1986-87 Johnson 120 V4

[Joey]

On a 1987 Aquasport 170 Striper
So, when I bought this bought, the sea trial was fine, engine ran like a new one.

I took the boat out for the first time today on my own.  As a note single-handed launching and retrieval is a breeze.  Now for the motor details.

I ran for about 35 min at 4500 rpm, ran great.  Temp gauge was in the center-line, pissing like a race horse, and piss water was luke warm, if that.

I hit some chop and then the motor started spitting, like it was running out of gas.  Ran it up to 5000 rpm and it started to sound like it was running out of gas.  Backed off the throttle to idle and it was fine.  Ran it up to about 3/4 throttle and just and it hull started to jump out of the hole it sounded like it ran out of gas and quit.

Motor started right back up.  I ran back to the dock at 2000 rpm and it ran fine the entire time.  If I pushed the throttle up higher it acted like it ran out of gas.

I have not done anything, just got home.  My initial thoughts are to pull the fuel filter, and pour it out, see what my gas looks like.  I will also pull the plugs and take a look at those.

Anyone have any thoughts on this?

I should also note, this is a VRO engine, the VRO is disconnected and the oil is mixed in the tank as fuel goes in.  Before I went out I topped the tank off with 9.5 gallons and the proper mix for that amount.  The previous owner had just filled the tank prior to my purchase. and also put the proper amount of oil in the tank.

--Joe

[slvrlng]

Sounds like you have crud in the tank that gets loosened up when you hit rougher water. Might need to be drained and cleaned.

[fitz73222]

Replace the water separating fuel filter if so equipped.

[Georgie]

X3.  Those sound like textbook contaminated fuel symptoms.  ok at low rpms and flat water, but the second you increase RPM or hit a chop your combustion begins to fail.  Hopefully you have an in line filter or, even better, a water separator w/clear bowl.  As Lewis mentioned, you may need to drain all your fuel to be sure.

[Joey]

Thanks for all the info.  I will start with the fuel and post my results as I progress.  I do have a fuel water separator (spin-on oil filter looking type with no bowl), and it looks like it has not been changed for a while.

Perhaps I should replace with a unit that has a bowl that can be drained and is visible as to the water content in the unit.

--Joe

[fitz73222]

Joe,

For this exersize get 2, cheaper Seachoice or Sierra replacement filters from Walmart and see if it cures the problem. If you do have contaminated fuel, it will clog those filters up quickly. If it cures the problem then upgrade later to the nice Parker or Moeller filter/bowl assemblies. There may be nothing wrong with your fuel and it was just time to change the filter because of a long service interval.

[Joey]

So, I removed the fuel separator filter and poured it out.  Holy crap, it was a mess.  Here are some pics, and YES, this glass was spotless clean and clear BEFORE I poured the fuel from the filter in it.



and..



I also pulled the plugs, they did not look bad.  I also tested the compression and results were:

125
123
124
122

I tested to see if I had spark, and I had spark at every plug.

No doubt that fuel is an issue, I will grab a couple of filters.  Anything else I should check while I am doing this?

Joe

[fitz73222]

Compression is perfect assuming your numbers came from no more than 4 compression stroke cycles; not just cranking the engine over until the gage stops climbing. Put the new filter on it and go for a test run. If it starves for fuel within a short amount of time but has improved, run the engine on a standard 6 gallon tank with known fresh fuel to verify there is no other fueling issues and if it runs fine after the switch to the remote tank, dump the fuel in the main tank (responsibly) then refuel the main tank with 12 gallons of fresh fuel, replace the filter again and test run. By design, some of the replacement fuel filters will react and intentionally swell and shut down flow when the filter pleats become saturated with water in order to preserve the powerhead from destruction. Racor filters have this "water overload" feature.

[dbiscayne]

check the fuel lines from the tank to the engine too, I've had the same symptoms from the fuel line collapsing from the suction of the fuel pump.  Couldn't see it happening from the outside, but the inner liner of the fuel line was mush.
If somebody squeezed the primer ball as I tried to get up on plane it'd run pretty good, otherwise it wouldn't give much more than idle.

[flounderpounder225]

I've seen that crap before, if it was me, I would bite the bullet, get the tank emptied and cleaned and be done.  If there is a fuel polishing service available, I would go that route depending on how much fuel you are carrying, I was plagued by that nasty stuff, got towed in twice.  Just my .02$

[Joey]

Compression results were taken on about 3 revolutions, certainly no more than 4.   I couldn't see the gauge until after the fact, so I just bumped the ignition key with a quick "one thousand one" count and checked the gauge, which is the way I was always told to do it.

[Joey]

So I wanted to give an interesting update.

I changed the filter, even though I filled the filter with fuel and primed the line, the motor was a little hard to start.  Took about 6 or 7 tries, but she started up.  I ran her for about a min with a little bit of hesitation out of her and then it cleared up.

I ran her for 45 min in some light chop at 4000 RPM (25mph) and only every now and then did I get a little hesitation out of her.  For the most part (99% of the time) she ran perfect.  I had another boat with me, a friend with a brand spanking new Triumph with a 70hp Yamaha on it that has only been in the water 3 times, and he just bought her 2 weeks ago.

This is the funny part.  He came out with me to tow me in if I had any problems and a mile out his motor gave out.  I ended up towing him back to the dock.

I wanted to thank everyone for the assistance in getting my back in the water.  I think I will have call around about getting my tank cleaned out as well.

Joe