Super Jet 46 carb

[alme7airbi]

Hey guys, I bought 2 46mm mikuni carbs for my super jet 701 with boyesen intake manifold. And I have couple of questions

Will v force 2 reeds fit in the boyesen manifold?
Can I do y fitting or should I drill another hole for the pulse line?
How should I connect the two carbs for the throttle? Can I use the 38 ones?

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[alme7airbi]

The v force 2 were big so I sanded them down so they could fit

And I decided to go on with the Y for the pulse line

I just have to figure out how to put the throttle link for the carbs


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[bored&stroked]

Dual 46's on a 701? Thats a LOT of carb.
Personally, I drill the second pulse line for 44's, I would certainly do it for 46's as well.

 

[TheBuzzard]

You're not supposed to Y the pulse line. Either use that slave setup from the other carbs or drill another pulse hole in the other intake tract. That intake has the carbs spaced far enough apart that you don't have to cut the throttle shaft to get coupler linkage in there. Just get a throttle shaft coupler kit. I've had many a race boat with 48s on there but they were highly ported and modified. 46s will make it Rev higher but you might lose some bottom end. 44s are good enough for most 701s unless you want max top end. And honestly that intake and reed setup is way overkill . You won't notice any more power over a lesser intake and maybe some carbon tech reeds. You got money wasted in that whole setup

 

[Tucker]

You're not supposed to Y the pulse line. Either use that slave setup from the other carbs or drill another pulse hole in the other intake tract. That intake has the carbs spaced far enough apart that you don't have to cut the throttle shaft to get coupler linkage in there. Just get a throttle shaft coupler kit. I've had many a race boat with 48s on there but they were highly ported and modified. 46s will make it Rev higher but you might lose some bottom end. 44s are good enough for most 701s unless you want max top end. And honestly that intake and reed setup is way overkill . You won't notice any more power over a lesser intake and maybe some carbon tech reeds. You got money wasted in that whole setup

I just bought some 44s and going to run a PHP intake. High comp head lightened flywheel some porting b pipe. Is that a solid compliment to what I already have ? 44s that is

 

[TheBuzzard]

The stock setup off any Yamaha 760 is all you need with these jets

 

[Mobile Chernobyl]

The stock setup off any Yamaha 760 is all you need with these jets

Stock 760 jetting is 1.5ns and 95gr spring right? So your reccomendation looks like a bigger seat and softer spring for a lower popoff?

 

[alme7airbi]

It ran but it was bogging when hitting the throttle like it was rich so I put 100 for the main and 140 for the low jet nothing changed same issue the spark plug was dark brown I guess it was perfect but still bogging. When I installed the reeds I flashed a light from the crank case side and saw a tiny bit of light I don’t know if it caused this problem. When going full throttle it was bogging in 6000rpm. And btw I blew the piston ring in the first tank after rebuild didn’t break the engine, after starting it for the first time went full throttle for 2min don’t ask why, it was a close call but I didn’t blow the engine just damaged the dooms and piston.


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[Dorny119]

Curious where you are at with this setup. Got it working? I have a Blue Ported bottom/top 735 with lightened flywheel, high comp head, B pipe, MSD enhancer and a 10/16 Hooker. Dual 38s on it now. I have it tuned very well, hits great down low and I had GPS at 53mph. Not 100% sure on the RPM. I think around 6,800. I know that sounds low for highest RPM. I can't get it to rev much higher in the water. Sounds perfect at high RPM with no hesitations, and the plugs are a nice toasted color. I would like to try dual 46mm setup next.

 

[kevbo]

It wont rev any higher because of the pipe, not the carbs. I did a test installing different cases/ carbs under the same cylinder and pipe. Would you have guessed that a stock single 44 on a 650 case would turn the same rpm 6900 and top speed as a 760 case with a pair of 44s? It certainly did under 81mm pistons. The difference was the 760 case and carbs made the pipe hit harder. Torque falls off fast if you have a tuned pipe, theres little you can do for more rpm without shortening the pipe and/or raising the exhaust port. Over the past 20 years I have been able to tune and ride many different OEM based cylinder and intake combos. I can say that a pair of 46s do work but almost always need a richer pilot/popoff mixture for good response when compared to 44s. A pair of 44s need a richer pilot/popoff than a single 44. A stock pair of 38 can be tuned leaner than that and still have good response.

 

[Dorny119]

It wont rev any higher because of the pipe, not the carbs. I did a test installing different cases/ carbs under the same cylinder and pipe. Would you have guessed that a stock single 44 on a 650 case would turn the same rpm 6900 and top speed as a 760 case with a pair of 44s? It certainly did under 81mm pistons. The difference was the 760 case and carbs made the pipe hit harder. Torque falls off fast if you have a tuned pipe, theres little you can do for more rpm without shortening the pipe and/or raising the exhaust port. Over the past 20 years I have been able to tune and ride many different OEM based cylinder and intake combos. I can say that a pair of 46s do work but almost always need a richer pilot/popoff mixture for good response when compared to 44s. A pair of 44s need a richer pilot/popoff than a single 44. A stock pair of 38 can be tuned leaner than that and still have good response.

Veryyy interesting. So you think power basically falls almost strait off at a certain RPM once the pressure wave just isn't making it back fast enough for the shorter exhaust port opening time? I am familiar with the concept of the two waves and how they work. I installed a switch on my ski to kill the dedicated water to my pipe momentarily to get just a bit more RPM. Drying out the pipe, hotter exhaust gases, faster pressure wave (due to the speed of sound increasing in hotter gas), a bit more high RPM power. I am definetely surprised at your results. I would think the better cases and carbs would contribute to greater power overall. I guess if that pressure wave doesn't come back at the right time at high rpm it's pretty detrimental. I wonder how some of these people are getting 7500-8k rpm? Prop pitched way down? But at the end of the day that pressure wave will behave the same regardless of prop.

 

[kevbo]

The pump load is ever increasing with rpm, it can hold the engine at any rpm you set it to. In order to get good power response the pump must be set on the light side, a few rpm beyond max power. If the pump holds at or below max power the throttle response will be slow. The effect is that rpm wont rise much when a flatter prop is installed but response is better. As far as pipes go there are a couple of options. The original wet pipes generally run under 7000rpm, there are some short ones that will turn more. Most of the dry pipes were made for super stock racing. Those are the ones that work over 7500rpm. A low port cylinder with a wet pipe is easy to make work well since they will pull an overloaded pump better. Getting a high port and short pipe to respond well can be a huge obstacle. You often have to use lower pitched impeller.