12mph at FULL THROTTLE

[BOOSTINTT]

so i bought a project 1999 challenger twin 787
guy i bought it from said it ran great (in salt water) just needed maintenance

i checked both engines have 150 psi in each cylinder.

first time i turned them on seemed as they were in WIDE OPEN THROTTLE

bought new (used) carbs on ebay from running skis for each engine but didnt "set" them for my engines just installed them

i took it to the water... (lots of smoke but it kinda went away after a while)

i got the boat to do 12mph full throttle.

since then..

i installed 2 new wear rings (did not see or replaced the neoprene seal)

changed one of the water regulators

checked the carbon seals, they looked good intact, just a little loose from the shaft (im not sure if they are supposed to be firm on the shaft)

checked, cleaned and reinstalled all 4 rave valves, they move up and down freely.

disconnected the red and black wire for the rectifier but that didnt change anything..

def not the throttle cables.. i reved up the engines manualy and they top out at about 4k each give or take a little.

i just took the waterbox out just to see if it was exhaust obstruction and still wide open throttle tops out at 4k rpms


out of the water my boat idles at 3.2k and 3k rpms. when full throttle they rev up to 4k and 4.5k rpm.

in water they idle at 1.2 and 1.5k rpms and top out at 4k rpms and 12-15 mph is all i can get up to.

the boat also shakes and trembles while hitting the throttle.

im running out of ideas

 

[LouDoo]

It sounds to me that most maybe all your problems are the wear rings. Replace both wear rings.

Lou

 

[BOOSTINTT]

i guess. it just doesnt make sense that because my wear rings are completely gone dried out, my boat revs up but doesnt go anywhere. can someone explane this to me.

 

[LouDoo]

You have a condition known as cavitation. Your boat is powered by two jet pumps, so just think of it as a pump, what is happening is your moving air instead of water through the pump.

Lou

 

[BOOSTINTT]

You have a condition known as cavitation. Your boat is powered by two jet pumps, so just think of it as a pump, what is happening is your moving air instead of water through the pump.

Lou

that makes sense. i took out one of the pumps.. wear ring completely gone

the other pump is stuck on the shaft.. i let it sit overnight with some pb blaster (hope that does the trick.)

ordering wear rings tonight!

 

[LouDoo]

Here's a real good thread about replacing the wear ring(s). It's not really a bad job, you'll need to order an impeller removal tool. Should be about 12.00 to 15.00. Who ever you order the wear rings from should have the tool.

http://www.seadooforum.com/showthread.php?30720-How-To-Changing-Your-Wear-Ring

Lou

 

[BOOSTINTT]

im using an old seadoo shaft as the impeller remover tool and a pipe wrench. going to clearwater tomorrow to do some fishing so i'll stop by SBT and pick up the rings

thanks for your help

Here's a real good thread about replacing the wear ring(s). It's not really a bad job, you'll need to order an impeller removal tool. Should be about 12.00 to 15.00. Who ever you order the wear rings from should have the tool.

http://www.seadooforum.com/showthread.php?30720-How-To-Changing-Your-Wear-Ring

Lou

 

[BOOSTINTT]

finally got the new wear rings from SBT.. does anyone know if the little lip on the ring goes up or down when inserting it?

 

[skewba98z28]

The lip goes up or if you think of the pumps in the boat it goes towards the front of the boat. How does the neoprene seal look? There should be a foam looking ring stuck to the pump shoe on the boat where the mating surface of the jet pump meets the boat. I usually replace them when pulling the pump. If there bad it will cavitate even with a new wear ring.

