removing pick-up tube from 31 gallon gas tank

[AnthonySci]

2005 Mercury 50 hp, 2 stroke,
consistently surges about 100 rpm's at full WOT, at 7/8 Throttle, runs smooth and strong, 4400 rpms, 21 mph.
This pattern began 5 engine hours ago when I ran the motor out of gas. I only use non-ethanol gas.

The last time out, I ran this 50 hp from a separate 3 gallon non-ethanol gas can--then at full WOT, the motor ran smooth and strong at full throttle, 5300 rpm, 28 mph.
In the afternoon, I switched back to the 31 gallon main tank. The WOT surging returned immediately. I have already replaced the water / gas filter; the old one from last year's 10 hours of use had NO water on the bottom when I poured it into a glass jar.

 

[AnthonySci]

I'm going to remove the pick up tube and see if it has an obstructed screen on the bottom of it. The underfloor 31 gallon gas tank is in a 2004 17' Smokercraft Stealth. If there's a screen, I'll remove it and throw it away!

 

[Chris1956]

Also check the antisiphon valve for a clog.

Alternatively, the fuel pickup tube on my SeaRay had a screen under the tube. The tube unscrewed from the pickup fitting.

 

[AnthonySci]

Thanks Chris, mine does'nt have a antisiphon valve.
Took quite a bit of doing to remove the pick up line fitting. Only have an 8" round access hole that's located directly in front of the 50 hp Mercury on this Smokercraft Osprey.
I needed to use a crowsfoot socket and repeated sprays of "PB penetrating Blaster" on the pick up line threads.
A 7 piece set of crowsfoot ratchet open end wrenches from 3/8 to 3/4" sells for $9 at H. Freight.

After completely unthreading the pick up line, I lifted it vertical like 8" freely--then it felt "stuck". After violently and repeatedly pulling it straight up--finally it came free. The screen on the bottom of the pickup line was catching.

The screen was clean--the mesh is like 1/64th of an inch! Maybe all my violent yanking up to get the screen through,MAYBE whatever debris fell off. Maybe the debris became caught in the screen when i ran it out of gas back in November and also February, (I'm crossing my fingers).

I removed the screen and threw it away.First for filtering, I have a fuel/water separator and then the standard Mercury inline filter just before the 3 carbs.

Tomorrow, I'm going kokanee fishing, I'll see what happens at 100% WOT.

 

[Scott Danforth]

the fitting at the top of the pickup tube is the anti-siphon valve. there is a small check valve and spring in the fitting.

 

[87-rona]

I have a 87 glastron 2.5 merc stalling , I’ve change the plugs , fuel filter , emptied the fuel tank refilled w non ethanol I put some sea foam in it runs for about a min I’ll give it throttle and stalls out I made some adjustments on carb (kinda winging it )

 

[87-rona]

New to site

 

[emoney]

87-rona, if you're looking for help with the problem, you'll want to go to the top of the applicable engine manufacturer forum and start a new thread. Lots of great folks around with a ton of knowledge. Welcome.

 

[AnthonySci]

Response to Anti SiphonValve: The "barb" end threaded fitting (threads horizontally into the pickup line on my 2005 Smokercraft 31 gal tank does NOT have a spring loaded anti siphon valve inside it. I removed it; it was clean as a whistle and i could see clear through it.

From yesterday running my boat on the water, here's a more detailed description of symptoms:
My 31 gallon tank inputs into a Mercury fuel water separator that some boat mechanics installed when I bought the brand new 6 ho Tohatsu from them last June, The 31 gallon gas link connects onto the input side, Then on the output side of the filter, there are two brass outlets--one hose goes to the 50hp primer bulb fuel hose, all since May 2020 with brand new 3/8" fuel hose. The other output goes directly to the 6 hp Tohatsu primer bulb fuel 5/16" hose.
The 6 hp ALWAYS runs strong, hours of trolling and the occasional WOT that gives me like 5 mph.
In March, concerned because I had run the 50 hp out of gas while at WOT and then the surging above 4400 rpms began happening consistently , even with running brand new premium non-ethanol gas. I replaced the fuel water separator filter. The gas inside the old filter was clear and NO water was present.

