runaway engine

[bammajamma]

I have a 97 seedoo challenger 1800 with 787 engines. One of the darn engines didn't want to shut off till I pulled the choke.
Has anyone had this problem and has found the exact problem that has cause this to happen. I have read other posts but there were not answers that said what it was and how they fixed it after changing or fixing the problem. example would be ( I change the carb gaskets and that was the cause of the runaway lol) any help please.

 

[jammin777]

i had a 97 gsx runaway on me twice and had zero problems! sometimes they runaway just because. but a vacuum leak can be a source.

 

[LouDoo]

I know you mentioned it in your post, but the first place I would look is the carb. base gaskets.

Lou

 

[ski-d00]

runaway is fairly common, more so on the 951. just pull the choke like you did, nothing else will stop it.

without a load, these motors run very freely and it just happens. I wouldn't look for a leak if it runs perfectly on the water.

if the throttle cable isn't adjusted properly, or the idle is set too high, or is you rasp the throttle heavily, these all can cause runaway.

 

[ken0276]

The runaway issue is caused by the carb butterfly not closing all the way.

 

[AdamXP800]

The runaway issue is caused by the carb butterfly not closing all the way.

This is not always the case with a runaway. There are many reasons for a runaway. Sometimes it happens when there is no underlying issue. With no load on the motor it can happen easily

 

[ken0276]

I have been fixed this issues a lot on my two stroke model boats, the butterfly won't close perfectly is caused the engine for not stopping, that's why they used the choke to kill the engine.

 

[AdamXP800]

I have been fixed this issues a lot on my two stroke model boats, the butterfly won't close perfectly is caused the engine for not stopping, that's why they used the choke to kill the engine.

Ok........ If you "have been fixed" so many of these it must be the only cause.
Haha I'm jk

 

[Sportster-2001-951C-Stock]

They can run away, not unusual. A vacuum leak can cause it(such as intake manifold leak, worn crankshaft seals, or misadjusted caburetor butterflies), but more often there's nothing wrong found. Make sure your choke works properly so you can stop it, these are high performance 2 stroke engines and they're on the edge of the tuning curve. They won't run away on the water when the jet pump has a load of water, though.

A little piece of carbon in the combustion chamber can become an ignition source.

The engine begins to go into compression ignition mode(dieseling) and there's no load on the engine so off it goes....... This phenomenon is actually rather common for 2 strokes but especially the Rotax motors.

Recheck anything that was recently done to the engine, especially any intake tract work, how does it run otherwise, are the spark plugs a nice cardboard brown? Change them if they;re black and loaded with carbon, or tank it our and run it at 75% throttle for 10 minutes, that should clean the plugs up by burning off carbon.

The choke is your friend, make sure it's working properly and pull it immediately when this happens.

 

[Sportster-2001-951C-Stock]

I have been fixed this issues a lot on my two stroke model boats, the butterfly won't close perfectly is caused the engine for not stopping, that's why they used the choke to kill the engine.

A sticking butterfly or throttle cable can aggravate the condition and is ONE of the common findings but a sticking throttle doesn't cause the engine to diesel, and usually there are other signs of sticky throttle like higher than normal idle in water.

So yes, the throttle system needs to be checked to make sure it's not sticking, but this may not be the root cause in this case, there may not be a root cause aside from the engine having enough compression and the right combination of temperature, humidity and air/fuel mixture and perhaps even a small piece of carbon in the cylinder, just enough to coax compression ignition conditions.

Just by adjusting idle too high can coax the engine to slip into compresion ignition mode and run away, it's just like a vacuum leak. A too lean fuel mixture can cause it, perhaps the idle mixture screw(s) can be opened 1/8 turn to enrichen it a little.

Also, could be the carburetors need rebuilding, they may have gum in them. Gray colored fuel lines are the clue, these fuel lines corrode inside and plug the carburetors with gum, this restricts fuel flow through the tiny passages of the idle and low speed fuel circuits.

How does the engine run otherwise, is the throttle response crisp or are there flat spots/areas where the operator has to "nurse" the throttle, indicating carburetor issues? Not good if the answer is yes, the motor is running too lean and won't last long that way.

A 2 stroke engine can be destroyed if it's not running right b/c the fuel system is too lean, the pistons will overheat and burn the oil film on the cylinder walls, causing a seizure. A carbureted(specifically, wet manifold) 2 stroke engine receives it's lubrication by virtue of the fuel carrying the lubricant to the wetted surfaces such as cylinder walls and crankshaft bearings, if the cylinder is not being fueled properly then it also isn't receiving the lubricating oil and may seize.

