50 Yamaha 6H4

[Andrew 4CE]

Have mid 90's Yamaha 50hp 6H4.

Anyone know what RPM I should be chasing with this motor and what RPM is too high?

Rev limiter is disconnected (came that way when I bought it).

I'm using it on an Aquarius inflatable Thundercat/SLT mostly for recreational fun and some racing. But I'd like the motor to last some

Thanks!

Andrew

[Ballistic]

6H4 is a 40HP engine.

Check if your carbs say 6H5 and if the tuner is square.

[Andrew 4CE]

Sorry, correct. This has been converted to a 50 with carbs and tuner.

[88workcar]

8000rpm all day and again tomorrow and next week and on and on.

[Ballistic]

Don't listen to that. total bs.

I do believe the 1994 and older blocks are a bit better/stronger then the newer ones.
Replace the stock metal reeds by CCM ones and 6500 would be doable but it won't peak power there.

[Phil McDaniel]

Sorry ya not there yet mr. Ballistic, but jason's right. 8,000+ all day every day and let's go fishing days. All on 87 octain gas. Don't talk down to somebody just you haven't been there and done that.
Phil

[Ballistic]

I wasn't talking to anyone except the topicstarter. Seeying him stating that he wants the engine to last i was just warning him that 8k of RPM's will kill his engine in no-time. Plus it has no use at all doing it. The block delivers 50hp at 5500 to 6000rpm and running it to 8000 won't change a thing. Maybe even worsen it.

Its not built for 8000rpm and thats that.

[Andrew 4CE]

Thanks for info.

So averaging out... something in the low-mid 7's sounds reasonable and see how it goes.

[Powerabout]

is that 8k with a built up crank?

[Ballistic]

is that 8k with a built up crank?

Either way, thier tacho's must be setup wrong if they are reading 8000rpms..

By the way, the yamaha's run out of thier port timing above 6000rpm soon so youll actually lose power if you run it above that.. let alone 8000rpm lol