engine goes to full RPM at start up!!!

[don't sink]

Mercury 210 carb coming out of winter- started and motor goes to full or close to full RPM - YIKES! I checked the linkage and everything seems to be moving freely as it should

What else should I be checking? I'm afraid of blowing this motor up!

 

[Sportster-2001-951C-Stock]

Yikes, don't blow it up! Check again, perhaps the throttle linkage is binding or was misadjusted, thus isn't fully returning to the idle stop. Or possibly there's a huge air leak in the intake manifold.

Perhaps something like a hose or fogging plug on the intake system was left off or disconnected during the winterizing process?

 

[racerxxx]

Can you manually operate the throttle linkage to verify your are at idle?

 

[don't sink]

I see nothing wrong with the cables or linkage- I had my daughter move the throttle back and forth and it looks good. Now i'm not talking about a 500 rpm difference here...this thing is starting at 4000 rpm which is scary. I fog this motor and it self drains so I do nothing in the area of removing plugs or hoses. I'm going to pull off the air cover on the carbs and see if all 3 butterflies are truly closed but the motor would still need fuel to run this way so its confusing.

Please keep the ideas coming!! Sometimes we can look at something the wrong way and not see the right way till it is pointed out.

 

[don't sink]

Got me thinking about the air leak....are there freeze plugs on this motor? [I probably should know this I know!] Lets say one popped out would this cause the issue?

 

[XP 787]

Freeze plugs are only in cooling passages. An air leak would have to be somewhere in the intake area.

 

[don't sink]

I hate to ask but would this be caused by an ECM that is bad? Please say no due to price! Tonight I will hunt for air leaks

 

[XP 787]

I don't think an ECM has any thing to do with it since its carbed but I could be wrong. If next time you start it and the idle is ok spray intake gaskets with some carb cleaner and listen for changes in idle. This will help you determine where the leak is. Also check vacuum hoses.

 

[XP 787]

Make sure you spray the carb cleaner on a somewhat cool engine, not after it has been running for a while.

 

[don't sink]

The problem is getting it back to a low idle! 4k rpm is not a good setting for testing lol!

 

[racerxxx]

Let's just verify one thing at a time, we can speculate all day long on this or that, but we just need to start at the easy stuff.

Sent from my SGH-T889 using Tapatalk

 

[don't sink]

I agree so that's why I am going after an air leak and then will report back.

 

[buckeye_paul]

Sounds like your low speed steering assist is engaged. Check behind the helm and make sure nothing is caught on that cable. Check the termination on the motor side as well. It might be bound up there.

 

[Sportster-2001-951C-Stock]

The throttle linkage should rest on the stop screw, usually the top or bottom carb, there's only one stop screw to control all the carbs and all the carbs are synchronized by fine throttle linkage adjustment that should not be adjusted unless you understand how it works.

I agree with the poster above, some steering systems will open the throttle slightly when at the end of travel to left or right, this gives some navigation aid since steering is a function of engine speed (no engine thrust = no steering).

But 4,000 RPM isn't exceptionally fast necessarily, a little faster than perhaps it could be (check the factory spec on this), have you ever started the engine out of water before? The reason I say it's not exceptionally fast is the jet pump will drag the engine speed down with a load while the boat is sitting in the water, so engine speed will be higher by about 2x when the boat is out of water.

How familiar are you with running your boat out of water? I don't have a sportjet and I can't speak with absolute authority as I've only seen very few of them but 4,000 RPM doesn't sound incredibly fast. My Rotax motor idles 3200 RPM out of water and that's a normal phenomenon.....

I think there might not be a real problem unless you're certain 4,000 is exceptionally fast, that motor can handle 4,000RPM without any danger. I think you should back the boat on the trailer into the water then start it up and see where the idle speed settles, it WILL be about half at least, I guess.

So give that idea a thought?

If you are quite familiar with how your boat normally runs on the trailer (Trailer running is not considered a comprehensive diagnostic testing method, basically only used to see if the boat is capable of starting), and are absolutely convinced the engine has a problem I still think you should back it into the water for a test but it is possible one of the crankshaft seals is leaking air inward, providing air for the engine to run faster than normal. Any air leaks in the induction system can cause this. But again, 4,000 doesn't seems exceptionally fast to me necessarily unless you're certain it's abnormal.

 

[Sportster-2001-951C-Stock]

BTW, that carbed motor is considerably more preferable IMO, to the later fuel injected versions. Definitely a keeper long term, due to being vastly more simple and less expensive to repair.

I'll add an FYI, (not b/c I think this is the current issue but just as a "What could go wrong, how will I know?" heads-up for hopefully the distant future)

One thing about all 2-stroke engines is if one carburetor or injector is improperly fueling a cylinder the power will be noticeably down from normal and this can cause damage to the fuel-starved cylinder. So, if the engine isn't making power like it normally should then you should avoid running it until finding the problem b/c lack of fuel to one cylinder can cause damage.

