Merc 2 Stroke Power Fuel Delivery Fluctuation Issues

[CTsalt12]

Hi All,

First off, happy friday to everyone.

I had an issue more than once last year that usually resolved itself, but still makes me uneasy.

When up on plane at cruising speed, I would seem to lose power temporarily, and once it went all the way down and shut off.  The fuel primer bulb would be deflated.  After giving it a second and pumping, it would start back up and work again.  Sometimes it would lose RPMs, then speed back up way faster.  It seemed like the fuel delivery would be slowed down, then sped up to compensate for itself.  Like I said, it usually resolved itself and went back to normal.

Is it as simple as a new fuel line/primer bulb?  New fuel filter?  I usually do new fuel filter once a year.  I did a fuel sample for water or debris, nothing I could see. 

There is one thing I should mention.  I have a wooden dowel plug in my fuel tank.  This sounds crazy I know.  Long story short, I fill my fuel up directly through the fuel tank below deck via the deck hatch.  I use a wooden plug to seal male end of the the fuel tank where the fuel line should be attached.  Last year, it shrunk from gas exposure and fell in.  I have since replaced with a larger plug of course.  I'm sure you're curious why I have this ridiculous setup.  Reason being, I have an aftermarket tank installed by PO that was a bit too tall and didn't have a male end with an elbow, so the fuel like wouldnt let the hatch close all the way, and I would have water pooling up on my fuel tank and persistent water intrusion through the sender.  Permatex around the sender and this plug solution fixed it finally.

Sorry for the marathon post, your help is appreciated!  Fitz, especially yours!

[fitz73222]

Hey Jimbo,
First, fuel techincally doesn't become fuel until gasoline and air mix in the carbs and is drawn into the engine. The carbs manage a ratio 14:1 of air and gasoline mix in order to ignite the "fuel' in the engine. 14 parts air to 1 part of gasoline. All engines run on this fuel to air ratio in order to combust in the cylinder. In order for the gasoline to be delivered properly to the engine to create "fuel" the gasoline as it is delivered to the engine must be replaced with air in the fuel tank as the gasoline is drawn into engine or if the draw of fuel is not replaced with air to maintain a neutral pressure balance then the engine will continue to vacuum the gasoline from the tank until it reaches the limits of the fuel pump and the engine starves for gasoline making the bulb go flat until the engine slows down or stops from lack of gasoline.

So two things cause fuel starvation, no air to replace the gasoline in the tank (improper venting) or an obstruction of gasoline to prevent adequate fuel flow (plugged filter or fuel lines) either issue will mess with 14:1 air/gas ratio and the engine wont run well. So if your primer bulb is going flat both of the delivery venues should be considered. So make sure the fuel filters and lines are clean and the tank venting is working properly and I still don't understand the wooden dowel part of the equation. 

[GoneFission]

Wood dowel?     Is this on the vent line?  That would cause a problem after running a while and the bulb would go flat. 

Maybe a pic or two of this setup?   

[baby1]

hey there //what year is the motor?  soft bulb /means / bad fuel pump  replace pump

[fitz73222]

Baby1,
If the bulb is going flat that means the pump is sucking fine, its trying to pull fuel to the point it's sucking the bulb flat but something is holding the gas back. This isnt an engine problem.

[CTsalt12]

Hi Guys,

This is helpful.  Regarding the wood dowel.  I think I went into too much detail here and made it confusing.  Long story short, there's a 4 inch wood dowel in my fuel tank that fell through the fuel fill neck.  This could be inhibiting fuel flow through the pickup, but this could only happen when the fuel is low enough for the wood to be floating level with the pickup which is less than an inch from the bottom of the tank.  I am procrastinating about pulling up the sender and taking this piece out, and  having to re-seal it, but I think I'll add it to my to do list today..

