Hesitation upon acceleration issue

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Jan 31, 2007
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Hey guys...I've done as much research and troubleshooting as possible on this one and I just need to ask for more help.

My uncle's 1972 FJ40 (stock engine) keeps hesitating upon acceleration, although the engine idles very smoothly. It hesitates the most when the engine is under load or when you step on the gas abruptly.

The following changes have been made to the vehicle (one by one) in order to solve the issue. Although the hesitation problem has not been resolved, it has been reduced as a result of the following changes:


  1. Valve adjustment (no sticking valves or tight clearances)
  2. New gas tank (old tank had too much rust inside), new fuel lines, fuel filter. I tried installing my spare fuel pump to see if that was the issue as well, and no change in hesitation.
  3. Stock Carburetor rebuilt by 65swb45 (Thanks Mark) The carb now has the correct accelerator pump which it did not have before.
  4. Wiring harness from key switch to coil, regulator checked and cleaned.
  5. battery cables, ground connections checked/cleaned
  6. new distributor cap, spark plugs, plug wires, regulator, air filter
  7. electronic ignition (Petronix) installed with new coil. Point, condenser, ballast resistor, old coil, removed as possible culprits.
  8. Vacuum is pulling at a steady 22 inches of mercury during idle.
  9. I've played with the timing and idle mixture for hours. Seems to hesitate a little less when timing is set to 21 degrees BTDC and the idle screw is opened more than 1.5 turns from closed position, and the idle rpm is increased to 700+ rpm

Where do I go from here? I first thought I had a fuel delivery problem, then I started looking at the electrical stuff, and everything else mentioned above. Your help is greatly appreciated.

soy_boxes131.jpg
 
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Vacuum leak? Spray some carb cleaner around the carb and intake manifold while the engine is running and if the idle changes you've found a leak.
 

Downey

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You're probably running out of fuel or spark, only on a hard acceleration. If I'm right, I don't suspect the Pertronix because they are so dependable, and because you've explained that you hooked it up corectly (with 40,000 volt coil). That then leaves fuel starvation. Mark A. is one of my best friends on the planet, and I respect his right to believe he is one of the few on the planet who can rebuild a factory carburetor, and make it stick. I'd have a little come to Jesus talk with Mark to see if he can shed some light on the subject
 
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How does it run if you disconnect the vacuum advance/retard from the distributor?

Hey guys...I've done as much research and troubleshooting as possible on this one and I just need to ask for more help.


  1. I've played with the timing and idle mixture for hours. Seems to hesitate a little less when timing is set to 21 degrees BTDC and the idle screw is opened more than 1.5 turns from closed position, and the idle rpm is increased to 700+ rpm
 

JohnnyC

Long ago TLCA# 2231
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Jun 17, 2005
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UpState Ny, Wells Me
do you have a vacuum advance or retard dissy?

then are you sure its hooked up right?

you dont want to have the retard dissy hooked up to ported vac

is you centrifugal advance working? had you check it? you may have a weight hung up?

BTW just throwing out ideas :) sound like you have tried alot of different things


BTW i've had a bad run of bad advice these days :rolleyes:
 
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I have a stock retard dissy. I've tried disconnecting and plugging up the vacuum line to the distributor. There is no change in hesitation. Why is my vacuum so high at a steady 22 inches of Hg? Does that eliminate the possibility of a vacuum leak?
 
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with vacuum that high i doubt you have a vacuum leak, I'd look into fuel filter problems. I'm not much help being i have the same problem.
 
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with vacuum that high i doubt you have a vacuum leak, I'd look into fuel filter problems. I'm not much help being i have the same problem.

With the gas tank being brand new, the fuel filter is nice and clean every time I check it. Hopefully we can find a fix for both our cruisers.
 
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Southern Utah
When you hit your throttle, and it brings up a flat spot, that is generally caused by to much gas being sent to the motor from the accel. pump.. most people think it is caused by your motor not getting enough fuel, but it is actually most often too much gas being sent from the accel. pump.
 
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When you hit your throttle, and it brings up a flat spot, that is generally caused by to much gas being sent to the motor from the accel. pump.. most people think it is caused by your motor not getting enough fuel, but it is actually most often too much gas being sent from the accel. pump.

I believe Nagalfar is correct. I took the spark plugs out of my 78 FJ40. They were grey, they way they should look. I put them in the 72 FJ40 which is having this hesitation issue. The hesitation did not go away. After driving it for about a quarter mile. I took the plugs out, and they were pitch black. They were also damp with gasoline.

There is definitely too much gas being pumped through. Where do I look first to troubleshoot? The carburetor was just recently rebuilt with a new accelerator pump. Could it be that I need another kind of accelerator pump?
 
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Atascadero, CA
I have a stock retard dissy. I've tried disconnecting and plugging up the vacuum line to the distributor. There is no change in hesitation. Why is my vacuum so high at a steady 22 inches of Hg? Does that eliminate the possibility of a vacuum leak?

i've been through my fair share of advance problems and from what you said about unplugging it and the hesitation doesnt change, it should get worse, alot worse without the vacuum hooked up. from what your saying i would look deeper into that advance. i dont know what style dizzy you have but some have a spring that controls how hard it is to advance and it is common for that to get stuck or something in that linkage to jam. i would get a hand vacuum pump and hook it up the the dizzy and then take the cap off and see if you can see it advancing as you pump up the vacuum. you can also pump it up by hand while the engine is running and check your timing to see how far it advances.

-miles
 
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The unit attached to my stock distributor on the '72 only retards the timing.

My '78 cruiser has a retard and advance distributor. With the retard port disabled and the retard vacuum line plugged, the vehicle accelerates just fine.

Would a disfunctional retard unit on the distributor of the '72 cause the vehicle to hesitate?

I installed a new distributor from Specter about 6 months ago and ran the vehicle with no apparent change in hesitation. I ended up just returning the dizzy and installing the old one back.
 
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May 19, 2004
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Midwestern Flatlands
I believe Nagalfar is correct. I took the spark plugs out of my 78 FJ40. They were grey, they way they should look. I put them in the 72 FJ40 which is having this hesitation issue. The hesitation did not go away. After driving it for about a quarter mile. I took the plugs out, and they were pitch black. They were also damp with gasoline.

There is definitely too much gas being pumped through. Where do I look first to troubleshoot? The carburetor was just recently rebuilt with a new accelerator pump. Could it be that I need another kind of accelerator pump?

Check the float level in your carb
 
Joined
Jun 22, 2006
Messages
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Southern Utah
I believe Nagalfar is correct. I took the spark plugs out of my 78 FJ40. They were grey, they way they should look. I put them in the 72 FJ40 which is having this hesitation issue. The hesitation did not go away. After driving it for about a quarter mile. I took the plugs out, and they were pitch black. They were also damp with gasoline.

There is definitely too much gas being pumped through. Where do I look first to troubleshoot? The carburetor was just recently rebuilt with a new accelerator pump. Could it be that I need another kind of accelerator pump?

What carb are you running?
 

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