BF9.9 RPM's hunting while trolling.

Hi folks, first post so go easy on me! I've poured through any thread that seemed possibly relevant with no luck maybe someone has an idea. My problem is the new to me engine won't hold a steady RPM when I'm trying to troll, it will slowly creep up or down I can correct it with throttle input and it will hold for a while then start to hunt off in either direction. Say I'm trying to hold 1400 rpm it will bugger off to 3000+ or drop right to nothing and eventually chug and stall, it never corrects itself.

It starts well when cold on the enrichner and kicks down as it should when warm, but once warm and trolling if I don't catch it on one of it's downward trends and correct it with the throttle it won't restart without adding some fast idle input.The little exhaust port on the back of the midsection has some pretty good black staining below it, and sometimes the exhaust smells rich but not always. Ocasionally it will stall when I pull it back to neutral too.

It's pretty random, it may hold steady for an hour, or it may hunt every five minutes it's geeting annoying. I've done all the obvious stuff serviced the carb, fresh plugs, fuel filter, changed the engine oil as one tech said he's seen fumes from the crankcase vent system cause this problem before but it persists.

The exhaust staining and smell tell me it's a carb/fuel problem but it has remote controls too so could it be a mechanical problem with my linkage in the control box or a sloppy cable? How do I confirm everything is on the up and up in that system? Is there a way to test/bypass the enrichner, do they fail often? That's kind of an expensive part to just throw at it. Any other thoughts?

TIA, John

Hi triplenickel. Welcome aboard the forum!

That does sound like an aggravating problem. My first thought while reading your post is that it sounded like it could be a remote control or under the hood linkage issue. But, it could well be other things too.

As far as it being the enrichener and should you test it, I would think not. Here's why I say that; It starts fine cold, idles up for a minute or two and then idles back down. That says to me the thermo valve is working as designed.

BUT...is it really? I guess there is a remote chance that it is malfunctioning.

Here's how that is supposed to work:

When the engine is cold, the bystarter is in cold start configuration. After start up, the valve receives voltage form the charging system that electrically heats an element that changes dimension and pushes against a spring that would normally keep the valve in rich mode. After charge voltage is removed at shut down, the element slowly cools and allows the valve to reset, over time, back to cold start mode. If you suspect that the bystarter is causing you problems by returning to the enrich mode while the engine is running, it could be one of two things.

The charging system has stopped charging and has allowed the element to cool or...
The element or the wiring to it is intermittently going open and allowing it to cool.

Checking for the first scenario is easy. Simply have a voltmeter handy when you go out and when the problem occurs, check to see what the charging system is doing. If she's not charging then you have found the problem.

The only way to prove the valve would be to take it off and power it up and watch it for some time. If it starts moving from lean (extended) to rich, cold start (retracted) with power applied, then it is bad. I have not seen a bad one in the 6 years I've been dealing with these but that only means failures are rare, not unheard of.

Proving the wiring to the valve is a bit harder. My approach would be to take the supply wiring off at the valve and attach it to an automotive headlamp that I have rigged as a test device. Wire the headlamp in as if it were the bystarter using it as the load for the circuit that you can see when it is working or not.

Now disconnect the supply wire from the charging system and apply power at the beginning of the positive side of the circuit with a jumper to light the lamp. Start "wiggle testing" the wire. Any fault in the power or ground side of that circuit will be readily seen when the headlamp goes out.

Ok, what if it's not the bystarter?

You might want to look under the hood at the parts on this page of boats.net. You don't state the year of your motor so I just picked one.

http://www.boats.net/parts/search/H...SHIFT SHAFT (REMOTE SPECIFICATION)/parts.html

Check items 3,4,6,8,31,43 and any others of those in that area that may be causing problems.

It also occurs to me that you may have a cylinder dropping out and then coming back on line intermittently. It is absolutely AMAZING how smooth these little twin engines can run on only one cylinder. There is a whole "nuther" set of paragraphs to write troubleshooting if that is the case. Sometimes all it takes is that the operator is paying close attention to the vibrations and "pitch" of the sound that the engine is making coupled with an awareness that cylinder dropout could be taking place.

Why don't you repost with your engine's year model and frame number along with any other info you may have so that others here may have a suggestion or two for you.

Good luck.

Good morning jgmo, thanks for the reply. I want to lean towards it being a fueling issue simply because of the rich exhaust and black sludge coming from the exhaust port in the mid-section but what confuses me is why the RPM's will randomly increase so much. I could understand a dirty carb causing the stalling condition but not the increasing RPM's. All those items in the fiche you linked are tight, I haven't opened up the control box by the helm yet but I'm not convinced that's the trouble.

It's not dropping a cylinder, when it's on one of it's downward trends I've removed one plug lead at a time and both are definiteley fireing. I wonder how much better an ultra-sonic cleaning would be than me with sprays and poking small wires ito passages. This boat did come from the States and sat for a while since the previous owner passed away, I have no experience with the high blend ethanol fuels but can't help but wonder if that's my whole issue. I also want to open up the inspection port on my fuel tank (built in) and see what's happenning in there. Thanks again.

Ok, you stated in your first post that you "serviced" the carb. Then, you state on your last post it "sat for a while".

These carburetors will not tolerate anything but the BEST in thorough cleaning after they have been laid up with fuel in them. I would say that you are correct in assuming it is a fuel issue. Most guys find that they have to clean the carburetor more than once to get it right.

The float chamber HAS to come off and all passages need to pass a steady stream of spray or air. The accelerator piston passage that goes up into the main body MUST be completely clear from the float chamber right up to the venturi.

And, the idle adjustment needle valve MUST be removed to completely get the idle passage cleared properly.

The Jet Set oring and idle needle valve oring should NOT be re-used and great care has to be taken to get them back in without damage during re-assembly.

The Jet Set tube can harbor some very small pieces of debris that can be hard to see with the human eye.

The idle, transition and main orifices at the throttle plate MUST exhibit total flow from all feed passages. This usually looks like a six foot stream of carb cleaner when the main and transition are fed with a spray can and a fairly strong "powered waterfall" effect from the idle orifice.

Getting these clean usually involves back flushing through the drillings themselves or a great deal of time in an ultrasonic cleaner with solution.

I would also agree with your vetting of your gas tank and the integrity of all the fuel lines and primer.

Let me know if you need any guidance in going through that carb and I will be glad to help you work through it. I don't recommend even reusing the jet set or idle needle valve but you can if you wish. Having new gaskets and the parts on hand before you start makes the task go more smoothly and quickly. The boats.net is a good source of reference pictures and the parts themselves. They do ship internationally.

Good luck.