Started engine on LS2000 and it went to WOT and wouldn't kill with any of the switches

[jjtherocketman]

Happened twice today out of the water at my house. Recently had the carbs rebuilt and tuned and after getting my boat home, I decided to crank the engines to see how they were starting. Starboard engine started up fine, but was idling at a high RPM (4-5K RPM). I tried rev'ing the throttle and it went even higher and then went Wide open. Immediately killed the ignition switch and removed the key...still running WOT. Pulled the lanyard kill switch, still WOT. Ran back to the clean out plugs compartment and opened that, still WOT. NOTHING would kill the engine! Finally pulled the choke out on that engine and it died. Waiting a few minutes, then tried it, started ok, but eventually the exact same problem happened. Nothing would kill the wide open throttle condition and kill the engine except the choke. HELP!

 

[Beachbummer]

Air leak past the throttle plate?

Mis-adjusted throttle controls? Stuck Open?

You will want a visual on the throttle plates before trying again.

 

[jjtherocketman]

Air leak past the throttle plate?

Mis-adjusted throttle controls? Stuck Open?

You will want a visual on the throttle plates before trying again.

Yep, my mechanic says airleak. I finally got ahold of him and that's what he said as well. Once the engine gets rev'd up like that, you don't need spark any more if it has an air leak, so even if you kill everything, it screams due to the existing heat/fire already there like a diesel engine. But dang, it freaked me out having never experienced that before. He suggested stuffing a shirt or rag up the tail pipe next time to kill it versus the choke.

 

[Cobra Jet Steering LLC]

yes air is leaking in the intake runs lean and heats the carbon on top of the pistons creating a diesel effect, The way to shut it down if it goes nuts on the trailer is to give it wide open throttle with the key off.

 

[jjtherocketman]

yes air is leaking in the intake runs lean and heats the carbon on top of the pistons creating a diesel effect, The way to shut it down if it goes nuts on the trailer is to give it wide open throttle with the key off.

That's a bit surprising because it was already wide open and screaming at 7,000 RPM-ish.

More importantly, is my only option to solve this issue a complete overhaul? Or start with trying to find the air leak and see if that can be re-sealed (if I'm lucky, perhaps it's up high around the intake manifold?)?

 

[FSH 210 Sport]

That's a bit surprising because it was already wide open and screaming at 7,000 RPM-ish.

More importantly, is my only option to solve this issue a complete overhaul? Or start with trying to find the air leak and see if that can be re-sealed (if I'm lucky, perhaps it's up high around the intake manifold?)?

Did the engines run okay before your carb work?

Perform a leak down test on the engine to check for the air leak.

 

[Cobra Jet Steering LLC]

Yes it is screaming but it is running LEAN the throttle body was shut if you open the throttle it will shut off as long as the ignition is turned off. Doing this floods the hot cylinders with air and fuel , thus extinguishing the glowing carbon and with no source of ignition the engine stops quickly .
Could be a crank seal or an intake gasket reed valve gasket etc. remember the fuel in a 2 stroke travels through the crank case before it gets drawn into the cylinder. In any case I have had the same issue with 2 stroke engines doing that over the years and the way to shut it down is as I described. Otherwise you just stand there in disbelief as it screams itself to death. I had numerous experiences with 2 stroke engines doing that in my many years. But it's your boat do whatever you like.

 

[Cobra Jet Steering LLC]

My first bit of advice is to go over the last job someone did to your engine ,since this is a new issue, it is most likely related to the carb rebuild or an oil line fell off or if it is not using oil injection any more perhaps he knocked off a block off cap. or the base gasket for one of the carbs is leaking.. Also I would not try to block the exhaust when it is screaming like that, aside from personal injury you can also harm the exhaust hoses or the engine gaskets and seals .

 

[jjtherocketman]

My first bit of advice is to go over the last job someone did to your engine ,since this is a new issue, it is most likely related to the carb rebuild or an oil line fell off or if it is not using oil injection any more perhaps he knocked off a block off cap. or the base gasket for one of the carbs is leaking.. Also I would not try to block the exhaust when it is screaming like that, aside from personal injury you can also harm the exhaust hoses or the engine gaskets and seals .

I appreciate the advice and suggestions. My mechanic did just remove the oil injection system this go around after rebuilding all of the carbs on both engines. The intent was to insure those cylinders get enough lubrication as they are getting older and probably due for a full rebuild. One cylinder was starting to get lower on compression (about 10-15 psi lower than all the rest). This recovered some of that loss.

Any "rough" thoughts on how much a complete single engine rebuild should run me? I'll likely do both engines of course, but I'm looking for a "per engine estimate" to know what I'm in for. My guy is usually pretty straight up and reasonable on everything he's charged me in the past. But just wondering what I can expect.

 

[Cobra Jet Steering LLC]

It has been may years since I had a 2 stroke so unfortunately I am not up to date on pricing but if you check with www.sbtontheweb.com prices for rebuilt engines you should have an idea of what to expect.

 

[jjtherocketman]

It has been may years since I had a 2 stroke so unfortunately I am not up to date on pricing but if you check with www.sbtontheweb.com prices for rebuilt engines you should have an idea of what to expect.

Thanks, that was helpful knowing what a fully refurbished engine goes for (about $1500 at this time). Seems like TIME is the key on those, not to expect anything quickly. They have to have your Core first, then sit and wait for them to deliver the new engine.

 

[Beachbummer]

Maybe with a little smoke or even visual observation you can determine where the leak is. might just be a seal or a lose fastener.

 

[4x15mph]

Sounds like you have an air leak and with the carb racks being taken off you will want to make sure new gaskets were used. If you have the high rpm’s again, try pulling the choke out. If that causes the Rpms to go down, you can be sure the engine is running lean due to an air leak

If your engines eventually need to be rebuilt, I used full bore online and did the work myself. It took some time but it was pretty easy if you have a manual.