My car shudders (for want of a better word) when i'm driving at lower
than abour 2000rpm.
I can cope with it will pulling off, but it also does it when im just
driving along normally and the only way to stop it is to drop down a
gear.
Sometimes it gets pretty rough (30-40mph in 4th gear is worst) and i'm
starting to get concerned.

The problem has been getting worse over the last 500miles or so. Its
always done it a little bit when pulling off and is a lot worse when
its hot (sitting in town traffic and queues for half an hour type of
hot), but its getting really bad now.

Does anybody have any advice or ideas about what could be causing
this?

Its a simple open loop LPG kit on a carbed car.

On Tue, 21 Mar 2006 21:28:37 +0000, Tom Woods
wrote:

My car shudders (for want of a better word) when i'm driving at lower
than abour 2000rpm.
I can cope with it will pulling off, but it also does it when im just
driving along normally and the only way to stop it is to drop down a
gear.
Sometimes it gets pretty rough (30-40mph in 4th gear is worst) and i'm
starting to get concerned.

The problem has been getting worse over the last 500miles or so. Its
always done it a little bit when pulling off and is a lot worse when
its hot (sitting in town traffic and queues for half an hour type of
hot), but its getting really bad now.

Does anybody have any advice or ideas about what could be causing
this?

Its a simple open loop LPG kit on a carbed car.


Does it do this on petrol, too?

I'd suggest starting by checking out the ignition system (if it's
points ignition, make sure the contact breaker and condenser are OK,
with the right points gap, and check the timing. Also make sure the
distributor cap and rotor arm are in perfect condition, the leads are
good, and the plugs are new. Perhaps reduce the plugs gap by 3 thou
from standard).

Then see if you have any induction leaks downstream of the mixer (a
squeezy bottle of water, squirted over the induction tract -
particularly any joints, manifold gaskets, etc - while the engine is
running - listen for the engine note to change - avoid getting water
on the electrics and ignition components).

--

TSH

For email, replace 'SpamOnlyToHere' with my initials

LPG info. page: www.tshargrave.co.uk
Now with added Biodiesel (and getting a bit out of date)

On Wed, 22 Mar 2006 02:49:22 +0000, Stewart Hargrave
wrote:

Does it do this on petrol, too?

I'd suggest starting by checking out the ignition system (if it's
points ignition, make sure the contact breaker and condenser are OK,
with the right points gap, and check the timing. Also make sure the
distributor cap and rotor arm are in perfect condition, the leads are
good, and the plugs are new. Perhaps reduce the plugs gap by 3 thou
from standard).

I checked the plug gaps and they were okay, but i dropped them down
slightly anyway.
It now shudders slightly less, but still does it.

It is happening on petrol too, though to a much lesser extent. Its
only just noticable.

Is this likely to be down to a weakness in the igintion somewhere?

The complete system (plugs, leads, rotor arm, cap and points) has been
replaced within the last 6 months and the coil a couple of years ago
(before the car got laid up for 2 years). It all looks good by eye.

I will try setting the points next, but they were done only a couple
of thousand miles ago so shouldnt be bad (and cant be as bad as the
old ones which it happily ran on!), and swapping bits over from my
other car.

Then see if you have any induction leaks downstream of the mixer (a
squeezy bottle of water, squirted over the induction tract -
particularly any joints, manifold gaskets, etc - while the engine is
running - listen for the engine note to change - avoid getting water
on the electrics and ignition components).

will try this after ive swapped some bits over, though ic ant see why
it would suddenly go?. inlet manifold gasket is also fairly recent,
and there not much else in the path of the gas other than the carb.

On Sat, 25 Mar 2006 16:01:18 +0000, Tom Woods
wrote:



It is happening on petrol too, though to a much lesser extent. Its
only just noticable.

Is this likely to be down to a weakness in the igintion somewhere?

Quite possibly; LPG gives the ignition a harder time than petrol does,
so any weakness is likely to show up more on LPG.

If it's the sort of shudder that seems to be caused by one cylinder
misfiring, you could try disconnecting the plug leads one at a time
with the engine running[1], and see if you can isolate the cylinder.
Then you could try swapping leads and plugs between cylinders, and see
if the problem moves or stays where it is. This may help you isolate
the problem.

[1] Use of rubber gloves recommended. And insulated pliers. If you
have electronic ignition, this is not recommended anyway, but you've
mentioned points, so you're unlikely to do any lasting damage either
to the ignition system or yourself[2]. Unless you have a heart
pacemaker fitted.

[2] Though it can still hurt like buggery if you do cop a spark.

--

TSH

For email, replace 'SpamOnlyToHere' with my initials

LPG info. page: www.tshargrave.co.uk
Now with added Biodiesel (and getting a bit out of date)

In message , Tom Woods
writes
On Wed, 22 Mar 2006 02:49:22 +0000, Stewart Hargrave
wrote:

Does it do this on petrol, too?

I'd suggest starting by checking out the ignition system (if it's
points ignition, make sure the contact breaker and condenser are OK,
with the right points gap, and check the timing. Also make sure the
distributor cap and rotor arm are in perfect condition, the leads are
good, and the plugs are new. Perhaps reduce the plugs gap by 3 thou
from standard).

I checked the plug gaps and they were okay, but i dropped them down
slightly anyway.
It now shudders slightly less, but still does it.

It is happening on petrol too, though to a much lesser extent. Its
only just noticable.

Is this likely to be down to a weakness in the igintion somewhere?

The complete system (plugs, leads, rotor arm, cap and points) has been
replaced within the last 6 months and the coil a couple of years ago
(before the car got laid up for 2 years). It all looks good by eye.

I will try setting the points next, but they were done only a couple
of thousand miles ago so shouldnt be bad (and cant be as bad as the
old ones which it happily ran on!), and swapping bits over from my
other car.

Then see if you have any induction leaks downstream of the mixer (a
squeezy bottle of water, squirted over the induction tract -
particularly any joints, manifold gaskets, etc - while the engine is
running - listen for the engine note to change - avoid getting water
on the electrics and ignition components).

will try this after ive swapped some bits over, though ic ant see why
it would suddenly go?. inlet manifold gasket is also fairly recent,
and there not much else in the path of the gas other than the carb.
Distributor ignition advance system, if the car has been laid up for a
couple of years? Sort it on petrol first.
--
hugh
Reply to address is valid at the time of posting

On Sun, 26 Mar 2006 13:19:58 +0100, hugh ] wrote:

Distributor ignition advance system, if the car has been laid up for a
couple of years? Sort it on petrol first.

It's been driving fine for the last 6 months. It was laid up before
then.
Do you mean the capsule on the side of the dissy (which is
disconnected as this worked better for lpg), or the internals of the
dissy (which i presume arnt static?)

On Tue, 21 Mar 2006 21:28:37 +0000, Tom Woods
wrote:

My car shudders (for want of a better word) when i'm driving at lower
than abour 2000rpm.

It was all down to the points, which had virtually no gap! (it was
surprising it ran atall!). I didnt know they would wear so quickly!