yamaha 90 misfiring

[m.muir]

I have a yamaha 90 that was running great and then lost power above 2000 rpm and now misfires when idling.Its only been used twice since new head gasket,water pump,fuel pump diagphram,new plugs and fresh fuel

 

[Semloh]

Re: yamaha 90 misfiring

So you it was running great and then you replaced all these items and it has been running badly since or it ran good once after the repairs? <br /><br />Motor info?

 

[m.muir]

Re: yamaha 90 misfiring

It was running great after the work the two times i used it and then just lost power.It is an oil injection model.I dont know how old the engine is .The only nubers i can find are 90aeto and 6h1.I have also noticed that the plugs keep going black

 

[jim dozier]

Re: yamaha 90 misfiring

Pull the plug wires 1 at a time (ground the loose plug wire) and check which cylinder isn't firing right. Then check spark with a spark tester. If you don't have a good spark start checking ignition components. Then spray premix into the carb throat of the offending cylinder, if it picks up you need to look at the fuel system (carb) for that cylinder first.

 

[m.muir]

Re: yamaha 90 misfiring

I have already checked all plugs and they all seem to be sparking properly

 

[jim dozier]

Re: yamaha 90 misfiring

From your oringinal post you did not say the carbs had been rebuilt. If not it sounds like that is next on the list.

 

[m.muir]

Re: yamaha 90 misfiring

The carbs werent rebuilt.Do I have to buy a kit for rebuilding the carbs?.Also how easy a job is it?

 

[jim dozier]

Re: yamaha 90 misfiring

If you haven't already, go to the bottom of this web page and buy a manual, best $30 dollars you will ever spend on your boat. The manual knows all. Usually a kit is available for rebuilding carbs. If so it would probably include all or part of the float valve assembly, and new gaskets or O-rings that should be replaced. Outboard carbs are pretty simple and it is a job easily done. Removing them is probably more difficult than rebuilding one. Remove them, disassemble them, clean the carb, with emphasis on the orifices inside, with carb solvent and compressed air (you can buy a can of air at Radio Shack if you don't have compressed air) and install the rebuild kit parts. The important thing is that its not a beauty contest for the outside, it is the inside of the carb that counts. Spraying carb cleaner in the carb throat while its still on the engine doesn't count.

 

[m.muir]

Re: yamaha 90 misfiring

I have a manual so I'll try and remove the carbs and rebuild them and see how it goes.Thanks for your help