Freestyle 750 engine

[Austin]

Can you build a 750 bottom end with small pin cylinders and pistons? or do you run big pin pistons? Im building a 750 for freestyle and I know small pins have better low end because the lower porting. Is it possable?


Also looking for 750 parts for short block.

 

[Vumad]

From GroupK http://www.groupk.com/k750.htm

The "BIG PIN" 750 series - The 1995 and later 750 motors differ greatly from all the previous 750s in several important ways. 1) The wrist pin and big end of the connecting rods have been enlarged for better durability (hence the term "big pin"). This means that the pistons of the early and late engines are not interchangeable. 2) The inlet tracts, reed cages, and carburetors have been downsized slightly to increase inlet tract air speed. This increased airspeed results in much better overall acceleration. 3) The cylinder has much higher exhaust ports than any previous 750s. These larger ports work for these 750s because of the improved low end power offered by the smaller inlet tracts. While some of these parts are interchangeable with earlier 750 models, we don't recommend it. The SXi cylinder will yield poor results on an Xi and vise versa. The low exhaust port/large inlet tract, and high exhaust port/small inlet tract seem to be matched designs that don't like being mixed.

 

[Austin]

Thanks vumad! So I shouldn't mix around motor parts. What does everyone think would be the better motor for a "low end" based engine? I have dual 46 red tops, factory pipe, r&d head. I still need to buy a motor and I have no idea what I should buy! Im planning on doing some freestyle porting but not much. I was also planning on doing forged pistons and a welded crank.

 

[Vumad]

Low end? Buy a Superjet motor, 62T cases with 61x cylinders with a conversion bedplate that bolts into the X2 with Kawi style couplers to bolt to the Kawi pump.

Otherwise, I don't know if there's any difference b/t the big and small pins. Some swear by one or another. I wouldn't know the difference unless someone told me where the motor came from.

 

[LeftysRule22]

Id go with the big pin. Some have said the small pin offers better bottom end but in my opinion the big pin pulls better everywhere. If anything the bottom end is the same between the two and big pin owns the mid high ranges.

The two motors I ran were both bone stock so that's what I'm basing my comparison on.

Sent from my 3VO

 

[Vumad]

Id go with the big pin. Some have said the small pin offers better bottom end but in my opinion the big pin pulls better everywhere. If anything the bottom end is the same between the two and big pin owns the mid high ranges.

The two motors I ran were both bone stock so that's what I'm basing my comparison on.

Sent from my 3VO

Good point.

Look at Kawi's history. Every year they change something. It's not like they do extensive testing before they bring a product to market. The 650 is a perfect example. Started with a 28mm carb and performs a lot better in later years with a 38mm carb. I dislike Kawi because they let their customers do the extensive testing of their product they should have done. I think it's safe to say with anything Kawi, the newer it is the better it performs. This is likely true with the early vs late model 750 motors. In a side by side, I'd choose the big pin myself too. It's probably not worth several hundreds more, but a few bucks probably.

 

[Austin]

Okay good point Thanks for the input. I was think big pin would be smarter. My original plan was to do a ported 701 in it with yam 144 pump but buget came in to play.

 

[kevbo]

Kawasaki 750-800 cylinders are completely interchangeable. Its the crank, case, and pistons that are different. For best response get a 92-95 single carb cyl or an 800 sxr cyl. Always make sure to verify clearance between the crank wheels and sleeve when using an early cyl with a big pin crank. All that GroupK literature was published in 1995, the bastard year for big pins. They had very small carbs and very low transfer ports. Everything 96+ is good stuff.

 

[sxipro02]

Im with kevbo, if your starting from scratch go with a 800cyl or a small pin cyl and a 750 case. If you get small pin pistons and rods you will have less rotating weight which will add to the low end brap. Call tim at Zforce, he has a crap ton of knowledge hes willing to share and is priced very reasonably. He help me out alot when doing my build last winter. I stuck with all big pin stuff since I already had it and it was in great shape.
I hate to say it but the best way to go is a Yam 701 with the conversion plate, they make a crap ton more on the bottom end. you could sell off your kawi parts and piece together a nearly stock 701 with pipe and head that would stomp a modded 750. I know this first hand, mine is bored and ported and still dosent perform like a yam on the low end, it will however leave them way behind on the mid and top.

