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7/07/2018 9:52 AM  #1


Low speed bucking surging, whatever ya call it

‘66 289, Edelbrock 650  and Exelbrock mild but not stock cam, T5, power brakes. Car is acting like.its in to high of a gear at low speed. For example normally I can cruise 25 mph in third now I have to drop to 2nd. When I first put the motor together it did this and I adjusted the timing for max vacuum and that fix it. I have 19” of vac and can’t get it to run right. Anybody got an idea what’s wrong?


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
 

7/07/2018 10:00 AM  #2


Re: Low speed bucking surging, whatever ya call it

I'd probably start by cleaning out the carb.  A low speed surge can be a sign that its too lean.  If you haven't recently changed anything with the carb (metering rods or jets) then the likely culprit is something is stuck in one of the jets and partially occluding it. 

Another thought, when's the last time the fuel filter was changed? 

 

7/07/2018 11:18 AM  #3


Re: Low speed bucking surging, whatever ya call it

TKOPerformance wrote:

I'd probably start by cleaning out the carb.  A low speed surge can be a sign that its too lean.  If you haven't recently changed anything with the carb (metering rods or jets) then the likely culprit is something is stuck in one of the jets and partially occluding it. 

Another thought, when's the last time the fuel filter was changed? 

Just did all that and it ran fine. Disassembled the carb, cleaned and put it back together with new gaskets. Didn’t change metering rod or jets. New fuel filter.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

7/07/2018 4:25 PM  #4


Re: Low speed bucking surging, whatever ya call it

A vacuum leak could cause the same symptoms, and would be most noticeable right at and just off idle, which is where we typically cruise (1,500RPM give or take I'm assuming).  Try driving it around with a vacuum gauge on it and see what it does when the bucking/surging occurs. 

 

7/07/2018 7:05 PM  #5


Re: Low speed bucking surging, whatever ya call it

TKOPerformance wrote:

A vacuum leak could cause the same symptoms, and would be most noticeable right at and just off idle, which is where we typically cruise (1,500RPM give or take I'm assuming).  Try driving it around with a vacuum gauge on it and see what it does when the bucking/surging occurs. 

 
That's what I'm thinking. It ran really well after I reworked the carb. I'm going to try putting the vac gauge on it and see what I come up with.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

7/08/2018 5:41 AM  #6


Re: Low speed bucking surging, whatever ya call it

If you can't find an obvious leak, unfortunately small block Fords are somewhat notorious for leaking at the bottom of the intake ports into the lifter valley.  So if spraying all the possible leak points with carb cleaner doesn't produce any results there may still be a leak in an area that effectively cannot be tested. 

 

7/08/2018 4:10 PM  #7


Re: Low speed bucking surging, whatever ya call it

Just a thought - which port on the carb (Edelbrock 1406 I take it to be) is your vacuum advance hose hooked up to? It should be hooked up to the port on the passenger side of the carb.


68 coupe - 351W, 4R70W, 9" 3.25 -- 65 convertible - 289 4v, C4, 8" 3.00
 

7/08/2018 4:30 PM  #8


Re: Low speed bucking surging, whatever ya call it

TKOPerformance wrote:

If you can't find an obvious leak, unfortunately small block Fords are somewhat notorious for leaking at the bottom of the intake ports into the lifter valley.  So if spraying all the possible leak points with carb cleaner doesn't produce any results there may still be a leak in an area that effectively cannot be tested. 

 
I had this problem twice. It was suggested to me by MS that it was my intake gaskets. I had never heard of such a thing so I got a boroscope and saw gaskets sticking into the intake runner port and also saw gaps where the gasket should have been on both heads. It involves taking the carb off to look at it and it is not easy to get the probe down there to look. I also saw the intake valves loaded with carbon.


70, ragtop 351W/416 stroker Edel Performer heads w pro flow 4, Comp roller 35-421-8. T5
 

7/08/2018 5:40 PM  #9


Re: Low speed bucking surging, whatever ya call it

I recently installed an Edelbrock Performer intake on my car and finding the right gaskets was a real PITA.  The Edelbrock gaskets were recommended, but they were not right for the water passages in the heads.  I had a couple sets of gaskets lying around the shop, so I checked two more intake gaskets I had, and they had the same problem.  Then it dawned on me that what I had, and apparently the Edelbrocks too, were designed for later engines (I know the ones I had were for 5.0s).

I finally found a set of Mahle gaskets that looked exactly like what I took off the engine,  MS15172, fit like a glove.  I used Permatex Aviation Form A Gasket to seal the ports (both sides of the gaskets, intake face, and head), a few dabs of Permatex Hi Tack to hold them in place, and a little silicone around the ports.  Its a lot of prep, but seals like an absolute dream.  Plus, with the Permatex, if the bolts loosen up, even if it starts to leak a little, you can just tighten it back down and it will reseal because that stuff never really hardens.  Of course, install the intake, run the engine up to operating temp, allow it to fully cool, and retorque the bolts. 

