Can anyone please give me a discription of how those work together. Anything from a basic explaination to more technical will help me. Is it the impeller doing all the work pushing water? Is the jet pump accelerating the water also? If so how does it work? How does the jet pump turn on? My motor acts like its in neutral but Im having trouble troubleshooting mostly because Im just not knowledgeable about how it works.. mostly with this propulsion system. Any info is greatly appreciated.
-
This site contains eBay affiliate links for which Sea-Doo Forum may be compensated.
jet pump impeller propulsion 101
- Thread starter gcha1727
- Start date
- Status
It is a propeller(impeller) inside a tube . It spins on a shaft from the inboard motor. As the impeller spins inside the jet or (impeller tube) it forces water out at a very high velocity making the boat move. There is no jet or pump. As simple as I can put it. I am sure its more complicated but that is the essence of it.
Looks to me like you have 3 posts for a similar problem.
As I understand it , the jet pump is the propulsion unit. Its driven by the driveshaft/motor combination. Ideally , if there arent any air leaks from the hull , or pump shoe , or seals around the driveshaft , the pump sucks up water from the lake or river youre in and pushes out the back , pushing you along. If air is getting in there , then your effective propulsion is going to be considerably less.
Cavitation is the condition where air has gotten into the pump thru a leak in one of the sealing surfaces , allowing the impeller to spin up to full RPM without a full load on it. Typically ( from what Ive read here ) the motor will get to the high RPM range easily with 1/2 or less forward momentum from normal.
Around here , advice is to check your wear ring , the black sealing surface around the impeller , for gap. I cant quote the exact number but I recall a file folders thickness or less between the impeller edge and the wear ring.( Voodoo ?) Check your drive shaft seal and make sure it is greased . DONT pump grease till it spills out of the seal , just pump enough to make it move and check it often. The other grease fitting on the PTO ( attached to the engine) is greased up to keep the splines on the driveshaft from getting torn up during regular operation. Lastly , and I have little hands on knowledge here , check your pump shoe for leaks. I dont know how to do this particularly, so i suggest doing a search for " pump shoe leaks" , and see what you can find.
On my boat, the neutral safety switch was stuck and the boat( 95 twin eng. 657x Speedster) didnt make any RPM past 3500-4000. I took the throttle handle assembly out , lubed the switch with silicone spray and put it back together. It ran great after that. I guess they call that the " rev limiter" so that the boat doesnt accidentally get away from you at the dock in neutral. My wife caught a pantleg on the handles and proved to me exactly why that was made that way. Luckily all we had was hurt pride. I'll never dock on that side again.
I hope that helps , and any of the experts please correct my advice if Im wrong.
Jim.
As I understand it , the jet pump is the propulsion unit. Its driven by the driveshaft/motor combination. Ideally , if there arent any air leaks from the hull , or pump shoe , or seals around the driveshaft , the pump sucks up water from the lake or river youre in and pushes out the back , pushing you along. If air is getting in there , then your effective propulsion is going to be considerably less.
Cavitation is the condition where air has gotten into the pump thru a leak in one of the sealing surfaces , allowing the impeller to spin up to full RPM without a full load on it. Typically ( from what Ive read here ) the motor will get to the high RPM range easily with 1/2 or less forward momentum from normal.
Around here , advice is to check your wear ring , the black sealing surface around the impeller , for gap. I cant quote the exact number but I recall a file folders thickness or less between the impeller edge and the wear ring.( Voodoo ?) Check your drive shaft seal and make sure it is greased . DONT pump grease till it spills out of the seal , just pump enough to make it move and check it often. The other grease fitting on the PTO ( attached to the engine) is greased up to keep the splines on the driveshaft from getting torn up during regular operation. Lastly , and I have little hands on knowledge here , check your pump shoe for leaks. I dont know how to do this particularly, so i suggest doing a search for " pump shoe leaks" , and see what you can find.
On my boat, the neutral safety switch was stuck and the boat( 95 twin eng. 657x Speedster) didnt make any RPM past 3500-4000. I took the throttle handle assembly out , lubed the switch with silicone spray and put it back together. It ran great after that. I guess they call that the " rev limiter" so that the boat doesnt accidentally get away from you at the dock in neutral. My wife caught a pantleg on the handles and proved to me exactly why that was made that way. Luckily all we had was hurt pride. I'll never dock on that side again.
