Outboard confusing issues

[fritz3000g]

Hi there,

I've got a Yamaha 9.9 hp 4-stroke on my Mac25, and it's been giving me hard-to-diagnose problems.

The basic symptoms:

• Runs fine for the first 10 minutes
• After 10 minutes, it sputters above 1/4 throttle

These are classic fuel flow issues. My first inclination was the tank or fuel line, then the engine compression, then the fuel pump.

What I've tested:

• Tank, hose, and pump ball all seem fine. The ball gets and stays hard when I pump it. When I open the carburetor bowl and pump the ball, copious fuel flows through.
• Fuel pump seems fine. When I disconnect both fuel hoses, I can't blow air the wrong way. When I crank the engine, sufficient pressure is being produced.
• Compression isn't out-of-this-world, but is decent for a 1989 motor (125 and 135)
• Carburetor is clean as a whistle - I thoroughly cleaned and soaked it. Also, it idles like a dream, and I've never heard of carburetor issues which didn't affect idling.

One curious symptom is that pumping the hose ball when slightly above 1/4 throttle seems to help. However over 1/2 throttle pumping the ball does nothing. Given how much fuel the ball pumps through the carburetor bowl I would have thought it'd do more.

Any ideas on what else I could try?

[Ponaldpe]

Have you made sure the tank vent is open? Fuel filter ? Soft fuel line collapsing?

[Hamin' X]

Check for inline fuel filter and replace if found.

~Rich

[Ponaldpe]

Gleaned from facebook "Macgregor 26 Owners" Page.

John Dekkers
6 hrs
Oh the joy a 26 cent o-ring can bring! For 3 years since we purchased our 26X I have struggled with fuel starvation problems. There always seemed to be air in the system and the problem was worse when either tank ran below half full. I have replaced virtually every connection, filter and even the primer bulb in the pursuit of an easy solution. I finally had to get serious about fixing this as twice this year I have had the engine fail, leaving me in a precarious situation causing rapid deployment of the anchor. Using clear tubing I tested each connection to check for air until I sourced it all the way back at the fuel tank. After verifying that the barbed elbow fitting wasn't leaking I found that the pick-up tube in the tank is installed with an O-ring seal I'm sure many other X owners have these same "LPT 12" tanks by Tempo as they fit very nicely. Honestly I'm amazed these didn't leak from the factory as the plastic seam on the pick-up tube leaves a horrible sealing surface. After cleaning up the surface with a razor and a fine file I attempted to re seat the original o-ring and while results were encouraging it wasn't perfect. So, after learning these tanks are obsolete and parts are made from unobtaineum, I embarked on a quest for a replacement O-ring. After exhausting my local auto parts stores searching for a perfect match, I finally gambled on the closest one I could find which was a 7/16 O-ring that was much fatter than the original but much to my delight, fit right in with a little di-electric grease. How that skinny seal was supposed to work when a thick one fits I'll never know. Testing revealed - NO MORE AIR!! = ONE HAPPY SAILOR!!! So if you are finding air in the primer bulb (you can feel the difference) a lot and have some of these 20 year old tanks, I would make this your first stop. Hoping this might help others. Cheers!

[Seapup]

The older T9.9s have been know to get a vapor lock in the fuel pump when running that will do exactly what you describe. Let it cool and pumps & starts fine again. The new pump is designed differently to avoid the problem.

[fritz3000g]

Thanks for the advice folks:

@Ponaldpe: Yes, the vent is open. I don't think there's a fuel filter, though I can look back through the service manual again. There is a strainer, but it's clean. Fuel line isn't collapsing. The ball gets soft when it's sputtering, but retains its shape. You're saying that there's sometimes a fitting inside the fuel tank that can allow in air? That's an idea - I can take it apart and see if there's anything like that in mine. He said that he was feeling air in the primer bulb. How can you tell?

@Seapup. Hey, great find! Do you know if the new pump can be installed on an older motor? Is there a link to an article that describes this problem?

[sailboatmike]

One of my fuel can caps was faulty and while having the air screw open there was no air getting in, might be worth checking

[Seapup]

@Seapup. Hey, great find! Do you know if the new pump can be installed on an older motor? Is there a link to an article that describes this problem?

http://www.yamahaoutboardparts.com/foru ... h3901.html

I have a 1992 and 2007 Yamaha 9.9 and between the two have had a few fuel related issues. Still figuring one out right now...
A suggestion straight from Yamaha for the 9.9 is to install a 10 micron filter and water separator, do it. The generic 10 micron fuel water separators with inspection bowls are only about $20 online. A little moisture absorbed from the atmosphere can cause ethanol separation which will start corrosion in the carb. Once the finish has been compromised inside the carb its an ongoing battle with keeping the idle jet clean.

[fritz3000g]

Thanks SeaPup will do.

Any thoughts on whether it's possible to test to see if the fuel pump is getting vapor lock? I suppose I could run with the top open and pour water onto the fuel pump from a water bottle to keep it cool. Any better ideas?

Thanks for the tip on the water separator. Is that still needed if I run ethanol free gas? I suppose $20 and the freedom to use ethanol gas would pay for itself in a year.

Jer...

[Seapup]

Maybe run a test by bypassing the pump with a gravity fed line from a portable can above above the carb level.

[LoHo]

If the diaphragm in the fuel pump is old and brittle, it won't keep up at higher speeds.
My brother had a similar problem; someone had tried to siphon gas and lost the hose into the tank. It swelled and softened until it looked like a jellyfish and would cover the fuel exit hole, especially when the tank was low. Took a while to figure out, as it would work again a while after the fuel pump suction was relieved.

[Interim]

I have a 1994 t9.9, and have been having problems too. It will cut out when it is cold, usually recapturing its spirit and continuing to run, but sometimes dying. A squeeze of the fuel line bulb, hit the starter, and we're running again.

But my more serious concern is that I get fuel in the oil. Do you have this? I think they hold a quart, but I took out a quart plus half a cup last winter. I just changed the oil at the dock a couple weeks ago because it was happening again. I don't understand how the fuel gets in there; it must be going around the rings. I replaced the head gasket last year, which didn't help.

My new clue is that the cooling water, even after running at 1/4 to 1/2 throttle for 10 minutes, is still cold. I am wondering if I have a thermostat or other issue, so it isn't warming up, and we're not getting complete combustion.

All theories are welcome.

--john

[Tomfoolery]

My new clue is that the cooling water, even after running at 1/4 to 1/2 throttle for 10 minutes, is still cold. I am wondering if I have a thermostat or other issue, so it isn't warming up, and we're not getting complete combustion.

My BF50 Honda ran like that at the beginning of the season, in the driveway with a hose and muffs. The hose water was very cold, as it always is in the spring, but normally the pee stream warms quickly. Not hot, running at idle or some speed (unloaded, of course), but noticeably warmer than the near-ice water from the hose.

This spring it was cold. Pulled the thermostat, and it was stuck full open. Put in a new one, and it warmed right up as it usually did. Didn't notice it 'making oil', though, but it never got out of the driveway like that, so no history with running it that way.

So there's that.

[fritz3000g]

Mine gets plenty warm - no problems with it running cold. But I do get some fuel in the oil. I've been confused by this, since the engine compression is good making me think it's not the rings.

[Interim]

That's interesting that you are having the same issue. Can it be related to your fuel flow issue?

So how can fuel get in the oil, if it is not past the rings, and the headgasket is good?

I don't know the pathways very well.

--jf