt. Have the advance set to 12 degrees, have a steady 20 pounds of vacuum at idle and idle rpm is 1000. My problem is the car idles beautifully and once up and going drives and accelerates perfectly. Now from a stop it dips real low in rpm once you try to accelerate the car either dies or comes real close to it. PLEASE HELP!

mustang6
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Re: 68 auto stalls off idle acceleration, need help.

Post #2 by mustang6 » Fri Oct 07, 2016 3:29 am

First thing I would do is (with the engine off) look down the top of the carb and operate the throttle, looking for the accelerator pump shot of gas. Your symptoms exactly match a bad or misadjusted accelerator pump. Those pump diaphragms commonly fail and leave you with a bad off-idle hesitation. I've even seen rebuilt carbs where the accelerator pump doesn't work because the internal check ball is missing.

Scott
Scott

68 Mustang 200 ci, 250-2V head, H/W 5200, Dual Headers, Comp Cams 252H, DSII w/ MSD 6AL, T-5, V8 suspension.

65 Ranchero 200 ci, late 170 head, Autolite 1101, 3.03 3 speed, Maverick 8" 4 lug rear with 3.55 gears.

68BlueStraight6
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Re: 68 auto stalls off idle acceleration, need help.

Post #3 by 68BlueStraight6 » Fri Oct 07, 2016 9:27 am

So with the engine off, just pull the throttle a little bit or full run to check the shot of fuel being sent? Is there a common setting for the pump as in using a feeler gauge between the adjustment screw and the pump diaphragm?

Thank you.

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Re: 68 auto stalls off idle acceleration, need help.

Post #4 by CZLN6 » Fri Oct 07, 2016 10:38 am

Howdy Blue:

Can we assume that you have the stock 1968 Autolite 1100 carb? Scott's suggestion is the 1st thing I'd be checking too. There is an adjustment on the accelerator pump. It is done by moving a roll pin to one of two hole that are marked "H" and "L" for temperatures above 50 degrees and L for temps below 50 degrees. Other than that it is a go/no go system. Check for the squirt first. Take a look down the carb while you have someone press the go pedal to the floor. Keep us posted.

Adios, David
co-author of the Falcon Performance Handbook
http://www.falcon6handbook.com/

68BlueStraight6
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Re: 68 auto stalls off idle acceleration, need help.

Post #5 by 68BlueStraight6 » Fri Oct 07, 2016 1:26 pm

Yes, stock autolite 1100 rebuilt by KP carbs. I haven't had a chance to test the squirt upon someone pushing down the throttle yet as I am still trying to get through my Friday at work. Can you elaborate on the adjustment of the accelerator pump though?

Thank you.

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Re: 68 auto stalls off idle acceleration, need help.

Post #6 by CZLN6 » Sat Oct 08, 2016 12:29 pm

HOwdy Back:

Q- "Can you elaborate on the adjustment of the accelerator pump though?"

A- Yes. The only adjustment to the accelerator pump system is selecting which hole to position the roll pin. The 'H" hole position is a leaner squirt, from the accelerator pump system because warmer, above 50 degrees, requires less gas. The "L" setting hole provides a richer squirt. If the temperature is below 50 degrees the engine requires more gas. Changing the roll pin hole will not fix a weak pump plunger. A rebuild kit will include a new plunger. The rebuild kit instruction sheet will also identify the location of the required check balls. TIP- when rebuilding plan to work in a clean, well lighted area. I like to work on an old white sheet to keep things from rolling or bouncing onto the floor. Be sure to change the fuel filter and add an inline filter as well.

In most cases when the accelerator pump is working up to standard the "H" pin position works fine. The automatic choke should provide the extra richness need for cold starts and warm up and the "H" setting will be more economical mpg wise. In the days of the Mobil Mileage competition a common practice was to disconnect the accelerator pump all together, and just carefully feather the throttle pedal on take off and acceleration.

FYI, the accelerator pump in the 1100 carbs was a weak part of the system. The plunger can be made of various materials but all seldom last more than a few years in normal use. Daily driving and on engines with a manual trans shorten the time between carb rebuilds. But even with an auto trans and mostly highway driving a rebuild is likely necessary every few years.

FYI- a weak accelerator pump can be crutched by increasing the initial advance setting by 5 degrees over stock specs. This will also help with power and economy. And by richening the low speed idle screw setting. This will hurt mpg some.

