Where is your vacuum coming from for the vac advance? Webers that I have seen do not have a vacuum port.

its on the intake mani,,, you can just see it in the pic

those stacks have been changed for decent ones that hold my "air flo" simple foam filters in place,

LINK FOR PIC

Even in neautral it hits a wall at 7000rpm and wont rev any higher,,,

i can turn the spring and i can push the retainer down,,, hard to gauge KG's though, will see if i can find a push scale, what i did do is check that i only have about 4mm from full open to valve bind...

Had somone helping changing my jets while i was playing under the valve cover, and yeah, in went the wrong air correctors and well, my Machined flat top mazda pistons took a break... blowing crank case vapour out like mad.

ehh, I killed the unkillable,,, funny that its a mazda part that failed lol

Don't free rev an engine to 7000rpm, thats
not gunna tell you squat. Only bush
mechanics free rev engines, it just breaks
stuff

Actualy it will tell you if its load based or not, in my case it isnt load based which cuts down my searching for the solution by about 50%

I would think that one rev up to 7000rpm is one whole heap better than the extended time it takes to get the car up to 7000rpm in 2nd or 3rd gear let alone the difficulty in actualy listening to the problem due to wind noise.

Either way I already know its valve related, will play with shimming and clearance this weekend and drive the motor into the grave, already purchased a replacement A15 (cheap as chips here) and will build a bottom end with better pistons than the "trial and error" setup i did first time round.

How can you say its valve related if your ignition is not doing its job?

If you are using vacuum for the distributor, then it needs to be 'ported' vacuum from the carb, not from the manifold. The only sidies I have seen with vacuum port are solexes.

I would take off the vacuum can, up the base timing to 12-15

because I have ran from 28deg to 36 deg total advance and it did the EXACT same thing at EXACTLY the same RPM,

I have also tried using my old points dissy, same thing, same RPM, and I have also changed coil same thing same RPM.

Fair to say its not likely to be ignition?

i was thinking that, try another dizzy and coil, but u have already.

i think your on the money with valve spring
control, suprising how often that is over
looked. The end result is usually valves and
pistons crashing-which makes a big mess!!

Edit: The point about free revving is that it
does not correctly simulate problems which occur
under load. I have had ignition
problems undetectable in the pits but cronic
and undriveable on the track. If an engine is
going to fly apart, especially with standard
parts, it will be with big revs & no load.

That is exactly why i free rev'd it, ignition problems tend to be more load based/show up more under load,,, one free rev is a quick way to work out probability of ignition causing it

For now ill have to build up another motor with mazda pistons, this time ill try find a set that had drilled holes for the oiling not slots, I knew those slots would cause drama but honestly this motor was a "trial and error" setup and cost me next to nothing, wanted to find out what would work for me and my power goals, now its time to do it right, pity no one seems to have stock of the A15 high comp's so ill build a 3rd forged motor when i have time!