1999 Seadoo GTX RFI Engine Bogging issue

[N1GHTR1D3R0411]

Alright since I’ve previously made this thread a lot has been done to this ski. Here is the list of stuff done to it already.
• New SBT 787 Rotax RFI engine
• New OEM rotary valve and cover is machined properly. Clearance on the valve is .013 thousandths of an inch with valve installed without the oring as stated in the service manual
• New motor mounts installed and aligned with the transom with SBTs alignment tool
• New Quantum fuel pump, filters, fuel regulator, and found new Bosch injectors (got lucky finding OEM Bosch injectors) gas tank was cleaned out and am only running 90 octane ethanol free
• New impeller and wear ring installed by previous owner
• Broke in new engine as SBT stated on their website.
• Oil injection pump has been tested and reinstalled, primed correctly and alignment marks lined up at idle
• Idle adjusted correctly at 1,500 RPM in the water
• NGK BR8ES spark plugs gapped to .020 thousandths of an inch

There is a number of other things done to this ski that doesn’t regard the issue it still has.

The issue I am having is bogging of course. Runs great out of the water. Idles good and revs fine only until it hits 5,000 RPM. After that the engine sounds like it misfires and bogs with little throttle response. After taking out the plugs they do not look fouled but I still clean them anyways. After that the ski runs great again out of the water until revved to around 5,000 RPM. This issue also persists in the water as well. I am at a complete loss and do not know what else I need to check.

 

[N1GHTR1D3R0411]

I’ve been having issues with my 787 rotax RFI. Top end was rebuilt has 152 compression on both cylinders. Oil pump was deleted and running premix 40:1. Injectors are not clogged and put new strainers, fuel pump, and regulator has great fuel pressure. Has a new impeller and jet drive. It wasn’t starting while in the water at all only until I ran it for awhile on the hose. Could there be something in the cooling system being clogged? It didn’t bog down and die until I hammered down for 10 seconds.

Now it seems it’s fouling plugs immediately and doesn’t run at all.

 

[burtshaver2021]

I would say that your injectors May have a bad spray pattern. Have you had them professionally cleaned and tested lately?

 

[N1GHTR1D3R0411]

I would say that your injectors May have a bad spray pattern. Have you had them professionally cleaned and tested lately?

I bought new ones and they didn’t work at all, do you think I’d have to have them programmed? I reinstalled the old ones because they seemed to have an okay spray pattern just from cranking.

 

[burtshaver2021]

No, they don’t require any programming

 

[N1GHTR1D3R0411]

No, they don’t require any programming

I wasn’t too sure, so the new ones were bad out of the box. Is it a possibility the crank seals could be bad too?

 

[burtshaver2021]

I wasn’t too sure, so the new ones were bad out of the box. Is it a possibility the crank seals could be bad too?

I would doubt the new ones were bad out of the box, I had only mentioned the injectors because I’ve had issues before with fouling plugs and the injector cleaning resolved it.

 

[burtshaver2021]

You could try running a fuel pressure gauge while your riding and see what your fuel pressure does when you hammer down on it

 

[N1GHTR1D3R0411]

You could try running a fuel pressure gauge while your riding and see what your fuel pressure does when you hammer down on it

What’s the best way to attach a gauge while riding it?

 

[burtshaver2021]

What’s the best way to attach a gauge while riding it?

You would need to get the proper fittings maybe from a parts machine or maybe they are available at OSD marine, but unhook the fitting from the fuel rail and hook a brass T fitting there with a hose going up to a fuel pressure gauge that you can see while riding

 

[Mekanix]

Can't run rfi's on premix. You need the oil pump. The injectors won't work with oil.

 

[DaddyLoafin]

Can't run rfi's on premix. You need the oil pump. The injectors won't work with oil.

they will, but only for a limited time lol

 

[Mekanix]

they will, but only for a limited time lol

You got that right

 

[DaddyLoafin]

You got that right

lol i learned that one the hard way

 

[N1GHTR1D3R0411]

Can't run rfi's on premix. You need the oil pump. The injectors won't work with oil.

