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Honda BF8A (1994) intermittently choking

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bxdobs

New member
Have used this motor for 7 years with no issues on a fresh water sailboat ... usage is low (minimal 15 Gallons of fuel per season) ... motor nears hull speed at 50% throttle ... marginal prop depth limits higher throttle except under calm conditions so rarely run at greater then 50% throttle

Issue ... the motor was running smoothly at about 30% throttle when it suddenly sounded like it throttled back (when motoring we lock the throttle) this wasn't a case of the lock disengaging ... within seconds the motor resumed it's previously set RPM ... thinking the almost empty fuel tank might have picked up some moisture (had been very hot then humid) I decided to changed over to our full tank. The behavior didn't improve and it actually started getting worse to the point where it was more like choking response at any percentage of throttle above idle

We tried going out again on another occasion but encountered the same issues plus had a real struggle to get the boat back in under windy conditions without consistent power it is easy to loose control of this boat

At that point I:

- dumped and refilled the empty tank with 91 octane 0% Ethanol
- drained the carb via it's drain screw
- cleaned the needle/jet valve
- checked the plug wires
- visually inspected the fuel filter for cracks or contamination (clear filter)
- checked the carb fuel (looking for any signs of water)
- checked the engine oil (looking for any contaminants)
- checked temperature
- checked intake and exhaust ports
- checked all the fuel linkages for choke and throttle
- ran up the motor for 30 minutes both in an out of gear tied up to dock with no repeat of the issue

Yesterday because it was calm we decided to try our luck ... the motor started fine and idled fine for several minutes before we ventured out ... minutes later we were again back in this Extreme Choking mode.

- the motor almost behaves like it has the choke wide open (confirmed that choke was physically in run position)
- aggressive throttle up down can momentarily restore normal run condition but then quickly reverts to this intermittent CHOKING mode.
- some throttle settings appear to do better then others
- so far the motor hasn't actually died during this condition it just stays running roughly
- on all three outings we were able to limp back in under almost idle power but that was touch and go on windy day ... yesterday was more so as idle was sounding like it would die any moment

I suspect idling is getting worse due to continued running of the motor in this strange mode (the plugs are possibly getting fouled) ... I haven't check the plugs yet because they are difficult to get at with the boat in the water.

Looking for suggestions?

Thanking you in advance for your time.
 
It sounds like you have already done a lot of checking.

Here are a few more things that you can check externally (without taking too many things apart)....

1. Temperature...you said you checked it...what was the temperature? Thermostat opens between 140 -150 deg F, except for engines in Serial number range 1000004 -1199999 where the thermostat opens 158 - 176 deg F. So make sure it is coming up to temperature.

2. Check the timing marks. There is a "T" with a line on the flywheel should align with the rear mount for the recoil starter (by the cam pulley) and the punch mark on the cam pulley with the punch mark on the top of the engine between flywheel and the cam pulley.

3. Change...do not just check....the spark plugs NGK DR5HS.

4. Check the oil and see if it is too high or fuel diluted. Oil should be a little below full mark. When checking the oil for this motor, you do not screw the dip stick all the way in....just put it in to where you would start screwing it in.

5. Make sure that you tank is vented. Loosen the cap if not sure.

At the shop, compression, spark and timing are the first things that I would check. However, it is a bit hard to do that on the boat.

Since you checked so many things, pay close attention to the timing, oil level and spark plugs.

A few places to start.

Mike
 
Thanks for your response

hondadude said:
It sounds like you have already done a lot of checking.

Here are a few more things that you can check externally (without taking too many things apart)....

1. Temperature...you said you checked it...what was the temperature? Thermostat opens between 140 -150 deg F, except for engines in Serial number range 1000004 -1199999 where the thermostat opens 158 - 176 deg F. So make sure it is coming up to temperature.

Used the old fashion wet finger approach ... the engine was cool enough to touch with a wet finger

2. Check the timing marks. There is a "T" with a line on the flywheel should align with the rear mount for the recoil starter (by the cam pulley) and the punch mark on the cam pulley with the punch mark on the top of the engine between flywheel and the cam pulley.

Not sure if this motor has a timing chain ... When my Toyota had issues with a stretched chain, the engine was both hard to start and it continually ran like S$%t ... the puzzle with this Honda is that it appears to work fine for a bit then it goes in and out of running properly

3. Change...do not just check....the spark plugs NGK DR5HS.

The motor's current installation on the back of the sailboat transom makes it very difficult to remove the spark plugs while in the water

4. Check the oil and see if it is too high or fuel diluted. Oil should be a little below full mark. When checking the oil for this motor, you do not screw the dip stick all the way in....just put it in to where you would start screwing it in.

The oil is at the top of the full mark without being screwed in ... the oil is clean and shows no signs of contamination

5. Make sure that you tank is vented. Loosen the cap if not sure.

Both tanks are always vented which is why my first thought was the weather may have caused some condensation to occur inside the almost empty tank

At the shop, compression, spark and timing are the first things that I would check. However, it is a bit hard to do that on the boat.

I would have to pull the boat out of the water to do this and at that point I would not put it back in until next season ... it is looking more and more like our season is over due to this issue ;(

Since you checked so many things, pay close attention to the timing, oil level and spark plugs.

A few places to start.

Mike
Click to expand...
 
The motor needs to come to temperature to run correctly.

Also, this motor has a timing belt and it is possible that it jumped a notch or two.

Mike
 
I too thought plug fouling/failure as I read your post. I think you may need to "bite the bullet" and pull the outboard for troubleshooting/maintenance if you want to restore reliability.

Look in the ends of the plug wires while you have them off and make sure that there is no "rusty colored" look inside the boot. It's an older outboard and...sometimes....the plug wires and coil do need to be replaced. It's just the way it is.

The rusty color look is a sign I have seen often on failing, high resistance plug wires. BUT..the plugs themselves are WAY more likely to be the issue. I say that because it runs good some of the time. If it were a coil or the wires, it would likely run bad ALL the time.

The gas tank vent suggestion..(run with cap loose) is another EZ check. Don't fail to try that.

Good luck.
 
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