Super Jet Converting a 701cc (62t crankcase) to a 760cc (w/64x cylinder)

[Yamer-Jammer]

I have a 701 64v(62t case) and want to put a 760 cylinder on it. Understood that the exhaust ports are 2mm higher and it will not have the bottom end of a 61x cylinder. Plus the exhaust bolts holes are larger on the 760 cylinder which requires inserts. I am hoping that I can counter the low end loss with a lightened flywheel, MSD enhancer ignition & coil, cold fusion lightened couplers, with ported cylinder and case. All of this in addition to what I already have: R&D head, Moto Tassanari reeds, R&D reed spacer, and factory b pipe. I am also curious what will need to be done with the jetting on the carbs for the larger cc’s? Anyone who has got one of these dialed-in and recalls the jets used, please pass that along(and what carbs you used). I am looking for people who have done this conversion and have good things to say about it. Moreover any pointers on what worked and what didn’t work, would be appreciated. Thanks guys!

 

[Sospikey]

I've been down the mix-and-match road. Save yourself the headache and pick a reputable builder, decide on a budget and go from there. Just my 2 cents.

 

[StandupWI]

I plan on doing this conversion real soon. I would also like anymore info people have on it.

 

[motoman96]

I've been down the mix-and-match road. Save yourself the headache and pick a reputable builder, decide on a budget and go from there. Just my 2 cents.

Ding ding ding!!!!! Couldn't agree more. Personally I would suggest calling Art Gomez at Jetworks as he has been doing this for 20 years. He will give you strait up answers based on trial an error. He knows his shyt!

 

[ryan]

dont do it. its not worth it. unless you get it ported. poke the 701 to 84mm and run if you dont want to go for porting.

i should read more before i post. lol send the cylinder to art at jetworks he will hook you up. best porting out there for a 760. you can only do so much with a 760 cylinder. the 701 will make more power. (low end)

 

[McDog]

Great advice in this thread.

 

[Freakrider]

Chuck at XScream decks the base of 760 cyl to lower port timing, ports it and then cuts custom domes to compensate for deck height...sj762 has one and it has great bottom end hit with BB power.

 

[Yamer-Jammer]

More info for anyone looking to do this. This is not a "mix and match" setup. These motors came in Yamaha WaveVentures, WaveRaiders, GP760s, and XL760s. Yamaha uses a 62t crankcase bottom end (identical to the 701 EXCEPT that it has a second pulse line, more about this below) and they use a 64x cylinder, pistons and head -vs- a 61x cyl, pistons and head on a 701.

The extra pulse fitting is due to different OEM carbs. 701's come with dual Mikuni 38mm (one pulse fitting) and the 760's come with dual Mikuni 44mm (two pulse fittings). You can either start with a 760 62t case or convert a 701 62t case. The secondary brass pulse fitting can be bought from any yamaha dealer. The case would have to be drilled and then the pulse fitting pressed in.

If you pick up a 760 motor from one of the sit down models listed above it will also come with a different flywheel, stator and the stator cover will have a hole for an oil injector. You can use a block off plate or switch to a 701 stator and cover. I have a $600 TBM flywheel that I want to run, so I will require the use of a 701 62t style stator and stator cover.

I have a 701 in my ski now and a 760 in pieces in my garage that I can take pics of to help visualize this if anyone wants... Let me know.

 

[Yamer-Jammer]

its not worth it. unless you get it ported.

I agree. Every builder that I have talked to about this strongly recommends porting the cylinder. General porting costs that I am finding are $200 to $400 depending on the type/level of porting.

 

[Polish jet pilot]

cutting the base of cylinder is a very good and cheap option, then just open up the exhaust, machine head/domes a bit and you have a nice motor

 

[go4it743]

it would be nice if xscream had a 64x top end package on there site, like the 61x top end package

 

[SUPERJET-113]

Chuck at XScream decks the base of 760 cyl to lower port timing, ports it and then cuts custom domes to compensate for deck height...sj762 has one and it has great bottom end hit with BB power.

Thats a great idea, and I dont know how much it costs, but i bet it would probably equal out to about the same price as if you just had big bore sleeves installed in a 61X cyl.. Just guessing on price though, dont know which way is really the cheapest.

 

[AtomicPunk]

it would be nice if xscream had a 64x top end package on there site, like the 61x top end package

Call them there is SOOOO much more they can do than they can possibly put on their site.

 

[davidescu_radu]

Call them there is SOOOO much more they can do than they can possibly put on their site.

62T cases with only one pulse line can be easily machined to acomodate the 64x sleeves inside-so boring can go to 85.5 mm
Than the second pulse line is needed.

 

[Nuklear6]

To get the most bottom end out of the 64x cylinder you do need to cut the bottom of the cylinder or top of the cases, cut/adjust transfer Ports to compensate for lowing of cylinder, then re cut the squish relief in the combustion chamber domes. That being said, before I started doing all that I ran a 760 on 62t cases with Honda bond 4 as a base gasket, and just cut the base gasket thickness out of the squish band on the domes. It ran great with a ton of bottom end (def more then even a ported 701). Used OEM dual 38s, 75 pilot, 135 main, 1.5 ns, clipped 115 g spring (45_48 pop off). 180psi compression with stock flame arrestors. Would want a 9/15 prop if using a mag or tbm, or a 10/16 if running stock pump.

 

[kevbo]

Most of the "low end" problem will be solved by boring the nozzle and use a low pitched impeller. Response may still be a little softer but it will make more thrust than a stock ported 61X cylinder. A pair of 44s will make the pipe hit a little harder. Tuning is not difficult but must be done on an indevidual basis.

 

[stefan]

I wash not a big beliver in the 62t cylinder then i saw this video http://www.youtube.com/watch?v=gBOeizwp0w4 it is board member zeski25 no doubt he has some skillz. But stil that 64x cylinder is making some power, think the setup is 64x 760cc cylinder, dual 48 mm riva bomb, PFP pipe,total loss,solas mag pump. Soo now i just got a 62t cylinder deck bottom 1.5 mm cut domes 86 mm bore and ported realy eksited too try this cylinder out.

 

[SteveZimmerman]

A few years late on this thread but wondering if anyone knows people currently modifying the 760 cylinders? Chuck at X-scream no longer works there. Who else could do the work or has the porting specs for the cylinder? I know people that could do the machining work if I had some porting specs to go off of.

 

[VXSXH20]

A few years late on this thread but wondering if anyone knows people currently modifying the 760 cylinders? Chuck at X-scream no longer works there. Who else could do the work or has the porting specs for the cylinder? I know people that could do the machining work if I had some porting specs to go off of.

760 Rework= @Nuklear6

 

[x2mafia]

Or - @holeshot