Yeah I’m going to hook back up the oil pump. I ended up buying an engine from SBT because the crank seals are bad and the rotary valve was shot. Now I’m trying to source an alignment tool to rent so I don’t have to spend $400 on a tool to use once.

 

[DaddyLoafin]

Yeah I’m going to hook back up the oil pump. I ended up buying an engine from SBT because the crank seals are bad and the rotary valve was shot. Now I’m trying to source an alignment tool to rent so I don’t have to spend $400 on a tool to use once.

you can go the route of the home made one. not super accurate but works good enough

 

[N1GHTR1D3R0411]

Alright since I’ve previously made this thread a lot has been done to this ski. Here is the list of stuff done to it already.
• New SBT 787 Rotax RFI engine
• New OEM rotary valve and cover is machined properly. Clearance on the valve is .013 thousandths of an inch with valve installed without the oring as stated in the service manual
• New motor mounts installed and aligned with the transom with SBTs alignment tool
• New Quantum fuel pump, filters, fuel regulator, and found new Bosch injectors (got lucky finding OEM Bosch injectors) gas tank was cleaned out and am only running 90 octane ethanol free
• New impeller and wear ring installed by previous owner
• Broke in new engine as SBT stated on their website.
• Oil injection pump has been tested and reinstalled, primed correctly and alignment marks lined up at idle
• Idle adjusted correctly at 1,500 RPM in the water
• NGK BR8ES spark plugs gapped to .020 thousandths of an inch

There is a number of other things done to this ski that doesn’t regard the issue it still has.

The issue I am having is bogging of course. Runs great out of the water. Idles good and revs fine only until it hits 5,000 RPM. After that the engine sounds like it misfires and bogs with little throttle response. After taking out the plugs they do not look fouled but I still clean them anyways. After that the ski runs great again out of the water until revved to around 5,000 RPM. This issue also persists in the water as well. I am at a complete loss and do not know what else I need to check.

Alright since I’ve previously made this thread a lot has been done to this ski. Here is the list of stuff done to it already.
• New SBT 787 Rotax RFI engine
• New OEM rotary valve and cover is machined properly. Clearance on the valve is .013 thousandths of an inch with valve installed without the oring as stated in the service manual
• New motor mounts installed and aligned with the transom with SBTs alignment tool
• New Quantum fuel pump, filters, fuel regulator, and found new Bosch injectors (got lucky finding OEM Bosch injectors) gas tank was cleaned out and am only running 90 octane ethanol free
• New impeller and wear ring installed by previous owner
• Broke in new engine as SBT stated on their website.
• Oil injection pump has been tested and reinstalled, primed correctly and alignment marks lined up at idle
• Idle adjusted correctly at 1,500 RPM in the water
• NGK BR8ES spark plugs gapped to .020 thousandths of an inch

There is a number of other things done to this ski that doesn’t regard the issue it still has.

The issue I am having is bogging of course. Runs great out of the water. Idles good and revs fine only until it hits 5,000 RPM. After that the engine sounds like it misfires and bogs with little throttle response. After taking out the plugs they do not look fouled but I still clean them anyways. After that the ski runs great again out of the water until revved to around 5,000 RPM. This issue also persists in the water as well. I am at a complete loss and do not know what else I need to check.

 

[N1GHTR1D3R0411]

Also it has a new battery, and rectifier tested good.

 

[Mekanix]

Looks like you have ruled out everything except for a colapsing exhaust system.
Could be in the can or it's more than likely the exhaust hose from the can to the outlet that is collapsing internally.

 

[N1GHTR1D3R0411]

Looks like you have ruled out everything except for a colapsing exhaust system.
Could be in the can or it's more than likely the exhaust hose from the can to the outlet that is collapsing internally.

Yeah true, it’s just odd that it only does it after 5,000 RPM. Then after setting for 5 minutes it runs great only until 5k