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!
