1997 speedster rpm loss of 400 with last half inch of throttle lever.

[Hoptwoit]

Both motors completely rebuilt with new cranks, bored .25 mm over, new rotary valves, rotary valve housing machined. All fuel lines are black and I blew all hoses clear through the various res and on positions. Fuel baffle pulled and inspected was clean. New fuel. Carbs set to book values. Starts great idles great, pulls hard, so surging. flat out the last half inch forward on the left throttle only. Doesn't run rough it just seems like it looses RPM. Goes from about 6600 down to 6200 with the last bit of throttle. right engine got the same treatment and seems fine. High speed screw adjustment makes no difference.

Any ideas

 

[rusty nail]

starving for fuel? right size fuel lines? right size filter? at WOT it wants all the fuel it can get.

 

[POPPS]

Sounds nuts,,,compression test on new top end?

 

[Hoptwoit]

The fuel supply to the carb is not the issue. I originally set the pop off and bent the needle valve lever so it was slightly below the metering chamber floor. The lake test resulted in surging above 4500 rpm. Starving for fuel. This is a single carb setup so all the fuel for the engine needs to come through this one needle. I bent the needle lever So it was flush with the floor and I got great results but still the one I described above. I’m thinking of going up one size needle and then if necessary up one jet size on the main.

 

[POPPS]

Is your popoff within specs?,,,I have only bent the needle arm,,when someone else has bent it,, change the springs and or the needle to get proper popoff,

 

[Hoptwoit]

pop off spec is 38, +- 12 psi I'm at 32 and 31 . at wide open throttle the needle will be off seated the whole time according to mikuni. I think this is a straight out flow issue. The same carb is used on most engines with smaller jets, but there are two of them. this setup is working pretty hard to flow 8.5 gph through that needle valve on a single carb. That's 1.13 pints per minute through that little needle. a 2.0 needle with a gold spring will keep me at 32 psi and allow more flow. since the single carb setup is a little unique to this year of speedster I'm thinking most are used to dual carb setup.

 

[rusty nail]

I had your boat before my 98 that i am currently working on.....single carb. I opened up the carb, cleaned and did full rebuild when i first purchased it years ago. I did not have to modify/change any carb parts in order to reach WOT. i had it up over 7000 a few times on flat water. Kinda scared the crap out of me. Something small must be wrong with your setup and it just needs a little tweak.

 

[Hoptwoit]

6500 is pretty fast on this boat. It cruises nicely at 4500. I’m going to put a few hours on it to break in the engines. I’ll stay out of the high end. I’m also going to replace both impellers and wear rings. The left side looks new and has the correct seadoo pn the right one is a little chewed up. Since you had one before what impellers were you running?
once the impellers are matched a comparison will be easier. Heading to a bigger lake today so I can get some easy hours on the engines. I’ll do a compression check after and some plug reading if the water is calm. I’ve gone through the setup several times and can’t see anything wrong with it.

 

[rusty nail]

Just stock impellers. There are quite a few comments within these forums from experts that say changing impellers will sacrifice out of the hole torque or at the other end, top speed. So the stock setup was done well by seadoo to optimize both.

 

[rusty nail]

Because the speedster has two engines there is plenty of torque to pull a big tube with three kids so i never even thought of needing more out of the hole....and at the other end like i said earlier, i rarely approached top speed and when i did it was by far fast enough for me.

 

[Woodshoe]

I had the same issue, was a throttle cable adjustment problem.