HST with Yamaha Pro V

Hi Randy,

I have the above mentioned engine which is bone stock except for the exhaust work. It's a 1993 Pro-V 200. I believe that motor is the same power head as a 225 Yamaha but choked down w/ the stock tuner which I've pulled off. I've put a tuner on it (G-5?) and pulled the liner, drilled holes above the cavitation plate; 4 on each side at 3/8" each.  I'm wanting more.  I've spoken to a couple of people and thought I'd throw this past you too. I am planning to install a set of 220 heads and want to bore my carbs out to 36 mm from stock 34mm. Is this a good place to start?  Also, I've been advised to go w/ a custom set of heads (92 octane friendly), bored carbs, and a flywheel. I've been told this will net me fairly significant gains in the 270 hp range. Sound right? I'd like to steer from porting at this time.  How about l/u? I have a nose cone on a stock l/u w/the p/u's on the side above the prop shaft. I'm thinking of changing the entire l/u to one with low water pick up's along with a "whale tail" on the cavitation plate and a blow out ring. Good plan?  In short Randy, I wanting to mid 90's and hope this will get me there.

In the event you can help, and I've been told you could, I'd drive my boat down there and have you dial it in for me. I'm running 12" set back (manual) and still trying to find the sweet spot as far as height. I do a little skiing.  I have a 29 SRX 14 and a 1/4 which appears to be over the hub exhaust and a High five 25" for skiing. I currently spin at 6300 rpm. I bought this boat in 94 and the key tag is an Avon Marine tag.  It's a bruiser colored boat, black w/ blue metal flake and it had an 88 Yamaha (200) on it when I bought it. I've changed the seats since.

Thanks in advance,
Colin Bodley
Winnipeg, Canada
89 HST



I remember your boat. Rick Powers used to own it and it ran in the mid to high 90's then. You have most of the right stuff already, props, tuner, etc. Removing the liner and drilling the holes probably hurt the power output. I've tried it in the past and it always went backwards on performance. I suspect the Yamaha needs some backpressure to run at the rpm it likes. (7000 and below)  If I had your boat I'd run the 220 head and cut it .050". This will give you the best pump gas head and I've tried them all. I tried a bunch of 36mm carbs but didn't see a thing in a gain. The intake is the flow restriction, but it only needs to be changed if you plan on spinning over 7000. The motor would need massive porting changes to run and make power at those rpms. The heads with the timing set at 25 degrees, with the 225 pipe, will make 240 to 250 crank HP. The next thing will take you to 270+ hp. The exhaust port height on the top 4 cylinders is different than the bottom 2. You need to match the top 4 to the bottom 2. On some motors this was over .060". Yamaha does this to make the motor a better bass motor. I found on a boat like your HST it was up to 500 rpm. The gearcase is fine and if you run the gearcase above the bottom you will find the thing will pound itself apart. The bearing carrier and propshaft are not the most robust. I always tried to make the boat work with the gearcase propshaft at about 1/2" below the bottom. This is why the setback is so short compared to other Merc powered HSTs. I found that you can go 100 plus with the propshaft at that height, so no worries. If you do the porting and the heads with the 29 RX you'll have a clone to my personal HST that I had in 1989 and '90. That boat would go just under 100 and your boat had a 200 like this when Rick had it. It ran about the same, so your goal is in easy reach. The stock vertical reed 200 it had was put on before the boat went to Canada.

In the past I've run just about every mod part for Yamaha's out there. I blew up a lot of motors using other peoples " heads and carb conversions". The Yamaha parts I've suggested we've used on at least 50 motors. The combo plain works. More importantly it doesn't cost you thousands of dollars to blow stuff up. If the porting is something you don't want to tackle, call me or e-mail me at gpiracing@charter.net . I think you can have an excellent HST and hope this gets you thinking over the cold weather that is now upon us.




Please submit whatever questions you have to IHRTechTalk@yahoo.com.  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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