 

[Austin]

Good news! I bought a custom fresh motor and tons of stuff with it for really cheap! First off this is a small pin 750 freshly bored 1 over to a 763, It has been pump gas freestyle ported, new crank seals, welded crank, brand new ada head w/22 cc dome will put a SP at 220 psi so need to find some 26 or 28cc domes to trade for to get my motor at 175 to 185, dual stage boyessen reeds, freestyle wet wolf pump cone, lightend 650 fly wheel, and new gaskets. Then hopefully this spring before I finish the ski I will have my pump blue printed, put pump stuffers in, and put a swirl big hub in it then get my nozzle bored. I think this ski should hal @ss when Im done.

 

[Austin]

I like to have some top end on my ski so that is one of the reasons i didn't get a 701. Last summer I was running my x2 as a 650 limited ski and I raced a 701 and beat it on the top end and it was a stock sj. obviously it got me on the low end but did come back and win.

 

[kevbo]

I am installing a 144 pump in my (back flip) X2, one of the few with steering moved aft 12" and built in footwells. It has been an easy mod so far, the pump shoe will be the only challenging part to mfg. Looks like it will get a bigpin lower with an XI cyl.

 

[sxipro02]

Sounds like a good setup so far austin, someone correct me if im wrong but if you run a 650 flywheel you will need to run 650 electronics too.
on a side note, hand on to your stock pump cone, I ran a wolf cone with my stock motor and a 12/18 but when I put the built motor in and a 9/17 I had to put in the stock cone to fight cavitation, it wouldnt hook for crap. I noticed more hit on the bottom and alot more top end with the stock cone as well.

Im in the process of grinding out the flat spots in the pump veins now, is that what people call blueprinting? dumb question I know....

 

[N3vrSat1sfied]

I know ill sound like all the members on the forums now... But from experience, save yourself the time and money, and do a yami conversion! I did about everything to my 750 motor and still didnt have the punch I wanted. put a 62t 61x motor in and it was the best decision I made. Now I just ride a superjet but I do miss the Yamasaki sometimes.

 

[kevbo]

I have both 701s and a 750 with many cylinders at my disposal. By the time I port a 701 to make the same power as the equivalent ported/piped 750 the throttle response is no better. I found the difference in low speed thrust in the pump more so than the engine.

 

[sxipro02]

I struggled with the yam/kawi decision myself. Im more than commited now and couldnt be happier with the outcome. Austin, post some pics man! this winter cold sucks, we need ski pics to get us by lol. BTW is this build going in a X2 or a stand up?

 

[N3vrSat1sfied]

I have both 701s and a 750 with many cylinders at my disposal. By the time I port a 701 to make the same power as the equivalent ported/piped 750 the throttle response is no better. I found the difference in low speed thrust in the pump more so than the engine.

I had a ported 750, factory b pipe, lightened flywheel, msd, ada head, several carb options (best was a 42mm Sudko) I also tried different pipes.

Then I put in a ported 701 62t 61x with dual 40's ada head lightend flywheel, msd and the throttle response was night and day. Same pump. Although if i still had that boat i would of put a yami pump or a mag kawi pump in. Still wasnt quite the response a Similar set up sj had.

EDIT: Sorry for the slight derail, just something to think about. Back to his question, deciding between big pin and small pin.......

 

[Austin]

Its all going into a x2. I started a build thread you guys can watch. As soon as I get the motor and all the good stuff I will post pictures of it. I think motor and new stuff will be here next week. This is the link is http://www.x-h2o.com/threads/...inter-x2-build

Also I am running 650 electronics.

 

[Austin]

I have rode a dozen sj's and 750's and for the money 750 is a lot more worth it for me.


Also What is the most compression I can run with pump gas?

 

[sxipro02]

Since your running a small pin you'll prob be using a timing advance plate. I'd stay around 180psi with good oil