I give up
 

Thought I found a fuel system problem, but no effect. Port motor runs at the dock, will not pull under load. Ran fine when I put it up last winter (doesn't everyone say that?). Stbd motor running fine.

Will entertain offers for new set of low time motors, installed, tuned, tested, dock-to-dock your service, or offers to buy the boat where is as is.

-Greg

1989 32 Scorpion
Twin 250 Yamaha 1993 Carb (one good, one I havn't a clue)
Comes with new rub rail (not installed) and new graphics (not installed)

Greg,
Had the same problem on a big block a few years ago. Turned out to be a clogged fuel filter (and I mean clogged). It would idle, run on plane for a while and then crap out and not restart until the clog settled back down....
Hope this helps,
Ken

Not really an outboard expert, but here are a couple of ideas. First it may just have a bad water pump impeller, it may appear to move water, but under load it does not push enough water, motor gets hot, eletronic retard most outboards have, kicks in, keeps the motor from burning up. Second idea, could have a bad part in the ignition, under a load it breaks down. Ignition parts ie, coil, power box, ect should be able to be ohm checked with a service book. Lastly may the excelerator pump is bad on the fuel system. These are things over the years we have had to repair on our pontoons if this helps. MR

Thanks for the ideas, but already tried most of them. New fuel filters last wekend, fresh fuel, oil tanks are full, engine temp right on normal, pulled and cleaned electrical connections. I have no way to test the electronics and no luck getting anyone I trust to come either. It won't pull under load long enough to get on plane, but will rev to 5k at the dock in gear with the prop half buried (enough to keep the water pickups under water).

I tried to test the fuel pumps/system to see f I could find something good on the good motor and poor on the bad one. Put a vacuume/pressure gauge on both motors. Neither motor shows any vacuume on the inlet side of the water seperator, nor any pressure on the outlet side of the fuel pumps. Based on the readings I wouldn't expect either motor to run, but both motors do run (long enough they would suck the bowls dry if they wern't pulling fuel) and the stbd one will pull to 4k RPM trying to get on plane while the port won't go over 2k. Guess outboard fuel systems just don't run high enough pressure to register/measure.




-greg

Sounds like something is either preventing fuel from entering the motors, or preventing exhaust from exiting.

I'd Seafoam the motors, could be excessive carbon buildup, especially exhaust ports and tuner, or gum/varnish in the carbs and lines in the motor. Fill the fuel filters with it and spray it directly into the carbs. Merc and Yamaha have their own brands but I like Seafoam. Works best with boat out of the water.

Also check to see if the fuel lines/primer bulbs collapse under load, it might be time to replace. Easy check is with portable tank to motors.

Any warning lights/horns?

That must be a sight.

The motors probably only have 30-40 hours since I last decarboned them (and that time it didn't seem like there was any buildup that burned out) and they are usually run at high RPM, don't spend much time at idle. I store it over the winter with the carbs dry to minimize any varnish possibility. Under load at the dock I could see the carbs flowing from the high speed jets, so they aren't blocked.

I pulled the plugs and one had some carbon the others all were fine (I found that one carb had the idle too lean, seems to be better since I opened the idle screw the same as the other carbs).

The primer bulbs were replaced last year, but I may try a new one as it's easy to do. I thought about a fuel restriction, which is why I tried to check the vacuume on the system upstream of the pumps, but didn't get any reading. Either the pumps don't pull at all (and they do keep the bowl filled) or their isn't any restriction on the intake side. Both motors read the same, and one motor pulls fine so that test didn' seem too conclusive.

Problem is I really don't have enough time to keep fiddling with them and so far have made no headway on finding anything.

Thanks -Greg

It kicks up a nice rooster tail filling all the way across the creek!

I know nothing about outboards but if this was a car I would be looking at ignition.PM me your address and I will send you an inline spark checker.Ignition wires will do exactly what you described

1993 yamaha 250s?????

first thing i would check is the stator....from there hav a QUALIFIED yamaha tech rebuild and tune the carbs....also make sure you are running the right RESISTOR plugs that yamaha reccommends...also as a easy chek clean and tighten alll battery connections....i guarantee one or two of those problems are lurking and causing you this trouble....

if you think its a fuel restriction switch fuel lines from one motor pickup to the other....if i can help in any other way just ask...

sounds like carbs to me...very common with Yams that have sat for along time ,rebuild carbs on the port motor, had a 94' 200 yamaha if it sat more than 3months it would do the same thing, good luck

What are the fuel pumps like on those motors. The older OMC pumps would fail and just fill the lower 2 cyliders with fuel. Would idle find but wouldn't pull under load since the plugs would just get washed out.

George - Wish I could find a qualified Yamaha tech to work on them. The one I tried knew less than I do. The good mechnic I had found moved out of the area I've heard some good reports about the shop on Kent Island, but I have no way to get the boat there (no trailer and they have no water access), and their on-site tech was booked a couple months out making it pretty unusable. It has the spec plugs, checked and all but one was burning right one (one had some carbon foul, found the idle screw on that carb was too lean). Also replaced all the plug caps last year as found a couple that had gone bad. I'll look at the manual and see if checking the stator is something I could undetake or not. I've rebuilt the carbs before, but I can see fuel coming from the high speed ports this time, which was the problem when they clogged before.

