06 18hp nissan 4stroke runs but will not top out

m1man

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My 2006 Nissan 4stroke 18hp starts fine and idles but when I open the throttle, it bogs and will not top out. New gas, fresh oil change. Was doing it intermittently now all the time.
 

pvanv

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Year is irrelevant. Assuming your model is NSF18B2. Clean your carburetor, change plugs, verify oil is not even a drop over full. The accelerator pump in the carburetor may be clogged or otherwise malfunctioning.
 

m1man

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Well, I cleaned the carb, fuel line filter, changed plugs. Still will not top-out without bogging. Could the rubber drive belt jumped timing?
OK, I answered the drive belt question, all three points do line up.

Now, how do you check the accelerator pump?
 
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pvanv

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You can check timing with a timing light. They seldom if ever jump a tooth. What method did you use to clean the carb?
 

m1man

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I completely disassembled carb, no residue in bowl, cleaned all parts with gumout spray carb cleaner, sprayed through all jets and ports. I only use Non-ethanol fuel in this motor and always have.
 

pvanv

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I completely disassembled carb, no residue in bowl, cleaned all parts with gumout spray carb cleaner, sprayed through all jets and ports. I only use Non-ethanol fuel in this motor and always have.
Generic carb spray is not aggressive enough to do a proper softening of the organic varnishes in the tiny passages; a 4-plus-hour bath in real carb dip, followed by a liberal spray-out with gumout-type acetone-based spray is a lot more effective. Did you remove the jets and the emulsion tube nozzle and clean them as well? Did you disassemble and check/clean the check valve balls and plunger for the accelerator pump while it was apart? That requires a tiny, maybe #0 Phillips driver. You may have a jammed ball check in the pump. Is the plunger return spring in good condition? Did you check the ABS solenoid for proper extension as the motor warms up? While non-ethanol fuel is preferred (and reduces a lot of problems), you must still empty the carb at the end of every day, either by idling it out, or by opening the drain screw; otherwise, fuel varnishes will accumulate surprising quickly in the tiny passages of the EPA-rated 4-stroke carbs of all brands.
 

m1man

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I always run the fuel out of the fuel line and carb by idling out. I'll get a can of the bath type cleaner and give it a try. I did Completely disassemble the carb when I cleaned it, there is tarnish on the brass fittings but they were still no obstructions. I pulled the ABS solenoid off and cleaned it, not sure what the cold and hot extension lengths should be. I'll check the spring and ball once I remove it and get it disassembled again. BTW it's a 2003 model not a 2006. Thanks for the help Paul.
 

m1man

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OK, Disassembled carb again, completely, soaked overnight in carb and parts cleaner, all the brass parts look new, blew out all ports with acetone carb cleaner, reassembled and put on the motor, checked the abs solenoid, when warm it was extended. still from about half throttle to max bogs. I attached a link to the video so you can see for yourself. https://youtu.be/xU6L0hKw4FA
 

pvanv

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You really should not run the motor at those speeds without a load on it; you can throw a connecting rod. There is a rev limiter... the sounds you are getting don't seem to be the staggered-ignition limiter engaging... but it could be. I would verify everything. Check timing, check valve lash, inspect plugs, etc. Odd that the intake noise gets less when you go above half throttle. I would like to see what a tach shows as the speed point where you are limiting.
 

m1man

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Paul, can you tell me what the valve lash specs are? Plugs are new and timing is good.
Thanks,
mark
 

pvanv

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Full info is in your Factory service manual. Intake 005 - 007 in, exh 007 - 008 in.
At what RPM does the motor limit?
 
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