I'm in the process of selling my Roadster - very sadly I must say but no choice! My buyer has had the car checked by the R.A.C and all is well apart from a small flat spot on acceleration according to the R.A.C man. The buyer wants me to find out what this is before parting with his cash. What is the way to do this? Do I have to go to a Mazda Dealer for them to do a diagnostic check? If so I suppose it will cost me an arm and a leg! Can this be done by any garage? I must say I have noticed the flat spot but it is tiny. (7/00)

Plugs, leads and air filter are the first things to check. Second tier to check are fuel pressure and injectors.

If you know someone with the same car try swapping bits for a hour or so.(7/00)
Consider changing the spark-plug leads if they are fairly old (costs 50 quid or so), or else consider having the timing advanced a little bit (default is 10, but you can safely go to 12 or 14 degrees). That should cure the flat-spot. (7/00)
I have a 1990 roadster and I too have a small flat spot. Only notice it when I am pulling away in too higher gear and te revs are very low. I have changed plugs, leads, and air filter and it has never made any difference. Was wondering if going to 12 deg timing might get it sorted? (7/00)
If you get a little 'hesitation' on low revs just after changing gear, advancing will fix that. Try it. If you don't like it, it's easily reversible. As for "takes hours to do" - we managed to it in seconds to some '5s at a recent classic car show in Dublin. (7/00)
Many Roadsters have a flat spot 'cos the timing is well retarded so that they can run on 92 octane petrol (available in Japan). They tend to be set somewhere round 6 - 8 deg BTDC. Dealers worth their salt retime them to 10 deg and adjust the idle (which goes too fast if you don't). I think most of us are agreed that 14 deg works fine - any more and you will loose top end power. (And have to use 97 octane petrol). But apparently up to 18 deg has advantages at lower revs - never tried it myself. (7/00)

The 16valve engine needs a good amount of revs (4000+) before anything happens even with a well tuned car. Could you be mistaking a flat spot for a "characteristic" of a 16v engine ?

Ambient temperature could also be a factor. On my car with a JR Cold Air Induction Kit I find my car runs far better at low temps than higher ones. If I could get a mod that produced such a difference I would be ecstatic. The timing advance takes about 10-15mins with practice and makes a noticeable difference.

I can't believe the garage did the standard (cue sucking through teeth) "Dunno guv... could take several hours" and then recommended NOT to go ahead with it ? Is this a new era of honesty I see before me even though his information was wrong ...? (7/00)