 

7/08/2018 6:54 PM  #10


Re: Low speed bucking surging, whatever ya call it

Ron68 wrote:

Just a thought - which port on the carb (Edelbrock 1406 I take it to be) is your vacuum advance hose hooked up to? It should be hooked up to the port on the passenger side of the carb.

 
Passenger side.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

7/09/2018 7:26 PM  #11


Re: Low speed bucking surging, whatever ya call it

Sounds like a lean issue I had on a Holley back in the 80's try fattening it up a touch and see what happens.
 

 

7/15/2018 8:28 AM  #12


Re: Low speed bucking surging, whatever ya call it

Update on the off idle bucking problem. I did the carb cleaner test and turns out the carb to manifold gasket was leaking. I had recently rebuilt the carb using the Edelbrock kit and used the thick gasket included in the kit. I swapped it out for a much thinner one I made myself and tightened the mounting nuts down with a very short wrench. Problem solved, runs like a scalded dog! Thanks for all of the help guys.


"anyone that stops learning is old, whether at twenty or eighty"Henry Ford
     Thread Starter
 

7/15/2018 10:16 AM  #13


Re: Low speed bucking surging, whatever ya call it

TKOPerformance wrote:

I recently installed an Edelbrock Performer intake on my car and finding the right gaskets was a real PITA.  The Edelbrock gaskets were recommended, but they were not right for the water passages in the heads.  I had a couple sets of gaskets lying around the shop, so I checked two more intake gaskets I had, and they had the same problem.  Then it dawned on me that what I had, and apparently the Edelbrocks too, were designed for later engines (I know the ones I had were for 5.0s).

I finally found a set of Mahle gaskets that looked exactly like what I took off the engine,  MS15172, fit like a glove.  I used Permatex Aviation Form A Gasket to seal the ports (both sides of the gaskets, intake face, and head), a few dabs of Permatex Hi Tack to hold them in place, and a little silicone around the ports.  Its a lot of prep, but seals like an absolute dream.  Plus, with the Permatex, if the bolts loosen up, even if it starts to leak a little, you can just tighten it back down and it will reseal because that stuff never really hardens.  Of course, install the intake, run the engine up to operating temp, allow it to fully cool, and retorque the bolts. 

I can attest to that.
  Back in 1973 I used Permatex Aviation Form a Gasket to assemble a C-85-8 for my experimental home built. I have the same container which  is still  used on my auto projects. GREAT STUFF!


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

7/15/2018 2:51 PM  #14


Re: Low speed bucking surging, whatever ya call it

BillyC wrote:

Update on the off idle bucking problem. I did the carb cleaner test and turns out the carb to manifold gasket was leaking. I had recently rebuilt the carb using the Edelbrock kit and used the thick gasket included in the kit. I swapped it out for a much thinner one I made myself and tightened the mounting nuts down with a very short wrench. Problem solved, runs like a scalded dog! Thanks for all of the help guys.

Good deal, glad you got it sorted out!
 

 

7/16/2018 3:53 PM  #15


Re: Low speed bucking surging, whatever ya call it

Rudi wrote:

TKOPerformance wrote:

I recently installed an Edelbrock Performer intake on my car and finding the right gaskets was a real PITA.  The Edelbrock gaskets were recommended, but they were not right for the water passages in the heads.  I had a couple sets of gaskets lying around the shop, so I checked two more intake gaskets I had, and they had the same problem.  Then it dawned on me that what I had, and apparently the Edelbrocks too, were designed for later engines (I know the ones I had were for 5.0s).

I finally found a set of Mahle gaskets that looked exactly like what I took off the engine,  MS15172, fit like a glove.  I used Permatex Aviation Form A Gasket to seal the ports (both sides of the gaskets, intake face, and head), a few dabs of Permatex Hi Tack to hold them in place, and a little silicone around the ports.  Its a lot of prep, but seals like an absolute dream.  Plus, with the Permatex, if the bolts loosen up, even if it starts to leak a little, you can just tighten it back down and it will reseal because that stuff never really hardens.  Of course, install the intake, run the engine up to operating temp, allow it to fully cool, and retorque the bolts. 

I can attest to that.
  Back in 1973 I used Permatex Aviation Form a Gasket to assemble a C-85-8 for my experimental home built. I have the same container which  is still  used on my auto projects. GREAT STUFF!

That is good stuff, Rudi. I used it plus a silk thread to seal the crankcase halves of a Continental O-200 in a Cessna 150.
 


68 coupe - 351W, 4R70W, 9" 3.25 -- 65 convertible - 289 4v, C4, 8" 3.00
 

Board footera


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