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Old 12 March 2006, 17:25   #1
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converting a 9.9 yam to a 15

I have had a couple of questions regarding what it takes to upgrade a 9.9 yam to a 15

here goes

i have attached a pic of my particular engine, you will note the engine plate on the side of the engine as Steve cant find his so this is where it is on my engine. this modification was done on this style of engine rather than the older squarer ones

the next pic is me pointing to a metal stop that restricts the throttle from opening more than around 60%

if the background you can see the gold colour of the reed block, this is just bolted in place between the block and the carb

took me around 20 mins to do the work and that included a t-break

another pic of the engine from the side.

costs were as follows

bending the throttle stop out the way ....free

buying a new 15hp reed block....around 28 quid

buying a new 15hp sticker for the front and back.....around 2.80 each

i purchased a 12 pitch prop to take advantage of the extra power....50 quid

the benefit of the 50% increase in performance and increased economy....priceless

it is amazing how much more these reeds open compared to the 9.9 item

well worth doing
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Old 12 March 2006, 18:03   #2
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I did the exact same a job a few years ago to a 9.9D (square one as you call it) it didn't have the 60% throttle stop on that model, the only two differences were, the 'stops' on the reed block were quite different, restricting the reed travel by at least 50%, ie, how far open the reed could bend., remedy, carefully re-form the back stop to the same form as a 15 (had a 15 bits to compare). This made made all the difference in the world. the other major change, was the carb throat size, can't remember exactly, think the 9.9hp was 22mm, and the 15hp was 28mm. I sourced a 15hp carb, but it really made no noticable difference to the performance, if anything, with the smaller carb on, the low end response was better.

So, if you have a 9.9D and want a 15D, all you really need to do, is mod the reed block.
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Old 13 March 2006, 04:38   #3
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Johnny
I've got the old square type Yam(i thought it was 10hp?),so it is possible to uprate it with alterations to the reeds rather than purchase new?and you don't need the 15hp carb? and did you take advantage of a bigger prop like Hugh?
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Old 13 March 2006, 04:48   #4
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Quote:
Originally Posted by Dino
Johnny
I've got the old square type Yam(i thought it was 10hp?),so it is possible to uprate it with alterations to the reeds rather than purchase new?and you don't need the 15hp carb? and did you take advantage of a bigger prop like Hugh?
Dino and Jonny, a friend Steve contacted me regarding his engine which is the older squarer one, he is not sure of the hp as he cant find an engine plate, do you know what cc your engines were and if i forward you a pic of his engine that he sent me could you confirm this engine type is the same as yours......if you could pm me your home email address i will forward you steves email and copy him in as he is keen also to boost the power on his engine

thanks in advance
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Old 13 March 2006, 04:54   #5
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here are the pics of steves engine
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Old 13 March 2006, 05:01   #6
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Hugh
That made me go and have a look at it!i't a 6m4 s 9.9d ,so now i've learnt something,your mates looks identical to mine.Hope that helps
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Old 13 March 2006, 05:05   #7
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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

Quote:
Originally Posted by Dino
Hugh
That made me go and have a look at it!i't a 6m4 s 9.9d ,so now i've learnt something,your mates looks identical to mine.Hope that helps
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Old 13 March 2006, 14:20   #8
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HI HUGH THANKS ITS GOOD TO HAVE A FONT OF KNOWLEDGE ON YOUR SIDE ,THANKS FOR EXPLAINING MY CASE, IF THERE IS A WAY AF UPGRADEING THE POWER THAT WOULD BE V GOOD. .IN LIVERPOOL THE THERE ARE 2 MAIN SHOPS AND BOTH ARNT REALY INTERESTED UNLESS YOUR SPENDING THOUSANDS . WHEN I TOOK THE ENGINE IN FOR SOME ADVICE HE WASNT SURE WAT ENGINE IT WAS OR IF IT COULD BE DONE, BUT WAS SURE IT WOULD BE 200 PLUS PARTS AND SAID THE READ VALVE WOULD NOT BE 30 IT WAS GOING TO BE A LOT MORE AND THE STICKERS WOULD BE 50 SO ANY HELP IS VERY WELCOME STE THE DJ
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Old 13 March 2006, 15:08   #9
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Interesting
Outboards are a new thing to me . I have years of experience with cars and bikes and am a qualified mechanic . I just don't understand why seem to make 2 power variations of the same engine .
Having just shopped about for a new engine and compared wieght vs power etc i found that half the engines I looked at could be upgraded and some i was told simply needed a restrictor removing . for instance the mariner 25 is a 30 with an inlet restrictor removed ?? seems daft to me .
My honda 20 is the same as the 15 so why buy a 15 , have a 20 and don't open the throttle so hard
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Old 13 March 2006, 15:32   #10
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1. its cheaper for the manufacturer to just restrict the one engine than to go back to the drawing board and design a whole new unit with a different set of parts to produce.

2. you have to be very carefull putting an engine on a boat that is above the rated hp for it - the manufacturer of the boat will not be so ready to repair or replace it when youve snapped the transom in two if you over powered the boat.
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