I have a 1985 Honda 10 that I bought new and it probably has over 1000 hours on it and I have had a few of your symptoms. A couple of other things you might try. Your carburator may be running rich and building up at slow speeds and it will take a good bit of sputtering at wide open throttle to blow it out. This happened to me yesterday on Tahoe. Check your plugs and if their carboned up try leaning your carb out. Another thing I do every time I'm on the water, is unplug the fuel line and burn all the gas out of the carb. This makes all the difference in the world. I do it even if I'm going out the next weekend. Hope this helpos. Tight lines.
I'm not all that familiar with outboards - I've got a small 2.2hp for my tender and I had a 115hp on an old boat of mine that I've done general maintenance on - but don't know what you mean by "high gear." *Do you mean it bogs down at WOT?
If you're not getting the RPM's up at WOT when it's cold - or it's taking longer to "warm-up," I'd take a look at the choke. *Does it have an automatic choke? *If so - check it to make sure it's not sticking or failing.
It doesn't sound like a fuel problem to me because once it warms-up - it's fine. *So - what changes on a motor during that time? *I'd think the choke would be an issue.
That said - fluid change isn't a bad idea - and I'd also pull the plug and at least clean it - see if there's any wear or build-up and, if so, replace it.
triggerfish, thank you so much for the response. When I didn't any any response, I didn't think anyone cared. :-[ I really appreciate the response and I think I'll just dump the gas I have now into my lawn mower and replace the fuel filter.
By the way, was it difficult or expensive to replace the carb?
I have an outboard problem I am hoping you can help me with. I have a 2003 Mercury 15 HP 4 Stroke outboard that I used for about a year, without any maintenance or problems, until recently. It takes a long time to "warm up" before it will run in high gear. I shift it in high gear but it wouldn't go fast for about 10-15 minutes. Maybe it's time to change the oil? Spark plugs? Fuel filter? A complete tuneup? Any help is appreciated. :-[