Yamaha 50hp missing rev range

Jizm · 27 August 2007, 18:33

chaps,

got a wierd one here, went out today and the engine would not rev past 2300rpm, no alarm sounded or anything so don't think it was that. But it was like the motor was 'bouncing' at those revs and would not go any higher no matter what. I had a good look at the manual and I am thinking maybe a dodgy charge coil (high speed) or suspect CDI unit maybe. Got home and had a go at it in a test tank and low and behold the fault had disappeared but it has done this before! I earthed out the pink alarm wire and that brought on the buzzer and the engine seemed to limit itself to just under 3000rpm but no 'bouncing' as such.Anyone got any thoughts on this? Does my motor have a low and high speed charge coil? Anyone know the wire colours, as the manual is a bit inaccurate!
cheers
Jiz

jyasaki · 27 August 2007, 19:35

Fuel delivery problem? That may show up while running, but not when revving with no load. Usually won't trigger an alarm.

Could be electrical/electronic, though, so you may be on the right track as well.

jky

Rogue Wave · 27 August 2007, 19:39

Is it a 3pot 2 stroke if it is I'd check the wiring loom from the throttle I had this problem changed the loom all ok

Jizm · 27 August 2007, 19:44

Yep, 3 cylinder, 2 stroke, do you mean the loom from the 703 control box?

Rogue Wave · 27 August 2007, 20:16

I do I really do. you are welcome to bring it round to our unit and we'll have a go at it. FOC

Jizm · 28 August 2007, 20:54

Quote:

Originally Posted by Rogue Wave

I do I really do. you are welcome to bring it round to our unit and we'll have a go at it. FOC

Bloody hell stu, I would not have thought the loom would do that! Cheers for that info, not too dear to replace either. I may well take you up on your offer in the near future.

Sods law tho', the fault is not there anymore! Ran it in a test tank, in gear at 2000rpm or so, for an about an hour and the prob did not return. It ran as sweet as a nut and I had to stop it in the end as the tank water was getting very warm! The only thing I did find was that the flywheel had worn through one of the crank position sensor wires, so I repaired and re-routed that. I dis-connected that as a test and the motor ran a little rough but not too bad. I also put the bare wire to earth to see if it created the fault but i didn't so no luck there anyway.
Couple of things I am not sure of:
Why does my motor have a crank position sensor?
Is it to govern the timing of the spark as the motor only appears to have one pulsar coil not three as I expected?
Does my motor have a high and low speed charge coils as there are only 2 wires (brown & blue) when I was expecting three, unless it grounds through the motor?
Why do the lighting coils have a red link wire between them as none of this really corresponds to the schematic (seloc manual) I have?

thanks
Jiz

mccabe · 30 August 2007, 20:40

Just in case change the plugs and check that all leads are making contact with the plugs.it can be so simple you could miss it!

Jizm · 31 August 2007, 14:37

Quote:

Originally Posted by mccabe

Just in case change the plugs and check that all leads are making contact with the plugs.it can be so simple you could miss it!

Agreed, Just picked up a set of plugs as a matter of course.

Jizm · 01 June 2008, 20:52

This has reared it's ugly head again today.

Thought I'd cured it, obviuosly not! Anyone got any ideas?
(while I try to source a control loom at a reasonable price, as per stu's suggestion)

floater · 02 June 2008, 10:23

i had a same problem a couple of years ago with a 30hp yam 3 cyl 2 stroke
turned out to be crap in one of the carbs there was a piece of material bloking the throttle needle i think thats what you call it this was cleaned and it sorted it out but as you say ran fine in the tank as soon as under load no power

the way the chap who fixed mine found it was to run the engine with air intake off and squirted in some "quick start" in to the carbs to identifiy which one was faulty

Andy

Andy JC · 02 June 2008, 11:22

Quote:

Originally Posted by floater

i had a same problem a couple of years ago with a 30hp yam 3 cyl 2 stroke
turned out to be crap in one of the carbs there was a piece of material bloking the throttle needle i think thats what you call it this was cleaned and it sorted it out but as you say ran fine in the tank as soon as under load no power

the way the chap who fixed mine found it was to run the engine with air intake off and squirted in some "quick start" in to the carbs to identifiy which one was faulty

Hi Andy

Sounds like a similar problem I'm currently having with with my 3 cyl Mariner('91, 50hp), took it out yesterday and had full rev range for about the first 10 mins then suddenly wouldn't rev past about 3000rpm ish(no rev counter so an educated guess

) Full power did return briefly in a quick burst a couple of times but then went all together

Spoke to Nos yesterday and he said either a duff plug or crap in one of the carbs. I changed all three plugs while out on the water with no improvement so guess it might be a carb problem.

