717 problem running WOT, revving down to 5000rpm

[swill777]

I recently bought a used 1998 Sportster boat (which according to the repair manual has the dual 717 engines). The starboard engine runs great, WOT around 7000rpm, runs strong. The port engine, runs a little under 7000 rpm @ WOT, maybe around 6600-6700, for a short time, then revs down to around 5000 rpm, and it keeps doing this... 5000, then revs to 6500 or so, then 5000, then 6500 or so, back and forth.. eventually even at WOT it will only run @ 5000 rpm. If you pull the choke cable, the engine will rev down, then all the way back up to 6500-6700 rpm, and run there for a short time again (5-20 seconds).
It seems that it is not getting enough fuel when this is happening, and of course I suspect the carb on that specific engine... I really haven't looked at anything yet on the engines, and I am new to these engines and boats.
I assume the fuel filter is on the main fuel line and is used for both engines? If so, then I guess that's not the problem. I haven't looked at the plugs yet, but I was thinking about just replacing them all the way around with new ones since this thing was used and they don't have a service record on it.
Is there a way I could just clean the carb (on the motor) or off the motor before getting a re-build kit? Or should I just take it off, and do the rebuild? Is there anything else you guys recommend doing to narrow down this issue? Thanks a ton!

[dsolie]

Re: 717 problem running WOT, revving down to 5000rpm

Take them off and do a rebuild, you might as well do both motors. Fresh plugs and snip your plug wires back to expose fresh copper.

[swill777]

Re: 717 problem running WOT, revving down to 5000rpm

Looking at the SeaDoo repair guide is says the following for the carb type that I have: Mikuni diaphragm BN-40i-38 with accelerator pump

It also says I have the 717 engines, is that correct?
So is this the right rebuild kit from SBT???

http://www.sbtontheweb.com/Merchant2...oduct_Count=15

When I use the parts locator guide on SBT and choose a 1998 Sportster 1800, everything refers to a 787 engine and Mikuni SBN carb?

Where can I look on the engine and/or carb and verify exactly what I have??? And if everything is stock, would it be the Mikuni BN and 717 engine?

[dsolie]

Re: 717 problem running WOT, revving down to 5000rpm

On the front of the motor, above the flywheel cover, there will be a black plate on the motor, it will have the motor size.

Are the motors straight up and down, or mounted on an angle...

[swill777]

Re: 717 problem running WOT, revving down to 5000rpm

Straight up and down.

[dsolie]

Re: 717 problem running WOT, revving down to 5000rpm

Then you have a 717. A sportster 1800 to be exact.

In 98 the;
Speedster had a single 787
Sportster had a single 717
Sportster 1800 had dual 717's
Challenger had dual 717's
Challenger 1800 had dual 787's

SBT has there engines WRONG on the site..

You need these carb kits:
http://www.sbtontheweb.com/Merchant2...oduct_Count=16

And some carb gaskets form your local dealer.

[swill777]

Re: 717 problem running WOT, revving down to 5000rpm

The Official Sea Doo Service manual says "BN" carbs instead of "SBN" carbs.. did they make a mistake too? I just want to make sure I get the right kit. It says this exactly in the tech specs section of the repair manual for the 1998 Sportster 1800 "Mikuni diaphragm BN-40i-38 with accelerator pump". Is that the SBN??

Also, can I get the carb gaskets online too? The nearest SeaDoo dealer is around 65-70 miles from me. Thanks!

[dsolie]

Re: 717 problem running WOT, revving down to 5000rpm

Accelerator pumps on a 717?? That's a first...

Do me a favor, and please take a picture of your engine bay. Post it up on here.

[skisol]

Re: 717 problem running WOT, revving down to 5000rpm

Dan,
In '97 they gave the 717's a single carb and from '98 it they gave it the single carb with accelerator pump.

His boat got a single carb with accelerator pump, the fuel pump is seperate mounted on a plate on the magneto housing and not part of the carb.

[dsolie]

Re: 717 problem running WOT, revving down to 5000rpm

Interesting! didn't know that...

[skisol]

Re: 717 problem running WOT, revving down to 5000rpm

And than on the latest models, don't know exactly what year that started they plugged off the high and lowspeed screws on that carb.

[swill777]

Re: 717 problem running WOT, revving down to 5000rpm

I changed the plugs last night and trimmed back the wires and re-terminated the boots.. gapped the plugs at .021 like it says in the service manual. The external fuel filters were freaking dirty as hell, so I cleaned those out too...

I couldn't get the air filter housing off because I don't have the right size hex bit.. I'm going to get a set today... but I fired it up, and noticed that the engine idles around 2000 rpm out of water, the manual says it should idle at 3k.. so I guess I need to adjust the idle screw.. I will check the in-water idle tonight too...

Another person told me that maybe I should just try taking the carb off first, opening the side with the internal fuel filter, replace/clean that part, put it back together and try to run it.. He said those frequently get clogged up. I guess it's worth a try since I am going to order the rebuild kits anyway.. and eventually rebuild it.. If I took it apart carefully should I be able to get it back together without damaging anything.. or is this a really stupid plan.. I am just curious to see exactly whats causing my issue in the carb, and maybe to get my boat running better before this weekend while I am waiting on the kits.

So guys, I will take a picture of the engine bay and carb setup once I get the air cleaner housing off... you guys think I just have one carb then right? So I just need 1 rebuild kit per engine, correct? Can you guys please verify the correct part # from SBT once I take the pic of the bay and carb? Thanks!!

[swill777]

Re: 717 problem running WOT, revving down to 5000rpm

Guys, another question if you don't mind.
I assume there are seadoo carb gaskets that are used to mount the carbs after they are rebuilt.. can you use the red rtv sealant or some type of gasket maker instead?? If not, where can I get these online?

[dsolie]

Re: 717 problem running WOT, revving down to 5000rpm

You can get the gaskets from any online shop.. Like rivayamaha.com

do NOT use RTV.. It will not last and you will have a blown motor before you know it.

If the external filters were clogged up, there is a good chance the internals are as well. You can pull the carbs off and clean out the internal filter very easily without having to re-build the carbs.

[swill777]

Re: 717 problem running WOT, revving down to 5000rpm

Great... I am definitely going to look at those internal filters asap! I read the following in the service manual... Thanks for the help

At installation, pay attention to the following:
Install carburetor(s) with gasket(s) to intake manifold
(rotary valve cover for the 787 engine).
If applicable, synchronize carburetors before installation.
Refer to Carburetor Synchronization.
Apply Loctite 577 on screw threads. Then, install
screws with lock washers and torque to 20 N•m
(15 lbf•ft). This will prevent screws to jam to ease
further removal.
- CAUTION
Failure to apply Loctite 577 might lead you
to damage carburetor to allow its removal if
screws are jammed.

Do you guys use something else other than Loctite 577 when re-installing the carb?? I can't seem to find it anywhere locally.. Is there something I can substitute?