FYI- the 1968 Autolite 1100 is down on cfm compared to '67 and earlier 1100s for 200 engines. The earlier 1100s were rated at 185 cfm. The '68 1100s were rated at 150 cfm. The '68 1100 lost the Spark Control Valve and gained a distributor with both centrifugal and vacuum spark advance. The improvement in the distributor does not make up for the power loss, when compared to earlier 200s, due to a smaller cfm.

Good luck and keep us posted on your progress.

Adios, David
co-author of the Falcon Performance Handbook
http://www.falcon6handbook.com/

68BlueStraight6
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Re: 68 auto stalls off idle acceleration, need help.

Post #7 by 68BlueStraight6 » Sun Oct 09, 2016 3:04 pm

So pulling in the throttle while looking down the throttle body, it appears a plenty healthy stream is jetting out. Now when I took the air filter off, I did notice fuel seepage around a few of the screw heads as well as all along that plastic rod. I was able to tighten the screws each about a quarter turn. Not sure what to do about the rod leak though. Not sure how to attach images in this forum.

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Re: 68 auto stalls off idle acceleration, need help.

Post #8 by CZLN6 » Mon Oct 10, 2016 11:42 am

Howdy again Blue:

Top screws loosening over time is not unusual. Seepage is not unusual with these carbs but not leaks. Clean those areas and inspect regularly. Leaked gas will evaporate very quickly, especially on a hot engine, but will leave a stained mark behind as a tell-tale indication.

Since you have a healthy squirt, next try advancing the initial advance another 5 degrees over the stock 12 degree setting.

How old is the KP rebuild on the carb? Is this carb the original carb or a rebuilt replacement?

What position is pump arm roll pin in? If it is in the "L" position, it may be getting too big of a squirt on low speed take off.

Adios, David
co-author of the Falcon Performance Handbook
http://www.falcon6handbook.com/

68BlueStraight6
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Re: 68 auto stalls off idle acceleration, need help.

Post #9 by 68BlueStraight6 » Mon Oct 10, 2016 1:16 pm

Carb was my factory carb which I was told was in great shape. It was rebuilt roughly two months ago. The roll pin is currently in the H position.

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Re: 68 auto stalls off idle acceleration, need help.

Post #10 by mustang6 » Wed Oct 12, 2016 12:52 pm

Can you post a few pictures of the carb, distributor, vacuum advance routing, connection to auto transmission vacuum, etc? Did it do this before the rebuild? Perhaps that was the reason for the rebuild but it didn't fix the problem?
Scott

68 Mustang 200 ci, 250-2V head, H/W 5200, Dual Headers, Comp Cams 252H, DSII w/ MSD 6AL, T-5, V8 suspension.

65 Ranchero 200 ci, late 170 head, Autolite 1101, 3.03 3 speed, Maverick 8" 4 lug rear with 3.55 gears.

68BlueStraight6
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Re: 68 auto stalls off idle acceleration, need help.

Post #11 by 68BlueStraight6 » Wed Oct 12, 2016 2:52 pm

Sure can, but what do ya'll suggest as far as posting pictures to this forum? There is no attachment tab.

mustang6
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Re: 68 auto stalls off idle acceleration, need help.

Post #12 by mustang6 » Fri Oct 14, 2016 4:30 am

You have to load them somewhere else and link to them here.
Scott

68 Mustang 200 ci, 250-2V head, H/W 5200, Dual Headers, Comp Cams 252H, DSII w/ MSD 6AL, T-5, V8 suspension.

65 Ranchero 200 ci, late 170 head, Autolite 1101, 3.03 3 speed, Maverick 8" 4 lug rear with 3.55 gears.

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bubba22349
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Re: 68 auto stalls off idle acceleration, need help.

Post #13 by bubba22349 » Fri Oct 14, 2016 1:47 pm

You can find all the info you need on how to post pictures in the below link, you can use one of the free hosting sites to post your pictures. Good luck :nod:

viewtopic.php?f=47&t=48863
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.


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bubba22349
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Re: 68 auto stalls off idle acceleration, need help.

Post #15 by bubba22349 » Tue Oct 18, 2016 3:29 pm

Looks like you have the correct Autolite Carb (i.e. Without the SCV.) Now we just need to see which distribitor parts you have. Good luck :nod:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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