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check vent on the fuel tank
if it is EFI and ECM controlled , could be fuel pressure problem not high enough
If it has a data point run the fault codes
If your 115 Yamaha SHO VMAX outboard engine is experiencing RPM fluctuations at speeds over 3500 RPM, it may be due to a few different factors. Here are some things to check:
Fuel supply: Make sure that the fuel supply to the engine is consistent and free from any debris or obstructions. Check the fuel filters, fuel lines, and fuel pump for any signs of damage or clogging.
Spark plugs: Check the spark plugs to make sure they are clean and functioning properly. If the spark plugs are worn or dirty, they may cause the engine to misfire at higher RPMs.
Throttle position sensor: The throttle position sensor (TPS) sends a signal to the engine control module (ECM) to adjust the fuel and air mixture. If the TPS is not functioning correctly, it may cause the engine to fluctuate at higher RPMs.
Air intake system: Make sure that the air intake system is clean and free from any debris or obstructions. Check the air filter and air intake hoses for any signs of damage or clogging.
ECM software updates: Check with your Yamaha dealer to see if there are any available software updates for the ECM that may improve the engine's performance.
If you are unable to diagnose and fix the issue on your own, it may be necessary to take the engine to a professional technician for further diagnosis and repair.
? 2:29 www.youtube.com/watch?v=sMmionreldM Dec 29, 2012 - Uploaded by Peter Richards
Engines for 1989 Larson boat with dual 115 Yamaha 4 StrokeEngines. ... Outboard Yamaha 150 HP DIRTY idle JETS, Motor will not idle .
Could be a variety of things. Vapor lock from a leaky carb. Carb running too rich. Engine overheated. Heck, could even be some weird wiring gremlin. Hard to tell for sure, but a good solid carb clean and reset should help either way...
Some Honda's have slow running (below 3500 rpm) coils and fast running over (3500 rpm) coils. they are behind the engine cover on the side but could be at the front, depending on the bike. Sounds like your slow running coil is breaking or broken.
The carbs on 2 strokes are always needing a little adjusting, either your plugs are somewhat foulded, carbs gummed up from setting, restriction in fuel delivery, linkage could also be biding slightly. These are the general issues, any more would require a tech to get hands on and test them. But if your savy enough to adjust the carbs, just bump the idle up a tad after you check everything out. I am guessing that this may clear up on its own, but may need a bump.
hi,says here you had the carbs redone,it sounds to me like the carbs were not rebalanced after installation,if you do any work at all ocn carbs it is quite important that the carbs be properly rebalanced,it only takes very minor adjustments inside carbs(even a scratch on a jet)or different torque settings on screws etc will trow the balance out,if you get this done i think your problem will disappear..hope this helps
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