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Hi everyone, I have a Yamaha 90HP 2 stroke, 1985 model. I would start and go on as normal then suddenly the motor starts to shake violently and lose power. If I come back on the throttle it would seem to behave normal again, but as soon as I power up the shaking would come back. I have done the following to try and fix this. Rebuilt the three carbies, new fuel pump, spark plugs, new fuel. Last time I went out it started to doing this again and then wouldn't start at all. Usually as goes with the 90 you look at the key and it starts. I finally got it going and it was running terrible all the way back to the ramp and for no reason it would suddenly power up and behave normal. I pulled it out of the water and tried to start it and it wouldn't start. I took out the plugs and there was no spark in any of the plugs. Mucked around for quite a while at the ramp, then again for nothing particular that I did, it fired right up as normal. So, I don't think its a fuel thing. What gives the coils their power to spark? Could it be the ignition switch? Again she seems to start fine. I am at a loss. Could it be the processor and where is this located on the motor. I am stuck and would appreciate any thoughts. Thanks You, John.
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I think this issue could be the power pack. But I don't know how to test and replacement is expensive. I can't think of anything else it could be. Has anyone ideas or do I just shell out the $800 - $1000 and be done with it. Come on guys, have a look and any comment is much appreciated. Thanks. John. -
You need to pick up a service manual and read up.
It gives step by step procedures for testing and what equipment is needed for the tests along with the specs. Money well spent.
There are charge coils and pulser coils to test they are inputs to the CDI and then there are the outputs from the CDI to test . You will need a peak reading meter made just for reading these voltages.
Then there are the high voltage coils to test.Comment
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I dont answer tech questions by PM
have you tested the alarm system to see if all the audible and tach visual indicates work?
if it goes into any alarm condition it misfires,shakes and RPM is limited to about 2000.
to test the ign system requires a meter capable of reading PEAK voltages.
most cant.
seirra makes one for about 125 dollars thats analog but works well.
or you can get the CDI DVA adapter that fits most digital meters using banana leads.
without it the ign system simply cannot be properly tested.
with the correct meter the CDI output voltage can be eaisily monitored and confirmed or eliminated.
if its an alarm condition and you buy a CDI assy you will still have the problem and a spare CDI.
if its a stator or pulser coil issue and you buy a CDI you will still have the isue and still own a spare CDI.
see where I am going with this?Comment
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I haven't tested the alarm system. I do have the manual. I have started reading however it is large, about 700 pages. Covers all horse powers. I like to read the manual. I don't get any alarms when the motor is running. It is so hit and miss. Thanks for your comments. I enjoy your comments and will try, let's see what happens. John.Comment
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The manual should be broke up into different sections and it should be fairly easy to find the ignition section.
Is this motor self oiling or do you mix the oil and fuel?
I believe the alarm can be tested by grounding the pink wire that goes to the over heat temperature switch with the key switch in the on position.
The Yamaha service manual is a lot better it does not cover all those different motors only the one you bought it for and is less confusing.Comment
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Hi everyone, I managed to get a second hand power pack and many other parts for a good price. I changed the power pack over and the boat ran nice. Good start up, good acceleration and running. Thought some out there would like to know end result. Thanks for the help and comments.Comment
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