99 GTX LTD Carb Rebuild Question-is it supposed to be like this?

[MoDawg73]

Hello,
While rebuilding my carbs, I noticed that the rear carb fuel inlet is not free flowing. I sprayed gum out into it, and most of it came back out the same way. Some went through, but most did not.

I put it on the pressure checker to blow some air through it, and my pressure gauge was reading 40 psi while I had it connected to a 50 psi source. the part was out of the carb, disconnected. When I shut down the air, it returned to zero.

Same thing when I did my pop off test. It went to 40, popped, then stayed at 40 as long as I had the air turned on. It is almost like there is a pressure regulator in the inlet.

I assume it is not supposed to be this way, and that there is some blockage, but I wanted to ask to see if there is an integrated check valve or something like that in this piece.

Any help,would be greatly appreciated.

Thanks,
Ken

 

[Matt Braley]

Yes that fitting should be open. No check valve but a small hole to keep fuel pressure up so it clogs easy.

 

[MoDawg73]

Matt, thanks for the help. I edited the post because as I reread it, I don’t think it accurately described what I was seeing.

It sounds like it may be operating normally then, if it is a small hole designed to keep pressure up.

Air does go through it, just not much.

 

[Matt Braley]

There should not be any psi build up at all. It just won't flow like a normal wide open 1/4" fitting will.

 

[MoDawg73]

Thanks. Any tips on how to get it cleaned out? I am soaking it in sea foam now. Have tried a piece of wire but it gets hung up. Is it possible to remove the inlet tube to clean it and put it back?

 

[Sportster-2001-951C-Stock]

There's a fuel inlet and fuel return outlet on the carb, the outlet is the fuel return to the tank, which has a restrictor in the passage. The inlet itself, is free-flowing. So, if you apply pressure to the inlet, some of the pressure will be bled off to the restricted fuel return.

Is this an SBN 46i on a 951? If yes, high pressure might damage the fuel pump pulse diaphragm or the two fuel pump check valve disks inside of the magneto (front) carburetor, the rear PTO carburetor has no fuel pump.

Don't modify the return fuel outlet restrictor orifices in these, they're calibrated orifice diameters to maintain correct fuel pressure. Just clean them, the orifice is quite small.

I just use carburetor cleaner or brake cleaner. Sounds like they're probably fine as is.

 

[MoDawg73]

This is a 951. It is on the PTO carb. It sounds like it is a restriction, but I am definitely working on the fuel input line.

Is booming it in water for a time a decent idea?

 

[MoDawg73]

Boiling it in water. Sorry for the typo

 

[Sportster-2001-951C-Stock]

If you mean boiling just the cover by itself, yes. The cover has no parts inside that water might damage. After boiling you can blow it dry or even carburetor cleaner solvent will dry it out.

It seems odd the inlet is clogged, are you sure?

 

[MoDawg73]

Well, there is some fluid flow, but not much. If I squirt gum out in the inlet, or in the hole on the inside of the cover, some comes out, but not much comes out the other end.

Tried boiling it, but it didn’t do anything. I guess I just need a new cover.

Anyone have any idea where one could buy one? I can’t even find a parts listing with the non-pump cover listed.

 

[Sportster-2001-951C-Stock]

Man, I thought that angled tube is the fuel return, not the fuel supply. The reason I say that is the fuel supply hugs close to the carb body and if the tubing of is too large you can't push the tubing onto the barb b/c it's too close to the carb body.

 

[Matt Braley]

It is the fuel return.

 

[MoDawg73]

It is the fuel return.

Matt,
I don’t understand. I thought it was the fuel input for the carb without the fuel pump. Why are you saying it is the fuel return? I thought that it supplied to the fuel. The interior opening mates up with the fuel filter.

Please help me to understand.
Thanks,
Ken

 

[Matt Braley]

The fuel comes into the front(mag) carb from the 5/16" fitting that faces the bottom. Then it goes from the mag carb to the rear carb via the shorter 1/4" fittings that face eachother. From there the return fuel comes out of the plate in the pic and bends around the top of the mag(front) carb to the plastic fitting. From the other side of the 1/4" plastic fitting it goes back to the RET fitting on the fuel baffle.

 

[Sportster-2001-951C-Stock]

This is a different model Mikuni carburetor, the locations of inlet/outlet are different then the SBN 46i, this is, the SBN 38 I believe. But you can see the fuel inlet supply, fuel pump and fuel return with the restricter orifice at top of image. Functionally, the PTO carb is the same setup but doesn't include the fuel pump.

 

[MoDawg73]

Ok guys. Thanks for your patience and helping me understand. So what I thought was the fuel input is actually the fuel return. The input is actually clear. Should the return have a restriction like I described ?The return on the PTO is connected to a t fitting which goes back to the gas tank and the fuel return of the Mag carb.

 

[MoDawg73]

Crazy thing is the manual picture appears to have it the other way.

It appears to have the return fitting as the one on the main body and the input as the one on the pump cover.

Also, the markings on the pump cover have an arrow leading out where the fitting is on the main body. Made it confusing as heck.



But my photos before I took it apart had it installed as you described. The fitting on the pump cover was attached to the fuel return T-fitting, and the fitting on the PTO body was attached to the fuel output on the Mag carb.

I think I have it now.

Thanks for all your help!

Ken

 

[Sportster-2001-951C-Stock]

The fitting you're attempting to unclog is the fuel return of the PTO carb, it has a restricted orifice inside. This angled tube is "T"'d with the MAG carb return and then returns to the tank. Both of these returns have an restrictor orifice in them. The inlet fuel supply for the MAG carb is an internal passage from the fuel pump, with a 1/4" nipple to feed the PTO carb inlet nipple. Fuel inlets are not restricted. The purpose of the fuel return restrictors is to allow fuel pressure to build but not reach excessive levels, a pressure smoothing effect, if you will..

Then there's a pulse port on the MAG carb to operate the fuel pump by using crankcase pulses.

 

[MoDawg73]

Ok. I think I got it. Thanks again!

 

[Sportster-2001-951C-Stock]

Any time, any other questions just ask.

 

[R-u-n2it]

That was confusing, especially the pic of the cover on somebody's head. Sorry, couldn't resist.
Without restriction the fuel couldn't overcome popoff spring pressure and allow fuel to pass, this is what made sense to me, fuel system without float bowls is like Fuel injection circulation. Where is the hybrid PWC's since the electric powered everything deal started? Electron Powered PWC.... coming soon. The pump/stator all in 1 unit. And we thought these electrical systems were complicated.

 

[mikidymac]

That was confusing, especially the pic of the cover on somebody's head. Sorry, couldn't resist.
Without restriction the fuel couldn't overcome popoff spring pressure and allow fuel to pass, this is what made sense to me, fuel system without float bowls is like Fuel injection circulation. Where is the hybrid PWC's since the electric powered everything deal started? Electron Powered PWC.... coming soon. The pump/stator all in 1 unit. And we thought these electrical systems were complicated.

View attachment 42217

Like te nikola Wav?

 

[Sportster-2001-951C-Stock]

It's on his knee but who's counting fine hairs? The battery will cost as much as the hull in an EWC and who rides just an hour or so?

 

[R-u-n2it]

The battery would probably be the hull.... {;o)

 

[R-u-n2it]

That ski looks kinda like a Spark, lol, fitting name anyways.