Air in the return line

[MAL]

I am working on a 1996 Seadoo gts. I have noticed the there is a steady stream of air bubbles coming out of the return line at the carb, but there are no air bubbles going into the carb. I pressure tested the pump side of the carb, and it held 4PSI for about 30 minutes. There is some air in the supply lines, but the pump is not sucking them down from the high point at the water separator even when revved. Is there a way to measure the pump output and where could those bubbles in the return line be coming from if the pump held pressure for 30 minutes.

I have had a little time to think about this. Is it possible if the pump is weak, that air can back feed through the low or high speed jets due to there being a vacuum in the chamber? I decided to test that theory by adding a T in the return line and putting 1PSI pressure in the tank. I was expecting the pressure to diminish as it ran. The added pressure did not stop the bubbles in the return line, and the pressure in the tank increased to 2PSI.

 

[MAL]

I tried new check valves in the pump, but the new check valve did not pass the suck blow test, so I ordered the entire pump. Even if this fixes the air bubble problem I am still genuinely curious about where they are coming from?

 

[burtshaver2021]

From what I am seeing there are very few places where air could be coming from to be present in the return line. Since the fuel pump held 4 pounds of pressure when tested at the pulse fitting on the carb and you have no bubbles in the line coming to the fuel inlet I would take a guess and say they are entering at the fuel inlet fitting. I will say that my one encounter with clear fuel line was not good, had a dickens of a time trying to get them to stop sucking air and eventually I changed them all out for good quality Continental fuel line. I found the ID of them was not quite right and would fit loosely compared to the black fuel line which was slightly difficult to get on and off.

 

[MAL]

Looking at that picture there is not much room for a vacuum leak letting in air. When I disconnect the return line and apply vacuum to the return barb on the carb, I get the same bubbles showing up in the return. It looks like I need to double check everything around the inlet barb. I pressure tested the inlet and return line at the same time, so I guess that I was testing to the needle and seat also. I did not pressure test the pulse fitting. I used the blue polyurethane fuel line and I had used 2 fuel line zip ties on every fitting. When I do my pressure testing I don't even use zip ties.

 

[burtshaver2021]

Looking at that picture there is not much room for a vacuum leak letting in air. When I disconnect the return line and apply vacuum to the return barb on the carb, I get the same bubbles showing up in the return. It looks like I need to double check everything around the inlet barb. I pressure tested the inlet and return line at the same time, so I guess that I was testing to the needle and seat also. I did not pressure test the pulse fitting. I used the blue polyurethane fuel line and I had used 2 fuel line zip ties on every fitting. When I do my pressure testing I don't even use zip ties.

I thought you had pressure tested the fuel pump with 4 pounds. That should be done as well

 

[burtshaver2021]

carb. I pressure tested the pump side of the carb, and it held 4PSI for about 30 minutes

Yes, I thought I had read that in your previous post. You out this 4 pounds of pressure on the pulse fitting correct?

 

[MAL]

I connected to the inlet and return line at the same time with a T and pressure tested the check valve chamber. So air is not escaping into the pulse chamber from that test...or out through the needle and seat at 4 PSI. Is that not a legitimate test? I will test the pulse fitting when I reassemble after the new pump gets here.

 

[burtshaver2021]

I connected to the inlet and return line at the same time with a T and pressure tested the check valve chamber. So air is not escaping into the pulse chamber from that test...or out through the needle and seat at 4 PSI. Is that not a legitimate test? I will test the pulse fitting when I reassemble after the new pump gets here.

Sounds like it might work as a test, I would just test it as per the manual. 10 pounds in the fuel inlet with the return blocked off to see if needle is being held open. And 4 pounds in the pulse fitting to see if fuel pump gasket is sealed. What brand are the fuel lines out of curiosity? Keep an eye on them, I did some research and I see a lot of posts saying they get hard and crack in a short time period.

 

[MAL]

The fuel line is LeMans corporation brand. I took the advice from this guy

For me clear lines are a huge help with diagnostics. Assuming that my problem is not the brand new fuel line that is double zip tied, I would have never found this issue with out clear lines. Every time I cold start the ski, I watch the fuel lines. You can see why they stumble until they get warmed up...its air in the lines working it's way out.

I could be wrong, but it seems that pressuring both the inlet and supply is basically the same as blocking off the return and pressurizing the inlet. I think I saw someone do it that way before and it just made sense to me.

 

[burtshaver2021]

Yes, my personal preference is the rubber/nitrile fuel line because it is more pliable and has a better resistance to fuel and heat than the polyurethane. I could never get the polyurethane lines to seal up. I only had one machine that came with them so my experience is limited with the polyurethane fuel lines but messing with them that once trying to get rid of the bubbles on my 95XP was enough. Went to the continental and found they felt better, but whatever works, I’ve been wrong more times than I’ve been right. Let us know how it goes with the new carb. Good luck

 

[Venturian1]

Could it be sucking in air through a loose or cracked fuel hose upstream of the carb? or fuel selector valve leaking?
Tiny Bubbles entering through the fuel filter O-ring? I've seen hoses hold pressure but leak under vacuum. The only place air could be forced into the system would be at the pulse diaphragm. Then from the fuel inlet on the carb, everything back to the fuel tank is on the suck, Except when the tank is full, then there's some gravitation. I once pulled off the fuel feed hose at the carb and a steady flow of gas ran out when the tank was full!

 

[MAL]

Could it be sucking in air through a loose or cracked fuel hose upstream of the carb? or fuel selector valve leaking?
Tiny Bubbles entering through the fuel filter O-ring? I've seen hoses hold pressure but leak under vacuum. The only place air could be forced into the system would be at the pulse diaphragm. Then from the fuel inlet on the carb, everything back to the fuel tank is on the suck, Except when the tank is full, then there's some gravitation. I once pulled off the fuel feed hose at the carb and a steady flow of gas ran out when the tank was full!

No visible bubbles were going into the carb...they were only going out the return line. I replaced the fuel pump body and it fixed the issue. I am still very interested in how the bubbles got in. Maybe the barb itself was loose, but that barb passed a pressure test at 4 psi...maybe that wasn't enough pressure. I haven't taken the time to check it out.