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Wondering if anyone can shed some light on this..

Do any of the 1995+ powerheads bolt up to the pre-'95 mid sections? for example can I bolt a 1996 powerhead to a 1993 mid, and if yes, will all the rest of the 1993 run the 1996 block properly (alternator, CDI, etc..)
From what I can see from parts catalogs, the 1993 and 1996 share the same powerhead to mid gasket. But any details would help.

Also wondering if the 1995+ heads with the centered spark plugs is a better design than the pre-'95 offset spark plug design?

cheers,
M

As far as I've ever seen all the powerheads will bolt to any mid. But in terms of electronics the bosses on the blocks are different. I don't remember what year is what when it comes to the electrics but they are different. Now, if you don't mind drilling and tapping some bosses on the block you can make things fit...but it's a pain. I've got lots of this stuff laying around if you need pieces.

Anyone know if the 1995+ head with the centered spark plugs works on the older style block?

Still looking for info regarding the above. Curious too if one style head runs better than the other. And if there are any details regarding related design changes: for example is timing different on the centre fire plug heads because of spark plug location...

Check Ron Hills site or a Thundercat site, there were posts comparing the heads. Fast Fred has his opinions posted. Overseas and in the southern states there are many people running 50 hp Yamahas both stock and mod. Some claim super performance from mild altered motors. The older ignition works best, so make sure you use a block has the correct boss locations. Weakest part is the crank. New they are $1000.00. Get your used one checked and if it is good, weld it. There was a fellow in Florida who did great porting work on the 50 hp. His motors ran strong and lasted. He did motors for some of US Thundercat racers. The older lower units were a push-pull shift. The later ones I believe we're a twist shift type. DOC would know.

Since the Six Mile Lake saw my mod 30/50 hp Yamaha I better mention it before someone else does.
This is the best combination of a stock, bolt right together motor Yamaha never made.
The 3 cylinder 30 hp Yamaha lower unit bolts right on a 50 hp Yamaha mid. Everything fits, even the drive shaft. The gear case is very small compared to the 50 hp. On a Pro 50 short shaft the motor ends up approximately 16.5 inches. Perfect on a 20 inch transom. The gear ratio is higher so you run 18 to 22 pitch and 11 diameter props. Bone stock motors with a reeds only change, rev over 7000. The boat handles better and motor has a lot of punch. Better for water skiing. Another unexpected difference, the motor is a better trolling motor and the motor turns 7000 all day long with no problems.

This can be just your everyday small boat. The stock aluminum 30 hp Yamaha props go to 14 pitch. Say your 30 hp Yamaha ran a 12 pitch. At full throttle it turned 5500 rpm. The 50 hp powerhead raises the rpm to 6500 and with no power trim you only add a few pounds. Plus the manual clamp bracket is the same for both motors. No new transom holes!

Thanks Don, I did find a few threads online where 50 mods are discussed, including mention of which style head is better (might not be conclusive). I'm pretty interested in trying a few mods on mine. Figured I'd get opinions here too just to solidify some of the ideas and anecdotes from around the web.

regarding spark plug and centre v offset.
centre is always better ( UNLESS for a specific fuel injected engine ) .