converting a 9.9 yam to a 15 - Page 2

Rogue Wave · 14 March 2006, 21:44

most 9.9 engines are detooned versions of more powerful engines. The reason is that somewhere in Euroe ( France I think) has a serious tax break (like no VAT ) on engines under 10 HP. Hence the 9.9 models offered by most manufacturers are usually detooned 15's and should be relatively easy to adjust/mod

Hugh Jardon · 14 March 2006, 21:50

it seems a lot of folks are interested in trying to upgrade their current engine to the more hp version, perhaps we should have a thread where folks can post talking about the mods done to engines to get them to the higher hps

Rogue Wave · 14 March 2006, 21:55

sensible idea

nugent · 15 March 2006, 06:48

i am curtrently looking for aux my self,, this could be the way to go then,
hugh me old mucka. can you just confirm which model and year if it matters that i am looking for to do this mod,,

Hugh Jardon · 15 March 2006, 08:30

mine is a 2001 or a 2002 i believe

it is the current more rounded model, cant dig out the actual model number till later but a pic is below

petren · 22 March 2006, 14:27

Quote:

Originally Posted by Hugh Jardon

So Jonny or any experts, can you advise if it is possible to upgrade Steves or Dinos engine to 15 hp by just adjusting the reeds or buying the new reed block without changing out the carb. my concern would be it running to lean and possibly burning a hole in the piston if the reeds are opened up but the same carb kept.......any advice for these guys

thanks guys

I just got my 9.9 Yamaha yesterday and the dealer performed the mod right in front of me. All he had to do is remove the throttle restriction and bend the reed valves. No additional parts. He said he's done quote a few of these as all his customers want that.

joakimhansson · 12 July 2006, 22:21

ask yamaha!

Hugh Jardon · 12 July 2006, 22:43

Quote:

Originally Posted by joakimhansson

ask yamaha!

ummm bit sore i see......

if you had read the first post properly you will see that i have been asked some questions via pms and was giving folks the benefit of advice i had had from yamaha dealers and sharing what it takes to convert a 9.9 yam to a 15 yam in an easy and cheap way. i had done it to mine and shared what it takes to do for themselves.

steve was free to phone yamaha but i could not advise him on his particular engine

does that help?

Nos4r2 · 13 July 2006, 02:15

Quote:

Originally Posted by Rogue Wave

most 9.9 engines are detooned versions of more powerful engines. The reason is that somewhere in Euroe ( France I think) has a serious tax break (like no VAT ) on engines under 10 HP. Hence the 9.9 models offered by most manufacturers are usually detooned 15's and should be relatively easy to adjust/mod

A lot of American lakes have a 10hp limit on them too so there's a lot of engines with 9.9 covers over there that are 15's...

gaviotapete · 13 July 2006, 03:01

ah nos,glad to see that you are around b/c you are probably the best one to ask about doing a horsepower upgrade to a 40hp Mercury. have you tried it? is it possible?? how about yammie 75 going to 90??

Jizm · 19 July 2006, 17:05

OK, my engine is a 1996 849cc triple 2 stroke 50hp, same cc as the 60 and 70. Any idea what they do to restrict these?

Jizm · 21 July 2006, 16:25

For those who are interested, midrange yams ie 50, 60, 70 have same block but different carbs and possibly head so not to difficult but could be expensive to upgrade!

Nos4r2 · 01 August 2006, 01:34

Quote:

Originally Posted by gaviotapete

ah nos,glad to see that you are around b/c you are probably the best one to ask about doing a horsepower upgrade to a 40hp Mercury. have you tried it? is it possible?? how about yammie 75 going to 90??

Sorry, only just saw this Pete.

Don't know about the yammies-never owned one.

That 40 merc of yours has a powerhead that looks strikingly similar to the old blueband 50-which never actually made more than 45hp at the prop anyway as they were crank rated at 50hp. If it's the same powerhead I'd leave it as a 40. I've never looked at the 2 side by side though so I'm not really qualified to comment.

The trouble with wanting to up horsepower in general on larger outboards is that unless you've got the blueprints or both engines in front of you then there's no way to tell what to do.
Just because an engine uses the same block doesn't mean it uses the same carbs,main/idle jets,head profile,or pistons for a start-or the same size reeds,transfer or exhaust ports. You'd need to know the full specs for the ignition system too. It's very easy from a manufacturing POV to change a programme on a CNC machine to change port heights/sizes on the assembly line and get a few assembly monkeys to fit parts from a different box but a totally different proposal to do it all by hand.

The other thing to beware of is something it appears Yam used to do on motorcycle engines back in the 70's (It probably doesn't apply now and it's an observation based on what I've seen so don't sue me!).

The Yam xs250 (25hp) and xs400 (40hp)SOHC twins had the same bottom end bar the output sprocket-the only differences were the barrels,pistons,head and cam. Yet if you fitted the 400 top end to the 250 they didn't last very long-usually throwing main or big end bearings. The only thing anyone could suggest as the reason for this was that the larger hp/capacity engines got the cranks that were better balanced and closest to machining tolerances and vice versa.

It's realistically cheaper and less hassle to sell the engine you've got and buy a bigger one if you want more HP.

gaviotapete · 01 August 2006, 01:48

thanks nos,
kinda what i figured.

doneaster · 30 June 2012, 15:34

Hi, Are you sure that bending the throttle stop out of the way is a safe thing to do? Will the engine over rev because the throttle restricter has been bent out of the way? I've looked in the Yamaha Service manual and parts manual for the 1997 models and the only difference is the reed valve assembly in the 15 hp allows the reed valves to open wider which allows more fuel and air into the compression chambers and increases the HP. I even found some info that indicated that the reed valve stops in the 9.9 can be formed slightly to the same specs as the 15 HP Reed Valve assembly so it really isn't necessary to replace the 9.9 reed valve assembly just adjust it.

Pikey Dave · 30 June 2012, 15:48

You're about 6 years too late fella

doneaster · 30 June 2012, 17:30

What kind of answer is that? I was only asking if there was the possibly of the engine over revving if the throttle restrictor was formed out of the way?

Pikey Dave · 30 June 2012, 18:23

Quote:

Originally Posted by doneaster

What kind of answer is that? I was only asking if there was the possibly of the engine over revving if the throttle restrictor was formed out of the way?

Welcome to RIBnet

Max... · 30 June 2012, 18:55

Quote:

Originally Posted by doneaster

What kind of answer is that? I was only asking if there was the possibly of the engine over revving if the throttle restrictor was formed out of the way?

I think the general term is:

spartacus · 30 June 2012, 19:04

Quote:

Originally Posted by doneaster

I even found some info that indicated that the reed valve stops in the 9.9 can be formed slightly to the same specs as the 15 HP Reed Valve assembly so it really isn't necessary to replace the 9.9 reed valve assembly just adjust it.

Would be worth seeing both reed valve assemblies side by side to see the differences.