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Old 05-12-2007, 11:34 AM
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Default 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)
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Old 05-12-2007, 12:36 PM
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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
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Old 05-12-2007, 12:37 PM
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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
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Old 05-12-2007, 12:49 PM
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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

Last edited by GregP; 05-12-2007 at 02:57 PM.
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Old 05-12-2007, 07:49 PM
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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?

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Originally Posted by GregP View Post
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).
That must be a sight.
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Old 05-12-2007, 08:22 PM
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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
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Old 05-12-2007, 08:24 PM
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Quote:
Originally Posted by BradH View Post
That must be a sight.

It kicks up a nice rooster tail filling all the way across the creek!
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Old 05-12-2007, 09:23 PM
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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
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Old 05-12-2007, 10:57 PM
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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...
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Old 05-12-2007, 11:02 PM
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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
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