I hope that helps , and any of the experts please correct my advice if Im wrong.
Jim.
Thanks for responding. That was useful/helpful information. I thought there was an actual pump behind the impeller. Ive been reading alot here on the subject the last couple days and that kind of tied it all together. I did find a leak today where the drive shaft goes through the hull. I think its called the carbon seal. Im not sure if that alone would prevent me from ever getting over 4k rpm. I need to also check my pickup sensor as a possible fault. I suspect that there may be multiple problems but atleast I found this one as a place to start. Hopefully its not hard to replace.
4000 rpms is the magic number for where the neutral safety switch kicks in. That is where the rev limiter is set for neutral.
The carbon seal leaking would let the engine rev to full rpms (7000 or so) without the boat moving as much as it should.
If all is working as it should, when the engine spins to 7000, the boat should be moving forward pretty well, but if it gets right up to 7000 without pushing forward, you either have a worn wear ring or air getting into the system.
The carbon seal leaking would let the engine rev to full rpms (7000 or so) without the boat moving as much as it should.
If all is working as it should, when the engine spins to 7000, the boat should be moving forward pretty well, but if it gets right up to 7000 without pushing forward, you either have a worn wear ring or air getting into the system.
I can only get it to 7k out of the water. its never gone past 4k in water. The neutral safety is working properly (atleast the comp is getting signal change N-F). I dont there is a fuel/carb prob. I did find a leak at the rubber boot thats next to carbon seal. Im gonna try to repair/replace that asap. The boot and seal have a little play when I grab it...is that normal??? Also Im going to get a gauge today to check impeller gap. Any other suggestions?? Thx
phough5757
New Member
Just a Question.
Does this Motor have Rave Valves? Could that keep it down to 4K RPMs?
Does this Motor have Rave Valves? Could that keep it down to 4K RPMs?
play in the boot and seal is normal and expected. Be sure there is plenty of pressure pushing the carbon against the seal.
As mentioned above, check those RAVES.
As mentioned above, check those RAVES.
just checked impeller clearance and its well within range. I still want to repair/replace protective boot and carbon ring but Im now finding out its prob gonna be a big job for me. Ill check raves 1st. Can the raves actually keep it under 4k??? I thought they were more for performance...
still at 4k on water. It goes past 7k out of the water. I think I have no choice but to start tearing into the driveshaft/pump assy. At the very least I need to get that boot next to carbon seal out. Got a small leak there. My wear ring has some knicks in it. Im not sure if its normal wear and tear. Impeller and ring are in good range. Im assuming I ll need to start in back and work my way forward. ANYTHING IN PARTICULAR I SHOULDNT OVERLOOK??? My pockets are not deep but I dont want to do this twice. I should also note I have no history on this boat but it does appear that all the parts on the drive shaft in the engine comp. look brand new. ANY SUGGESTIONS OR THOUGHTS ARE WELL APPRECIATED...
only one motor will not go past 4k under load. It works well until 4k, just like my other motor. I did find a leak at boot were driveshaft leaves engine bay... Im taking it apart now but im not sure if that will cure the problem... ANY OTHER THOUGHTS??? ALSO ANY TIPS ON GETTING THIS CARBON RING OFF THE CIRCLIP??? Thx
with pump still attached to boat, remove the grey shield, locate the steel collar, and push it toward the back, to expose the metal c-clip, then pop it off. Might need a wrench/something to "twist" the steel collar to break it free first, before try'n to push it back to expose the c-clip.
With one motor stuck at 4k, do a volt test at battery, first to see if charging system is working, holding rpms at 5500, with only that motor on. Should read around 13.5-14.5 volts. If good, then i'd pull the rv/carbs off and its manifold, to expose the rotory valve, bring front/mag piston, to TDC, then check/degree its points, should be 147*/65*. After this, report back to forum.
With one motor stuck at 4k, do a volt test at battery, first to see if charging system is working, holding rpms at 5500, with only that motor on. Should read around 13.5-14.5 volts. If good, then i'd pull the rv/carbs off and its manifold, to expose the rotory valve, bring front/mag piston, to TDC, then check/degree its points, should be 147*/65*. After this, report back to forum.
- Status
Similar threads
