The Ford Barn

chuck stevens · 07-07-2021, 01:24 PM

I have had a lean bucking at low speed with my 8BA, over the 4th I talked to a Mopar guy who experienced the exact same thing with a 360 dodge. The symptoms he experienced, and the things he tried, matched everything I had done. He found out Mopars have porous intakes on certain years. This gives you a very hard to detect vacuum leak on the inside of the manifold.
I have changed both the intake and carb but, my question, could this flathead have a small crack inside the intake runners that opens up after it gets up to temp? It always starts and runs, but bucks at 30-35 mph badly.
I thought maybe someone else may have come across this.
thanks for your input, Chuck.

rotorwrench · 07-07-2021, 02:05 PM

I've never had a problem with a cast iron 8BA or 8CM. Some of the mid 30s aluminum intakes had problems like this. You may have a sticky valve. Loose distributor bushings can cause intermittent miss.

19Fordy · 07-07-2021, 02:27 PM

Could be a bad condenser. Change it and see what happens.
I had that same problem on my 8BA and it was a bad condenser.

JayChicago · 07-07-2021, 07:07 PM

“lean bucking at low speed”.
How do you know it’s due to a lean condition? If it is, pulling the choke a little should make it run smooth.
Both bad condenser and bad coil will often work fine when cool, then start to fail when warm.

chuck stevens · 07-08-2021, 06:40 AM

It had Petronix with their coil, I switched back to standard points and condenser, the distributor, is a sbc turned down to fit. It does run some better with the choke pulled. But I can take the idle mixture screws almost out with no response, with both carbs same. 15 inches of vacuum at idle.

Shoovel · 07-08-2021, 07:19 AM

Sponsored Links (Register now to hide all advertisements)

Chuck,
My 39 had a similar problem. It would surge at that speed, not really buck. I rebuilt the 94 carb and changed the jets to 51’s from the 55’s that was in the carb. I found that I had set the float too low, so I re-set the float level and re-installed the 55’s. What an improvement.
I have 19” of vacuum at idle. Hope this may help. Good luck.

19Fordy · 07-08-2021, 09:33 AM

Chuck, I have used the Holley 37-720 kit with excellent results. You will find parts in the kit that you won't need. To make the job easier when you rebuild your carb, build a little stand to support the carb. Buy a spray can of carb cleaner and wear safety glasses so the carb cleaner doesn't blow back into your eyes. Take photos as you disassemble, if needed.
The kit is easy to install. Use a drop of oil on all the rubber o rings.
https://www.summitracing.com/parts/hly-37-720

I have also used this Holley kit with excellent results. I didn't notice any difference between the this kit and the 37-720 kit.
https://www.ebay.com/itm/30402649768...MAAOSwJfVeMUMW

ALSO: I bought this book before rebuilding my Holley 4160. It is a huge help and does a great job of explaining "what is what" and "what goes where". Also, Google "how to Rebuild A Holley 4160 Carburetor" and you will find lots of helpful You tube videos.
https://www.thriftbooks.com/w/holly-...dition=4327555

Also, I would also now buy this book and follow the instructions shown:
https://www.musclecardiy.com/tech-ti...rebuild-guide/

Not trying to spend your dough but, the information and confidence you derive from these books will inspire you to tackle the job if you have never done it before.

One last comment: If you have a heavy hand, be sure to use an inch pound torque wrench when you reattach the float bowls as the threads are easily stripped because of over tightening. I did that one time and had to install a Helicoil. If you just gently snug the screws you will be fine as the gasket only needs to compress a little bit. Be gentle. Practice to get the "feel" of using an inch pound torque wrench BEFORE you assemble your carb. as the specs. are very low in. lbs..

BUBBAS IGNITION · 07-09-2021, 09:06 AM

Internal vac leak may be found by hooking a vacuum gauge to the dip stick tube , should have zero vac .....

Bored&Stroked · 07-09-2021, 04:21 PM

Quote:

Originally Posted by BUBBAS IGNITION

Internal vac leak may be found by hooking a vacuum gauge to the dip stick tube , should have zero vac .....

For that to work, you'd have to plug the breather tube as well . . .

supereal · 07-10-2021, 11:59 AM

Make sure your gas tank cap is correct. An incorrect one will produce a vacuum in the tank, reducing fuel delivery. We have found radiator caps on fuel tanks.

