2005 8 HP Honda Carbon fouling

[wapiti]

I have a 2005 8 HP Honda trolling motor that spews carbon, especially after running at low rpms for awhile. It starts and runs OK. Dies after trolling for 30 minutes or so, on start up it belches a carbon cloud and then runs OK for another 30 or so minutes. I have taken it in to a local Honda shop twice and they cannot seem to determine why the excessive carbon except that they think it is running too lean. They have cleaned and adjusted the carb, replaced the plugs, etc. and have run the motor on their fuel tank, with no success. Their recommendation is to replace the carb. Has anyone else had similar problems with Honda trolling motors? Any suggestions for a remedy?
wapiti

[Larry H]

Do you mean carbon, like a cloud of dust, or do you mean a cloud of smoke? If smoke, blue smoke is burning oil, black smoke is excess fuel. Black smoke could be caused by a stuck float, which is causing the engine to run rich.

[wapiti]

Larry;
It is a cloud of carbon dust that is emitted. Oil on water produces a multi-color sheen. This emission is definitely not oil but black carbon soot particles. Did a compression test and the compression was very good. The shop has looked at the carb twice could they be overlooking the stuck float?
Thanks for the info.
wapiti

[Sea Wolf]

If it's emitting black particulate smoke, it sounds to me to be running rich (carburetion), or possibly cold (thermostat), as the black particles represent unburned fuel.

Are the plugs in the proper heat range for continuous slow running?

I wonder how they concluded that it could be from running too lean?

Joe.

[Wandering Sagebrush]

I am not sure if this is a new model or classic 8, but the older classic 8s were famous for running cold, VERY cold. Check your oil to see if it has a chocolate look to it (another symptom). I put a new thermostat and hotter plugs in my classic. I finally just got the new model, only because I didn't trust the classic in the ocean.

[Larry H]

wapiti,

I see that Sherwood Park is at 700+ meters, about 2400 ft. elevation. Carburated motors run richer at altitude as the air is thinner. If you are running at a higher altitude than Sherwood Park, that could be contributing to the rich running.
If the carb has been overhauled and is ok, replacing it won't help. The shop should be able to tell you specifically what is wrong with the carb you have now before spending the $$ for a new one.

I would follow up on the thermostat suggestion and also check for the correct spark plugs. I would use the brand and type recommended by Honda, not a replacement from a comparison chart. If the motor is running rich, the plugs will be black.

One additional thing is to try a different gasoline. I was servicing a motor once where the owners gas caused the engine to foul its plugs, but the shop tank did not.

Carbs can be expensive, I would try to be sure that the ignition, thermostat, and fuel are correct before spending the $$.

[Nunya]

First thing I would do, would be to run some sea foam or yamaha ring free through the motor and clean out all the carbon, then see how it runs.

[T.R. Bauer]

Carbon fouling?????

You have got to be kidding me. Even my 6 hp Evinrude twin (2 stroke) can idle all season and not carbon foul. A four stroke normally has no trouble with that. But, with that said, I would check to make sure the choke is not sticking somehow in someway as this causes a really rich condition (easy check as you don't have to take anything apart except the cover). Then, I would check to see if they actually torqued the nuts (all of them, included the manifold it is bolted too) on the carb to see if they were loose as this will cause a vacuum leak and can cause the carb to go full rich in some cases.

With the simple stuff out the way and if you have still found nothing, it is time to check the float to see if it is sticking or set way too high (a float that is too high will cause a rich condition). Then, while you have the thing apart, you might as well clean it really well with intake cleaner and put a carb rebuild kit into it. Make sure you thoroughly clean all tubes and tiny passages or you will likely be doing it again. You will probably find the carb has some varnish, maybe some other gunk, and generally dirty if it wasn't stored correctly - sometimes even if they were.....God knows I have had my share of fuel system troubles over the years and I am pretty meticulous about how I store a motor in the off season.

I strongly suspect that the shop is right, the problem is in the carb. It is tough to tell what it was without a full dissasembly, and even then sometimes hard to tell what exactly was dirty as it doesn't take much crud to screw things up. You can replace it (normally the best, but hideously expensive), or try to clean it up and rebuild it. They are actually suprisingly simple in my opinion, but unless you are used to turning wrenches you may not want to tackle the job.

As others have noted, putting a new thermostat, hotter plugs, and checking the ignition system are all good things to do, but most likely if your engine is running really rich and carbon fouling, it is a fuel system problem. But is is alway good to cover all the bases - especially if they are easy

Good luck to you and let us know what you find.

Tim

[neblig]

I have the same motor, and have had similar problems. My partial solution is to run the motor at WOT for about 5 minutes prior to trolling. It seems to help, but the motor just seems to get more fuel at idle than it needs. Hence the eventual stall. It just seems to want more work to do than it gets at a slow troll. Works fine at mid to full throttle. Sound familiar?
Rob

[wapiti]

Hi Rob;
What you have indicated would seem to backup some earlier suggestions that the motor is running too cold at idle. I think i am going to try the hotter plugs and new thermostat before looking at a new carb. The Honda shop has told me they have cleaned and adjusted the carb three times with no success in reduction of the carbon fouling. Anyone know what a hotter plug would be for this 8hp Honda?
What about thermostats, there is probably only one available?
Thanks!
wapiti

[Sea Wolf]

If you can't solve the problem of needing more loading to keep the engine from loading up, you might try a partial trolling plate or dragging something, like the oft used 5 gallon bucket (!)

I know it's a backasswards solution, but.............

Changing the prop to a lower pitch usually won't help reduce boat speeds at very low rpms, as the slippage is pretty great anyway, and the existing thurst drives the boat pretty easily.

Joe.

[Spike]

Wapiti
I had a 2002 Honda 8 hp that would always foul out the number one, or top cylinder plug. after alot of trial and error and then alot more research I found out that there was a design flaw with the intake manifold so that the top cylinder ran considerably richer. That is all I can remember and I dont know if this effects your engine or not
Chuck

[T.R. Bauer]