Honda 40 rough idle when warm

S

ScottS

New member
Hello,

I have a 2002 Honda 40 HP, which starts instantly and runs very well. However, if I've run it hard for a short period it will then idle roughly. For example, immediately following lot's of fast starts and stops in a row such as when towing a tube. It will idle rough and at only around 500 RPM. Normally, it would be idling around 950 RPM. The motor won't appear overly hot and the cooling system indicator is sending out water. The motor has been stored per the manual and the impeller was recently changed. Any ideas?

Thank you in advance for you replies. I've really enjoyed reading this website over the past few years. I especially enjoy reading how folks have customized their boats.

Thanks,
ScottS
 
Scott, sounds like your choke may not be closed completely. Take the cover off the next time it happens and try pushing on it with your finger and see if that clears up.

If that doesn't work, you may need to raise the idle speed a little. It's easy to do.

Charlie
 
Charlie,

I gotta disagree on this one. If the motor starts right up WHEN COLD, then most likely the choke is working properly.

Scott,

Does the motor idle ok at any time? If not, then the idle circuits in the carburetors may be plugged or restricted.
 
There are a few things to look at here. If the motor is idling rough after warming up odds are that one of the carbs has the idle circuit plugged or the choke is sticking closed. On the other hand you could also have a vacumn leak that only shows up on a warm engine causing it to run lean. Finally you might have an electrical problem with a coil or plug wire that has carbon tracks and it is only a problem in a warmed up state.

My guess is that it is a plugged idle circuit on one of the carbs. This is a typical problem these days as the idle circuits seem very easy to plug on some Honda's (IE: My mid 80's 7.5 plugs up every 2 weeks).

Take a can of carb cleaner with you next time you have the boat out. Then when you start having the problem take the engine cover off and spray down the intake runner, exterior of the carb and all gaskets in the intake system. If the engine speed picks up or the motor smooths out you have found a vacumn leak that needs to be taken care of. If nothing can be found this way then you likely don't have a vacumn leak and it is likely the idle circuit of the carb that is plugged (or more likely partially plugged).
 
Yes, it idles perfectly any other time. In fact, I can spend an hour or two going slowly at idle and low RPM speeds without any problem. The engine sounds wonderful going fast or slow. But, once I do several hard starts in a row it will start to idle roughly. Since I don't push the engine hard very often, I'm not too worried in the short-term, but I am worried that this problem will worsen over time. My closest Honda dealer is 1-1/2 hours from my home, which is why I would like to attempt to correct this myself.

ScottS
 
Back
Top