"FUEL" fitting on PTO Carb (951 engine)

[jakknz]

For TLDR summary, see bottom

So 951 carbs have a "PULSE" cover plate with a barb attached on the mag carb and a "FUEL" cover plate with a barb attached on the PTO carb - both located on the fwd side of their respective carbs, you can see"PULSE" or "FUEL" words in raised letters on each. The "PULSE" barb sees air that can flow through both directions due to pressures within the crankcase in order to operate the carb diaphrams and move fuel. From what I've researched, the "FUEL" barb is for fuel return back to the tank (fuel flows out of PTO carb and into tank through this fitting).

I have 2 skis, both run 951 engines that I recently rebuilt but haven't run. On one ski's PTO carb, I've taken off the PTO's fwd cover, put compressed air to the "FUEL" barb (where the fuel hose connects), and can't blow air into it. BUT air will flow if I put compressed air in the opposite direction of flow (so now I'm introducing air on the opposite side of the barb and blowing it out of the barb not into it). There seems to be some sort of a check valve in it that allows the flow of fuel (or air in my testing) from out of the PTO carb but no backflow into it.

On the other ski, I took its PTO "FUEL" cover off and can blow air through both directions. Something is wrong with one of them.

Ultimately, my questions are as follows: Is this cover and barb supposed to allow fuel to flow in only one direction? If so, how integral is this check valve? Do I need a new fitting in order for the ski to run properly (or a check valve in the fuel line coming off the barb)? Will fuel pressure be maintained if this check valve isn't functioning properly?

The last thing I want to do is toast my newly rebuilt engines.

TLDR

-PTO Carb has cover with "FUEL" on it
-I have 2 skis I'm doing carbs on
-One ski's "FUEL" cover allows flow in one direction
-The other ski's "FUEL" cover allows flow in both directions
-Which one operates correctly?

 

[mikidymac]

Not exactly......

The pulse line only connects to the engine and is just an air chamber that moves the fuel pump diaphragm.

The fuel inlet is the large hose going into the MAG carb.

Then the hose in the picture connects the fuel supply from the MAG carb to feed the PTO carb.


Finally the last fitting returns excess fuel to the tank.

I think the 1997.5 ones might have been plumbed a little different. What year and model do you have?

 

[jakknz]

Thanks for the response!

1998 GTX Ltd
2000 GTX

Both are mostly the same plumbing wise. It’s not the fuel inlet on the mag carb - I’ve attached a picture for clarification showing the one I’m talking about.

 

[mikidymac]

The "Fuel" fitting is the return for the PTO carb then it picks up the fuel "return" from the MAG carb and back to the tank

I don't have a set handy to see if there is a check or not but @Dr Honda might know this one.

 

[jakknz]

Exactly. So on the one set of carbs, the "FUEL" fitting flows only in the direction of the arrow in my pic. On the other set, the fitting is free flowing which would allow a backflow.

Again thanks for the help, I couldn't come up with much info on any of my searches. When you did the write up for the carb rebuilds, do you remember cleaning this part at all?

 

[SabrToothSqrl]

Man, I feel like I know this one. Lol i've done dozens of these. There are 3 hook ups on carbs.

1 fuel in
2 pulse line
3 fuel return

there are check valves inside the MAG one that only allow fuel to flow one way, via using the pulse line to 'power' the fuel pump.

if I had them infront of me I could do it.

If it's any help, the fuel line should be the bigger one, and the return is smaller diameter.

 

[mikidymac]

I understand his question now but sadly my only 46i carbs are on my 2001 XP and I ain't taking them off.

He is basically asking if the return fitting on the PTO carb is supposed to have a check feature on it?

 

[jakknz]

Exactly! Right where the hose connects is the barb that's inserted into the cover. I think there is a check feature there. I'm sure Seadoo put it there for a reason, and running without it seems to not be a good idea.



I just wanted to know if anyone else had first hand experience with it. If it isn't working, could that contribute to a potentially lean condition? Now you know why Im concerned.

I've got all the fittings, hose routing, etc. figured out. This is just puzzling me because that part of the carbs isn't exactly easy to find.

 

[SabrToothSqrl]

I do not believe it does. At least not that I recall seeing. You can check the diagrams online.

I do not see one.

http://epc.brp.com/Index.aspx?lang=E&s1=1c516505-bfc9-49f2-959b-10a251ad90e6

 

[jakknz]

It's not one you can see though, it's internal and would be inside right around the area my arrow is pointing to. Using your link, the parts catalog includes what I pictured above as an assembly - P/N 270500405 - and that's as far a breakdown as I can get. I think the only way to check it would be to have either a new one or one off a verified functional carb.

OR, I have the same cover that is bad (missing the barb) I got off my old parts ski. I may have to do a dissection in the next day or so to see exactly what is going on inside this thing. I'll do that and post back with the results.

 

[mikidymac]

I am pretty sure they do not have a check, it is typically just a restrictor orifice.

 

[racerxxx]

No restricter in there. Just rebuilt a set of those carbs. There is a restricter in the accelerator pump line to slow the fuel recharge. It's actually called a recharge jet and is in the little gray line, burried. And yes, it only goes one way, the inside is tapered.

 

[mikidymac]

Your correct there isn’t a separate restriction piece. I just meant the outlet hole is sometimes smaller to restrict the return flow.

like the top hole at the screwdriver tip.

 

[jakknz]

I did some surgery yesterday to figure this out. There isn't anything in there, just a VERY small hole for fuel flow. Will try to post some pics of the carnage soon. All I can say is to make sure you clean this fitting properly, it can clog very easily.

Thanks for the help guys