[CLM65]

Keep in mind that wood is more dense than water, and even more dense than gas.  A piece of wood will initially float quite well when first dropped in water or gas.  This is due to all the open spaces or cells in the wood.  However, over time, the wood will become saturated and it will sink.  And since gas is less dense than water, the wood will tend to sink faster in gas than in water.  I'm not sure if this is causing your problem, but I wouldn't necessarily discount it due to the initial bouyancy of the wood.

[Capt. Bob]

Is there an anti siphon valve on the tank itself?



Possible debris stuck in the valve.

Here's a good read:

http://classicaquasport.com/smf/index.php?topic=12406.0

[baby1]

I think everyone knows soft fuel pump  bulb // is a classic singe of fuel pump fail ///it is one of the // descriptions in the repair manual//
/ the other good idea is to run on a portable tank to test /
// for obstruction   this will tell you if it's a blockage /
// re runs good on portable tank it's a blockage
/look at anti flow valve on the built in tank  they are bad for blocking /
 runs the same its the fuel pump /// on the outside chance if you have really bad compression // the fuel pump will stop working because it works off the  up/down   crank case pressure 

[fitz73222]

 baby1

Join Date: Nov 2014
Posts: 10

 Re: Merc 2 Stroke Power Fuel Delivery Fluctuation Issues
« Reply #8 on: Today at 12:48:28 PM »QuoteI think everyone knows soft fuel pump  bulb // is a classic singe of fuel pump fail ///it is one of the // descriptions in the repair manual//
Baby, so I'm not confused, please explain in detail how a bad fuel pump makes a primer bulb go flat?

[baby1]

 I sorry I don't have time// but please, just look in any repair Manuel//  it is due to not    having enough  pressure in the system  ( if you have pressure the bulb is hard/// if you don't have pressure  the bulb is soft  :-) the fuel pump provides pressure ) 

[baby1]

hear is more on fuel bulbs /////A Primer on Primers

Proper Installation of Primer Bulbs in Fuel Lines

Purpose of the Primer

Unlike your automobile engine, which typically has an electrical fuel pump located in the fuel tank itself that delivers fuel under pressure to the engine, most outboard motors have only a simple diaphragm fuel pump that operates from engine vacuum. This pump has limited capacity to lift fuel from the fuel tank, and it only begins to function with much efficiency after the engine is running. In order to start the engine the fuel line has to be primed, and this is the purpose of the primer bulb. If its fuel line is not primed even an engine that is in perfect tune will will require a great deal of cranking to start. Rather than wearing down the battery to prime the fuel line, a small primer bulb pump is almost universally provided.

The primer bulb would seem like a simple device that does not require a great deal of explanation, but there are several details of its installation and use that may be overlooked.

Construction

Almost all primer bulbs consist of a flexible rubber bladder or bulb with inlet and outlet connectors. One-way check valves are located on the inlet and outlet side of the primer bulb. A slight spring pressure keeps the check valves closed, but not enough pressure to prevent the engine fuel pump from drawing fuel past it once the engine is running. Thus fuel can flow easily through the primer bulb in only one direction. Primer bulbs are almost universally marked with an arrow or some other identifier to indicate the direction of fuel flow through them. The inlet and outlet fittings typically contain a hose barb and these are generally available in three sizes to fit commonly used fuel lines. (Lower horsepower installations use 1/4-inch or 5/16-inch ID fuel lines; higher horsepower engines require 3/8-inch ID fuel lines. Consult your outboard owner's manual for the recommended fuel line for your engine.) Use a primer bulb whose connections are sized to match your fuel lines.

When the primer bulb is squeezed, the pressure created closes the inlet valve and opens the outlet valve, allowing fuel in the bulb to flow toward the engine. When the bulb is released, the suction created closes the outlet valve and opens the inlet valve, drawing fuel from the tank into the bulb. Repeated squeezing causes fuel to be lifted from the tank and pumped to the engine, until the fuel line is filled and the bulb becomes firm.

