Air in the fuel lines. 2002 Merc 125

[Levie17]

I’ll attach a link to the video I took. You’ll see air, but when it stops, it’s due to me pressing the fuel bulb.

no air in the lines from the tank to the bulb. No air from bulb to “molded” Merc fuel line. This is where the oil line enters and the “bleeder” line enters.

any thoughts?

could it be an engine issue that is pushing air back through? Or is just that I need to find the leak in the lines.

thanks!

https://youtu.be/iWRXiu9G22I

 

[Texasmark]

I never did what you did but here is the recent data I pulled out of the book in answering another person's fuel pump related question: There is a light vacuum at the input of the fuel pump which, when pumping fuel with the engine running, puts out a couple of # of pressure to the carbs at idle up to 10# max at WOT. The vacuum is the fuel pump sucking on the fuel line to get fuel out of your tank.

When you squeeze the bulb you are pressurizing the fuel line and sending a "slug" of pressurized fuel along a line that was limping along with the fuel pump pulling on fuel with it's vacuum. The engine sounds fine to me and it didn't miss a lick.

I'd find something else to worry about. Grin

 

[dsiekman]

I am dealing with a similar issue, though mine may be a bit worse. I definitely have air in the line and I am not getting enough fuel to the carbs to keep it running for more than maybe 45 seconds. The advice I have received so far is to check and/or replace all fuel fittings (hose clamps, pickup tube, and possibly fuel line) from the tank to the motor.

 

[Texasmark]

If you have cracks in the line and that is not only the line to the engine but the fuel lines in the engine, then surely the pump will be sucking in air rather than fuel and that should show up as reduced WOT RPMs. Fuel external to the fuel lines anywhere can be a clue that the lines have deteriorated and developed holes or cracks. Pumping the bulb up hard and moving fuel lines around is an easy way to find this.

I had black specks of fuel line in my carbs on a 2002 90 hp in 2012 (at 10 years of age) having been operated on ethanol the whole time, by me. I also have a 2002 115 that I bought last year operated only on gasoline with Mercury's #1 fuel conditioner that a swab run up in the lines came out clean indicating no deterioration over a longer period of time, and no fuel residue on any of the hoses.

Air in the fuel line can exit the carburetor venturi port if the fuel in the bowl drops low enough to allow the needle valve in the carb to unseat and the check valve in the squeeze bulb isn't seating properly. This manifested itself in the rig I bought with the 115. The squeeze bulb/fuel line was old so I immediately bought a new EPA approved Mercury/Quicksilver 3' 5/16" fuel line and oval bulb (in a package)....not the diamond shaped OEM bulb of yesteryear.....that worked!!!!

I have a built in tank in the boat and upon wanting to start the engine, I had to squeeze the bulb a couple of dozen times to get it firm. I cut the line and installed an aluminum after market check valve between the bulb and the tank and wala.....first squeeze bulb was like it is when the engine is running....soft, and 3-4 squeezes and it was firm. The point here is that had the check valve in the bulb been working properly I wouldn't have had what I had. So if relying on the bulb check valve for something, I wouldn't.

On replacing the lines, great idea. Lot of blabbing here but it covers my experiences with things of which you may be considering.

 

[emoney]

I am dealing with a similar issue, though mine may be a bit worse. I definitely have air in the line and I am not getting enough fuel to the carbs to keep it running for more than maybe 45 seconds. The advice I have received so far is to check and/or replace all fuel fittings (hose clamps, pickup tube, and possibly fuel line) from the tank to the motor.

If the fuel lines are due for changing, that's good advice because as Mark mentioned, ethanol can eat up the old style lines pretty quickly. I just had an issue that I'm pretty sure was simply because there was a leak at the new glass type inline filter I installed. I changed out fuel lines from the pump to the carbs and went back to the original plastic filter to solve the problem, but when I was pulled out the glass one, I noticed I hadn't gotten the top fitting on tight enough so I'm pretty sure that was the problem.

 

[Texasmark]

Mercury zip ties aren't like the average zip tie. Inspect one and you will find that the lock ring has a curved inner surface which closes the gap made by the lock ring giving you complete compression on your fuel line. I got mine off ebay.

 

[fisics67]

Not an expert here, but I have an idea for you I think.

If you have an external tank, try elevating it above the motor and test run it. Gravity should keep your fuel lines slightly pressurized. This should eliminate, or lessen, the chance of your fuel pump sucking air through an potential leaks.

 

[dsiekman]

So the pump was definitely having issues. Rebuilt it, used a little gasket sealer between the pump gasket and the block and fired it up. No more bubbles! Took it for a run this morning but I'm only getting about 4000 rpms and a little stumble. Wondering if it is still a lack of fuel or if it is an electrical issue. I replaced the stator because it was arcing to the block so wondering if that screwed up something else.

 

[Texasmark]

Just squeeze the bulb. If it recovers it's lean. Did you say you changed the fuel filter? If not and it responds to the bulb get a new one.

Diddling with the stator, I'd check the timing and link and sync for fuel and timing relationships vs throttle position. I doubt L-S would be stumbling, course timing has to keep increasing as the throttle increases to get Max RPMs and you said you were maxing out at 4k. If the advance isn't there don't know how you could get it. That Merc has a fuel saver LS whereby once throttle is maxed out, backing off starts closing the butterflies but leaves the timing fully advanced for a certain amount of throttle reduction....then the butterflies and the timing are reduced.

1996 and newer 4 cyl engines:

Full throttle operating range: 4750-5250 RPM; Idle F gear boat in motion, 675 +/- 25....(fast enough to keep engine running and slow enough for clean shifting without gear crunching essentially).

Timing: Idle 4*ATDC - 6*BTDC...basically TDC. Max timing: 3000 RPM 23* BTDC; Cranking speed, (plugs out, 200 RPM type thing,) 25 BTDC...(.right out of the manual).

 

[Levie17]

Update: I began the process of changing out the fuel lines and found that one of the lines from the accelerator pump to the bottom of the engine (assuming cyl 4) was not clamped and was also torn. Repaired it, no more air in the lines. Hoping for a good water test today at some point. Planning to get my hands on some merc cable ties at some point.