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  1. #1

    Default 2006 Yamaha 25HP 4 Stroke. Need help won't stay running. Did all below already....

    Replaced fuel line hose and priming bulb. Replaced Fuel Filter. Two new spark plugs. New starter relay( last season the old one stuck one time and the starter kept running. (Luckily boat has a battery disconnect switch). Removed fuel line from exit at fuel filter and before fuel pump plenty of gas when you squeeze bulb. Disconnected outlet fuel line on fuel pump to carb and cranked engine. Plenty of gas flowing from pump. Also removed and disassembled fuel pump and all parts were cleaned, were in perfect shape including the one way valves and the diaphragm. Also bench tested pump and it worked find as you push in on the pump plunger which is cam activated.

    So it appears I have good clean fuel flow all the way to the carb. Spark was checked and confirmed. Used a bit of starting fluid and immediately ran but once the ether dissipates it stalls out, it will barely idle for sometimes up to 30 seconds. Multiple attempts to idle up or put in gear are quickly met with a stall. Lots of hesitation if you try to increase engine speed.

    Next removed carb and placed on bench. Disassembled bowl and inspected float, a little dirty but float and float spring appeared to work fine so I didn't disassemble the spring under the float. Holding carb upright float worked perfectly. Removed high speed jet and cleaned thoroughly and replaced. It's hard to tell if they are clogged but I recall blowing some air through it and carb cleaner and it was clear (inlet hole and two cross holes further down on the threads. The smaller "jet" which is covered with a rubber stopper doesn't appear functional and I was unable to free up to see if it's actually a jet or some kind of plug, it is after all covered with a rubber stopper. cleaned all remaining ports/holes in float bowl and reassembled the bowl. Next took off the plate covering the top of the carb and it was clean, diaphragm intact cleaned all channels and ports and reassembled after testing plunger component. Working properly. Put carb back on and tested. Motor started and again stalled and then wouldn't stay running. So next I drilled out the brass plug covering the air/gas mixture and messed with that incrementally and couldn't get anything substantial, won't stay running. So, not sure what to do next or what I may have missed....Time for a new carb? Thanks and sorry about the long post.

  2. #2

    Default Re: 2006 Yamaha 25HP 4 Stroke. Need help won't stay running. Did all below already....

    Well it looks like I'm wrong about the small jet with the rubber grommet. Will have to use a screw extractor I guess to get it out then buy a new jet and reinstall.

  3. #3

    Default Re: 2006 Yamaha 25HP 4 Stroke. Need help won't stay running. Did all below already....

    Replaced old carb with new yamaha eom carb $$$ ran fine on the muffs after starting...took boat out for a test and still getting sputtering when attempting to accelerate but will accelerate under full throttle and run. When backing off throttle it seems like it's missing and occasionally will backfire through carb if you rev it up at idle in neutral. I've checked both gap and resistance on new plugs all ok there. I now suspect a coil issue but what's the easy way to check resistance in the coil and help isolate the problem and I also need the ohm specs for this coil. Also replaced thermostat with new one. I will occasionally get a warning horn at idle now after running a while and it doesn't stop until it cools off but for the life of me the engine appears normal temp wise and the pee hole is warm showing correct thermostat operation. Again I'm trying to assess overheat switch of some sort or oil pressure warning switch is faulty.
    Last edited by whaler200; 06-12-2020 at 03:26 PM. Reason: add info

  4. #4

    Default Re: 2006 Yamaha 25HP 4 Stroke. Need help won't stay running. Did all below already....

    Quote Originally Posted by whaler200 View Post
    Replaced old carb with new yamaha eom carb $$$ ran fine on the muffs after starting...took boat out for a test and still getting sputtering when attempting to accelerate but will accelerate under full throttle and run. When backing off throttle it seems like it's missing and occasionally will backfire through carb if you rev it up at idle in neutral. I've checked both gap and resistance on new plugs all ok there. I now suspect a coil issue but what's the easy way to check resistance in the coil and help isolate the problem and I also need the ohm specs for this coil. Also replaced thermostat with new one. I will occasionally get a warning horn at idle now after running a while and it doesn't stop until it cools off but for the life of me the engine appears normal temp wise and the pee hole is warm showing correct thermostat operation. Again I'm trying to assess overheat switch of some sort or oil pressure warning switch is faulty.
    I have a 300 yamaha and I had a alarm going off and I thought it was a oil problem since I have a temp gauge and pisser was flowing I didnt think it was temp problem after 3 days of checking everything out with the oil including a new float in main tank on motor its a 2 stroke I come to find out there is a sensor in the fuel bow on the motor that was holding water to set off the float in the bowl causing the alarm to go off
    so my advice to you is to change your water separator and filters and see if the problem persist

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