07-07-2021, 01:24 PM	#1
chuck stevens Senior Member Join Date: May 2010 Location: upstate new york Posts: 758	more on the 8BA problems I have had a lean bucking at low speed with my 8BA, over the 4th I talked to a Mopar guy who experienced the exact same thing with a 360 dodge. The symptoms he experienced, and the things he tried, matched everything I had done. He found out Mopars have porous intakes on certain years. This gives you a very hard to detect vacuum leak on the inside of the manifold. I have changed both the intake and carb but, my question, could this flathead have a small crack inside the intake runners that opens up after it gets up to temp? It always starts and runs, but bucks at 30-35 mph badly. I thought maybe someone else may have come across this. thanks for your input, Chuck.

07-07-2021, 02:05 PM	#2
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,422	Re: more on the 8BA problems I've never had a problem with a cast iron 8BA or 8CM. Some of the mid 30s aluminum intakes had problems like this. You may have a sticky valve. Loose distributor bushings can cause intermittent miss.

07-07-2021, 02:27 PM	#3
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,921	Re: more on the 8BA problems Could be a bad condenser. Change it and see what happens. I had that same problem on my 8BA and it was a bad condenser.

07-07-2021, 07:07 PM	#4
JayChicago Senior Member Join Date: Jan 2019 Location: Chicago Posts: 728	Re: more on the 8BA problems “lean bucking at low speed”. How do you know it’s due to a lean condition? If it is, pulling the choke a little should make it run smooth. Both bad condenser and bad coil will often work fine when cool, then start to fail when warm.

07-08-2021, 06:40 AM	#5
chuck stevens Senior Member Join Date: May 2010 Location: upstate new york Posts: 758	Re: more on the 8BA problems It had Petronix with their coil, I switched back to standard points and condenser, the distributor, is a sbc turned down to fit. It does run some better with the choke pulled. But I can take the idle mixture screws almost out with no response, with both carbs same. 15 inches of vacuum at idle.

07-08-2021, 07:19 AM	#6
Shoovel Member Join Date: Mar 2021 Location: Milton Ontario Canada Posts: 83	Re: more on the 8BA problems Sponsored Links (Register now to hide all advertisements) Chuck, My 39 had a similar problem. It would surge at that speed, not really buck. I rebuilt the 94 carb and changed the jets to 51’s from the 55’s that was in the carb. I found that I had set the float too low, so I re-set the float level and re-installed the 55’s. What an improvement. I have 19” of vacuum at idle. Hope this may help. Good luck.

07-08-2021, 09:33 AM	#7
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,921	Re: more on the 8BA problems Chuck, I have used the Holley 37-720 kit with excellent results. You will find parts in the kit that you won't need. To make the job easier when you rebuild your carb, build a little stand to support the carb. Buy a spray can of carb cleaner and wear safety glasses so the carb cleaner doesn't blow back into your eyes. Take photos as you disassemble, if needed. The kit is easy to install. Use a drop of oil on all the rubber o rings. https://www.summitracing.com/parts/hly-37-720 I have also used this Holley kit with excellent results. I didn't notice any difference between the this kit and the 37-720 kit. https://www.ebay.com/itm/30402649768...MAAOSwJfVeMUMW ALSO: I bought this book before rebuilding my Holley 4160. It is a huge help and does a great job of explaining "what is what" and "what goes where". Also, Google "how to Rebuild A Holley 4160 Carburetor" and you will find lots of helpful You tube videos. https://www.thriftbooks.com/w/holly-...dition=4327555 Also, I would also now buy this book and follow the instructions shown: https://www.musclecardiy.com/tech-ti...rebuild-guide/ Not trying to spend your dough but, the information and confidence you derive from these books will inspire you to tackle the job if you have never done it before. One last comment: If you have a heavy hand, be sure to use an inch pound torque wrench when you reattach the float bowls as the threads are easily stripped because of over tightening. I did that one time and had to install a Helicoil. If you just gently snug the screws you will be fine as the gasket only needs to compress a little bit. Be gentle. Practice to get the "feel" of using an inch pound torque wrench BEFORE you assemble your carb. as the specs. are very low in. lbs.. Last edited by 19Fordy; 07-08-2021 at 04:54 PM.

07-09-2021, 09:06 AM	#8
BUBBAS IGNITION Senior Member Join Date: May 2010 Location: SPEEDWAY INDIANA Posts: 4,148	Re: more on the 8BA problems Internal vac leak may be found by hooking a vacuum gauge to the dip stick tube , should have zero vac ..... __________________ If it Makes Spark, we do it !!!! www.bubbasignition.com [email protected]

07-10-2021, 11:59 AM	#10
supereal Senior Member Join Date: Jul 2014 Location: Iowa Posts: 1,634	Re: more on the 8BA problems Make sure your gas tank cap is correct. An incorrect one will produce a vacuum in the tank, reducing fuel delivery. We have found radiator caps on fuel tanks.