Hi everyone,

1098cc
manual
1.5 single SU
refurbished, swept 45D with electronic ignition
electric fuel pump
standard twin box "pea-shooter" exhaust with cast iron manifold.

I'm having one nuisance of a problem and I was wondering if anyone had any issues like this before.

Ok, so my main symptoms I am experiencing is a slight jerkiness/fluttering when I get to medium/higher revs, say 2500-3000+RPM, in all gears. Mostly noticeable when pushing the car like, uphill or on highway. Easy cruising, not so much, if at all. It does it engine cold or hot.

It's hard to explain but, for instance, when I pull out of my driveway and head up the hill into town, I can make it to 3rd gear and cruise on up, and you can feel a slight jerkiness to the motor. The car doesn't totally misfire exactly, it just has what I would describe as an "uneven driving" feeling. A subtle rocking, or jerkiness. I even come back when the car is warm, and it still does it!

When I take the mini onto the highway/arterial roads, with a very smooth surface, you can really notice the jerkiness and almost hesitation in the motor. Sometimes you will get a noticeable "tug" of a misfire too. Although I'm not getting a loud bang or sudden jerk of a "complete" misfire. I liken it to the feeling of fish tugging on the bait at the end of a fishing line - not quite the big "bite" of a complete misfire, but more the noticeable tug-tug-tug of something there. It's really annoying!

Any ideas? Here is a list of things I have checked over/replaced.

Electrical

-Switched distributor to a swept/refurbished 45D with electronic ignition module - cap is fine, rotor fine.
-New ignition leads, checked their tightness and assure are making a good contact. Even resistance checked them.
-New NGK bp6es spark plugs, gapped to .8mm
-Swapped around coils, they are both used, but have multimetered both of them. Still the problem exists...
-checked voltage to coil on LV side at ~12.5v which I assume is fine.
-cleaned up engine earth with a wire brush and battery negative as well. Terminals are all good.

Carburettor/Fuel

-rebuilt my 1.5 SU, new seals, new jet, dashpot spring, re-bushed spindle etc I bought a recommended needle from WinSU, although, it ran woefully rich, so I switched it to a ADF needle from an old carb, ran great before these symptoms.
-checked float, no leaks. new needle and seat.
-new electric fuel pump (non-SU type)
-replaced fuel filter
-checked for adequate fuel flow
-plenty of oil in dashpot
-new manifold gasket
-spark plugs are a chocolatey brown
-checked manifold nuts tightness, and carby mount nuts for tightness.
-always use 98 fuels
-checked float bowl for crap and blew out the jet as well to be sure.

Mechanical

-Checked and reset timing to at 10deg TDC at idle, advance works. Does not have a vacuum advance module.
-checked and reset valves, nothing stood out as abnormally loose or tight.
-compression tested, all cylinders at around ~140PSI

As you can see, I've nearly done it all!
But yet, everytime I drive it.. brrrrrmmmmmmm.put.put.put.brrrrrrrrr...
It loves to happen at a higher rev band!

My biggest question is.. to kick off.. has anyone experienced this "subtle misfire"?
-Any recommendations on a new needle I could buy? Im running an ADF at the moment.
-Can you have valve issues, without a compression test picking it up?

Thanks in advance!

so everything was good before this misfire started, then suddenly one day this miss started? no other changes?

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As far as I understand, yes, it just "begun". The car ran quite well before..

I noticed it when I had a week of crazy misfiring/engine cutting out/being thrown back and forth with the engine cutting in and out.. turns out the advance plates in my distributor where loose, so I swapped to a rebuilt 45D with electronic ignition module.

At that point I thought the "fluttering" was linked with the same horrid lurching/cutting out I was experiencing. I'm not sure whether they came at the same time, but I certainly noticed it during the same period.

Changed the dissy, cutting out/lurching went away which was great, but the fluttering lives on..

