Stuttering when running

[Rubce]

Hi All

With it being half term I have a taken a few days off work to time spend with the family. Today we went to the National Trust owned Quarry Bank Mill, Styal near Wilmslow. Excellent place to visit with water wheels, stationary steam engines and working looms etc to see. We went in the Stag was which was its first run out since cleaning the top section of the carbs at the weekend. She ran fine for the first 15 miles or so and then started to stutter. Dropping a gear and revving it seemed to clear it, but then the stutter would re-appear later on.

Plugs and HT leads have only been on 12 months (3,500 miles), the distributor cap and rotor are brand new. Coil is at least 5 years old. Luminition ignition fitted. Carb diaphrams are in okay condition. I am puzzled as to why the stuttering seems to be intermittent.

Any suggestions apart from the usual process of replacing one bit at a time to see what stops it?

Regards

Bruce

[flying farmer]

I would hazard a guess at the dreaded needle valve problem. On last years New Years day run my estate suffered the same problem when we stopped at the castle. Whoever was following could testify to the clouds of black smoke when we left!
What happens is the float chamber gradually overfills and makes it run rich on four cylinders. Giving it some welly sucks in more fuel than the leaky float valve is letting past temporarily restoring the fuel level and smooth running. When you ease off the right pedal the whole cycle starts again
I would try the inertia switch off, let it run dry, inertia switch back on again trick first
Neil

[Rubce]

Well today was one of those when you go forward two steps and back one! I was off to Paddocks to pick up various bits and decided to take the Stag. Before setting off I popped open the bonnet and hand another gander at the carbs. School boy error noticed as I had forgotten to refit the vac advance pipe after cleaning the carbs. DOH

With the vac pipe connected the car ran a treat to Chester. So upon arrival at Paddocks I cancelled the part of my order which was for new needles and valves as I didn't think the car need them after all. On the way home the car started to stutter again No where near as bad as yesterday but enough to irritate me. DOH!

Whose needles and valves do people recommend?

Whilst looking at the carbs I also spotted that they are very early ones as they don't have the temperature compensators fitted. Presumably that this means they are original to the engine given that it is an early Mark 1 with the additional temperature sensor fitted at the rear of the block.

Regards

Bruce

[stag157.7]

Well today was one of those when you go forward two steps and back one! I was off to Paddocks to pick up various bits and decided to take the Stag. Before setting off I popped open the bonnet and hand another gander at the carbs. School boy error noticed as I had forgotten to refit the vac advance pipe after cleaning the carbs. DOH

With the vac pipe connected the car ran a treat to Chester. So upon arrival at Paddocks I cancelled the part of my order which was for new needles and valves as I didn't think the car need them after all. On the way home the car started to stutter again No where near as bad as yesterday but enough to irritate me. DOH!

Whose needles and valves do people recommend?

Whilst looking at the carbs I also spotted that they are very early ones as they don't have the temperature compensators fitted. Presumably that this means they are original to the engine given that it is an early Mark 1 with the additional temperature sensor fitted at the rear of the block.

Regards

Bruce

I notice you state you cleaned the carb tops

have you replaced the diaphragm back in the correct position in its slot?
have you got the carb tops fitted back on correctly,oil passage overflow/vent casting to the outer edges?
check you have not mis -aligned/cross threaded a damper assembly as this could stop a piston rising correctly

oil in the dashpots?

new needles i doubt will cure any hesitation
i use standard needle valves from soc spares with no problems


temp comps were designed to assist hot starting conditions by allowing more air in to the mixture#again doubt this would make a stutter on the carbs




alan


alan

[Rubce]

Alan

Thanks for taking the time to reply.

Yes there is oil in the dashpots
Yes the carb tops are back in the same orientation that they came off. I have photos of before and after.
The tops are on flat with no visible gap around their edges
Can't check tonight that the diaphragms are in their correct slots but I do remember lining them up and pressing them home. If they weren't then I suspect the top would not be sitting flat?

As regards cross threading a damper assembly, I am unsure as to which bit you mean as the damper slides in doesn't it. I did not remove the needles or the diaphragms from the dampers.

Regards

Bruce

[stag157.7]

Alan

Thanks for taking the time to reply.

Yes there is oil in the dashpots
Yes the carb tops are back in the same orientation that they came off. I have photos of before and after.
The tops are on flat with no visible gap around their edges
Can't check tonight that the diaphragms are in their correct slots but I do remember lining them up and pressing them home. If they weren't then I suspect the top would not be sitting flat?

As regards cross threading a damper assembly, I am unsure as to which bit you mean as the damper slides in doesn't it. I did not remove the needles or the diaphragms from the dampers.

Regards

Bruce

is it running OK with choke out, then gets worse as it warms up?

what color are yer plugs?
is it running too weak?
is the coil ok?
vacuum and mechanical advance all working ok?
what plugs are you running?
by damper i mean the black plastic bit you unscrew to fill up with oil,
i cross threaded one once and it stopped the piston rising correctly

[jbuckl]

Check voltage to fuel pump using an analogue meter.

Flickery needle = dodgy supply.

Can be the inhibitior switch contacts.

Seems to get worse with rising temperatures.

Can be isolated by 'hotwiring'

Inhibitor contacs easily cleaned.

