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2007 Honda BF50 Rough/Rich Idle

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Armandt

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I purchased the boat/motor about 2 months ago. Motor ran really good the first couple of trips out although it did seem to have a slight rough idle, but I took it as being normal. Then last week I went out bass fishing for a full day, I was mostly idling/going at slow speeds along the shoreline. After the first couple of hours the motor started idling really rough/shaking, it would even misfire every once in a while. By the end of the day the motor would just die at idle and even when going up to WOT on the way back to the boat launch it would bog down at around 4500rpms and the rpms would be erratic. Pulled the plugs shortly after and they were wet with gas and completely black(which probably explains the WOT issue due to fouled plugs). Motor seems to be idling very rich.

I have set the idle speed to 1000rpm up from 800rpm(which helped smooth out some of the motor shaking), synched the carbs, adjusted pilot screws to 2 turns out(they were at 2 1/2 turns out), adjusted the valves, and changed the spark plugs. Will be doing compression check tonight or tomorrow night.

After all adjustments I ran the motor at idle on muffs with new plugs and after about 30 min I pulled the plugs and they were wet/black again.
Took the boat out for a couple hours on Saturday and no more problems with WOT pulls strong and gets up to around 6000rpm with no hesitation or bogging. Still idles rough and seems like the longer the motor idles the worse it gets(guessing because plugs load up with fuel).

Could dirty carbs cause something like this? (by the looks of the screws/bolts id say they have never been pulled of the motor)
Also, could it be the starting enrichment valve that stuck open? Anyway to check this?
Ignition issue?

Any thoughts/ideas would be greatly appreciated.

Thanks,

Armandt
 
Armandt said:
I purchased the boat/motor about 2 months ago. Motor ran really good the first couple of trips out although it did seem to have a slight rough idle, but I took it as being normal. Then last week I went out bass fishing for a full day, I was mostly idling/going at slow speeds along the shoreline. After the first couple of hours the motor started idling really rough/shaking, it would even misfire every once in a while. By the end of the day the motor would just die at idle and even when going up to WOT on the way back to the boat launch it would bog down at around 4500rpms and the rpms would be erratic. Pulled the plugs shortly after and they were wet with gas and completely black(which probably explains the WOT issue due to fouled plugs). Motor seems to be idling very rich.

I have set the idle speed to 1000rpm up from 800rpm(which helped smooth out some of the motor shaking), synched the carbs, adjusted pilot screws to 2 turns out(they were at 2 1/2 turns out), adjusted the valves, and changed the spark plugs. Will be doing compression check tonight or tomorrow night.

After all adjustments I ran the motor at idle on muffs with new plugs and after about 30 min I pulled the plugs and they were wet/black again.
Took the boat out for a couple hours on Saturday and no more problems with WOT pulls strong and gets up to around 6000rpm with no hesitation or bogging. Still idles rough and seems like the longer the motor idles the worse it gets(guessing because plugs load up with fuel).

Could dirty carbs cause something like this? (by the looks of the screws/bolts id say they have never been pulled of the motor)
Also, could it be the starting enrichment valve that stuck open? Anyway to check this?
Ignition issue?

Any thoughts/ideas would be greatly appreciated.

Thanks,

Armandt
Click to expand...


Fuel enrichment valve is open (rich) until motor is running . 12-13.5vdc is applied the valve coil and will slowly close , 1-2 minutes. Consider purchasing the Honda carb manual through Amazon

This was the advice from Mike "Honda Dude" , solved my BF50 issues .

Tim
 
Definitely sounds like the enrichment valve.

After you are done, sync the carbs again. This engine REALLY needs perfectly synced carbs -- mine was shaking and dying at idle until I learned this.
 
Thanks for the replies.

Just an update. Did compression test and got 186, 186, 188. They are a little below spec but seem acceptable. I would imagine the cylinders are pretty covered in carbon from all the rich idling which might affect compression results.

Removed carbs last night and they were actually really clean, no gummed fuel anywhere and all jets/ports were clear. Gave them a good cleaning anyway with some carb cleaner and compressed air.

As for the starting enrichment valve... as far as I can tell it is functioning properly. Meets spec with measured 22 ohms resistance. Applied 12v power supply to valve, and checked carb passage after 5 min as per manual, and it was air tight. So the valve closed up just fine.

I also disconnected the enrichment valve at idle and metered the voltage from motor and it came in at 7.5 volts. Doesn't that seem a little low?

Any ideas??

Thanks
 
Let's back up a little...

When you sync'd the carburetors, did you pinch off the vertical hoses going between the carburetors...and the one going over the top carburetor? If not, resync. You need to isolate each carburetor. You will probably need to adjust the idle stop to keep the motor running when you do so....the idle decreases when the hoses are clamped. Likewise, when finished and removing the pinching devices, you will have to readjust the idle again.

Also,for 50's 2004 and later the idle mixture screw should be 2 1/8 turns out. Probably not significant for this problem.

The voltage reading does seem low...is this AC ? I do not think the manual says what it should be. So...7.5 might be correct.

You did not answer my question whether the motor starts relatively fast, then decreases in speed. If it does, then the bystarter operation is probably good.

Mike
 
I pinched off the vertical hoses between carburetor 1-2 and 2-3. The manual did not mention pinching the hose on carb 1 going back into intake manifold. Does that hose need to be pinched as well?

It is actually DC. The motor does seem to idle up around 1600rpms for the first minute or so then slowly decreases to 1000. Which makes sense as the bystarter slowly closes.

Just waiting on gaskets now, then everything will go back in and I will re-sync carbs. Maybe it will fix the initial rough idle. But since all 3 spark plugs are equally wet/black, could that also be related to carb sync?

Thanks
 
Yes, that hose needs to be pinched off too.

The black plugs are probably not related to the carb sync.

It does sound like the bystarter is doing its job.

Have you checked the thermostat to see if it is stuck open? That could cause the black plugs.

Mike
 
So I finally got everything back together yesterday. Took a look at thermostat and it was closed, took it out and cleaned it. Synced the carburetors again while pinching all 3 hoses, idle did not seem to get any better. Decided to decarb the engine with seafoam. Changed oil and plugs after decarbing. Ran the motor for 45min and no more black plugs. They look dry and light brown. Rough idle still there though.

I guess my next question is whether a slight rough idle is normal? Should this motor idle perfectly smooth? Here's a link to video of it idling.
https://youtu.be/oXtLIVI7zlw
 
I'm not sure myself. I have the same issue and am curious as to what height the valve is set. There is a adjustment piece to it and was trying to figure out the appropriate height.
 
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