Super Jet Dual or Single 44 Carb 718??? Help!

[eastcoastjumper]

I did all the porting myself, everything is fresh rebuilt engine and carbs, and the jetting was l recommended by Jet Maniac. Just not sure where to go from here.

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you can save yourself a lot of time using a single 44 with the specs i wrote above. Its very versatile, not crazy sensitive to temp changes, and youll be out on the water and not chasing jetting.

lets see some pics of the porting

 

[jetx]

Are u running oem Yamaha 44's or retail mikuni 44's?

 

[Roseand]

I'd go up a size on the main just to be safe. 147.5 is for standard bore.
Plus jetting can vary depending on the porting.. My main ended up being much, much bigger than most others typical ported 701 single carb..

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[Parsonsjb88]

Are u running oem Yamaha 44's or retail mikuni 44's?

Not exactly sure. There's pics in my build thread.

http://www.x-h2o.com/index.php?threads/158734/

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[jetx]

It looks like you have dual OEM Yamaha 44's...they jet differently than Reg retail 44's...I'm no tuning expert but my initial thought is your main is too low, when your coming down from a rev its starving for fuel...I think stock mains on these are like 130 or something that came in the stock 760.

If you can get ahold of @waxhead he might be able to provide some specs, have seen him talk about OEM 44's quite a bit over the years

Id try some more tuning before I give up on them, it's no real money out of pocket to get them tuned in and they should rip.

I've also heard filling in the crossover on the stock manifold helps the oem 44's work better

Not exactly sure. There's pics in my build thread.

http://www.x-h2o.com/index.php?threads/158734/

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[hornedogg79]

Do you have a restriction in your fuel return line?

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[Vumad]

I didn't read any of the posts, but I say oem 38s.

Everyone running motors for power, wether race or freeride, runs duals. They work better. A single means you are pretty much guaranteed to have one cylinder slightly rich.

So, if simplicity is more important than performance, save money on both parts and fuel and keep the stock. If 2 is 2 complicated, then single is an option is guess. If cost and effort aren't as much a factor, as performance, the only real question is what sized duals.

 

[Parsonsjb88]

Ya im pretty sure Ill keep the dual 44's. There shouldn't be any restrictions, the carbs were completely disassembled, carb cleaned, sonic cleaned, and all new genuine mikuni rebuild kits. Also all new fuel filters and hose.

So last night I disassembled my top end and just my luck with only 15 hours on the motor I've got damage to the piston and cylinders. Looks like I ingested some water and washed the oil film off the wall which caused the piston skirt to marr against the cylinders. Doesn't appear to be any damage to the ring lands or anything. I'm hoping I can do a hone, touch up the piston skirt, and new rings.

So back to the carb situation, anyone have any recommendations for jetting for the dual 44's? Is anyone running a setup similar to mine that wouldn't mind shedding some light on their jetting and experience?

 

[Parsonsjb88]

Heres Pics of the damage, repairable with hone and new rings? Do I need a new piston too? I'm already at max bore for the 61x apparently.

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[hornedogg79]

You must have a restriction in your return to build pressure. I have two setups like yours. I run a size 60 jet in the return line. I have 115L/120H in one and 115L/115H in the other. I run my pop off lower than jetmaniac recommends at 25 psi.

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[Parsonsjb88]

You must have a restriction in your return to build pressure. I have two setups like yours. I run a size 60 jet in the return line. I have 115L/120H in one and 115L/115H in the other. I run my pop off lower than jetmaniac recommends at 25 psi.

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The 44's have the built in restrictor in the carbs. I was told by a few people that it was unnecessary to run another in the line.

 

[Quinc]

Heres Pics of the damage, repairable with hone and new rings? Do I need a new piston too? I'm already at max bore for the 61x apparently.

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You can probably clean up the cylinder with some acid to remove the aluminum off the sleeve. That wouldn't cause your tuning to be off. Also the 61x can be bored out to 84mm.

 

[Roseand]

Muriatic acid, hone, new piston and rings and good to go.
It the ring lands are perfect you could maybe get away with just cleaning off the piston skirt but I'd put a new piston in to be safe.

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[Parsonsjb88]

You can probably clean up the cylinder with some acid to remove the aluminum off the sleeve. That wouldn't cause your tuning to be off. Also the 61x can be bored out to 84mm.

Ya the tuning I think was a combination of a few issues. One of which I think I was leaking water from my head into my combustion chamber. Either way seems like the consensus is acid, hone, rings, 1 new piston? If hone doesn't clean them up maybe bore up a size.

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[Parsonsjb88]

@Quinc , I was doing some reading and groupk mentioned that 83 was the max safe bore on the 61x cylinder. Or 84.5 on the 62t. I'm a little skeptical going any larger, have you seen many people do larger than 83 on a 61x?

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[Roseand]

Yeah lots will endup going to 84.

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[WB1994]

Everyone running motors for power, wether race or freeride, runs duals. They work better. A single means you are pretty much guaranteed to have one cylinder slightly rich.

Everyone running motors ..... are running for power. To say duals work better is pretty much untrue in alot of situations. And ive never had one cylinder run lean on a single carb setup. Never even heard that before. And i agree with eastcoastjumper , on these stock cylinder setups id put a stock carb setup by me up against anyone elses dual setup with the exact same mods.

 

[Quinc]

@Quinc , I was doing some reading and groupk mentioned that 83 was the max safe bore on the 61x cylinder. Or 84.5 on the 62t. I'm a little skeptical going any larger, have you seen many people do larger than 83 on a 61x?

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I have been running 84mm 61x cylinders on my stand up and wave blaster ported with 190psi compression etc. They make great power at 84mm. Stock 760 cylinders are also 84mm.

 

[Parsonsjb88]

I have been running 84mm 61x cylinders on my stand up and wave blaster ported with 190psi compression etc. They make great power at 84mm. Stock 760 cylinders are also 84mm.

Does that mean you can run stock size 760 pistons in the 701 if I bore to 84? Or are there other differences in the piston design?

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[Roseand]

Does that mean you can run stock size 760 pistons in the 701 if I bore to 84? Or are there other differences in the piston design?

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Same pistons.

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