Hello everyone,
I'm facing a problem that is very strange and which I cannot solve.
The engine in question is a 99H small bore, A+ engine. Slightly modified with a stage 1 kit, needle supplied by local dealer, type is unknown as declaration has been removed by grinding it out...
The engine basically runs very nice, pulls very strong although it suffers slightly lean mixture when accelerating for the first second or so - "thicker" engine oil in the dash pot helps for this problems.
My main problem is that I have to set ignition advance to ≈15° at idle speed!
Using the std. setting of 8° at 1500, the engine simply won't run, driving is nearly impossible, only using a lot of choke.
Advancing that much makes the engine run very nicely and it pulls strong.
So far, I've checked nearly everything:
- Spark plugs, HT leads, distributor cap, finger and condensor, coil is all new
- Valve gap is set correctly
- leakage test was 12-17% (which indicates ≈40k miles engine in good mechanical condition according to my garage), compression test was fine, althought I forgot the figures :-(
- Distributor was tested by the same garage and found to be working perfectly fine, mechanical advance worked as expected
- I've recently checked the camshaft timing, inlet is on full open at 106° which is correct as per Vizards book. (As the problems good worse after some time and no cause good be found, I've assumed valve chain lengthening and a change in chamshaft timing, that's why I've checked this, too.)
I *could* go away with the high advance, especially as my local mechanic told me that every now and then some 99H pops up which refuse to run with std. advance - even in std. trim - and requires a similar high advance.
But - the engine is very close to knocking. Especially at low speed with very little throttle - where vacuum advance is active - the engine knocks. I'm pretty sure that it doesn't do so at higher revs as the total mechanical advance of the distributor is only 12° in total, so it does not even reach 30° in total. (I can't hear it knocking at high revs but given the loudness in a Mini, this of course is no real prove...)
There might be something wrong in general with this engine which I might miss but I really have no more clue... Maybe someone is having an idea what to do/check next?!?
Thanks for any input!
Best regards,
Michael