Runaway Mtr

[SJ Thumpa]

95 701sn single carb, 210 even comp, race gas, riva non-girdled head, riva exhaust mani with old style performance wet pipe (looks like a dry but not), riva CDI.

Ex racing ski that the previous rider had mixed results with racing similar rn's.
Ski's been sitting with broken hull for six months. Motors always run excellent, smooth power, everyone likes it, only ever changed plugs and cleaned carb. Was running excellently on the last outing. Never been sunk just badly cracked tray.

Been starting it twice a week for 30 seconds.. It usually starts with one push of the primer and a blip on the starter and has always idled smoothly. Haven't been running it on the hose. Went to start it a couple of weeks ago and it wouldn't idle. Revved OK but no go at low revs (took a few seconds to die, seemed like no fuel/spark)

Cleaned the carb, new fuel filter, new fuel lines, cleaned fuel tank, swapped starter mtr, swapped neg lead, new plugs, cleaned and re-aligned pipe, checked compression, checked and cleaned up all electrical connections.
Started her up first time since doing the above last night (throttle cable disconnected) and same thing. Let it cool down between starts. On third start was attempting to slowly adjust ide up and:

Seemed like I may just have got it and then away she went. Revving to the max..... Scary sh**..... Pushed stop, pulled lanyard, full throttled it (no go). Pulled fuel lines at carb and air filter simultaneously, covered carb with hand. Finally died a couple of seconds later. Seemed like an eternity. Heart attack material. It was hot but not cooked.

Just wondering if you think its definitely a case/crank seal leak or could it be inlet mani gaskets? Has anyone else had this happen after having similar non idling symptoms? It definitely was not a stuck throttle. I didn't think this situation could arise with next to no activity and after running so well prior.

Turned her over this morning and all seems OK however I'll check the compression again later when my "plug earther" gets over her "mild" shock. And she claims she had the most miserable Valentines Day....hehe

Any advice appreciated.

 

[Boris]

Pressure test the motor to rule out air leaks.
Maybe you got it hot enough for the spark plugs to glow on your first start ups. Instant diesel.

 

[SJ Thumpa]

Thanks Boris, that was fast. I'll search the leak down test threads and figure the best way. Interesting, I,ve Never heard of glowing plugs causing dieselling. I gave it at least half hour breaks between the approx 30 second runs and had dinner before the last one. I did have to push the starter several times with revs before it would run but waited 15 seconds between pushes but still could be a possibility.

 

[BruceSki]

check your reeds... maybe you have a cracked/missing one... turning up the idle might let it run, but it will make it run away too.

 

[feartheride]

Do a search on dieseling many threads on this

 

[D-Roc]

air in the fuel supply line? lots of motor rev up and away if they are low on fuel, or are first fired up and are priming the air out of the lines. my motor has done it, my buddies team scream does it, my old 550 did it, some guy's x2 at daytona did it. or it could just be an airleak but thats hardly ever the case, lol.

 

[SJ Thumpa]

Thanks guys, going to replace mani gaskets, check reeds and switch carbs (I've got a spare with same jetting). Hopefully fix the idle problem.

D Rok, that could be the hassle. I had fuel flowing (minimal fuel in tank) however the filter never filled right up (was just above the outlet line) as it normally does on my other ski.
Thanks very much.

 

[crammit442]

A cold motor or a motor that hasn't been started for a while will frequently try to run away. Over prime it for the first start and then as needed until it settles into a steady idle. Doesn't necessarily mean there's anything wrong.

 

[2006superjet]

had run away happen to me its the most scary thing ever. i think i pulled both spark plug boots and got a little shoocked but it made it die.
desieling might have been the reason. i started a thread on it a while back