 

[Luv2Camp]

So what do you do if you removed the choke and installed a primer system in it's place? Had mine run away on me while I was winterizing. Started to spray the fogging oil and away it went. It was screaming. To make it worse, my flush hose fitting broke when I tried to get it attached to get water to the engine and it went on for about a minute like that. I cut off the fuel supply to make it stop.

 

[Sportster-2001-951C-Stock]

So what do you do if you removed the choke and installed a primer system in it's place? Had mine run away on me while I was winterizing. Started to spray the fogging oil and away it went. It was screaming. To make it worse, my flush hose fitting broke when I tried to get it attached to get water to the engine and it went on for about a minute like that. I cut off the fuel supply to make it stop.

Honestly, I don't understand why anyone would prefer a primer as opposed to a factory choke, some sales guys were lining their pockets, IMO.

So, it's really not unusual to experience a runaway, but since I have to be so careful about what the heck I say in my posts because there are some thick headed know-it-all's out there having fits b/c their reading comprehension can't keep up and they think everyone needs to remain stupid and unable to think for themselves, I can only suggest that there are plenty of ideas given in the thread above, and leave it at that.

 

[Dennis]

The answer to your question Luv2Camp, is to pump the primer when the engine starts running away. The extra fuel the primer is supplying will bring the run away under control.

 

[Luv2Camp]

The answer to your question Luv2Camp, is to pump the primer when the engine starts running away. The extra fuel the primer is supplying will bring the run away under control.

Thanks Dennis, I would not have thought to do that. I would have thought adding more fuel would only make it worse!

 

[Luv2Camp]

some sales guys were lining their pockets, IMO.

.

I am sure the $19 I spent on my primer system I installed did not line anyone's pockets!!! LOL.... For me, I like the primer system better as I get it to start on the first shot where with the choke, I did find it was cranking a bit. Plus I like to modify things! LOL...

 

[Dennis]

You're not alone. Alot of people think that. Not ENOUGH fuel (or too much air) is what is causing the run away.

 

[Sportster-2001-951C-Stock]

I am sure the $19 I spent on my primer system I installed did not line anyone's pockets!!! LOL.... For me, I like the primer system better as I get it to start on the first shot where with the choke, I did find it was cranking a bit. Plus I like to modify things! LOL...

To each his own of course. Primer almost cost you a motor, or may have....... They can runaway if they're a hair lean, read the above posts and the hundreds of threads prior to this one concerning the subject.

 

[Luv2Camp]

To each his own of course. Primer almost cost you a motor, or may have....... They can runaway if they're a hair lean, read the above posts and the hundreds of threads prior to this one concerning the subject.

Motor is still ok... I would not lose sleep if the motor does get smoked though as I am looking for a reason to replace it anyway as it does have either a leak in the case half or the RV seal!!!! Getting tired of the smoke generated at the first start up if it sits for a few weeks or the piss of oil out of the exhaust the first start if the season!

 

[Sportster-2001-951C-Stock]

Here's a whitepaper on the subject of 2 stroke engine autoignition, submitted to the Society of Automotive engineers:

http://papers.sae.org/982481/

 

[bammajamma]

I to thank all of you guys, one other thing I noticed I had some air bubbles in oil injector lines could that be a cause the lean condition?

To futher explain how this happen, I was running the boat out of the water at home using the hose so I guess with it not in the water could cause it to happen with no real load on the jet pump.

I have another ?^ when this does happen when you pull the key why do it not kill the spark plugs power?


Here is some more detail about the engine, the engine backfired, so pulled the engine and found that the flywheel cup was not aligned with the hole so I fixed that and the rotary valve was not set to 147-65 so I fixed that too. When I bought the boat the guy told me that he had it done by a mechanic, for hells sake that is one sorry mechanic who ever it was damn. More then likely it was the guy I bought the boat from that did it. For the other motor I had replace the crank it had a bent rod and that engine now runs great. I cleaned the rave valves and replaced the bellows and gaskets. I noticed that the rave valves on the runaway engine don't have the two grooves on them and they are just flat. Does that make any difference or is that just a rave makers difference.

Guess should mention the carbs are brand new and they have the Acceleration Pumps.


guess I take it to the water and see if running it on the trailer makes any change.



THANKS AGAIN FOR THE RESPONSES

 

[bammajamma]

update I found that one of the spark plug wires was bad and that only one cylinder was getting fire. so this caused the problem