2000 4 stroke won't go round and round yamaha

luskateer · Dec 20, 2011

I have a new to me 25 h.p. long shaft 4 stroke that doesn't want to go past top dead center with the electric start. I pull the plugs and turns over with no problem. With plugs in it goes one full turn and it appears the compression stops it from going further. Compression is about 125 btw. Tried other batteries and can only get one turn out of it. Is there a compression release mechanism?
thanks for any help.

jeffersondodson561 · Dec 20, 2011

Re: 2000 4 stroke won't go round and round yamaha

No compression releases are mainly for manual start mechanisms. First thing I would do is carefully inspect the wires for good connections from the battery to the starter solenoid/other side of solenoid to the starter. If you have run the boat with a weak battery that will damage the solenoid. You could get your voltmeter put the red lead on the batt positive end of the solenoid and the black on the other big end of the solenoid and crank the engine, should see no more than
.15 voltage drop across the solenoid. Or you could remove the battery cables and energize the solenoid and check resistance. I just would rather see voltage up to you.

Or you could crank the engine and monitor your starter voltage. A good starter will generally draw about 9.5 volts with properly charged battery.

Oh yeah don't forget the starter switch.

99yam40 · Dec 20, 2011

Re: 2000 4 stroke won't go round and round yamaha

You can do a voltage drop test in the cables from the battery and through the relay to the starter to find a high resistance problem , but a starter does not draw voltage. If you only get 9.5 volts at the starter when energized I would be looking at the condition of the battery and cables along with the connections.
It will draw current (amps) and the lower the voltage available at the starter due to resistance in connections and wiring the higher the amps will be to do the amount of work needed to turn the motor. If there are not enough volts and amps available then the starter can not do the work it is designed to do. Electrical theory kind of dictates that,
Volts X amps = watts. and watts are a measure of horse power ( work)

I thought 4 strokes normally had more compression than that. Are you sure you do not have a mechanical problem with the motor?

jeffersondodson561 · Dec 21, 2011

Re: 2000 4 stroke won't go round and round yamaha

99yam40 said:
If you only get 9.5 volts at the starter when energized I would be looking at the condition of the battery and cables along with the connections.

Uh...no

99yam40 · Dec 21, 2011

Re: 2000 4 stroke won't go round and round yamaha

Well I still think a 3 volt drop is too much, but may be just me.
On smaller motors I would think that it should not be but around 2 volt drop, but I have never measured it on the 4 strokes with their higher compressions.

Jeff what do you think about his 125 PSI compression?
maybe turning too slow

jeffersondodson561 · Dec 21, 2011

Re: 2000 4 stroke won't go round and round yamaha

Does seem like it could be more but gauges vary. Were the throttle plates wide open when the test was done?

luskateer · Dec 22, 2011

Re: 2000 4 stroke won't go round and round yamaha

WOW!
What a great response. Thanks,
I'll have to go measure the voltage drop. I tried bypassing the selenoid by going direct to the starter with no improvement. Connections are good and clean and battery cable is stock. Without plugs in it will turnover like a scared rabbit. Plugs in it grunts like my ex, one turn.
4 strokes should have higher compression. I have seen this in some 50 h.p. i've worked on. The throttle plate (single carb) was open during compression test.

99yam40 · Dec 22, 2011

Re: 2000 4 stroke won't go round and round yamaha

Remember cables can and do go bad internally without visible signs from the outside.
How did you do the compression test if it does not want to turn over properly?

bowmen · Dec 22, 2011

Re: 2000 4 stroke won't go round and round yamaha

make sure you got the right plugs if there to long the piston could hit them i think?

luskateer · Dec 23, 2011

Re: 2000 4 stroke won't go round and round yamaha

To do compression test i removed plugs and tested with a professional gauge. 3-4 grunts gives me 125.
plugs are the correct ones.
I'm hearing that this outboard may have been submerged during one of our hurricanes back when. Reportably it was saved and pickled. I've had the starter motor apart and rebuilt two times now. I'm wondering if the internals i.e. bearings or crankshaft is compromised in some way. Could the sideways thrust caused by the compression cause it to bind up in some way.

jeffersondodson561 · Dec 23, 2011

Re: 2000 4 stroke won't go round and round yamaha

luskateer said:
I'm hearing that this outboard may have been submerged during one of our hurricanes back when.

If it was submerged it should have been taken apart, chances their debris in the water that would warrant that. Don't you just love learning these details after the fact!

99yam40 · Dec 23, 2011

Re: 2000 4 stroke won't go round and round yamaha

Have you had the starter motor checked out by a rebuild shop to make sure the armature and coils are ok?
If either one has some shorting but not totally fried it will reduce the torque.
I have not used a growler in many many years to test the armatures, but they are important for testing.

Have you tried doing a leak down test on the cylinders, the motor does not have to spin to get the readings and will tell you a lot more about the motor than the compression test

Internal rusting of the shiny parts would be very likely. Did it ever run after going under and how much and how long ago?

luskateer · Dec 24, 2011

Re: 2000 4 stroke won't go round and round yamaha

hi, Not sure what a growler test is.....like a hi-potential breakdown tester?
could do leak down test but not sure how to do.
Motor ran after submerged . Don't know how long though.
have replaced the tilt motor and trigger. have replaced brushes on two separate starter motors. with no improvement on turning over

sschefer · Dec 24, 2011

Re: 2000 4 stroke won't go round and round yamaha

luskateer said:
To do compression test i removed plugs and tested with a professional gauge. 3-4 grunts gives me 125.
plugs are the correct ones.
I'm hearing that this outboard may have been submerged during one of our hurricanes back when. Reportably it was saved and pickled. I've had the starter motor apart and rebuilt two times now. I'm wondering if the internals i.e. bearings or crankshaft is compromised in some way. Could the sideways thrust caused by the compression cause it to bind up in some way.

After reading the first post, this was exactly what I was thinking. You seem knowledgeable enough to have already checked the oil level and for the presence of water or fuel in the oil so your next stop is the timing belt. Make sure the cam alignment is correct. You can cycle a 25hp motor by hand with the plugs in so I'm skeptical about it being a starter problem. Did you try the compression test with 1 plug in and one out. That might head you in the right directions.

99yam40 · Dec 24, 2011

Re: 2000 4 stroke won't go round and round yamaha

luskateer said:
hi, Not sure what a growler test is.....like a hi-potential breakdown tester?
could do leak down test but not sure how to do.
Motor ran after submerged . Don't know how long though.
have replaced the tilt motor and trigger. have replaced brushes on two separate starter motors. with no improvement on turning over

The growler is a tester for armatures that checks for shorting in them. The coils can be tested with voltage , but I have no idea to what voltage as this is a 12 volt system.
A starter/alternator shop should have the necessary equipment to test starter to rule that out and then you can look else where if needed

luskateer · Dec 28, 2011

Re: 2000 4 stroke won't go round and round yamaha

So it looks like the starter was defective. Sent it off with a new owner who's got an outboard expert in the family.
thanks for the help.

2000 4 stroke won't go round and round yamaha

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