Pop off test not working...

[Pointhunter75]

Look at that page and scroll way down to where it tells the procedure again, looks like maybe thats mikunis instructions. Now it does say to test from NO.4 as the fuel inlet. Even though they messed up and didnt show NO.4. Thats what confuses me! Lol they dont even show that main fuel inlet in either pic/diagram. It just seems to me like the inlet that is actually taking fuel from the tank should be the most important starting point to test

 

[Sportster-2001-951C-Stock]

There are a number of things about that writeup that I don't totally agree with, some of that is even straight out of the Mikuni manual(lost in translation from Japanese to English, perhaps).

Okay, so guess how I test my fuel pump... I use the CPR method(nice description, whomever came up with it). I connect a piece of tubing to the pulse line through which I use my mouth to push and pull on the pulse port (dry side of the fuel pump diaphragm), plug off the fuel return from the first carb(this is the carb that has fuel pump mounted on it) and with a "balloon" on the outlet of the fuel pump which normally feeds fuel to the second carburetor, it should fill the "balloon" as I push and pull on the pulse port using my mouth. I've also been known to(commit the sin of) putting a pickup tube in a can of gasoline and connect it to the fuel pump inlet then pulse the diaphragm with my mouth to confirm the pump does pump(this fills both carbs with fuel for an easier startup).

It's a straight forward (fuel pump) test guys, no need to make it harder than it should be. The pump is mounted to the first carb and feeds it directly, so there's no fuel line involved. The pump has an output port that feeds the second carb through a short piece of fuel line, and there is a fuel return(with restrictive orifice) coming from both carbs that "T's together and returns excess fuel back to the tank. Pulsing the pulse port moves the dry side of the diaphragm back and forth, a negative pressure pulse draws fuel in through the inlet check valve of the pump and a positive pressure pulse pushes that fuel out of the pump outlet check valve. Keep alternating the pressure, and the fuel is drawn in the inlet check valve and is pushed out the outlet check valve with the alternating positive and negative pulse pressure.

Of course if your check valves aren't working, the pump won't draw fuel in and push it out the outlet and inlet ports as it should.

So suck and blow, the fuel should move. Breath in, breath out.....

And, please don't swallow any fuel or spill fuel indoors, near any flame sources, light switches, or chain smokers, clean up any spills.

Guaranteed not to rust, bust, chip, peel or hurt the baby in any way......

 

[Pointhunter75]

Thanks sportster, my carbs aren't on the ski right now though. I tried the test and the balloon fills up with air on the outlet. When i take my finger off the inlet the ballon deflates. If i move the ballon to the inlet next to the outlet and plug the outlet it also inflates and deflates when i uncover the outlet. Is that what should happen? Seems like the inlet should collapse the ballon instead of inflating it.

 

[Sportster-2001-951C-Stock]

Thanks sportster, my carbs aren't on the ski right now though. I tried the test and the balloon fills up with air on the outlet. When i take my finger off the inlet the ballon deflates. If i move the ballon to the inlet next to the outlet and plug the outlet it also inflates and deflates when i uncover the outlet. Is that what should happen? Seems like the inlet should collapse the ballon instead of inflating it.

So where is the air coming from that fills the balloon, if not from the fuel pump inlet? Not from your mouth, your mouth is operating the diaphragm through the pulse port. You should only be able to put a small amount of air into the pulse port, not continuously blow through it.

Also, for this test, you realize the fuel return should be blocked off, otherwise any pressure developed will leak through the tiny orifice and out to atmosphere.

So if you are able to fill the balloon somehow by blowing on the pulse port, then it sounds like the fuel pump diaphragm must have a hole in it, or the fuel pump is incorrectly assembled.

Do you have a drawing which shows the correct gasket/diaphragm placement and was this fuel pump working before you dissassembled if to clean and install new parts?

I think the problem is something simple and the reason it's not making sense for you is the pump is assembled incorrectly, in that case it wouldn't make any sense.

Do you have access to the mikuni manual?:

www.mikuni.com/pdf/sbn_manual.pdf

 

[Pointhunter75]

I guess the air is coming in the main fuel inlet just as gas would from the tank. I'm blowing and sucking through pulse. Tiny amounts is all it'll allow. So I'm doing that part right. By it blowing the balloon up slightly on the outlet that means it would send gas to carb two correctly right? I'm blocking the carb 1 return off as you instructed. Everything in this carb is new mikuni. No holes in anything. I'm only using air in place of fuel for this test as the carbs haven't been back on the ski since rebuilding them.

 

[Pointhunter75]

Looked at the manuel and it's all correct. It has passed all other tests.

 

[Pointhunter75]

If anything is wrong it is that one or both of the clear check valves has the unnoticeable curl facing the wrong way.

 

[Pointhunter75]

Why wouldn't you want the balloon on the outlet to blow up when blowing sucking small pulses into the pulse? That means it's feeding air (gas) to the second carb.

 

[Sportster-2001-951C-Stock]

Why wouldn't you want the balloon on the outlet to blow up when blowing sucking small pulses into the pulse? That means it's feeding air (gas) to the second carb.

Good description. It would, you're correct, this is what you want to see. So, it sounds like you're doing this correctly. But, the balloon deflates, ideally it shouldn't but the valves aren't going to make a perfect seal. If you cover the fuel inlet, the balloon doesn't deflate, so that means both check valves are leaking some, perhaps it's an acceptable amount.

Well, those check valves may not seal perfectly, but they're working..... I might be concerned if they leaked backwards inconsistently, but as long as the outer perimeter of the disk is firmly pressed against it's seating surface over the 360* radius, I think you're okay. Try it again with a shot of WD-40 in the fuel inlet to help the valves seal a little and simulate a liquid seal, does the balloon deflate quickly?

I'm not convinced the pump won't work just fine the way it is, based on this. But if you feel it's not, then now is the time to disassemble and flip both valves over if you think you can make it work better. My valve disks don't usually have blue lines on them, and they are flat best I can tell, clear mylar disks as far as I've ever noticed so I'm not sure it's easy to differentiate which side the blue lines are on. But if yours actually are concave shaped, then the valves most likely wouldn't seal like they should if the disks were upside down.

 

[Pointhunter75]

I think im gonna remove the pump and put the old ones back in and do the test again and see what happens. Its easy enough to do. I'll let you know when i get around to it. Right now im trying to figure out the impeller torque so i can finish up the pump rebuild.

 

[Sportster-2001-951C-Stock]

The 155mm pump impeller to shaft torque is 85ft-lbs, with lok-tite blue, try not to get any lok-tite on the shaft seal, too much will run down the shaft. I dunno for sure what the torque for the smaller pumps is without looking it up, maybe the same.....

 

[Sportster-2001-951C-Stock]

Maybe you already located this procedure, this one looks like it's intended for the 140mm pump(unfortunately he doesn't specify which pump this pertains to, but the 155mm pump is torqued to 85ft-lbs based on the shop manual procedure) and note he's using lok-tite red:

http://www.seadoosource.com/impeller.html