First Gun - The carbs were drained for the winter storage to prevent them gunking up.

Garry - There are 3 pumps per motor, they were replace about 50 hours ago. I don't realy have a good way to test them. The mechnic who found a bad pump then has left the area, and I'm having a hard time getting anyone else with a good reputation to call me back.

-Greg

Ok, here's my attempt at checking timing advance. Even though I have a Xenon, battery powered timing light, it's still very hard to see the timing marks in the sunshine.

Both motors: I thought I'd use the inductive pickup to check that the coils are firing first. The port side cyls 1&3 (can't get my pickup down between the cowling to try the bottom cyl) will trigger the timing light. The stbd cyls 2&4 won't trigger the light at all (??). Motors were unloaded at 2000 RPM. Seems strange, but again the stbd behaves fine and it shows the same as the port, and the stbd is running fine. The motors do not sound like they are missing, so I can't figure out why the stbd cyls won't at least trigger the timing light.

at 2000 RPM the timing is at TDC. If I slowly raise the RPM to about 3000 the timing still is at TDC +/- a degree (it's really hard to see the marks). If I just blip the throttle I can see the timing move to 2-4 deg off TDC to the (-) timing mark side (but that is the short side of the scale and only goes to 10, it is the opposite direction that I would expect since the (+) side of the scale goes past 20). for a second or two, then it returns to TDC. The stbd motor movement is pretty smooth, the port motor is very erratic and jumps around a lot.

Maybe one of the sensors to the timing compter is bad or has a bad connection? I think there are 3 thermostat switches, a crank trigger, and according to my manual a knock sensor. I'll see if I can find any test specs for any of them.

-Greg

Greg,
It is sounding like an advance problem.. one way to check if it is fuel.. Saw a guy do this 30yrs ago.. Ran the motor with the cowl off and used a squirt can with gas and oil mix.. shot it right into the carb.. When he hit the one that wasnt working.. it made power.
In your case a shot of fuel in the carb might give some response.. But if I rememeber from my outboard days.. the timing should move around more than just a couple of degrees.. ???
if you have a knock sensor.. you should be able to see the timing retard when you tap the block.. I would think..
I hate when there isnt anyone in the area that has knowledge.. good luck with it..
are there any OB sites that may have more info? ..

D*ck

try scream and fly.......A lot of outboard freeks there......

Tried Scream and Fly with problems in the past, not many Yamaha guys there. If I knew how hard it was going to be to find good Yamaha service outside of FL I would have bought a boat with Mercs. If someone made me a good deal on some used 250/300 Mercs I'd switch just because I do know some good Merc mechanics in the area.

-Greg

If I were smart I'd give up, but I'm too stupid/stubborn so I keep trying to find something wrong that I can fix.

I found specs/tests in my service manual for some of the sensors that feed the timing computer, so thought I'd try to check them.

thermoswitch - my motor doesn't have anything with the wire color codes shown in the manual or in the location shown in the manual (nor does it have the style connectors shown in the manual, most of the CDI connections are bullet connectors not molded plug connectors). There is a boss there, but it was never drilled or threaded. On to the next sensor.

throttle position sensor - it was replace a couple years ago, but tested it today and it shows in spec.

crank position sensor - couldn't get to the connector without removing the voltage regulator and starter relay and didn't have that much daylight time left so let it pass for now.

knock sensor - my VDM doesn't record low enough voltage to check for 200 mVAC, but I could see the measured resistance change as I tapped the sensor so it is generating some signal, just can't tell exactly how much.

Since it has so hard to see the timing marks in the daylight before, I decided I would try to check the timing again last night as it was cloudy and getting close to dusk. With the darker conditions I could see the timing marks much clearer, and the timing was pretty stable. I had it in gear under load this time instead of free running like before, being very carefull not to fall off the boat as it still moves around some even running on the lift with the props just submerged. Idle timing and timing near full RPM were on spec at -7 and +18. It clearly was advancing today as I hit the throttle, and coming back to retarded as the RPM dropped back to idle.

It is "possible" that unplugging and replugging the sensor leads might have cleaned a bad connection. It is "possible" that it is behaving randomly (I really don't believe in or trust electricity). But, maybe the "fuel problem" guru's were right. I bought a stand alone tank on the way home today and filled it with gas, so hope that (weather permitting) I can try that on Wednesday. I ran out of light to test it today.

-Greg

Garry,

Next time I don't listen hit me in the head a little harder. I finally decided to try changing the fuel pumps (had tried about everything else) and even though they are only a couple years old (and not that many hours) the middle fuel pump has a hole. You can cap the outlet and blow in the inlet and hear the air coming out the diaphram driver port.

I hope to get out on the water later to day to test it again and make sure, but I'm hoping that is the (only) gremlin.

Thanks - Greg