[T3] slightly jerky acceleration - update, plus my original mail with the details

[chris wright <Christopher.Wright@sun.com>]

<x-flowed>Hi all,   Thanks to the people who have responded, a couple of 
people have said they needed more info re my problem in order to 
help further.  so once again, below is the original mail which 
has all the sordid details, and again, I'm sorry for the length 
of it.
Following your suggestions,
I've tried adding and removing washers from the accelerator pump 
rod to make it richer and weaker.  Currently weaker seems better. 
 The problem is now pretty much only when accelerating in 2nd 
between 20 and 25 mph, (if I floor it then it's fine).   The 
problem is now almost gone in 3rd and has always been fine in 4th.
The clutch bowden cable bend, it's fine, it's a new clutch etc, 
and anyway, this is long after changing into 2nd so the clutch is 
not involved.
Problem goes away completely when it's really hot after 30 odd 
miles of mixed driving.    Tickover is perfectly stable - ie: it 
doesn't vary after a fast run.
Re the suggestion on binding brakes, they are perfectly free, 
although the problem feels a bit like that.  You can imagine it 
best by imagining accelerating on a very bumpy road so that the 
car jerks over the bumps.

ORIGINAL MAIL:

 Accelerating between 20-30 in second and 30-40 in third,  the 
car is very slightly jerky or 'uneasy'.  Nothing I can do seems 
to change it but it now goes away when really hot.      Here's 
the background:
 Car is a 64 T34 with the original unaltered 1500S STOCK carbs 
now on new 1600 single port heads. (replacement stock engine with 
4K miles on it).

When the rebuilt engine was fitted, it came with a 009 dizzy. It 
seemed to run reasonably OK on this for the year's warranty but I 
wanted to go back to the original '64 only' vacuum and 
centrifugal advance dizzy, for both originality and smoother 
running.   Original Dizzy was rebuilt with new vac unit and 
points.   Car ran really badly, missing and jerking, it was 
terrible.  Refitted the 009 and it was just the same!!      I 
knew I'd scuffed the dizzy drive gear slightly by rotating the 
engine with the dizzy removed, and fearing it was this, I looked 
down at the teeth and the scuff was only on the tips, well above 
the point of mesh.  I smoothed the edges of the teeth with a 
needle file in case it was slightly rough.  (You can see it down 
the pump hole).   Having spoken to some engine builders I was 
reassured that these gears are not that easily damaged and it was 
unlikely I'd done it any harm, I persevered with the original dizzy.

Because the problem didn't seem to occur until I messed with the 
distributor, I tried all sorts of points and timing combinations, 
new plugs, leads, condensor, rotor etc and finally had a 
diagnostic check done which said that there was nothing wrong and 
the points dwell, vac and centrifugal advance were all within 
spec.   In the end, I found out that the timing needed to be set 
up with 2 plugs disconnected to get down to under 700 rpm for the 
10 degrees advance setting.
(The advance starts at 700rpm on this model dizzy).  This basic 
10 degrees setting gave it 12.5degrees at 900rpm tickover and the 
missing was gone!   (There is no pinking at this setting either, 
we run on 95 octane here! ).  But whilst it was running OK again, 
this very slight uneasiness on acceleration remained.  Another 
driver who tried it hardly felt it, so I know I'm being critical 
here, but when it gets really hot it disappears and it becomes 
such a smooth drive, I want it to be like that all the time.

Carbs have now had their spindles rebushed, washed out and 
rebuild kits fitted and I also fitted new balance pipe joiners to 
remove the air leaks and was very careful setting up the carb 
balance. I've just tried adding washers to the accelerator pump 
links to increase the pump emission but it doesn't seem to make 
much difference.  ( I've tried removing all washers now to make 
the stroke less and this seems to have improved it slightly).

The uneasiness disappears after about 30 miles fast running and 
the car feels perfect.  It's also OK when first on choke and fast 
tickover.

Anyone got any suggestions as to where to go from here?   The 
Pilot jets are g45s and the mains are x125s I think.  Venturis 
are 21.5mm I believe.   It's still stock 6v and I've tried a 
different coil.  The diag said the coil was fine.   Volts on the 
coil are 5.5 or so.  I've tried a direct 6v wire from the battery 
and it didn't help.

I hope this forums experience can give me some new suggestions.
Thanks, Chris

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