Yesterday at the river, I purposely did NOT hook the fuel line onto my 6 hp. I tyhought possibly the 6 hp was creating just enough a vacuum draw that the 50 hp above 4400 rpms surged because it just wasn't getting enough fuel to feed the hungry 2 stroke. Yesterday, the 50 hp came out of the hole quick and got right up on plane AND at 100% WOT ran strong and smooth!
I figured I had isolated the problem that indeed the 6 hp was creating just enough vacuum to restrict the 50 hp.
NOPE! After running on the river uninterrupted for like 15 minutes, then the 100 rpm surging returned when above 4400 rpm.
So I stopped the 50 hp motor, I disconnected the fuel hose to it, I started it and let it run like 15 seconds on the gas inside the carbs. Then I stopped the motor, I clipped the fuel line back on, got right up on plane and ran it at 100% WOT and it ran smooth and strong for about 3 minutes, then the surge above 4500 rpms returned. I then stopped the motor and repeated this process with the same results twice. By stopping, disconnecting the fuel line, then restarting, It seemed like I was able to release imbalance pressure and restart with normal pressure returning, if only for 3 minutes!

Next, I need to pull the diaphram apart and see if there;s any crud from the past owner running ethanol gas through older deteriorating gas lines.Two weeks ago, I finally replaced the last remaining piece of 3/8" fuel hose on the tank side of the primer bulb.

Definitely my problem is vacuum pressure related. Fishing last Thursday, in the late afternoon when the air temperature increased like 15 degrees to 80--the surging loss of power increased greatly, I couldnot even get up on plane!!! So I fished til almost sundown, Then the 50 hp ran strong got right up on plane with only the usual surging above 4500 rpms.

The primer bulb is a "Quicksilver" so it has been replaced at least once since 2005 new. I;ve only owned this boat for 13 months now, Perhaps the output side of the primer bulb with the one way ball / spring loaded--maybe the round ball has a tiny bit of "crud" stuck or jammed onto it--and it's just enough to restrict flow? But then why the 15 minute delay? Why does this problem consistently show up in the warmer afternoon temperatures here in the Nothwest, even back in March?
I'm tempted to go buy a Moeller primer bulb for $25. I hate to chase a problem with parts rather than diagnosis.
The inline fuel filter is after the fuel pump just prior to the 3 carbs. I replaced that filter last July 2019.

 

[AnthonySci]

The guy behind the auto parts counter when I described my Mercury surging problem said "Sounds like you got a thermal expansion problem. Unburned gas vaporizes into a gas and since outboards don't have a purge valve like car gas tank systems do--the pressure builds up just enough that your diaphram pressure feeding the gas can't quite overcome, thus your running too lean on fuel above 4500 rpms."

And like last Sunday, once the surging begins. I was physically purging my fuel system withexcess back pressure: When I stop the 50 hp 2 stroke. I disconnect the fuel hose. I start the motor and let it idle like 15 seconds on carb;s gas. I stop the motor. I reconnect the gas line. I start it up, get right up on plane and run at WOT like 5300 rpm strong and smooth--for about 3 minutes, then the surging above 4500 rpm returns. So definitely, some type of "back pressure" is building up in the fuel system.

The auto parts guy thought one of the 3 cdm's is just beginning to intermittent fail AND something to do with this occurrs after the CDM reaches normal operating temperature. What is that operating temperature, anyone know?

As always, thanks for any troubleshooting advice or help diagnosing this surge problem above 4500 rpms.

 

[Chris1956]

Is your fuel tank vented to the air? Check your tank breather. They can clog.

If you have a normally vented fuel tank, I do not think the auto parts guy is correct, as automotive fuel systems are sealed with a purge valve, vacuum system and a carbon canister system.

A boat fuel tank usually has a simple vent.

FWIW, I think you should have shut off valves between the water separator and both motors. That will eliminate any interaction between them, when one is running. I would expect it would be easy for the 50HP motor to pull air back thru the trolling motor fuel system.

 

[dingbat]

Had a similar issue in my boat a number of years ago. Ended up replacing everything in the fuel system from fuel tanks to motor to fix the problem.

I suspect the tank selected valve but don’t know that for sure.

My recommendations are below:

Replace and fuel line in excess of 6 years old. At a minimum..cut an inch off the end of each hose and reseat.

Check and double check that each and every fuel line connection is tight with the proper hose clamps. Screw type hose clamps don’t cut it.

After market primer bulbs are notorious for causing problems. OEM only. Evinrude and Yamaha make good bulbs

Change out the separator and gaskets if more than a year old.

Bypass or replace any tank select valves in the system

Splices piece of clear fuel line in the system right after the primer bulb to check for air bubbles when the problem arises.

