Yamaha 9.9 Missing/Limping/Weak once warmed up

[Andrew Bienhaus]

Good Day all, and thanks for ideas, in advance!

I got to this forum via Google, with hits on similar challenges with the same motor, but none of the posted solutions so far, seem to have cured it. :-(

So, here we go... as requested, fresh posting.

1985 Yamaha F9.9SK 4 stroke
I don't have a lot of history on it, but in efforts to repair and get rolling again, here's what we have done.
There was no spark, so I used a voltage adapter and DVM, to diagnose "bad CDI". Managed to get a used CDI, matched up all the wires, and we have spark and life!

Carb got well cleaned out before that, and jets are clear.

Took some priming, and had to push some oil out of the exhaust (probably was stored improperly) and got it fired up and running.

Good stream of water from the one jet. (is the second jet supposed to be squirting? or is it some sort of overflow?)

Got it on the boat, and went for a run. Pulled out nice, ran down the lake.
Get about 7 mins down the lake, and it bogs down to next to nothing... limping... sounds like firing on one cylinder, yet, if I pull a spark plug lead, neither one of them kills it... (both obviously does)

Fussing and fiddling, and I might get it to run full tilt... briefly.
But generally once I get it to run (which isn't super easy) I have to limp back to the dock.

Running tied to the dock, I can warm it up, and run, and reproduce the problem.

And, the onset of the problem... is rather quick. It feels like electrical cut out, deliberate almost.

So, the web hit here on the forum, that suggested oil pressure cut out switch replacement. (the one that has a wire running to the CDI, and the light on the front)
There is no light, ever... but maybe it's dead. (tell me if that is worth looking into)

Marina up the road 30 mins had a Yamaha replacement oil pressure sender, so I have now also replaced that.
Same issue... at about the same amount of run time.

Oil level is good. Fuel supply is good.
Squeeze ball doesn't affect anything.

It feels like a failing spark, yet, not.

While running back on limp, one of the times, I swear it felt like it overheated and siezed... yet water coming out is a nice temp (just slightly warmer than lake temp)... and after checking everything, I was able to start it and run it again.

Open to other things to check next... again, when it runs, it runs perfectly.
As others have described in the past.

Thanks guys!
Am close to the motor for a few days here, hopeful we can find something obvious or simple to check?

Andy

 

[99yam40]

use the DVA and meter if you want to rule out low or no voltage when problem shows up
timing light to see if timing stays in spec

compression should be checked to rule out damaged cylinders/pistons.

If all is good then you are left with fuel

 

[Andrew Bienhaus]

ok, where would you probe for voltage when problem is there? (before coil, at spark generator, pulse generator...?)

and, is there any temp related conditions on this motor, that might restrict the CDI/spark?
I can see a thermostat listed in the parts list, but not sure if it's a mechanical flow thing... or electrical?
If mechanical, is it maybe not opening somewhere? (is that a possibility, and worth checking)

thanks!

 

[99yam40]

does this motor have an indicator if it goes into rpm reduction mode?
does it work as it should?
What does it tell you when this happens?

Monitoring DVA voltages into and out of CDI will tell you if there is a problem with ignition system.
A KV meter/tester is needed to measure spark voltage from coil to plugs, but not many have one.

I am not sure if timing is retarded or if spark is affected to reduce /limit RPM if overheat or oil problem shows up

thermostat is mechanical
needs to be taken out and tested or replaced with new if overheating
also water pump needs to be reworked with a kit and inspect housing to see it it needs replaced

Tell tail comes out before running threw motor so it does not show the temp of the motor . it is just an indicator the the water pump is pumping

 

[Andrew Bienhaus]

Thanks.
Should the second tell tail hose also be dumping water? or is that an overflow? (it has two tubes running to the telltail exit point, but only one is ever streaming)

 

[Andrew Bienhaus]

Thermostat removed and tested, working. (boiling water from the kettle makes it open in a bowl)
Still don't fully understand second water dump tube, but maybe only opens and dumps when the thermostat is open? Or is an overpressure dump? (don't have access to diagram)

Have validated through Yamaha owners manuals for this year and similar, that pilot light for oil should be on at all times when there is good oil pressure. (bulb/led is blown however, it would seem, no resistance, open circuit)

To quote the book... if you ignore the lack of oil pilot light, the motor will indeed go into limp mode, where it runs roughly and limits you to 2000rpm.
(paraphrased quote from yamaha manual)

So, this is indeed what I am seeing.

Given where the oil sump is, unlikely point of failure. (low, and always in oil bath)

Have dumped oil, not pretty, (previous person working on it, apparently said they changed fluids, but meant only lower unit oil) so I am now suspecting oil supply.

