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Motor starts and runs good then stalls and will run at 3/4 throttle with no problem. I have changed all fuel lines from tank to carbs. Coils, cleaned carbs ,new plugs, fuel pump. Question is this is on a 2004 express with a 18 gal tank does the tank have a strainer? Going to check puls coil and cdi today, any thing else to check?
Did it just start doing this? Check for a strong spark at all plugs.
Did you clean carbs and put new rebuild kits in them? Ethanol is eating these carbs. You can't just clean one and put it back together with old components.
Run it off of a portable fuel tank and see if the problem goes away.
I’ve got a 70 and it was the fuel pump diaphragm.
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+1 on the portable fuel tank. You also need to check the fuel pressure. If you can post the model number, I can tell you the exact pressure you should have. Like Possum69 said, the diaphragm could be causing low fuel pressure but it's easier to check the pressure than just pull the pump apart.
I've got a 2003 Yamaha 90. Had a similar problem couple years ago. There's a fuel filter hidden behind the oil tank. Took tank loose to get it out of way. Cleaned the filter and that took care of mine.