 

[AnthonySci]

Yesterday, I fished from 6 a.m. to 5 p.m. I ran the 50 hp Merc off a separate 3 gallon can,
At 6 a.m. I ran 15 minutes at FULL POWER with NO SURGING!
9:30, I ran 5 minutes with NO SURGING,
10:30, as usual, get right up on plane and the SURGING above 4500 rpms returned!!! The problem has been isolated--not connected to the main onboard 31 gallon tank, nor from the 2019 F/W separator.

2 p.m. (air temperature 70 degrees), ran for 10 minutes, still surging above 4500 rpm. These surges are oscillating about 100 rpms,
5 p,m. HOLY COW! I can barely get up on plane! And when I do coax it up, above 3900 rpms the surging is oscillating wildly, swings of about 500 rpms!! Yet if i keep it at 3900 rpm, there's no surging, although just barely enough power to stay up on plane.

A week ago fishing, running off the 31 gallon tank, had similar pattern with one exception:
8 am, usual mild surging above 4500 rpm
4 pm, took a couple minutes to get up on plane. Surging at 4300 rpm.
5 p,m, Not enough steady power to GET UP ON PLANE! After 5 minutes, I gave up trying and went back to fishing with my 6 hp kicker.
7pm, gets right up on plane, mild surging above 4500 rpms.

This problem is deteriorating, gradually worsening. And the "back pressure is building as the use of the 50 hp motor goes. (You can see how, I only use the 50 hp at most an hour per trip,) The 6 hp has a anti siphon valve at the F/W separator output.

Yesterday while the surging was occurring, I placed a brand new CDM for cylinder #3, no effect; then #2, no effect, then #1 cylinder , no effect. BUT what if: 2 of the 3 CDMs are intermittently failing? And then the unburned gas vaporizes in the cylinder creating just enough a "pressure barrier" that has no means to purge, so that by 5 pm, the wild 500 rpm surge swings begin? That doesnt explain how a week ago, at 5 pm (air 80 degrees), I couldnt even get upon plane, So I troll with the 6 hp for 2 hours, then at 7 pm, gets right up on plane with mild surging above 4500 rpms. (air temp maybe 65 degrees)

Last October, with your help I was able to diagnose the trigger failing. I replaced it. Those symptoms gone!

All external gas hoses outside the motor are new. 2 days ago, I replaced the inline fuel filter that is just prior to the 3 carbs. I rebuilt the fuel diaphram 2 days ago. The primer bulb is Quicksilver. I have NOT replaced it---considering the symptoms I don't see how the primer bulb could cause this slwoly worsening (sure seems like an intermittent gradually degrading, worsening problem--

History, I bought this 2005 Smokercraft Osprey, 2005 Mercury 50 hp , 2 stroke, May 2019. The trigger began intermittent failure on June 17th, I replaced the trigger on October 8th.
Mild surging began on 11-22-19 after trolling for 6 hours, 2 pm.. Total hours that I have used this 50 hp = 9 hours.

As of yesterday, 6-17-19 I have runthis 2005 Mercury 2 stroke, 50 hp, a total of 17 hours.

 

[AnthonySci]

Also, the 6 hp is protected by an anti siphon valve on the output side of the 2019 F/W separator.
So, no the 50 hp is not drawing air from the 6 hp kicker.
Also, yesterday, I ran the 50 hp off a separate 3 gallon can--the surging continued and by 5 pm was highly disturbing surging wildly 500 rpms!!

 

[dingbat]

Putting a timing light or spark tester on the motor when it acts up would confirm or eliminate an ignition problem.

Installing a clear fuel line between the fuel pump and the fuel rail would confirm or eliminate a fuel delivery problem.

Vapor pressure issues on a 2 stroke?

Capacitors and field coils are notoriously for breaking down at elevated temperatures.

 

[Scott Danforth]

the information in post #9 should have been in post #1

nearly everyone on iBoats that attempts to run two motors from a single pickup has problems (use the search function)

Not saying this is all your problems, however you may need to run each motor off its own pickup. or add check valves in the lines. running two motors from one pickup is too easy for the running motor to pull fuel from the other engine's line

normally, I would state the surging is the fuel pump pulling air, however post #14 adds another fly to the ointment so to speak. I wonder if the fuel pump diaphragm is failing on the 50hp.

