I had the same problem with mine when i first assembled it, it wouldn't go over 7000 rpm. I was running dual mikuni 40's changed out to 44's and it solved the problem.

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I tried this once. Connect a spare dizzy vacuum advance to it and take the top off while the engines running. You'll see it fluttering at idle leading to strange advance characteristics. I'd disconnect it, check the timing without it and see if you still have the problem. I've never seen anyone run sidedrafts with vacuum advance even on roadcars. Initial advance somewhere around 10*~12* is a good place to start.

my cam is 280 inlet 276 exhaust .295'' lift . inlet opens 30 closes 70 exhaust opens 65 closes 31. clearance hot is .012'' on inlet and exhaust (all on my cam card). The cam grinder told me I can go down to .010''. curently running .011''. the timing is set 14deg about 1200rpm and is fully advanced at 3500rpm at 34 deg. no vacume advance.
I am not running as high a comp as you.

good luck.

Thanks!! very close cam to mine, it doesnt by chance say what the cold clearance is does it? also the seat pressure?

I took motor apart today, nothing major just some contamination damage on NO:4 due to pathetic air filters (next on the list)

What I did find is they didnt use the supplier GX spring washers/seat, they used regular flat round washers like the A-15 had stock... will put a post in the forsale/wanted section, inner spring must have had near no tension.

Sorry no cold clearance or seat preasure.

My other baby

When im not breaking the A15 (which is supposed to be my cheap run around)

Just to let people know for future searching & problem resolution

I redid the seats and retainers with B-projects parts (very fast servise!) and she is now reving CLEAN to 8500rpm! what a difference to now finnaly be able to finnaly use the motor to its full potential.

Next up is a slightly larger exhaust, 52mm must be restricting it a bit.

so there wasn't enough preload on the valve springs?

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When I read through the whole post I also thought that this sounded like a valve problem. Glad you came right. I took a drive one night with someone that had a A14 with similar specs to your A15. His did exactly the same. At 7000rpm it made a strange tapping noise. The guy also did'nt know what it was and said he decided not to rev it past 7000rpm due to this strange noise. I also told him it sounded like valves.

Just a bit off topic. Why Mazda pistons? And also what bore are you running to fit them. Did you bore your block to max?
Also what Mazda engine's pistons is it?

Yeah not nearly enough load! worked it out to be almost 4mm less inner spring load when using the flat washers,,, could kill the machine shop! trust it to be the only head I ever had them put together for me.

GXman, buy and A15 here in RSA and youll find out very fast we have no pistons that fit, my A15 was rusted BADLY inside, had to take it 1mm bigger bore just to get a good clean surface, I run a .5mm oversize Mazda E5 piston which has the crown machined off, rods resized to suit and the block skimmed to give me just over .4mm quench area at install height (IE the piston sits proud of the block by .4mm and im using a .8mm Nismo head gasket = nice compression for a flat top piston when using the smaller chambered H89 A15 head,

I am going to have another cam cut with a slightly closer LCA, this one is almost fluid smooth, car hardly sounds like it has a cam in it, could do with a little more tq upstairs so ill drop the LCA from 110 to a 108 or maybe 106 if im feeling brave.