Honda 50 EFI rough running at idle

jack keifer

We have a Honda 50 EFI on our 16 cruiser with about 250 hours. We spend many hours trolling at low idle, about 800 rpm. Until recently, it was running smooth while underway. Recently it started running very rough intermittently. I had changed the prop down to a 9 pitch in anticipation of our trip to Yellowstone Lake. I cannot see how this would have any effect, in my opinion it should have improved the situation. Next, I pulled the plugs. Although they looked clean, and the gap right in the middle of spec, I cleaned them up, and reinstalled them (these were the origionals). No improvement, so I installed new plugs, same brand, same heat range, no improvement. The problem exists only at low idle when underway. At any rpm above low idle, it runs just fine all the way to 6,000 rpm. It also is ok in neutral. Anyone have any ideas?
Jack

T.R. Bauer · Posted: Wed Aug 12, 2015 4:53 am Post subject:

Unless you have some coils going bad, corroded wiring, or some goofy carbon tracking, which is possible, but not that likely, it kind of points to fuel. With sparkling clean plugs it sure make one think lean condition. I would want to see fuel pressure, air fuel mixture, various sensor readings, and what the spark looks like while it's acting up to really make any assessment as there are lots of stuff that can cause this. You might just have dirty fuel and bad filter.....worth changing.

1TUBERIDER · Posted: Wed Aug 12, 2015 9:30 am Post subject:

Hi Jack

I had a similar problem at the beginning of this season. Besides a rough idle it was collecting water in the crankcase.

My problems included changing thermostats and dirt in one of the carbs.
I took the boat to a repair shop to fix it. They changed the thermostats and he tapped the carb (Not sure what he did) which cleared it otherwise I would have had a $500 carb repair.

I need to change fluids before I store the boat and completely drain carb bowls instead of just running fuel out of carbs while flushing. I also now use a fuel additive to help with long term storage and methanol.

Good luck and check your oil for water.

T.R. Bauer · Posted: Wed Aug 12, 2015 10:49 am Post subject:

It is probably important to remember when replying this is an EFI motor and that means it doesn't have carbs to clean out. I would continue to check the simple and cheap stuff for sure as it is probably overdue for changing. BTW, I forgot to ask, is the FI light on?

Blueback

TOGO · Posted: Wed Aug 12, 2015 5:04 pm Post subject:

My Honda 90 was running ruff at a idle. 80% of it running is at a idle or vary slow speed. My service dealer a Honda dealer suggested using Mercury additive #2 he pored a half a bottle in each tank (about 20 gal gas per tank) it cleared up the ruff idle. I now use the recommended amount when I gas up. Problem has not return.

Guy

BRAZO · Posted: Wed Aug 12, 2015 7:08 pm Post subject:

We have Honda 50's EFI - we also have the service manual. Honda sends out a service newsletter. One of the newsletters recommended that the Service Tech try Chevron Techron before any dis-assembly of the motor. After reading that, we now use Chevron Techron once a year.

I'd try that first.

T.R. Bauer · Posted: Wed Aug 12, 2015 11:04 pm Post subject:

If there is no FI light on, it really sounds like it could be dirty and clogged injectors as folks have mentioned. Seafoam works pretty well too. I'm still interested to see if the FI light is on. If so you have a hard failure somewhere. If not, all electronics are in working order. Or, at least the computer "thinks" they are.

Barry Rietz · Posted: Thu Aug 13, 2015 9:29 pm Post subject: Rough running Honda

Sounds like "T Bauer" has it correct! Dried "corn alcohol" in idle circuits!

jack keifer · Posted: Thu Aug 13, 2015 10:18 pm Post subject: Honda 50 rough running at idle

I am not familiar with the "FI" light. So I looked through the owners manual again and could not find anything there. Can someone help me out?
I am going to look into the additives.
Jack

T.R. Bauer · Posted: Fri Aug 14, 2015 12:42 am Post subject:

It's just the check engine light and controls the EFI system. I don't see how dirty injectors would cause it to come on. If it is on, flashing, or comes on and then goes off, the event will be stored in the computer.

jack keifer · Posted: Fri Aug 14, 2015 10:46 am Post subject: honda 50 running rough at idle

The check engine light has never come on. And it runs fine above idle. This engine has always had non ethanol gas and I use portable tanks, so at the end of the season I drain them completely into the Yukon, and I follow the book to drain the fuel system on the engine, including the on engine water separator, it never has any water in it. So I decided to take it in next week to the dealer for a diagnostic check.
Jack