Atb
julian

[Greenstag]

Hi Bruce
I've been plagued with a similar problem in the past and occasionally it comes back.
My engine was cutting out at junctions after a fast approach and de clutch.
I also suffered some very bad idling and acceleration. I could actually pull a plug lead off on one bank and hear no difference.
This was due to an extremely weak mixture on one carb after it been adjusted by someone who should have known better. They didn't locate the diaphram tab in the dashpot either and I only discovered it when I took the lid off...so worth checking.
Have you put both springs back in the damper assembly...you probably have but I mention it because i forgot once.
I also tested my vacuum unit and decided it was shot. A new one from Paddocks made a difference.
Hope you have some success
Dave

[Rubce]

Hi All

Yesterday morning I used the car to go to work. Cold and with the choke out she coughed and spluttered. Again it stopped when I floored the accelerator. Went out for a short spin this morning and she seemed fine!

Had another look at the car this afternoon:-

idles fine
diaphragms tabs are located correctly
damper springs are in position and working
oil in both pots
damper tops screwed in correctly
carbs tops on in the correct orientation and flat to the carb bodies
both damper assemblies appear to be functioning correctly as when I undid the securing screws they rose upwards
vac pipe in position
air filter pipes had a hole in the T piece which has now been replaced
air hose from brake servo is in place
new fuel filter fitted today
plenty of fuel being supplied by the pump as was evident when it filled the new filter
no visible fuel leaks from the carbs
pistons cleaned last weekend
diaphragms in good condition

Then checked the spark plugs and I am after peoples considered opinions as to whether the fuel mixture is correct or too lean. Three plugs checked (front 2 on nearside bank, front one on offside bank):-

Plug A : looks fine to me. Do you agree?
Plug B : Its striped! One side looks fine, the other looks lean! I am confused!
Plug C : Two photos as again it is striped. Is the front view running correct mixture? Back view of same plug is white! Is that plug running lean or correct? Again I am confused

All help appreciated.

Thanks

Bruce


Plug A.jpgPlug B.jpgplug C front.jpgplug C otherside.jpg

[Gresley]

Hi Bruce,

Not sure about the striped plug I'm afraid, but I would suggest that the mixture is a little weak or the plug is faulty. I have had several faulty plugs over the years. Regarding needle valves and so on, I have used the ones which Paddocks sell and 30,000 miles later they are still fine...

Brian

[grumpy2]

this is the fourth case of these symptoms I have come across in the past month (including my own car). In the two cases I've been directly involved with the cause has been sticking valves. In each case the car has had an intermittant 'misfire' yet the fuel and ignition systems check out fine. I was first put onto the possible cause by a fellow forum member whilst trying to diagnose the problem on a vintage Standard. I wonder if the new fuel mix is partly to blame?

[Ian Durrant]

Hi Bruce,
I think you are weak mixture too. If these plugs conditions are after only short running period (which would be my guess), then I think you may have so weak a mixture you aren't getting a proper burn, hence why one half of a couple of plugs are so overly clean. My bet is if you continue running like this your plugs will probably start to overheat and fail.

really you need a hundred miles or so on plugs before they will give you a proper diagnostic colour. Even jet black plugs could be just because short journeys mean you are mostly on choke. Best bet really is to use at least a colour tune or even a co meter like the gunson one.

[stag157.7]

Hi All

Yesterday morning I used the car to go to work. Cold and with the choke out she coughed and spluttered. Again it stopped when I floored the accelerator. Went out for a short spin this morning and she seemed fine!

Had another look at the car this afternoon:-

idles fine
diaphragms tabs are located correctly
damper springs are in position and working
oil in both pots
damper tops screwed in correctly
carbs tops on in the correct orientation and flat to the carb bodies
both damper assemblies appear to be functioning correctly as when I undid the securing screws they rose upwards
vac pipe in position
air filter pipes had a hole in the T piece which has now been replaced
air hose from brake servo is in place
new fuel filter fitted today
plenty of fuel being supplied by the pump as was evident when it filled the new filter
no visible fuel leaks from the carbs
pistons cleaned last weekend
diaphragms in good condition

Then checked the spark plugs and I am after peoples considered opinions as to whether the fuel mixture is correct or too lean. Three plugs checked (front 2 on nearside bank, front one on offside bank):-

Plug A : looks fine to me. Do you agree?
Plug B : Its striped! One side looks fine, the other looks lean! I am confused!
Plug C : Two photos as again it is striped. Is the front view running correct mixture? Back view of same plug is white! Is that plug running lean or correct? Again I am confused

All help appreciated.

Thanks

Bruce


[ATTACH=CONFIG]11936[/ATTACH][ATTACH=CONFIG]11937[/ATTACH][ATTACH=CONFIG]11938[/ATTACH][ATTACH=CONFIG]11939[/ATTACH]

HARD TO TELL FROM PICTURE

,BUT ARE THE CENTRE ELECTRODES BLISTERED?
are you using a fuel additive at all, plugs seem to suggest some spark masking
also looks like timing poss a tad over advanced,ruuning with weak mixture

i would change the plugs to ngk BP5E to ensure correct heat range


my opinion.


alan

[stag157.7]

HARD TO TELL FROM PICTURE

,BUT ARE THE CENTRE ELECTRODES BLISTERED?
are you using a fuel additive at all, plugs seem to suggest some spark masking
also looks like timing poss a tad over advanced,ruuning with weak mixture

i would change the plugs to ngk BP5E to ensure correct heat range


my opinion.


alan

forgot to add looks defo weak and causing excessive heat in the combustion chamber
try richening each carb by /4 turn at a time (anticlockwise) I bet stuttering goes

alan

[stag157.7]

forgot to add looks defo weak and causing excessive heat in the combustion chamber
try richening each carb by /4 turn at a time (anticlockwise) I bet stuttering goes

alan

its late thats CLOCKWISE
BEFORE I GET MY KNUCKLES RAPPED

AALAN