HOLY COW thats a lot of air in my fuel line!!!

[sutor623]

'95 E-rude 130HP

Hey guys, most of ya'll know I have been pulling my hair out with this engine for a while now. Everything from bad crankcase compression, warped carbs, etc.
I found air in my fuel lines a couple months back, and changed all fuel lines, connections, primer bulb, fuel tank fittings/anti-syphon valve and fuel/water separator.
Problems at this point are Hard starting/staying running and cackling/sputtering on throttle down.

After I changed all that, I ASSUMED that I was good to go. WRONG!! Check out this video. Where in the WORLD would all the air be coming from? That is an insane amount of air in the line. The clear hose before the fuel pump has NO air bubbles, so I know it is being drawn in from the fuel pump. The diaphrams are all new, and oil side is plugged good and tight. The housings are not cracked, but this is the first model VRO2 that did not have the O-ring (part #8) in between the main housings. I am guessing that this is why OMC added this O-ring.



Check out this air!! Can you believe that this motor had NO signs of running poorly at mid-range and WOT? Only issues I noticed was at start-up and sometimes throttle down. I guess for some reason the as the fuel pump picks up pressure it's not pulling in enough air to displace the fuel. Don't ask me, the darndest thing. Obviously I have a new fuel pump on the way, and will be checking for air in the line after I install it. Any feedback?

 

[BatDaddy1887]

I am certainly no expert when it comes to fuel lines and such, but to me, those fuel lines look a bit too large in circumference. Is there a reason you put larger than normal lines on the system? Did a mechanic do that? I'm very curious about that since I was always told to use either 5/16 or 3/8 fuel lines to reduce air in the system.

 

[sutor623]

Hey man, I'm pretty sure these big bore loopers call for 3/8" from tank to fuel pump and 5/8" from pump to fuel manifold. That's what I'm rocking!

 

[flyingscott]

Start by clamping the hoses down that is an air leak gotta find it. If the motor is running fine at mid range and wide open, that would lead me to a fuel restriction that can be overcome by the pump as the RPMs go up.

 

[ondarvr]

On the video it looked to me like there was a large air bubble sucked into the fuel pump a couple of seconds prior to it showing up in the line going to the carb.

Zip ties that aren't designed for hoses may not seal correctly, so you could still be sucking some air at the fittings.

A new fuel pump could be the solution though.

 

[sutor623]

Thanks guys. Ondarvr, there may have been an air bubble that was still in the clear line below the fuel pump since I had to re-prime the entire fuel system, but I started and stopped the engine numerous times. After a few mins no more air was coming from the boat side. I finally isolated the leak from internally at the fuel pump. My guess is a bad/warped VRO casing, or maybe even an improperly installed or bad from the factory diaphragm.

I had changed all lines, including fuel pickup from tank, and put all of those black plastic OMC fuel clamps on everything. So after I did all of that I was able to cleanly diagnose that the leak was from the fuel pump itself. I do believe there was another air leak pre-fuel pump before I changed everything out.

Here's the awesome news. I got the new fuel pump in today. It is the dual bodied non-vro pump from EMP, Part # 1399-7359 I hooked it up and primed her up, and fuel was priming all the way down the clear vinyl hose. (In the past if I primed it fuel would come down, then you would see air follow the fuel down the output of the fuel pump.) Started her up and ZERO air bubbles coming down that clear hose. I ran it for a few mins, gave it some throttle, and all is well!!

I will be getting her on the water this Friday to do some fishin' and get a good test run. I am almost positive that my throttle down cackling/gurgling/surging was directly related to this fuel pump.

Scott, the only thing that I can think of about this air leak not effecting WOT rpms is that the resistance is less to pull moving fuel from an already primed system under throttle, and at idle the fuel vacuum pressure is just not enough to keep the fuel rolling. (I believe there may be a small crack in the top fuel pump fitting. These older VROs, as you know, do not have replaceable fittings. Trash!!!) Either that or the air is de-priming the system of fuel when it is setting idle. I have dropped an ignition coil on this motor, and it will barely plane out, reaching 4300rpms or so. I have never experienced the loss of power or surging that most experience with a failing fuel pump. That is what kept me scratching my head! I guess I could have been leaning out that top cylinder, but I surely hope not. Luckily compression is really good and all cylinders pass the drop test at idle.

So that also leads me to believe that my backfiring and hard starting may be because when I push the key in to open the primer solenoid, the fuel drops down the primer lines to seek level with the rest of the fuel in the line, since there always seems to be air in the fuel output line when setting. Then, turn the key to start her up, and no fuel is going into the cylinder, rather sucking more air. Then when I give it throttle, it will stay running, but you would have to give it 2000rpms for 1-2 mins. before it would idle. (The warped plastic carbs probably didn't help that either.) Ill let you guys know how the run goes this coming Friday. Thanks for all the support. This engine had so many issues from setting 7 years. I have worked on many engines, but never once encountered one quite so puzzling, even AFTER installing a brand new powehead!!!

 

[Fed]

I wouldn't worry about it.
I don't think the air is coming from anywhere, 'it's just there' and I don't think the air is going anywhere either, again 'it's just there'.
If it ever reaches the carbies it will vent, I suppose you could purge it (or most of it) if it really bothers you.
I've seen the same in the filter on the suction side of the pump, it doesn't cause a problem.

 

[sutor623]

I wouldn't worry about it.
I don't think the air is coming from anywhere, 'it's just there' and I don't think the air is going anywhere either, again 'it's just there'.
If it ever reaches the carbies it will vent, I suppose you could purge it (or most of it) if it really bothers you.
I've seen the same in the filter on the suction side of the pump, it doesn't cause a problem.

Really? Maybe you are right. I ended up putting a new fuel pump on it anyway and that "trapped" air is gone. I had so much surging when throttling down I swore I was getting air into my line somehow.