Possible to convert 40HP to 50HP?

spartacus · 02 May 2008, 22:55

Hi

Is it possible to convert a 3 cylinder 2-stroke Yamaha 40hp Autolube (model 6H4 40V 1995) to a 50hp just by switching to a set of 50hp carbs?

Seems too simple to be true. I would have thought the CDI ignition would need to be changed regards sparks and what about autolube ratio?

Any thoughts?

Nos4r2 · 03 May 2008, 03:57

You'll need a parts microfiche for it to check.
If the part numbers for the ECU,main engine block and liners are the same but the carbs/reeds have lots of different parts then you'll get your answer.

Same deal for the autolube-if it's the same pump then you'll be OK, just make sure it's properly adjusted.

Jizm · 03 May 2008, 10:02

I thought the 30-40hp shared the same block and then the 50-60hp were the same motor with difrent carbs?

Nos4r2 · 03 May 2008, 10:49

I'll have a look at the microfiche later but I thought the 30 was an uprated 25.

Jizm · 03 May 2008, 11:46

Maybe it depends on year, but my 1996 50hp is 849cc as is the 60hp, the 40hp is listed as 698cc same as the 30hp of that year, all are 3 cylinder.
The current yam 2 strokes are different sizes tho'.
make sense to you nos?

Nos4r2 · 03 May 2008, 12:29

Quote:

Originally Posted by Jizm

Maybe it depends on year, but my 1996 50hp is 849cc as is the 60hp, the 40hp is listed as 698cc same as the 30hp of that year, all are 3 cylinder.
The current yam 2 strokes are different sizes tho'.
make sense to you nos?

Yeah, perfect sense-I was thinking of the earlier 2 cylinder 25hp.

spartacus · 04 May 2008, 10:01

I read a similar post on another site - that the (1995) 40/50 share the same powerblock (693cc). The 50hp carbs are a 1/4" larger as is the exhaust manifold. Swapping over both in theory should increase capacity, albeit with some tinkering and fine adjustment.

I don't want to wreck a practically mint 40hp, however that extra 10hp sure does sound tempting. For the record - my transom will take a maximum 50hp.