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Here there is an international boat show early in January. All of new models are on display and available for purchase. The Final Parts Book edition for 1992 models would have been May 1992. The two different styles of carburetor are listed in that book. The 1.25 and 1.50 bore sizes are original parts listed in that book and/or other parts books for the oval port, a T850 racer can use ANY carb that was available for ANY model year of production for the oval port motor. I am sure they will try the 1.50 bore carb first.

JUST A REMINDER ON HOW QUICK AN OVAL PORT IS ON THE RACE COURSE!!!
https://www.youtube.com/watch?v=wU2zON-6xsE

if the main jets went up from 52D to say a 58D what would need to be done with the top jet that is at the moment a 60D
or would this be best left alone ?

I ask this as on the older carbs when running a 52D main jet they had a 35D as the top jet !!! this seems a huge difference to the 60 on the later carb !!

that is a very fast boat in the video, good quality vid and some very good driving too.

Anytime you make a major difference from the stock main jet size on the 3 cylinder OMC you can expect the idle to increase. As I mentioned in a previous post, I think the idle will be over 1000 rpm with the jet change. For a T850 racer the high idle is not a problem. They do not shift gears, they start the motor in gear. They may need to change the top jet, testing will tell.

On another thread I was asked how I would build a laker runner oval port. After learning more about the motor I have changed my mind on the carbs I would use. I was going to use the large bore SST 60 carbs. I now would not start with them. Reasons: before this thread I did not know there was 1.5 inches carbs used. I had only seen the 1.25 carbs. As they refined this motor the manufacturer ended up with 1.25 carbs and the same jetting. The motor ended up being better overall. It did not need bigger carbs. My thinking now is the motor does not need the SST carbs and they may hurt the performance and shorten the engine life. We also know the last model of the carbs were the best. I believe the D1 and D2 numbers in the castings refers to Design 1 and Design 2. These was part of the refining process. So I would not throw the 1.25 out right away. If I had a good running powerhead. I would refresh it and make changes to run on the 15 inch I would try the small carbs first and then try the 1.50 carbs.

the small 1/25 bore carbs are just 60hp, the bigger 1.5 bore is 70hp, so there is where the power is.
a 50hp has even smaller carbs under 1.25 bore at the rear of carb !!!! yep tiny little things.

with the 60hp carbs (1.25 bore) you wont hit the limiter even with a 13 pitch test prop.
the engine just runs out of carb at around 6300 to 6400 rpm like this.. thats what I found myself.
and when I tested a 15 pitch same type of prop the revs are just the same as my 13 test prop, it runs out
of carb at 6300 ish, definitely not on the limiter.

how come the d3 and d1 carbs are on engines of different years. I mean both my 60hp 1995 engines had the s2 and the d1 carbs on both engines ???

I can only see the smooth finish on the backs of the D2 as the difference ?
everything else on the carb is the same, even the numbers on the top plastic bit.

what ratio of oil would you run in these for racing ? 40 to 1 or more and what oil would you suggest ?

The D1 and D2 are part of the castings. They could be exactly the same , but they are not from the same casting. Why they mix them up? I cannot answer that. The 15 inch I am referring to is the 15 inch mid section not the prop. On a T850 boat the motors run 22 to 24 pitch props and turn over 7000 rpm. The bridge port can run high RPM with stock jets. Since we have not had an oval port run with its stock carbs and stock jets we are not sure if it will do the same.
I will mention this one last time...This thread is about T850 and the oval port, I want the T850 racers to learn from it. It is Not about this and why they did that. Or about a non race application. Question period is over.

Bill is a good reference for these motors.

Bill Gohr
If the head you are using has a "G" stamped after the part number that would be the later one,
As far as those service bulletins from 90, 91 92, and early 93, most of them can be disregarded, lots of those were quick fixes trying to cover engines that were failing like popcorn so we really don't need to do all of them and remember if you have a 90-93 with a replacement oval port powerhead and the correct water pump you need to disregard them all.

calvin
Which year/years 56 inch motor is the best for mods or stock rebuilds?

Bill Gohr
[Which year/years 56 inch motor is the best for mods or stock rebuilds?]
You are going to build a powerhead for stock I would use nothiing but an Oval port powerhead