(for the internet researchers...)
The oil drain plug is also an oil filter screen, with o-rings, and all.
Replaceable, but also brass screen, so it's cleanable.
(now has o-rings pulled off, and is soaking in lacquer thinner)

Will report back later... want to let it soak for a few hours, in case of any varnished-oil-crap buildup.

And then will refill, and pull a few times with oil pressure sender out, just to make sure there is no "gunk" sitting in that passage.

the problem is 99% oil pressure cut out, I am pretty sure.

Andrew

 

[Andrew Bienhaus]

So!
Good day all, and to those either following up, or, now finding this post via google or the like.
To my fellow Cannucks, happy thanksgiving!

I hate it when folks leave things hanging, and don't post the final results or solution to a problem... but the problem expanded after the last posting, and, well, I had to prove out a few things first.

After the oil drain/clean from above, I had a good reading on the DVM from the oil pressure light wire. (light still broken, more on that below)
But, something new in the fuel supply popped up...

Ended up pulling the carb apart again, to find orange sand in it... and after much analysis, Ethanol gasoline had been used, there was water in the fuel, etc, etc, that whole old crime. So if you ever have trouble keeping it running, check that... there was a layer in the bottom of the float bowl.
There are a million other posts about ethanol "enhanced" gasoline posts on the web, you can see photos, etc, but we'd never really run into a problem... urban legends, things for people to whine about, etc.

Until now... :-(
I suspect that the new refurb metal gas tank we were using with this motor, was the problem. The gasoline was literally Gatorade-Orange colour... so likely absorbed some water, and then rusted the inside of the tank...

Anyhow!

once carb cleaned out, tank flushed, non-Ethanol fresh gas in the tank, lines flushed, filter replaced... she started up and purred like a kitten.
adjusted some idle stuff, and out for a boot around....

Ran for 30 mins, full tilt, up and down the lake. Solid voltage reading on the oil pressure sender.
Multiple uses since then, no issues.

So, even if you have a dead oil pressure light, you can still use a DVM (voltage meter) on AC 0-130v setting, to check the oil pressure output.
In my case, I believe the clogged oil filter screen on the drain screw was our culprit.
The motor was indeed cutting out into "limp mode".

As for the little green light, I have a replacement.
They don't make them any more, so you have to be ready to do a little custom work, and maybe solder... but I got an LED replacement bulb from www.superbrightleds.com - good guys, used them for lots before too. Even comes in green!
(their car headlight replacement LED bulbs are awesome!)

The Bulb:
https://www.superbrightleds.com/more...ofit-lan/2541/

part number BA9s-x-x-xVAC-LAN - select 120vAC, Green. (assuming you like green - but it also comes in red, amber, blue, and two shades of white!) ;-)

Anyhow, I had to cut and drill out the old pilot light housing, and then soldered the existing signal and ground wires onto the bulb directly, and then put it in with some hot melt glue to seal it up. (silicone would work just as nicely or better, but I was impatient)
Easy to test, just plug into 120v wall outlet.

Anyhow, back on the motor, it flickers even when you've pull started a few times... and as soon as it starts running, the light is on. Flickering, but on.
Drive and rev it up, and it's on solid.
So it's a GOOD indicator, in that if you see it flickering while at wide open, you might want to look into that.. ;-)

Oh, best part, these LED bulbs are 98 cents a piece... so you can afford to buy some spares, not that you will likely need them.

Other simpler option is to just drill a small hole in the "dash", and mount the LED directly into the new hole... I had already removed the old light and lead and taken home to the workshop, so that's why I went that way with "retro-fitting" it.



Have fun!

 

[ondarvr]

Thank you for the update, not enough people do it.

Very normal for small 4 stroke motors to act like this, they're very susceptible to junk in the fuel. Water in the fuel and bad tanks are the biggest challenge they see.

 

[Andrew Bienhaus]

yeah, the stupidest thing is that it's small enough to get past the fuel filter... or... I also suspect there may be something happening in the chemistry of the fuel when it thermocycles or just sits in the float of the carb, that caused re-crystallization. The filter was clean...

Anyhow, lesson learned.. have located gas station not far from cottage, that purposely has 89 octane without ethanol.

Even did some experiments where I left a drinking glass of fuel out in the open air, on a damp day, (under a porch roof) and over a few hours, enough water was attracted to the surface of the fuel, that it went cloudy, and eventually started to collect water in the bottom of the glass.
Good reason to have non-ethanol, and to keep breathing holes on tanks closed when not in use...