Carburetor 787 on seadoo xp720
- Thread starter mandriva
- Start date
- Status
glsmohio
Well-Known Member
That's a good question. If you put a factory pipe on the 720 I know that 787 carbs set up like they are on a 96 xp are perfect
mandriva
Active Member
Because the 787 carburetor is better than 720
mandriva
Active Member
yes agreed,i build a limited mod!
glsmohio
Well-Known Member
I think in the end of the day he just wants to be different. I know seadoo build the skis best as stock and you and other people dont see the point in changing things. Some people just want to play around I think with this older stuff...not saying it's a bad thing. I'm very guilty my self. A lot of people would tell him to buy a 787 and sh*t can the 720 but it's what his project is now and trying to play the game with the 720. I have skis from 580 to the twin 951 rxx and all my skis have stuff done to them . It's just the drive and fun factor I want....please post what u come up with on the carb settings though. I always like to learn.
JeremyD615
Well-Known Member
I think Miki’s point was that there are no gains to be had from swapping the carbs. A stock 720 with the stock carbs is already properly carbureted. Unless you’re moving more air volume through the motor with modifications, there’s no point in swapping the carbs, as you’ll just wind up over-fueling it.
Exactly, I was just saying you can't slap a set of 787 carbs on a 720 and use the stock 720 jetting in them.
I am all for modifying these skis but I was not sure of his performance intent so I didn't want him to expect more performance just from installing bigger carbs. If you add a pipe or even port the cylinders the 787 carbs are a great improvement on a 720 but you have to jet them correctly. With a Factory pipe on a 720 they are basically mandatory if you want it to live a good life.
If it is a bone stock 720 just keep the 720 38's and enjoy.
This is a really great read on the subject and great 720 information Group K HX Shredder
Carburetors and Inlet - Most full-out racing HX’s use a billet intake manifold fitted with 44-48mm carbs. With the larger carbs and inlet manifold passages, the inlet ports in the crankcase are also enlarged to allow the full potential of the big carbs to be realized. Unfortunately, the big carbs used on race boats also have “very” heavy fuel consumption that would not be acceptable for this project.
The stock HX uses Mikuni 38mm SBN carburetors. While these carbs work well on a stock machine, they are a bit undersized to create the kind of acceleration we wanted for this project. We found ourselves stuck between the desire for good fuel range and the desire for bigger carbs. The ideal solution was to obtain a pair of stock carbs from a 782cc 96XP. These carbs are very commonly available on Ebay and at PWC salvage shops nationwide for under $200. The 96XP carbs are identical to the stock HX carbs in appearance and fitment. The only difference is that they use 40mm butterflies and throats instead of 38mm butterflies and throats. The 40mm carbs bolt up perfectly to the 718`cc HX manifold, and even have the same cable attachment points for the throttle and oil injection cables. The stock HX inlet manifold has inlet runners that are 39.7 – 40mm in size, so it does not offer any restriction for the 40mm carbs. Given that inlet tracts of the stock 718cc manifold were just barely big enough to accommodate our new 40mm carbs, we saw little advantage in removing the choke plates. It bears noting that leaving the choke plates in helps slightly to increase inlet signal (a problem area for the 718cc engines). This increased signal helps the engine to carburate better, particularly at lower rpms.
The performance result of adding the 40mm carbs was very noticeable. There was a clear increase in the authority of acceleration, as well as slightly increased peak rpms. The jetting of the 40s did need to be changed to accommodate the fuel demands of the 718cc HX, but once the jetting was done, the HX started, idled, and accelerated perfectly.
I am all for modifying these skis but I was not sure of his performance intent so I didn't want him to expect more performance just from installing bigger carbs. If you add a pipe or even port the cylinders the 787 carbs are a great improvement on a 720 but you have to jet them correctly. With a Factory pipe on a 720 they are basically mandatory if you want it to live a good life.
If it is a bone stock 720 just keep the 720 38's and enjoy.
This is a really great read on the subject and great 720 information Group K HX Shredder
Carburetors and Inlet - Most full-out racing HX’s use a billet intake manifold fitted with 44-48mm carbs. With the larger carbs and inlet manifold passages, the inlet ports in the crankcase are also enlarged to allow the full potential of the big carbs to be realized. Unfortunately, the big carbs used on race boats also have “very” heavy fuel consumption that would not be acceptable for this project.
The stock HX uses Mikuni 38mm SBN carburetors. While these carbs work well on a stock machine, they are a bit undersized to create the kind of acceleration we wanted for this project. We found ourselves stuck between the desire for good fuel range and the desire for bigger carbs. The ideal solution was to obtain a pair of stock carbs from a 782cc 96XP. These carbs are very commonly available on Ebay and at PWC salvage shops nationwide for under $200. The 96XP carbs are identical to the stock HX carbs in appearance and fitment. The only difference is that they use 40mm butterflies and throats instead of 38mm butterflies and throats. The 40mm carbs bolt up perfectly to the 718`cc HX manifold, and even have the same cable attachment points for the throttle and oil injection cables. The stock HX inlet manifold has inlet runners that are 39.7 – 40mm in size, so it does not offer any restriction for the 40mm carbs. Given that inlet tracts of the stock 718cc manifold were just barely big enough to accommodate our new 40mm carbs, we saw little advantage in removing the choke plates. It bears noting that leaving the choke plates in helps slightly to increase inlet signal (a problem area for the 718cc engines). This increased signal helps the engine to carburate better, particularly at lower rpms.
The performance result of adding the 40mm carbs was very noticeable. There was a clear increase in the authority of acceleration, as well as slightly increased peak rpms. The jetting of the 40s did need to be changed to accommodate the fuel demands of the 718cc HX, but once the jetting was done, the HX started, idled, and accelerated perfectly.
- Status
