[alloutdoors]

When running can you try giving it a little choke and see if it will rev up? Also, have you examined the hoses for kinks, leaks, etc?

 

[alloutdoors]

By chance did you change the vacuum line as shown in the diagram or verified it doesn't have a small pin hole/air leak preventing vacuum

 

[alloutdoors]

My gut tells me it is a carburetor issue (jet, needle, etc.). This may seem like an unnecessary step, especially given a new genuine Honda carburetor but you might consider removing the carburetor, inspecting all gaskets, recheck all adjustments (factory settings), valves, screws, etc. Point is, I would go through the procedure once again, because it may be a simple oversight somewhere along the way. Additionally, I would inspect the air filter tube (between the box and carburetor) to ensure no blockages. Even though unlikely, I would switch out the plug as well.

 

[alloutdoors]

Yeah okay, seems like a good idea, I've been running the carb without the air box and filter even on, just open as it's in a very clean shed so I know no dirt will get sucked into the intake. May have to pull down the carb and inspect further. Also what plug are you talking about?

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Chances are when you get the filter area all closed up the issue will hopefully go away Sorry for not being more clear, but was referring to the spark plug. Again, may be a long shot, but controlling all things for fire/running properly need to be eliminated...