2000 40 hp honda warm starting / running problems

I have a 2000 40 hp Honda outboard that starts and runs like brand new when cold, first start up of the day, at all rpm ranges. After about approx. 1-1/2 hours of running, mostly back trolling at about 450-550 rpm's. the motor struggles to keep running even when I increase the throttle, it quits, doesn’t want to start and if it does start as soon as I shift it will kill. If I let it run in neutral and rev it up to about 1300 rpm it will kill. This usually goes on for at least 5-10 ten minutes of trying to restart / shift motor into gear. If by chance I can get it started and rev it up to about 2500 to 3000 rpm's in neutral, just letting it run at that range, after about 20-30 seconds it will surge up to about 4000 rpm's all on its own for a second or two and then return back to the 2500 / 3000 range, just like magic. If I can get it back to idle without killing and can shift it into gear I might beable to increase the rpm up to about 3000 without killing it, if I can get it up to this higher rpm range, I will probably be able to get it wide open up to 5500 rpm. Wide open it will run like brand new, not a miss or blubber. Last year I had similar problems, just not as bad. I took motor to the dealer and he rebuilt the (3) carbs, all new parts, new plugs and a complete tune up. I have not more than 4 hours of run time since at the dealer, he said the problem was with the carbs. Could it be an electronic problem since all of the mechanical work the dealer did didn't solve the problem ?Any help would be appreciated, it sure is a frustrating problem.

kriplur, hate to say this, but I'd wager your carbs are plugged again. These engines don't like to sit idle for too long. Stating that you have just 4 hours since last year implies that the motor has sat multiple weeks without usage. With today's gas, once you get to a couple of months with no usage, you can count on the gas deteriorating. Those little passages (in the carb) plus easily from this deteriorating. You could try some Seafoam and see if that clears things up. Some folks swear by it. To be fair, it's not just Hondas that suffer from this gas issue. I can't tell you the number of carbs I've cleaned that restored proper running - particularly at lower speeds. The transition ports are typically the issue - and they only contribute a percentage of the total fuel load at full throttle - thus the reason it's not often noticed at full throttle. These tiny holes in the carb passage are just behind the throttle plate. Copper wire and carb cleaner, along with compressed air can clean these out nicely. Good luck.

First, I do not see how you were idling at 450 -550 rpm. They are supposed to idle at around 950 +/- 50 rpm...the engine is barely running at 450.

When it fails...what do the spark plugs look like? If they are black, then they could be fouled due to idling for such a long time and the engine may not be getting up to temperature.

It is also possible that the idle mixture was set a little on the rich side.

Hopefully, you are using DR7EA spark plugs.

Make sure the oil level is about 1/4 inch below full. If the oil level seems to be increasing, that also points to the engine not coming to temperature. In addition to that, the valves and rings may be developing a carbon buildup.

Your spark plugs are the easiest way to tell that, without any additional test gear.

My thought is when you finally get it rev'd up, the motor is cleaning the plugs up as it is running faster....then away you go.

With the thermostat open, the motor temperature will be around 162 degrees F.

It sounds like you should have some further discussions with the dealer. He may have seen something during the repair that could lead to the final solution. We do not always find the complete solution the first time...no matter how hard we try.

Mike