Engine problem

[Jim Thacker]

2007 Honda 90 HP. I generally run it at 5800 RPM top speed but lately out of the blue it will start fluctuating the rpm from 58 to 53 and back and forth. So far I have changed the fuel pump, fuel filter and spark plugs but it keeps on doing that. I thought that maybe at 5500 rpm it would be better and it was for a while (maybe my imagination) but it is back. Whenever it starts to do this I throttle back to low 50's and it seems to go away. I can run like this for a bit and go back to 55 and it is ok for a while. Any clues out there?

 

[hondam]

Definitely a fuel pressure problem, change your high pressure filter inside your VST, this usually fixes it. Expensive filter (~$40) but easy to change, just 3 screws. If this doesnt fix it you may need to have the injectors cleaned. If you had diagnostic software you could confirm this by checking the ST fuel trim. Honda has oxygen sensors on all their fuel injected engines that monitors the actual air fuel mixture if the filter or injectors of dirty and not giving the engine enough fuel the O2 sensor will pick up on this and electronically richen up the mixture. The ST fuel indicates the deviation in this mixture from what it should be under normal conditions. It should read 1.00, and as it richen the mixture it will increase in .01 increments. 1.01 ok , 1.03, not big deal maybe old gas, 1.10 is very dirty and something needs to be cleaned, ive seen some as high is 1.25 which didnt even want to run.