Blew up 225+ Yamaha Excel....again

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A buddy has a decomputerized 1989 Excel that has Hydrotech heads, modified horizontal intake, big carbs (jetted up to 174s). Only running 22deg timing. First time it melted a piston he had 87 octane in it so we figured that was the cause as Hydrotech says needs 93. Put it all back together and melted another piston. This time I had told him to run closer to 40-1 oil to be safe. Still blew.....
Only cause I can think of at this point is that one of the fuel pumps is weak causing a severe lean condition at 5000 rpm+.

Any thoughts?

[99yam40]

got any pic of the pistons?
might help people under stand how they went

[rodbolt17]

piston failure analysis cannot do it without seeing the piston. typically detonation has 4 causes. over advanced ign timing,lean A/F mix. overtemping the combustion chamber or wrong octane fuel for the compression rating being used.
some of the old time racers actually added a high flow electric pump and ditched the originals.

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[99yam40]

Just in case Rod cannot open the thumbnail pic here it is

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Hide your children.......

[99yam40]

was it the same hole both times?

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No last time other side of motor.

[99yam40]

both time center hole?

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yes both times

[rodbolt17]

it definantly got lean.
I would switch to an electric pump and boost the main jet size,go a lot bigger and work it back down.
might also look for any air leaks at the reeds/intake. what kind of compression ratio did those heads give?
which carbs are you running?

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34mm Excel carbs. Stock jetting is quite staggered at 160 starboard and 168 port. Went to 174 no stagger. Could no stagger be an issue? Wonder why factory had to stagger? Distribution problem I suppose....
Compression was 155....highest I've ever seen on one of these.
One fuel pump was replaced due to snapped nipple too other apart and diaphragm was quite floppy. I'm thinking it was basically running on one pump since they feed a common rail. Good design in that it can get you home but if you don't know you can fry motor if you nail it. Electric pump and gauge way to go. What PSI?