Seadoo 717 Carb Rebuild Fuel Pump Problem

[JohnMetta]

Still working on troubleshooting and fixing my 2000 GTI. I rebuilt the carb but I'm not sure if I need to replace the fuel pump check valves.

I can't find any conclusive answer on the fuel pump. In the shop manual it states to blow in the inlet and the valves should allow air to move through. Also states sucking/vacuum should lock and hold.

Both ways for me allow air in/out. I've read that there is no 100% seal.

What is normal? Should any air be able to be vacuumed through the inlet. Same holds true for the outlet. I am able to blow air into it freely.

Thanks in advance.

 

[jcleary93]

When I checked mine before I wasn't able to get any air through it was a complete seal as far as I could tell

 

[JohnMetta]

I was reluctant to change those valves because I only have the aftermarket stuff right now but I replaced them and it did the trick.

 

[Sportster-2001-951C-Stock]

My feeling is normally you won't have to replace the plastic mylar disks unless they are bent or if the circular metal seat in the body is pitted from corrosion.

This pump has two check valve disks configured in series with a diaphragm in between the two. When crankcase pulses are transferred to the "dry side" of the diaphragm from up through the pulse hose that connects to the nipple on the crankcase the action of the piston in the crankcase produces an "air + and - pulse" that flexes the fuel pump diaphragm. This action pulls fuel into the pump through the inlet and 1st check valve then pushes the fuel out the 2nd check valve disk on the positive pulse, producing fuel volume and pressure.

If you suck on the inlet you should pull a vacuum, this tells you at lest one or perhaps both check valves are sealing as intended, you won't know if both or just one.

If you connect a piece of tubing to the inlet and drop it in a cup of liquid and connect another piece of tubing to the pulse posrt, you should be able to pump the fluid from the cup and through the fuel pump by using your mouth to "resperate" +/- pules on the pulse port tubing.

My check valves looked fine to me so I didn't change them. If I was rebuilding for others of course I would've. Once the carbs were back on the ski I connected the fuel line and pulsed the pulse port with a tubing connected to the pulse port to prime the carburetors and make sure it was pumping, that was my final test.

You should be able to pull a vacuum on the FP pulse port as well and it should hold. Else there's something wrong with the diaphragm like a hole or it's not installed correctly, for instance. Similarly, if you get a mouth full of liquid while attempting to "resperate" the fuel pump diaphragm, the diaphram has a hole in it or wasn't installed correctly.

Sorry if I made any mistakes, I didn't proof read....

Good luck, keep asking questions.

 

[Sportster-2001-951C-Stock]

I was reluctant to change those valves because I only have the aftermarket stuff right now but I replaced them and it did the trick.

Great. Perhaps you already know they have somewhat of a potato chip curl in them and the curl (concave) side goes against the seat. Otherwise they're more prone to leaking.

I would say the aftermarket FP disks should work just fine, it's the mylar metering plate check valves that often don't work well b/c they're too stiff.

 

[JohnMetta]

Thanks for the response. What kind of liquid should I use? Is water bad to test?

 

[JohnMetta]

They looked pretty flat to me. What exactly is the mylar metering plate check valve?

 

[Sportster-2001-951C-Stock]

Sorry, I meant concave side of the disk. The reason they have a curl in them is they're being cut from a long roll of plastic mylar sheet and the roll puts a curl in them. The curl will be greater on some than others depending on where on the roll it was diecut. You may not notice a curl and that's fine, some have a substantial curl.

All that counts is the check valve disk lies flat against it's seat the entire 360 degrees, to make a good seal.

You could use a light oil as a liquid, 2-stroke oil should work I guess. I just use gasoline but you may not want that.

The metering plate is the kidney shaped metal plate inside the fuel chamber, held by a single screw located opposite the round rubber metering diaphragm. There's an small oval piece of mylar screwed to that once you remove the plate you'll discover this check valve mylar reed there. This is the high speed circuit check valve that keeps air from coming back through the large venturi into the fuel chamber at low speed, also keeps fuel from dribbling out of the large venturi when it's not supposed to. Engine vacuum opens this reed valve once the large venturi has been exposed to high velocity air at upper throttle angles. I think for 787 engine this occurs around 4,000 RPM in water.

If the HS check valve on the metering plate is bent, missing, or too stiff (thick mylar) this can cause issues, it's an important piece and I leave it original unless I've got a real Mikuni part or it's definitely bent/cracked, which is rare to see. It lies flat, over a hole in the metering plate to seal it up until the large venturi sees vacuum. So some kind of throttle flat spot at about this time can indicate that piece of mylar was changed to a thick aftermarket one causing large venturi delay and a lean flat spot with hesitation.