Seal
http://www.shopsbt.com/jetski/76-101-08.html

and for location reference check the pic. (part 21)

 

[BOOSTINTT]

thanks! both pumps rebuilt

 

[BOOSTINTT]

i took it out just now and still nothing. gets up to about 12mph. rpms on both engines top out at about 4k. idles at 1200 rpms in water and 3k outside of the water. i installed new carbs and new wear rings on both sides.

even with the new wear rings (my old ones were completely destroyed) i couldnt get it to go faster than 12mph

 

[gbone87]

Have you check/cleaned the rave valves yet? Also pull the water regulators on your pipes off and take a look inside them and make sure the bellows are in good shape and the valves in the bottom of the housings are moving freely. Mine gave me problems on my 787 gtx. Also, i am not positive if this will cause the same syptoms but possible check your rectifiers by unplugging the red wires. I believe they can sauce rpm problems also. (someone feel free to correct me if im wrong). How does it rev out of the water on the trailer?

 

[LouDoo]

Check the rave's first. I could be the carbon seal's are worn out from over revving, causing cavitation. Did you replace the neoprene seals when you replaced the wear rings?

Lou

 

[BOOSTINTT]

hey lou i replaced on of the rave valves.. right side. but still nothing and i think that didnt make a differenct. i did not replace the neoprene seals when i did the wear rings.. not sure what those are and if i was supposed to see them when i took of the pump then they were not there.

correction.. i replaced one of the water regulators.. not the rave valves.

 

[BOOSTINTT]

i just removed the rubber boot and the carbon seals look fine. no damage to them.. just loose around the shaft.. is that normal?

also out of the water RPMs reach 4k and stay there at wide open throttle

 

[BOOSTINTT]

i just cleaned the 2 rave valves on one of the engines.. had some carbon build up but not too bad.. bellows were fine as well as springs and o ring.

no improvement. out of water idles at 3.5k and revs up to 4.2k rpms

 

[griz400]

read your post a couple of times, u say the previous owner said that each eng has 150 psi in each cylinder, or have you checked it ???
also, at idle out of the water, should be around 3k, and when in water should drop right around 1500, way just need some adjustments, new carbs come not really "preset", also, check your throttle cable adjustment, cause it should rev more than 4k, try it by hand on the carb, but, im not sure reading your first post, but a 787 needs around 150, anything less, your sorta "buttering cold corn"

 

[BOOSTINTT]

i personally checked compression. 150psi on all cylinders give or take.

i will try to rev the engines up by hand and see if that the problem.. i doubt it but we'll see.

 

[LouDoo]

I also read over the post again and I want to make sure that I understand what your saying. In your first post you say that at WOT your only reaching a speed of 12-15 mph. Recently in the thread you said it only revs. to 3500-4200 rpm, is that correct? Is that in or out of the water? Is this condition the same for both motors?

Your ski should top out at 6800-7000 rpm.

Lou

 

[BOOSTINTT]

tops out at 4.2k engine 1 and 4k rpms engine 2.. out of the water. so they should rev up to 6500-70000 outside of water correct?


they also go up to about 4k rpm both engines in the water.

 

[griz400]

im still, guessin a cable adjustment, cause (both) engines doin this

 

[BOOSTINTT]

tell me more about the throttle cables.. its two different ones one on each lever correct? so why would you think that might be an issue since they are independent from each other and im having issues with both engines?

 

[BOOSTINTT]

the carbs that i installed were not brand new.. they are used but came out of running jetskis... did i still need to "set" them to use on my enignes?

 

[griz400]

all right, dont start it, but put both levers in full wide open throttle, then go back and see if u can still move throttle by hand, this will tell you if the cables are adjusted properly, also, on the water, you move both throttles same time ??? and what do the sparkplugs look like ??? i remember my ski one time wouldnt move more than about 5-10 mph, i pulled up to dock, replaced both plugs, and bingo, was fine all weekend

you didnt mention replacing plugs

 

[BOOSTINTT]

yea its def not the throttle cables.. i reved up the engines manualy and they top out at about 4k each give or take a little.

spark plugs are brand new

i move both throttles when in the water.. one engine does seem to feel alittle smoother then the other when i only move one throttle handle at the time.