When the engine is running its fuel pump produces a suction that draws fuel past the check valves. The valves are designed so that even the modest pressure of the engine fuel pump will draw fuel past them. At idle speeds some engine fuel pumps may produce marginal pressure and may not draw fuel past the check valves. This can lead to stalling and other problems. OEM brands of primer bulbs have been designed to work with the fuel pumps in their engines, and their use is highly recommended over after-market products. Recently Mercury Marine came out with an improved primer bulb and is recommending it for all their engines. It can be identified by the yellow plastic line visible where the fittings join the rubber bulb.

Another important consideration is the flexibility of the rubber components. In the past decade it has become very common for gasoline fuels to be blended with ethanol. Unfortunately, ethanol tends to attack rubber and to reduce its flexibility. Any rubber components in the fuel system must now be made from alcohol-resistant rubber compounds. Older rubber hoses, primer bulbs, gaskets, etc., should be replaced.

Installation

The primer bulb is typically installed in the flexible rubber fuel hose feeding the engine. The fuel hoses are pressed onto the inlet and outlet fittings and retained with clamps. It goes without saying the engine fuel system must be leak proof, but it is also necessary that it be air-tight as well. Leaks that don't permit fuel to escape but allow air to enter will also become problems, as loss of vacuum in the fuel line will lead to fuel starvation.

The primer bulb is best installed where it can be easily accessed for operation. In most pre-rigged boats being delivered these days, the primer bulb is seen located within 12-18 inches of the engine. This is especially common on boats that have internal fuel tanks. Boats with on-deck fuel tanks may have the primer bulb located at the tank end of the fuel line. Of course, the primer bulb must be installed in the fuel line with the fuel flow direction arrow oriented properly, pointing toward the engine.

The primer bulb is generally placed close to the engine, and usually downstream of any fuel filters or water-separtors. Many new engines are delivered without a fuel disconnect fitting, and instead just provide a short stub of fuel line from the engine cowling. This makes a natural place to connect a primer bulb.

Orientation

It is also advantageous if the primer bulb can be position in such a way that during priming it can be oriented vertically, with the direction arrow pointing skywards. This will allow gravity and the weight of the fuel inside the primer bulb to help with the operation of the one-way valves. If the primer bulb is oriented with the flow arrow pointing downward, gravity and the weight of the fuel in the line above the inlet check valve may spoil its operation, and the primer will not work properly.

This subtle but important point—orienting the primer bulb skyward—is often overlooked in many installation, but it really helps the primer bulb to do its job. This trick was shown to me by an experienced Mercury outboard mechanic, after I complained that the new primer bulbs he had installed did not work well. The difference in results is amazing, and just by changing the orientation of the primer to vertical, its operation is much improved. In just a few squeezes it should be possible to fill the bulb with fuel.

Operation

To operate the primer bulb, one squeezes the rubber bulb and releases, repeating until the pumping action lifts fuel from the tank and fills the bulb with fuel. As the bulb fills its resistance to squeezing changes, and the firmness of the bulb signals the operator when the primer has done its job and primed the fuel line.

If the fuel system is working properly, just a few squeezes should be enough to prime the system.

Primer Bulb As Diagnostic Tool

The primer bulb is also a diagnostic tool that will tell you a number of things about your fuel system.

Engine Stalling or Running Roughly at Speed

If your engine begins to stall or run roughly several minutes after starting and when running at higher speeds, use the primer bulb to force fuel to the engine. If this restores the engine to smooth running, you have a fuel supply problem. There may be a restriction in the fuel line, or your engine fuel pump could be defective. If this happens even at idle speeds, the primer bulb may not be working properly.

Primer Hard to Prime

If the fuel line is difficult to prime, you likely have an air leak in the system. Check all fuel hose connections. You could also have a defective primer bulb, or not be orientating the primer bulb properly during priming. A likely place to investigate is the fuel disconnect on the engine. Be sure the connector is properly seated and is making an air-tight connection.