When they discovered the problem with your 30hp Yam I assume they had to remove the carbs to clean them, what sort of timescale did that take? If you remove the carbs for cleaning, do you need to re-balance them before re-fitting? Do you mind saying how much they charged to resolve the problem?

floater · 02 June 2008, 12:17

I dont know how long it took the guy as i left it with him and then picked it up a week later and £100 lighter

but it was a problem that i had had for a while all be it intermitent

when the quick start was squited in to the carbs it was an immediate effect ie we were going along at about 8knots not on the plane but at WOT the engineer squirted 1 carb nothing 2 carb nothing 3rd carb whoose it was like throwing the throttle full on (which of course it was !) then as soon as the quick start had burnt up the revs dropped another spray in to carb 3 and whoose we were off again

fine after they were striped and cleaned

Andy

Andy JC · 02 June 2008, 12:45

Cheers Andy

Jizm · 02 June 2008, 15:03

Cheers for the responses guys but I'm pretty sure my problem is electrical. The way the engine revs 'bounce' is the same as an engine behaves when it hits a limiter but obviously it's nowhere near the top of the rev range.

Jizm · 02 June 2008, 17:45

video of the outboard symptoms below:

[YOUTUBE]<object width="425" height="355"><param name="movie" value="http://www.youtube.com/v/F6WsnWbn0XQ&hl=en"></param><param name="wmode" value="transparent"></param><embed src="http://www.youtube.com/v/F6WsnWbn0XQ&hl=en" type="application/x-shockwave-flash" wmode="transparent" width="425" height="355"></embed></object>[/YOUTUBE]

9D280 · 09 June 2008, 11:55

I'll stick my necck out & say most intermittent nonsense is usually electrical!

I had similar probs on my 2- cyl. It was a shot spark plug - it started as an occasional hesitation, which slowly morphed into total failure over an afternoon & limping back on 1 cyl(thankfully not too far from the marina when it totally died).

I notice the problem recurrence is almost a year from when you cured it last. Try a new set of plugs again? What did you do last time that "cured" it for 10 months?

My old Suz 3-cl ran OK if a little underpowered on 2/3 cyls. My current 2- cyl behaved like a seagull on 1/2. I wonder if you are just running on 2 cyls? Try Unpluigging a spark lead and firing up. I suspect you'll find one of them off will make no diference, the other two it will barely run.

Jizm · 11 June 2008, 06:27

~Not sure I cured it last time. The times it has happened it has been after a slow running 6 knot spell up the river. If I don't do that it doesn't occur.

9D280 · 11 June 2008, 09:29

Aha! Sounds bit like a couple of old premix yams I used a few (!) years ago at a sailing centre. Basically they oiled up after 15- 20 mins pottering about chasing toppers in no wind.....

More questions -
If it's a 2- stroke, is it autolube? If not then every so often you'll need to open it up to basically burn out the oil! The sailing centre had a 25 (2 cyl) and a 30 (3 cyl), both would oil up after about 15 mins at pottering speed. The 30 (3 cyl) was worse - it really didn't like slow running at all, but the autolube 60 on the "big searider" would run all day at idle no problem. The problem dissappeared when the engines were upgraded to the then "new" autolube type.

Jizm · 14 June 2008, 07:19

Quote:

Originally Posted by 9D280

Aha! Sounds bit like a couple of old premix yams I used a few (!) years ago at a sailing centre. Basically they oiled up after 15- 20 mins pottering about chasing toppers in no wind.....

More questions -
If it's a 2- stroke, is it autolube? If not then every so often you'll need to open it up to basically burn out the oil! The sailing centre had a 25 (2 cyl) and a 30 (3 cyl), both would oil up after about 15 mins at pottering speed. The 30 (3 cyl) was worse - it really didn't like slow running at all, but the autolube 60 on the "big searider" would run all day at idle no problem. The problem dissappeared when the engines were upgraded to the then "new" autolube type.

It's an autolube, and removing the plugs and cleaning them or putting in new ones did not get rid of the fault.