removing pick-up tube from 31 gallon gas tank

[AnthonySci]

Chris, I agree. The U.S. gas sold with +/- 10% Ethanol content is a type of alcohol developed from a corn base that has many chemical compound additives that given enough time "sitting at rest" begin to react chemically with certain rubber-based hose or O-ring compounds and certain metallic compounds found within the fuel system of outboards like my 2005 Mercury.

These are chemical reactions. The 75 year old owner-mechanic marine repair shop did not mean "organic" biological organisms were growing inside my fuel system. It was simply his manner of speaking.

Yesterday, I spoke with a mechanic who repairs most any type of motor that burns gas from lawnmowers, chainsaws, outboards, to cars. After I described my motor's symptoms he said, "In the trade, what your motor is doing we call "hunting." Air is leaking into the fuel system causing a lean condition, thus the motor is 'hunting' for gas.
He advised to clean the 3 carbs' main jets and seat, the inlet jet and seat, and to check the torque on the main bolts fastening each carb to the face of the manifold.
Also, he said the face of the manifold over time may have become warped from heating and expanding and heating and...

 

[Chris1956]

Air leaks are classic reasons for surging of motors. I never heard of the term hunting. though.

Not sure what cleaning carbs has to do with it, but it shouldn't hurt. Normally you would spray gasoline mix around suspected leaking seals and listen for motor to speed up, to find air leaks.

New carb-to-block gaskets are a good idea. Checking torque of crankcase bolts is also a good idea. Does that motor even hav an intake manifold? Most 2 stroke Merc motors do not.

 

[AnthonySci]

Where are the crankcase bolts located?
No there isn't an intake manifold.

This "surging" problem began 11/22/19 when conincidentally I was running the 50 hp WOT on the main tank.
Because of covid fishing closed, sat in my garage from 3/20/19 to 5/7/2020 with non ethanol gas sitting in the 3 carbs.

5/7, 5/15, 5/20, 5/26: often NO surging during the first 15 minutes, then mild surging above 4500 rpm, occurs, inconsistent, unpredictable pattern.


6/2 ran WOT full throttle with no surging!
6/4, usual mild surging.

6/11 morning hours usual mild surge. 4 pm had to "coax" it up on plane. At 5 pm CANT GET UP ON PLANE! 80 F air.
at 7 pm, air much cooler: the usual mild surging returns.

6/13 FULL WOT & SMOOTH for 15 minutes! turn motor off for 10 minutes. Restart mild surging above 4500 rpms returns.

6/17 6 am - 10 am FULL WOT & SMOOTH. At 10:30 am mild surging.
At 5 pm WILD 500 rpm horrific surging above 3900 rpm.

6/18 6 pm, 80F--IMMEDIATE leaving the dock WILD 700 rpms surging for 15 minutes. Stop motor. Wait 10 minutes.
Mild 100 rpm surging returns all the way back to the dock.

6/23 7am mild surging. At 1 pm 85F air temperature-- unable to get up on plane!

6/25 typical mild surging pattern, air temp about 70F

6/29 from 6 am to 5 pm : a cool 60F day. Mild 100 rpm surging above 4300 rpm.
While running on plane, when I squeeze 4 or 5 times the brand new primer bulb, I can feel the liquid gas moving thru the bulb, the sound of the motor picks up in rpms a bit, smooths out--and then the surging actually degrades for like 30 seconds as the motor adjusts to the "usual" mild 100 rpm conditions around 4500 rpm.

 

[AnthonySci]

To be clear, I don't understand the inconsistency of this 2005 50 hp, 2 stroke, 3 carb, oil injected, surging problem.

There is a June 2020 consistent pattern when the outside air temperature is 80 F and above--guaranteed surging,
often WILD surging 500 to 700 rpm swings; and at times can't get a long enough concerted delivery of power to even get up on plane.

A definite change since May 2020, multiple outings with only mild 100 rpm surging above 4500 rpms. This was after sitting for 2 months because of covid closures.

Seems to me, if some one could explain what possibly caused such a downgrading physical fuel/air mixture limitation, yet inconsistent--yesterday 6/29 all day only 60F, only mild 100 rpm surges. Then I'd understand what specific area(s) to look at, that I haven't already replaced, cleaned, taken apart and examined...

Admitting my limited experience with 50hp outboard motors--doesn't seem like the cause would be from any air leaks of the numerous small black fuel hoses under the cowling betwee nthe carbs, filters, fuel pump, oil injection pump, fuel enrichment solenoid--if a leak began in any of these in November, how did the air leak enlarge and then randomly contracts hugely at times. Nope, this makes no sense to me, a driveway mechanic.

I will do the air leak / fuel spray test running under load on the river, once I line up a 2nd person to run my boat.

Seems more likely to me there's crud captured in the carb bowls--although that doesn't seem to explain the relation to air temperature and severity or not of surging. But what do I know? Very little about surging troubleshooting.

 

[AnthonySci]

I'm closing this thread; mechanically I've moved quite a ways beyond the original problem - topic of removing the pickup line from a permanent underfloor fuel tank.

Thanks to each person who responded, esp. Chris, I'm certainly learning much regarding older Mercury multi-carb, 2 stroke outboard motors. Paul

 

[AnthonySci]

Chris 1956 or another Moderator: Please close this thread.

And again, thanks for your help.

Problem: 2005 Mercury 15 hp oil injected, 2 stroke: inconsistent pattern of "surging" when running above 4300 rpms.

Diagnosis & repair: Three carbs on this motor. On carb #2, the float mechanism: the tiny metal spring clip on the inlet needle valve "clips" the flat portion of the plastic float body. On mine, the clip was NOT engaged. I carefully re assembled the clip in correct position (I had already gone through carb #1, and I observed the difference.). I Re-installed all 3 carbs, new gaskets etc. Ran the 50 hp at the lake yesterday--runs 100% smooth and strong.
50 hp now gets my 16 ft Smoker Craft Osprey right up on plane out of the hole now.

What I learned about high surging outboard motor on a 2 stroke with carbs:

1) Run on a separate can of new, clean gas. If surging persists, go to next step.

2) Purchase OEM carburetor gasket rebuild sets. Carefully disassemble, clean all orifices, jets, with spray carb cleaner using the small red spray tube (and WEAR safety glasses!) . Use compressed air through all openings. Carefully reassemble. Use a torque wrench on the carb to block main bolts. I had to call Mercury customer service: 8.3 ft lbs. torque.

(Side note: my 3 carbs were spotless inside, no crud, no gas "gel" that remains after the liquid gas has evaporated from months of sitting.)

 

[AnthonySci]

Closed.