Collapsed Primer Bulb

If the primer bulb collapses after the engine has been running or stays collapsed while priming this indicates a fuel line restriction upstream from the primer bulb. A defective check valve in the primer bulb could also be the cause. The fuel line filter or the fuel tank pick up could be blocked. A blocked fuel tank vent could also cause this. A quick way to check the tank venting is to temporarily open the fuel tank filler fitting. For some reason the fuel tank vent line thru-hull fitting is a favorite spot for wasps to build mud nests.

Primer Bulb Never Gets Firm

If you can fill the bulb with fuel but it never gets firm, you probably have a fuel leak downstream of the primer bulb. This could be a stuck float valve on a carburetor, or a fuel leak in the engine fuel pump. Many engines use a diaphragm pump, and if the rubber diaphragm has a pin hole leak, gasoline will be forced past it into the engine crankcase. It should only take a few squeezes to get a primer bulb to become firm.

If you have a fuel disconnect downstream of the primer bulb, disconnect the fuel line from the engine and see if the primer can now be pumped to firmness. If so, your leak is in the engine.

Primer Bulb Gets Soft While Engine Is Running

Most primer bulbs will lose some firmness when the engine is running. This is normal. The bulb should not run dry of fuel or collapse in suction, but it will tend to lose some of the hard firmness it had when initially primed.

[fitz73222]

Thank you Baby for the explaination but nothing is mentioned about the bulb going flat because of a bad fuel pump which I already know. To prove this theory, fire up an engine on a remote fuel tank, now close the valve on the top of tank and in about 5 minutes the bulb will go flat and the engine will shut off. In 40 years of working on outboards, I've never seen a bulb go flat from a fuel pump issue so thanks for the eye opener!

[baby1]

 this is the best information I can find

HOW TO: Testing your boats fuel system. 





Note, this was originally posted courtesy of Don S. Minor edits and pictures added by CaptJason

 A lot of you folks out there seem to be tearing into carbs quite a bit. Before you choose to open up a carb, you really need to look at what's feeding the carb first, and that is the boats fuel system.

 Boats seem to have a lot more problems with the fuel system compared to the auto industry. Mostly due to all the "Marine Specific" parts in the system required to make the system safe in a boat. Anti-Siphon valves, special fuel lines, water separating fuel filters just to name a few.
 Below is a way of testing your boats fuel system if you suspect a problem. Note, this is for testing the BOATS fuel system which includes everything up to the engines fuel pump. With any boat, you have to separate the BOAT side, from the ENGINE side, as they are 2 completely different things. It assumes (I know, bad choice of words, but you have to start somewhere) the fuel pump and carburetor are working properly.
 Most of the information below was just copy and pasted out of a Volvo manual. All I did was put it in one place and separate it from other information.


 The Snap-On fuel gauge mentioned below is not a necessity; any good fuel pump pressure/vacuum gauge will work or even a single vacuum gauge. I (Don S.) have one from NAPA that works fine for the tests. I (CaptJason) have a Matco branded one, and it works fine as well. If you do not know what gauge we are talking about. It is often called a compound meter. It will measure pressure and vacuum, and be made to be used on fuel systems. If you can not find one, they are available at Sears under the "Actron" brand name here.

http://www.sears.com/shc/s/p_10153_12605_00902179000P

 As with any special tool... Not everything will come in the box.You also need to make up some proper fuel hoses for YOUR boat... because EVERY boat is different. Most of the extra brass connectors and fuel lines/vinyl lines can be had in between NAPA auto part stores and home depot/lowes type stores. Since you probably won't be working on very many, get the right stuff and make your job easy and safe instead of difficult and dangerous. You will need specifically sized fittings that will fit the fuel pump, and or the boat side fuel line or tank. Don't even think about cutting that steel line and hose clamping a tee for the gauge to it. Steel line should not be cut. Besides, we are testing the BOAT SIDE fuel system, where steel line is almost never found. If you were TESTING THE ENGINE SIDE fuel system, there is often steel line (and should be) and this thread does not cover ENGINE SIDE fuel system testing.