Did you reset the float height after fitting a new needle and seat?

so the old distributor broke, then you put in another (rebuilt) distributor in and there is an issue?

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did I tell you that I won a trophy?

gtogreen: I have reset the float a couple of times. Turn the float lid upside down, place a drill bit of the diameter recommended by Haynes across the lid, then bend the metal float flange to that gap size? I've never bent the float all the way because there seems to be plenty of fuel, what gap do you go to? I think Haynes says between 3.18-4.76mm
I'm curious whether my needle is the culprit. I've done some reading and it seems an ABJ/ABP would be better for my car, at the moment i'm running a used ADF, something more useful for a 998, the ABJ is significantly richer than the ADF. If anyones got any better ideas, I'm happy to have a look.

Simon: I happened to notice the subtle fluttering at the same time is was having crazy misfiring/cutting out issues, at the time I believed they were the same problem. I replaced the dissy with a rebuilt one, it cured my crazy misfiring and cutting out, but didnt cure the more subtle misfire, so I beleive they are separate issues. If they were the same, swapping the distributor would have resolved it.

Looks like you have covered the basics. This may help.

Check the firing order 1342
Is the fuel new
Sounds like a faulty coil. You cannot test a coil with a multimeter

Std needle is AAY for an 1100 with a standard cam
Timing for an 1100 is 7 degrees

Did exactly the same as you and it was a coil. The ones I had where 30 plus years old.

Post the soultion when you find it.

Kiwiinwgtn

+1 for a new coil that matches your electronic dissy.

Ok, I'm looking at the "Gold Sports Coil" on Minisport. Looks like a neat enough peice of kit.

Although, it would be worth reading this small, but informative, little article on needles I've come across.
http://www.ahsdc.org/Files/Tech_Informa ... eedles.pdf

In the last bit, he mentions a test procedure and the feeling of a "see-sawing" action on a lean out, sounds suspiciously similar.

I have a friend running a gold sports coil, might ask nicely if I can borrow it, see what it does!

I reckon coil too.... put in a known good one, or take the one you have and put it on a known good engine

those needles you've been reading about don't look any better than what you have - http://www.morrismini.com/SUNeedlesV2.a ... &size=.090

forget about ABP, and ABJ will lean out at higher loads & WOT. When looking at needles, a richer needle isn't just a thinner one, what you want is a steeper angle - look at an AAW

_________________
did I tell you that I won a trophy?

Hot coil failing under load. They'll test okay when cold.

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1963 997 Morris Cooper
1964 Sunbeam Tiger
1969 Austin 1800
1969 Lancia Fulvia Rallye 1,3S

Have ordered a new gold sports coil from Minisport.

Reset float level to 4mm gap. Didn't change anything.

I will post the results soon!

I'm running a very tatty 30 year old Bosch GT 40 coil because it works and have been let down by 3 shiny new ones of unknown origin. I want my engine bay to look good but I'm NOT going to replace that grubby coil......!

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67 Deluxe
Dry suspension
1293cc, 11:1 comp, RE 282 camshaft, 45 Weber, extractors etc
4 synchro close ratio gbox
Cooper S brakes, no booster
Stealth box, as Doc says "goes harder and idles!"
RH tank cos I needed it crossing the Nullarbor etc..

It sounds like your distributions mechanical advance might be advancing too far up in revs. Check advance with a Dial back Timing lamp. Try set the timing at 5 deg and see if that helps. Also have a look under the bonnet in the dark see if you can spot any straying spark around ignition system, and check lead resistance, never mind them being new.

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"Let us remove your "SHORTS"

Well, the coil didn't do it. Not really surprised, as I have swapped the coils around - to get the exact same problem with two coils, used or not, is very improbable.

Adjusted timing to 5 deg and didn't stop it either.

I'm beginning to think it's a mid range + lean out, the problem I'm having is the roads are so bumpy it's hard to feel it but when I get on the coast, on the smooth roads you can really feel it.

Also, would sticky valves show up on a compression test?