Throttle needs to be pumped in order to maintain HP on xp800

[Red5]

Just bought a boat that previously competed in the world finals in havasu. I have changed heads back to stock heads so I can run pupm gas. When I ride the ski it seems that in order for it to maintain power you need to vary the amount of throttle. It also wants to bog down when you jump a wave or hit any turbulance.

Any ideas on what this could be caused for or what I should check?

Thanks,

Matt

[Bryan Glynn]

What exact mods are on it, and what's the carb setup?

[hanson_7]

Re: Throttle needs to be pumped in order to maintain HP on xp800

it's an old topic with no answer. so i'd like to follow up on this, since the same problem has happened to me. lately the water has been really rough and the boat would bogg massively after jumping several waves and making some wot turns. it seemed like the fuel is not flowing to the carbs, even though i just replaced the fuel line and fuel filter. the engine didn't shut down, still ran but wouldn't rev up. it jst gave me enough rpm to coast to the shore. But after i pump the throttle, the rpm and power would be back up and it ran strong again. However, on the smooth water this kinda problem never occured. the boat just run strongly and seamlessly from bottom to peak rpm at around 7k. the boat is not used for a long haul, mostly closed course with 1 or 2 long straight.

i thought it must be somekinda fuel starvation, so i tried putting a 90 size jet to the return line and it made the matter worse, carbs flooded and the boat wouldn't start, so i took it off.

on the boat:
1. buckshot magnum 46 [125 pilot and 120 main, 2.0 n&s, velocity stack instead of fa]
2. r&d pipe
3. stock impeller and nozzle, wetwolf aat
4. 92 octane pump gas territory

[pwgsx]

Re: Throttle needs to be pumped in order to maintain HP on xp800

how did it run with the aftermarket head?? I would say jetting if you only changed the head back to stock and nothing else.


On another note, someone said that it bogs after hitting waves or if its real choppy. Could the fuel be foaming and not getting a steady stream to the carbs?? I had a dirt bike that needed some things done to it b/c the fuel would foam in the carb before entering the engine and would bog a lot. Just a idea, but never heard of that on a jet ski.

[chrisamsdad]

Re: Throttle needs to be pumped in order to maintain HP on xp800

Could you have some water in your fuel tank that gets picked up from the chop.
Might just sit at the bottom of the tank in calm water.

[hanson_7]

Re: Throttle needs to be pumped in order to maintain HP on xp800

my suspicion exactly, it's either the foam or something in the fuel tank got sucked in to the carbs. i'll try putting an air-fuel-separator and will post the result. coz on the calm water [not glass], i could make a wot turns with no problems. only after a constant wave jumpings, the carbs acted like not getting enough fuel supply and refused to rev up.

thanks guys....

[pwgsx]

Re: Throttle needs to be pumped in order to maintain HP on xp800

I have no idea what the sea doo carbs are like, always had somone re-build them. Do they have a float bowl????

[TheBillCOllector]

Re: Throttle needs to be pumped in order to maintain HP on xp800

No float bowl. They have a needle and seat. In response to the original post, I would be checking pop off pressure too.

Your problem is intermittent. This means something is continually changing to cause you to gain and lose power sporatically. Pop off can cause exactly that if the carbs don't have the same pressure reading lifting the needle to allow fuel to pass. With the age of your ski and fact the carbs haven't been rebuilt, that would be the direction I go..


Correction! I have no idea how old the ski is, but pop off would cause your problem.

[Bill O'Neal2]

Re: Throttle needs to be pumped in order to maintain HP on xp800

What is changing is the diaphrams in those carbs are acting differently as you launch and unload the motor then reload the motor on landing, much the same as what happens when making hard turns on a tight bouy course.
The solution will be turning the carbs to face the diaphrams forward or backwards ( perferred position), and maybe making some adjustments to the pop off pressure. Some of the older carb setups had the diaphrams facing down away from the motor. They need to be facing forward or rearward to get rid of the bogging and or flooding problem.

When you have very high compression, like before you removed that head, you can actually get rid of most of this problem through tuning and adjusting pop off. But, when you lowered your compression, you took away some of your midrange torque and the ability of the motor to pull you through that part of your power curve. Right now, it is just stalling the motors ability to pull through the heavely loaded midrange. A less pitch impellor would certainly help now that you have less torque in the midrange. Sometimes, adjustng the water injection timing points can make some differences too, as the timing of the water injection is very important to the torque load on the engine and how the engine recovers from varing loads such as when the impellor is unhooked launching off of the waves and then suddenly landing and reloading the impellor. Does this ex racer XP have a reduced nozzel size ? That will make quite a difference too if you increase the size of the venturi nozzel back closer to the orginal oem size. Sometimes that alone is enough to reduce your type problem to a minimum.

[hanson_7]

Re: Throttle needs to be pumped in order to maintain HP on xp800

i have a pair buckshot 46 magnum with rubber diaphragms facing forward and backward [carbs are set up opposite of each other]. so if Bill mentioned diaphragms, so i assumed its related to fuel delivery within the carbs. right? perhaps i just try replacing the n&s 1 size larger? will a brand new 2.5 n&s correct the problem? i'll try it after i get back from king's cup in thailand, and definitely will post the result.

thanks again, all.....

[Bill O'Neal2]

Re: Throttle needs to be pumped in order to maintain HP on xp800

I have not installed a set of carbs and not had the diaphrams facing one way or the other, but never opposite directions.

Novi perfers that you face the diaphrams rearward unless something has changed since my last project.

Going to a larger needle and seat will only work if you need more fuel in the motor sooner, which may or may not be your problem. Give it a try and see what happens. A 2.0 needle and seat will flow all of the fuel necessary to feed a 46mm carb. A 2.5 will allow for a lower pop off pressure than possible with a 2.0, otherwise they will both flow enough fuel.

Remember, impellor pitch, nozzel size, timing curves and water injection all play into this deal too.

[radiocontrolhead]

Re: Throttle needs to be pumped in order to maintain HP on xp800

bottom line is, keep that ski stock! haha, jk.

[Bill O'Neal2]

Re: Throttle needs to be pumped in order to maintain HP on xp800

No, the bottomline is that he owns a modified XP and he wants it to run properly.

[Bill O'Neal2]

Re: Throttle needs to be pumped in order to maintain HP on xp800

BTW, Do you have a Buckshot V Tech carb setup?

[hanson_7]

Re: Throttle needs to be pumped in order to maintain HP on xp800

BTW, Do you have a Buckshot V Tech carb setup?

absolutely. and about the diaphragm, i don't remember exactly, but i think they're oposite of each other since the carb setup is upside down on the pto side. is that right? i only happened to rebuild, on my own, my carb once. however, prior to last week, the ski ran strong and flawless. btw, i put this ski back to stock [pump, nozzle, impeller, mpem, and head] except for the carbs and r&d pipe. i like it better stock, less hassle and more reliable. the previous setup was 200psi head, 12 vein skat pump with 17/22, r&d nozzle, and msd total loss. Ran very strong but i hardly finished the race, somtehing always happened on the way to heaven then bunch of fx140s passed me by either on the middle or end of motto. stock setup is the way to go since the competitors are mostly fx140s.

i'll try to rebuild my carbs again and test both the 2.0 and 2.5 n&s. will post the result asap.

thanks guys.....