 My rig is seen here. I have the compound gauge, a brass T-block, an appropriate sized adapters and barbed nipples. I have a rig for 5/16th and 3/8th sized fuel lines. Those are the 2 most popular sizes. Very small outboards may have 1/4 inch, and a plastic T is typically fine for those situations.

[/IMG]


 A couple of problems that can be caused by a defective BOAT SIDE fuel system is.
 1. Low WOT (Wide Open Throttle) rpms. (When the engine used to be fine)
 2. Engine dies out when running at any rpm.
 3. Engine surging at any rpms.

 Step 1 - Testing for an airbound/leaky system
 This is the easiest of the tests. For an airbound system all you need is the clear vinyl line and a couple of barbs. You do not need the gauge at this point. Splice the clear test line (and I say TEST LINE, because this is for testing purposes only, NO BOAT, should ever be used with vinyl line outside of TESTING PURPOSES!!)
 Start the boat up and run it. Look for bubbles in the clear line. A small bubble here or there every 20 or 30 seconds isn't a big deal, but if you get a somewhat steady stream of bubbles then you have an air leak. At this point shut the motor down and go through every clamp (most fittings should be double clamped) every fuel fitting, nipple, barb... etc all the way to the tank. Metal connectors and threads should be disassembled, cleaned and pipe doped. Do not use teflon tape, it has no place on a boat. But pipe dope with teflon works fine. Start up and retest. If you still have bubbles you missed something.... go back through your work.


Vacuum Testing Fuel System.... In other words... testing the BOAT SIDE fuel system for a restriction.

 To be 100% accurate.... This test must be performed with engine under load; which means running in gear on the water(not muffs) or in gear connected to a dynamometer.(which your probably not going to have... so do it on the water)
 Ensure that all fuel line connections are leak free, as per step 1.

However... this test can also be TRIED (and I can't stress the word TRIED enough) on the muffs, as long as you don't exceed 1500 rpms for more than a minute with good water supply.
 This is CaptJason's rule.... Don S. may have a different rule.
 I say you can TRY it because on a lot of boats you'll see the gauge indicating a problem immediately. If the gauge does not indicate a problem immediatly... you should still go through the test with the engine under a load as previously stated.

 1. Install Vacuum and Fuel Pressure Gauge such as Snap-on® Tools MT311JB or equivalent, and 8 in. (20,3 cm) of clear, fuel resistant vinyl hose into the fuel line at the filter fuel pump inlet fitting. (NOTE: On some engines there is a filter hard plumbed to the fuel pump, these engines should have the gauge attached to the fuel filter and not the pump itself. )
 2. Start engine and allow it to reach normal operating temperature. Run engine at full throttle (NOTE: As noted above, this is done under a load, not on muffs, if you do this on muffs, or in neutral, or not on a dyno... you take the chance of over revving, having a runaway, or just plain blowing up your engine... and possibly yourself!!!) for at least 2 minutes; observe vacuum gauge reading and check clear hose for air or vapor bubbles. Gauge reading must not exceed 4 in. of mercury (Hg) at any time, and there should be no bubbles visible in the clear hose.
 If you are getting bubbles check for.
 1. All metal fittings
 2. Wrong type hose clamp used (Use mini clamps not standard size clamps, double clamps on everything in between the pump and the boat)
 3. Filter seal leaking
 4. Pickup tube in fuel tank defective.
 5. Loose, cracked, corroded fittings in the system (including the tank and fuel filter or fuel line)
 Repair or replace suspect part, then make another vacuum test to verify repair.

