302 hesitation
08-29-2017, 06:33 AM
#1
302 hesitation
I have a 1972 Ford 302 in my 67 mustang backed by a tremac 5 speed. The past few days when I shift 3rd 4th and 5th at high rpm under a load it will jerk and hesitate for a moment. but only at a specific time and load, the rest of the time it's fine, I have an edelbrock 600 carb, and flame thrower 2 distributor. Spark plugs look ok and coil is good
I'm lost does anyone have ideas as to what may cause that?
I'm lost does anyone have ideas as to what may cause that?
08-29-2017, 09:07 PM
#6
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Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
Lets start with the free and easy stuff.
It seems odd that it only does it under load in 4/5th shift.
A hesitation or "engine bog" is often fuel related. one of the systems that is responsible for eliminating engine bog or hesitation during transition between no throttle and wide open is the accelerator pump.
This is worth checking the accel pump piston in the AFB 600 type carbs like you have is prone to wear and will leak past and/or deliver a weak pump shot.
To check simply pull the air cleaner off (is the air cleaner nice looking? or is it full of dirt?) and look down the carb ventures with the engine off roll on full throttle using the linkage you should see two solid streams of fuel **** out into the front ventures with good velocity so that they hit the little circle things in the middle of the ventures with good force.
Check that and see how it looks
It seems odd that it only does it under load in 4/5th shift.
A hesitation or "engine bog" is often fuel related. one of the systems that is responsible for eliminating engine bog or hesitation during transition between no throttle and wide open is the accelerator pump.
This is worth checking the accel pump piston in the AFB 600 type carbs like you have is prone to wear and will leak past and/or deliver a weak pump shot.
To check simply pull the air cleaner off (is the air cleaner nice looking? or is it full of dirt?) and look down the carb ventures with the engine off roll on full throttle using the linkage you should see two solid streams of fuel **** out into the front ventures with good velocity so that they hit the little circle things in the middle of the ventures with good force.
Check that and see how it looks
08-30-2017, 12:16 AM
#7
Ok i didn't see anything that looked dirty, even squirted some carb cleaner in there. I try to keep it all very clean and air cleaner filter looks good.
Let me elaborate on how it acts, maybe it will help. It has to be high speed (don't have a tach to know rpm but I mean high rpm) in one of the top three gears. For example in fifth, it will be fine until you get over 60 mph (sounds about like 1500 rpm) it starts hesitating but it's not continually, it's a couple seconds at a time and the faster you go after that point it will do it more and more, especially at interstate speeds (about 2400 rpm) and up hills. Going down a hill it's fine and flat ground varies. But if you are going 30mph for example and you mash the pedal in fifth, it'll bog a little like normal but it will do it without missing a beat. Same goes for forth, if I'm in forth going 50mph (about 3000 rpm) it'll do it bad but anything below that even up a hill is fine.
Let me elaborate on how it acts, maybe it will help. It has to be high speed (don't have a tach to know rpm but I mean high rpm) in one of the top three gears. For example in fifth, it will be fine until you get over 60 mph (sounds about like 1500 rpm) it starts hesitating but it's not continually, it's a couple seconds at a time and the faster you go after that point it will do it more and more, especially at interstate speeds (about 2400 rpm) and up hills. Going down a hill it's fine and flat ground varies. But if you are going 30mph for example and you mash the pedal in fifth, it'll bog a little like normal but it will do it without missing a beat. Same goes for forth, if I'm in forth going 50mph (about 3000 rpm) it'll do it bad but anything below that even up a hill is fine.
08-30-2017, 12:34 AM
#8
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Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
If you start from a dead stop and hammer it and accelerate as fast as you can until you reach 75 mph (maybe 7 or 8 seconds not sure how built that car is) what gear will you encounter the issue?
Does it pull great in first then fall on its face at the end of 2nd?
Does it pull great all the way through 2nd but fall on its face in the middle of 3rd?
Once its starts to hesitate if you leave your foot in it will it go away or just keep getting worse and stop accelerating?
Does it pull great in first then fall on its face at the end of 2nd?
Does it pull great all the way through 2nd but fall on its face in the middle of 3rd?
Once its starts to hesitate if you leave your foot in it will it go away or just keep getting worse and stop accelerating?
08-30-2017, 01:07 AM
#9
1st and 2nd are fine it'll do it towards the top end of third
If I stay on it it'll do it for a couple seconds and then come out of it but might start it again.
But it's specific if I stay below 40 in 3rd, shift to 4th and stay below 50, then 5th and stay below 60 it doesn't do it, doesn't matter if I shift casual or if I shift hard.
If I stay on it it'll do it for a couple seconds and then come out of it but might start it again.
But it's specific if I stay below 40 in 3rd, shift to 4th and stay below 50, then 5th and stay below 60 it doesn't do it, doesn't matter if I shift casual or if I shift hard.
08-30-2017, 01:16 AM
#10
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Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
I was wondering if it was a fuel pump but it doesn't quite match that either.
A fuel pump issue would be" pulls great in first at WOT but halfway through 2nd falls on its face and will not accelerate at all very rough running...back off then it clears up after 5 seconds or so.
Without being there this is quite difficult. Even being there might still be tough.
Im still pretty sure its fuel related.
You could always just keep driving it until it gets worse that works well for me when I cant pin down an issue.
A fuel pump issue would be" pulls great in first at WOT but halfway through 2nd falls on its face and will not accelerate at all very rough running...back off then it clears up after 5 seconds or so.
Without being there this is quite difficult. Even being there might still be tough.
Im still pretty sure its fuel related.
You could always just keep driving it until it gets worse that works well for me when I cant pin down an issue.