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"jerking" between low acceleration and accelerator released


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16 minutes ago, BlueTR3A-5EKT said:

Still have the issue on my car.   I am lengthening the lever at the carb to reduce its movement compared to the accelerator pedal movement.  Will see if it works.   I have cable operated throttle not rod.

 

 

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Cable too tight? Ive found theyre better with a little slack to account for engine movement and obviously the heaviness or otherwise of your right foot ;)

Stuart.

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Marco

Here's another possibility to add to your long list

I had a similar problem with my carburettored TR6, after months of head scratching I tracked it down to the fuel pressure from my electric fuel pump which was set a fraction to high, I assume the carbs were passing to much fuel at tick over speeds causing a sort of stumble. There was no leaks or smell of fuel just the judder.

I turned the regulator down a half psi and the issue was solved.

George 

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1/4” slack on the cable before the lever moves.

Mechanical original fuel pump fitted.

Doubled the return springs on the carbs and added an extra one to the accelerator pedal.

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6 minutes ago, BlueTR3A-5EKT said:

Doubled the return springs on the carbs and added an extra one to the accelerator pedal.

Well that`ll up the MPG at least ;):lol:

Stuart.

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13 minutes ago, stuart said:

Well that`ll up the MPG at least ;):lol:

Stuart.

I am being methodical with my ‘fixes’

After this comes a distributor swap to a unit with more mechanical advance.   From orig distributor maximum mechanical advance of 10 (20 crank degrees) up to 13 (26 crank degrees) from my other distributor, so I can then reduce the crank static advance back from 10-12 to 4-6.   This retains max advance between 30 and 32 crankshaft degrees.

This suggestion came earlier from Marco when he dropped his timing back and the car became like a snail.  My intention is to maintain the maximum advance at full revs but reduce the advance at tickover.   Yeah I know beware of overheating because the ignition is retarded.   

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5 hours ago, BlueTR3A-5EKT said:

1/4” slack on the cable before the lever moves.

Mechanical original fuel pump fitted.

Doubled the return springs on the carbs and added an extra one to the accelerator pedal.

Same as my TR3. It still kangaroos. My TR4 doesn’t do it but swapping the distributors and carbs left the problem on the TR3!

When I have the Webers fitted the kangarooing is much reduced. 
Like the rest of you I’m still picking at it. 

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There is no sense in adjusting more play

if the problem is the moment I turn the spindle (with any adjusted play down to zero that moment)

at the moment I start to open or close the trottle.

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11 hours ago, Z320 said:

There is no sense in adjusting more play

if the problem is the moment I turn the spindle (with any adjusted play down to zero that moment)

at the moment I start to open or close the trottle.

Yes I agree, my current fix will test to see if smaller spindle movements are better.    I am working towards the reduction of initial static distributor advance but maintaining the total advance at full throttle.   Like your manual advanced ignition motor cycle.

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I made and fitted a rising rate cam for the throttle cable but it’s made little to no difference. Next I plan to make a ludicrously large actuator lever even if I can’t get full throttle just to see if I’m going in the right direction rather than as a serious fix. 
image.png.ac6d613615bf128ae2c6cc4b16a63e90.pngimage.png.998337d91c9927cfc2241b1575021877.png

Edited by Drewmotty
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I don't get any "jerking" with my standard rod acutated system, unless I drive over a series of bumps in the road - which simply makes my right foot bounce up & down, fix for that is foot off throttle, & start again.

Bob

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Most of the roads around us in North Devon feature a series of bumps. “Assertive” throttle actuation overrides the problem which usually manifests at 10 to 20 mph along narrow country lanes. 
No problem at all on main roads. 

Edited by Drewmotty
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I have a bit of “variation in power” at around 1600-1800 rpm (PI car); this has nothing to do with the throttle arrangement, but I suspect with my AFR (a bit too lean) at that condition.

AFR around 15 then. Above 2000 rpm the issue disappears, with no noticeable change in AFR.

But it could be the play in the drive line to the rear wheels too, a sort of harmonic thing.

Waldi

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  • Z320 changed the title to "jerking" between low acceleration and accelerator released
  • 1 month later...
On 10/28/2023 at 11:55 AM, BlueTR3A-5EKT said:

Still have the issue on my car.   I am lengthening the lever at the carb to reduce its movement compared to the accelerator pedal movement.  Will see if it works.   I have cable operated throttle not rod.

 

 

image.jpeg

This longer lever gives a noticeable improvement but has not cured the kangaroo issue.    Next test will be moving the cable connection out by another 1/4” on the diameter, the furthest out hole.

NOTE.  The mechanical advantage makes the throttle pedal resistance lighter.   Fit additional throttle pedal return spring is the fix.

Edited by BlueTR3A-5EKT
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