 Gauge reads 0-4 in. of mercury (Hg) (vacuum)

 1. If you have air bubbles.... then you still have an airbound system. And you need to repeat step 1.
 2. 0 to 4 is normal, but no more than 4 Hg. If you are on the high side (close to 4) Then you either have a really really big boat with big gas tanks and that's okay....... or you have a problem/restriction causing the vacuum reading to read on the high side. If you have more than 4 Hg, then you have a restriction.
 If you fall in the latter. The 3 major things, most common things are a....
 1. Clogged fuel filter/fuel water separator
 2. stuck anti siphon valve
 3. clogged fuel tank vent
 If you are Joe the Boater with a smaller/mid size boat, start with replacing the filters first and checking the tank vent and retesting.... then move on to the anti siphon valve if need be and retest. Ideally you'd like to have the vacuum restriction as low as possible.
 If you still have a high reading. Its possible that you have a screen on the pickup in the fuel tank that is getting clogged. You can try forcing some compressed air down the fuel line to knock the stuff off (MAKE SURE IF YOU DO THIS THAT YOU TAKE THE FUEL TANK FILL CAP OFF!!!) Unfortunately though, if you have that much junk in your tank (and older boats will, especially steel tanks) the problem will likely resurface.
 If you still have a high reading, replace your fuel lines. It isn't common to have collapsed fuel lines, but it happens once in a blue moon. What is your favorite color moon? Make sure you replace lines with  Coast Guard approved type A1 fuel line Your going to have to get that at a marine store... the townie auto parts store is not going to have it.

 To refresh
 Gauge reading exceeds 4 in. of mercury (Hg)
 Supply side of fuel system has a restriction. Check points of possible
 failure as noted below.
 1. Water or debris in fuel/fuel filter
 2. Fuel pickup tube and screen blockage
 3. Fuel tank vent blockage (this one can be a biggie...... i swear... a mud doggers only purpose in life is to build nests in tank vents)
 4. Plugged external canister or carburetor fuel filters
 5. Inoperative, restricted or incorrectly sized anti-siphon valve
 Repair or replace suspect part, then make another vacuum test to verify repair.
 6. Bad fuel lines(uncommon)

 Testing the fuel pumps ability to create a vacuum
 The next biggest boat side (but semi-engine side) test is to make sure your pump is actually capable of pulling a vacuum. A fuel pump has to create suction in order to work. It is fairly common to have a pump that is worn out or clogged enough not to generate enough suction.... And the most common symptom is lack of WOT or WOT surging in carbed engines.
 This is another good test to do because alot of times when your testing the fuel system all you see is air in the clear line, as in no fuel, just air. If all you see is air in the line, then you either have a major air leak in the boats fuel system, or you have a fuel pump that's not capable of creating a vacuum.

 What I (captjason) does is this...
 1. I hook up my test rig in between the fuel pump and fuel(fuel/water seperator) filter.
 2. I start the boat up and let it warm up for a minute or 2.
 While the engine is running I pinch fuel line shut in between the FUEL TANK and the COMPOUND GAUGE. What should happen is the engine should run for a bit and the gauge should register that the fuel pump is TRYING to pull through the restriction that you made with the pliers.



 You need to have the pliers in the right spot as stated before. I use self locking hose clamp pliers, but any old pliers will work as long as they are not so serrated they will puncture/mar the fuel line on the outside.

 I have a "35 69 10" rule (Don S's) rule may vary.
 -What I mean by my rule is this. If an OUTBOARD fuel pump can not generate 3 to 5 inches of Vacuum at idle or high idle over the course of 10 seconds, then the fuel pump needs to be rebuilt/replace.
 -On a sterndrive with a conventional mechanical type, or suction type electrical fuel pump, If it can not generate 6 to 9 Hg of vacuum over 10 seconds then it needs to be replaced. A bit under the my rule isn't a problem as long as the engine hits WOT properly. If it doesn't, then the fuel pump is an item of consideration.
 This test is mandatory if all your seeing is air (no fuel) in the test line. It is the only way to know if the fuel pump is trying to bring fuel in and cannot because of an air leak, or if it is incapable of bringing fuel in.

 Here is what the face of the gauge looks like...


 Good luck guys and gals!!!
   
just because you found it that way does not mean it is supposed to be that way.

[baby1]

link http://forums.iboats.com/forum/engine-repair-and-maintenance/engine-frequently-asked-questions-faq/290505-how-to-testing-your-boats-fuel-system?t=283363