Weak sparks on 2002 25hp 2 stoke twin

[davetedd]

Can anyone help? Our yacht club RIB engine will not start and I need to know what voltages I should be seeing on the coil primaries? Does anyone have the data or a refererence to a manual which I could download? Or any advice? Thanks

 

[99yam40]

Re: Weak sparks on 2002 25hp 2 stoke twin

Give the model # and all you have done so far in fixing/troubleshooting the problem.
Are you using a DVA adapter or a peak reading voltmeter to take readings?

 

[davetedd]

Re: Weak sparks on 2002 25hp 2 stoke twin

Thanks for your reply. Engine is Yamaha 25NMO 6L2. The kill switch, oil level detector and engine temperature sensor have all been checked and are ok. The voltages have been measured with an ocilloscope at the coil primary feed and are during cranking 0.6V pulses with the coil connected and
8V with the coil disconnected. The coil primary resistances are 0.346 ohms and 0.284 ohms - I thought they would be the same? I cannot measure the secondary resistance with an ohmeter - all I get is an open circuit when I go from a needle inserted in the ignition lead where it comes out of the coil to the coil negative earth lead. The leads themselves read around 2Mohms from coil to spark plug cap and I guess that is some form of radio interference impedance. The plugs do spark during cranking but they are faint and yellow and we doubt that they will fire under compression. Any advice you can give will be much appreciated. As luck would have it, we are a British yacht club registered as a training facility with the RYA, and they are inspecting our safety boats on Friday this week

 

[davetedd]

Re: Weak sparks on 2002 25hp 2 stoke twin

I forgot to say we tried a new plug on one lead and it did not spark at all???

 

[rodbolt]

Re: Weak sparks on 2002 25hp 2 stoke twin

this is an international market engine.
I have no specs.
does this engine use a single coil with dual plug leads or two coils?

 

[davetedd]

Re: Weak sparks on 2002 25hp 2 stoke twin

Hi - the engine has 2 coils. We have made progress by squirting a syringe of neat fuel into the carb air intake and then the engine ran for a few seconds then stopped. A mechanic is coming in today to strip down the carbs so hopefully it will get fixed. Is there a spark tester we could use or make to check if the ignition system is providing the correct output for the spark? Thanks again for your input.

 

[rodbolt]

Re: Weak sparks on 2002 25hp 2 stoke twin

do a forum search on home made spark tester.
your carbs are clogged.
test peak voltage into the coil primary,test peak voltage into the CDI from the stator charge coil.
the two should be about the same and at least150V.

 

[davetedd]

Re: Weak sparks on 2002 25hp 2 stoke twin

Rodbolt -thanks for that. The mechanic said that there was not enough suction on cranking to draw fuel into the engine??? He was not able to fix it. The engine has a pull stater and there is plenty of compression so I will do as you say and strip the carbs down. We have fitted another one of our engines to the boat to give us time to get to the root of the problem. Thanks again for your input.