Hi everyone,
A quick summary of the question before I go ahead and waffle on with the details: if my CO level is 0.15% and the car bogs down badly at anything past 40mph, is this likely to indicate that my mixture is too lean, despite the fact that my spark plugs are already sooted up?
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This is a newly rebuilt engine that has so far done only 42 miles, so I really wouldn't want to get the mixture wrong whilst the rings are still bedding in.
The spec is 998+0.60" with 12G940 large-valve head, MG-Metro-ish camshaft, HIF38 and Stage 1 intake+exhaust. Needle unknown (chosen and supplied by engine builder).
As my old engine died of piston-ring failure (possibly hastened by my less-than-professional tuning abilities) I'd prefer to ask some advice rather than get it wrong.
I initially set up by checking ignition advance was at 10° as instructed by engine builder, and by setting mixture as per the usual method in Haynes (which in my opinion is nowhere near as straightforward as it sounds if you don't have a lifting pin).
The car had to be MOTed immediately. The CO value came back at 0.15% (HC 205ppm).
Surely this is a very low figure for an A-Series with no catalyst. Great for passing MOTs but it does sound to me as though the mixture may be very much on the lean side.
Bearing in mind that the car bogs down badly at 40mph and pretty much refuses to go any faster (I haven't pushed it past 2/3rds throttle for obvious reasons), and struggles up hills.
Is this also an indication of a possibly lean mixture?
I would just do the obvious thing and richen the mixture slightly to see if this improves running, but I've become confused by the fact that the spark plugs are already sooted up. Is this an indication that the mixture is not actually lean, or is it just because the 42 miles done so far have all been urban and at lowish speed (as detailed below)?
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So far the engine has covered the following mileage:
- 30 mins bench test by engine builder
- 1 mile to MOT centre and back
- another 1 mile to MOT centre and back
- 19 miles across town in heavy traffic
- 21 miles across town in light traffic
)
Would it be reasonable to just try pulling the choke out at 40mph and see if it responds any better?
I've contacted a local rolling road who are happy to tune the car professionally (and tailor the needle if necessary) in January, but they've told me to run for 500 miles first before I take it in.
As if you haven't guessed by now, I'm slightly paranoid that if I've got the mixture wrong for the first 500 miles, I'll get either borewash or valve seat damage.
My two local garages who work on Minis say that they don't touch anything to do with carb mixture as they say it's more trouble than it's worth for them to get involved.
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Additional question (much less important): The engine needs a good 15/20 seconds or so of cranking before it catches and starts, and it sounds as though its cranking quite slowly, despite the battery being fine. Is this normal, and is it just because the engine is still tight?