 

[AnthonySci]

I rebuilt the entire fuel pump diaphram, including both check valves.
I replaced the primer bulb and hoses. I have already replaced both fittings where the fuel "clicks" onto the fitting bolted to the front of the motor. with the fuel hose NOT connected to the motor, when I pump the primer bulb and depress the spring loaded round stop--liquid fuel squirts out.
I removed the vent hose where it connects to the fitting at the top of the 31 gallon on board fuel tank; i wasn't able to unthread the fitting so I ran a short piece of form wire thru it to ensure there wasn't any blockage.
Test run in the Columbia river--same pronounced high end surging problems continue. THIS 2005 Mercury 50 hp 2 stroke oil injected motor DEMANDS huge amounts of fuel to burn at WOT! Randomly, at times, I can't even get up on plane! Now makes no difference when I switch to a separatre 3 gallon gas can, The 6 hp kicker is NOT connected,it is un"clipped" at the motor; besides it's protected by an anti siphon valve at the fuel water separator brass "output" barbed fitting.

HOWEVER, when I took apart the fuel pump diaphram---in the "exit chamber" that then leads to the hose to the inline filter--inside this chamber, there were little flat pieces of white stuff, flat, about 1/8" x 1/8", maybe 15 pieces.

The 75year old mechanic where i bought the 6 hp tohatsu told me yesterday, "You got "stuff" growing in you r fuel system, Comes from the gas they sell these days, Even non ethanol has alcohol in it, they dont clean out the tanj=ker trucks; besides most likely you're getting old gas when you buy that non-ethanol gas at the pump. My mechanics out in the shop have a constant,never ending source of work--taking apart carbs and cleaning them out." The reason that I was there was to order the Mercury 3 carb gasket sets--so I could pull the carbs off, ((Last JUly, the carbs were clean as a whistle.

Last October, I bought like 5 gallons of non-ethanol at a remote little country store near where I fish. Wouldn't be surprised that's where my gas got :infected." November 22, 2019, the first time, the WOT, mild surging occurred (about 100 rpm's when running over 4500 rpm;s) In the morning at WOT, the 50 hp connected to the main tank ran ot of gas. AT the time there still was the micro mesh screen on the bottom of the pick up line--those white pieces I found in the fuel pump diaphram would NOT have fit through that screen. The fuel water separator would NOT have stopped the ALCOHOL, neither would the inline filter just prior to the carbs. Nope. But the ALCOHOL would have sat in each of my 3 carbs' bowls.

I'll post an uipdate after I clean my carbs.

IMO, everyone, at the end of a day on the water, run your big motor out of gas BEFORE you load the boat on the trailer!

 

[Chris1956]

I have never heard of anything growing in gasoline, even gasoline with alcohol in it.

Bacteria does grow in diesel fuel, however.

 

[AnthonySci]

Chris, I'm still learning as I work towards resolving this surging problem that has become progressively worse in just a few engine hours AND has become more & more inconsistent in patterns, more unpredictable with this 2005 Merc 50 hp, 2 stroke, oil injected.
9 engine hours since this mild surging problem began last November 2019.
I've only run this motor a total of 20 hours since I bought this Smoker Craft last May 2019.

from a small engine repair website 2015, http://blog.jackssmallengines.com/2015/04/see-ethanol-damage-up-close :

"Ethanol has a tendency to absorb water. The water moisture, along with ethanol, slowly deteriorates the metal parts of the fuel tank and carburetor. The white crusty deposits you see (in the photo on the website) collecting on this generator carburetor are the deteriorated metal particles. As ethanol eats away at the metal parts, as well as the rubber and plastic parts of the fuel system and carburetor, it leaves those corroded particles in the carburetor bowl.
These particles can clog the carburetor jets, causing extremely poor engine performance."

As soon as my Mercury carb gaskets sets arrive, I'll pull the carbs and dissemble and clean.

I appreciate all the posts and help from everyone on this iBoat forum.

 

[Chris1956]

Well, I think your older mechanic is repeating old wives tales about stuff growing in alcohol fuel. Alcohol in gasoline does clean out fuel systems, when it is first introduced. After that, the fuel system is clean.

Alcohol in gasoline does absorb water. If the fuel system has enough water, the alcohol/water will separate from the gasoline and cause motor running issues. of course, gasoline w/o alcohol does not absorb water, and the water can cause running issues. IMO, it is better to have the alcohol absorbing that water, tank after tank.

alcohol does deteriorate fuel system components, but modern fuel systems have alcohol resistant materials. The dirt you are seeing in your carbs must come out, and you should check your fuel lines and fittings, but it is inorganic. IMO.