 

[don't sink]

Well its raining out so no testing today but do have a few thoughts on the above

-Owned the coat for 6 years now so yes, I am use to out of water running and 800-1200 is the normal idle RPM. 4k is just scary!
-I was thinking the same about putting in water and starting- at least I know it won't overheat and I would feel more comfortable.
-I will laugh my as* off it it turns out to be something as simple and stupid as the steering assist- Never thought of that one but it could be easily the answer too!
-tomorrow I will dig into it based on your ideas and recheck everything again...and again

 

[Sportster-2001-951C-Stock]

The engine is continuously and permanently connected to the impeller so idle speed on trailer is expected to be higher than in water. That is, absent idle speed compensation. Although I doubt there's an idle speed compensator on your carbed motor if there is one that could be malfunctioning. I just don't recall ever seeing an idle speed compensator on any carbed 2-stroke engines but this IS a Mercury we're discussing....???

Regardless, air leaks will cause high idle speed and will damage any 2-stroke engine if run that way under load for very long b/c it causes a lean condition that will roast a piston due to heat. There is such thing as a "smoke test" many shops use where smoke is forced into the intake tract to discover leaks.

So I feel like either there's an air leak somewhere (such as disconnected or rotted hose in intake tract or could even be leaking crankshaft seal) or the throttle linkage isn't returning completely to the idle stop.

Steering assist - Seadoo installed on some boats a system at the helm which connects between the throttle controller and the steering box to bump up engine idle speed when the steering is turned against the limit lock but I'm not sure how they could've accomplished that trick on the Sportjet throttle controller, I don't think you have that feature?

4,000 RPM won't damage the engine, those things tach to near 8,000 I think? But heat will cause damage so don't run it for more than 30 seconds then let it cool. No point in running if you think there's a problem that hasn't been resolved, the results will be a predictably consistent 4,000 RPM.

It's too cold here to think about enjoying the lake yet.

Okay, good luck!

 

[Sportster-2001-951C-Stock]

Another possibility - Speaking of idle compensation, that's often achieved by manipulating the ignition timing advance scheme, and ignition advance is another phenomenon that can affect idle speed.

So if there's an electronic idle speed compensator device on that motor it could be malfunctioning or on most carbed outboard motors I'm familiar with there's a mechanical linkage that connects from the throttle linkage to, and mechanically rotates, the ignition trigger assembly for ignition advance as throttle is applied. That linkage connected to the ignition trigger under the flywheel could be binding or sticking and causing the ignition timing not to return to idle position.

Sorry I'm not more familiar with that particular engine, I've only seen a few and my memory really isn't that great anymore.

 

[Sportster-2001-951C-Stock]

Got me thinking about the air leak....are there freeze plugs on this motor? [I probably should know this I know!] Lets say one popped out would this cause the issue?

Nothing like that, freeze plugs are actually there for draining out the casting sand in the foundry. If one was rusted out you'd flood the boat with water due to a cooling leak but it wouldn't effect running, as least not directly.

Since you fogged the motor yourself I feel more confident the throttle linkage is probably binding so feel free while in the bilge to take your fogging oil and hose down the linkage pivots to keep them from corroding and binding. This includes the location where the throttle shafts in the carbs pivot in the carb bodies.

Also look for anything that might leave the ignition timing advanced, binding linkage or if there's an electronic idle speed compensator doo-dad, perhaps.

 

[don't sink]

it was the cable after all! Well sort of. See that red plastic piece on the left....that holds the cable in place at the engine. It has cracked and is allowing the cable to slip just enough to throw off the stator and cause the high rpms. Simple $10 part causing havoc!

 

[racerxxx]

Cool! Like I always say, use the KISS theor, Keep It Simple Stupid. Always start with the easy stuff and work up to the complex.

Sent from my SGH-T889 using Tapatalk

 

[Seadoobuddy]

Nice find. Cheap fix is good.

 

[Sportster-2001-951C-Stock]

Man, those were great little motors.

Give everything a good hosing down with Corrosion-x or fogging oil, too.

 

[don't sink]

Thanks to all for helping. I must have looked at the cable a 100 times and did not and would not have seen this crack if I did not hear a "click" when the cable seated itself on that one try. I heard the click and knew something was different as I moved the throttle and it took 1/2 hour of inspecting every component with a mirror to see the underneath and then I saw the crack! It only took a 1/4" of movement to cause the high RPM too- I was looking for an Elephant and it turned out to be a mouse!

Thanks again all.....now have to clean all the grease on everything! It never ends does it?