engine runs away - revisited

[surfjunkie]

i've seen many threads where people say their engine revs way up on it's own and people pull a muscle typing "air leak" as fast as they can.

but some folks have other theories such as dirty carbs, incorrect carb adjustment, low on fuel etc.

i tend to think there may be reasons other than an air leak mainly because i had a wb2 that did it once and never again. owned it 3 more years and rode the ******** out of it. never ever even acted like it was going to do it.

can anyone answer a few questions:

why does it do it even after you pull the lanyard. a normal running ski you can have the throttle wide open (kinda like an air leak) pull the lanyard off and it will shut off. why does the air leak interrupt the normal operation of the kill button or lanyard.

could it in theory do the same in the water. could you get dismounted and there goes the ski across the atlantic to...whatever is on the other side.

are there other clues to help narrow down the possiblities. ie this ski is very hard to start. takes many attempts (choke pulled, choke not pulled) also back plug kind of looks ashy white (lean) after running it. ski bogs off idle in and out of the water. but runs seemingly fine once your past that boggy bottom .

i dont want to just bust into it assuming my crank seals are bad. it's a back up ski so i have some time to theorize and pontificate.

thanks for any suggestions.

 

[surfjunkie]

more info...

when at idle out of the water it will kind of change idle speed up and down on it's own. some one said that sounded like it was starving for fuel.

the ski is pretty much stock, carbon fiber reeds and hi comp head is about all. it had a fp on it but i removed it and think i got the carbs back to stock. 130 and 65 jets? put a stock f/a back on and seated the mixture screws and backed them out to what the manual said. one lo speed screw seems stuck (cant back it out any further) and cant remember if i got to the suggested setting before it stopped.

thanks in advance

 

[SJBrit]

When a motor runs away it's "dieseling" which means that the combustion chamber is getting hot enough to ignite without a spark - that's why the kill switch doesn't do anything: the ignition isn't relevant any more. A lean condition will make a motor run very hot, which sets the whole thing off. Your rear plug reading and starting issues suggest you have that problem. I'd also guess that your off-idle "bog" is actually a lean hesitation.

<flexing so I don't pull a muscle>

I think you have an air leak.

 

[Matt_E]

why does it do it even after you pull the lanyard. a normal running ski you can have the throttle wide open (kinda like an air leak) pull the lanyard off and it will shut off. why does the air leak interrupt the normal operation of the kill button or lanyard.

Because the spark plugs get hot enough to glow (i.e., glowplug) so no spark is needed.

could it in theory do the same in the water. could you get dismounted and there goes the ski across the atlantic to...whatever is on the other side.

Not really. It doesn't work well under load (in the water). For a load, the engine needs a lot of power, and thus needs to be moving a lot of air.
An airleak (throttle closed) moves a very small amount of air. However, enough to make the engine run without a load.

 

[surfjunkie]

matt, how quick can a plug get that hot? this ski will run away immediately if i pull the throttle right after starting. that quick?

 

[surfjunkie]

<flexing so I don't pull a muscle>

:biggthumpup:

anyone venture a theory on my b2 doing it once and never again. scenario: down in the keys, had to idle in for like a mile or two to the ramp. put the ski on the trailer, blew out the water like normal and oh shiiiiiiittttttt! yes, i was once a typical couch newb.

 

[Matt_E]

If you are starting it up from cold, and it does it immediately, then I doubt that's the case.

 

[Gilligan]

My ski did this all last summer. I can't find an air leak. Maybe I am too lean, time to fatten it up!

It is torture to hear your motor rev up like that. 1st time is the worst..hitting the stop button pulling the plug wires....disconnecting the battery....and finally stoping. not because of the battery.

I tried the holding the throttle wide open and it works.

 

[Matt_E]

That works best. Pull the throttle WIDE open.

 

[surfjunkie]

could it be a problem with your gas tank not venting properly?

also, did you have the stock yami gas/water inline seperator?

the combination of those two things could possibly contribute to a runaway... its a remote possibility, but possible.. my ski used to want to run away when there was air in the fuel lines after not starting it for a while....the first 2-3 seconds after it started, you had to lightly feather the throttle..

i do have the stock seperator. and i dont know if the tank is venting properly. it doesn't get sucked in after riding for a few minutes. it has all the stock stuff, the plastic vent bubble in the handpole and the check valve thingy.

btw, this is the ski that always has a smell of gas more so than any other i've owned. dont know if that is relevant or not.

 

[Robert]

Once you get done trying those fixes, bring it over and we can pressure test it. Remember last year my blaster had the same exact symptoms. It was the crank seals. I went nuts swapping carbs, changing ignitions and so on.... I have a nice set of SRE's (that I know work perfect) that we can bolt on if you want to eliminate the carbs as a problem.
Thank God you have two skis.
BTW- Checked the waves tonight. Nice form, small, but glassy. I took of Friday!

 

[surfjunkie]

I took of Friday!

me too!:cheer:

not sure if i'll go over though. we're going camping at sebastian and i mainly took off to get the camper ready. if the waves hold i'll do an early session.

i'll take you up on the carbs switch offer. that would narrow it down.

thanks robert. this will be half your ski with all the help you've given me.

 

[sflsurfrider]

sounds like an air leak.

































:haha:

 

[oxnard111]

try just changing your fuel tank vent plastic white thingy, put a regular fuel filter on there

What exactly do you mean? Can you explain in more detail. My ski didn't dosen't have the vent tube bubble thingy in the handlepole, and it has the little water seperator that is on the exhaust side of the ski with the little cap on the bottom. In addition I believe I have the stock fuel filter, but what would you change it do? What do you nean by a "regular fuel filter"?

 

[sflsurfrider]

What exactly do you mean? Can you explain in more detail. My ski didn't dosen't have the vent tube bubble thingy in the handlepole, and it has the little water seperator that is on the exhaust side of the ski with the little cap on the bottom. In addition I believe I have the stock fuel filter, but what would you change it do? What do you nean by a "regular fuel filter"?

just run a short tube from the nipple on the tank to the check valve and dont run through the air/water seperator. if you choose to run through the seperator, keep the cap off the bottom and dont put anything on the nipple that goes toward the handlepole.

also, make sure your checkvalve is good. it should only let air pass through one way - toward the tank.

people do tend to run to yell "air leak" in these situations. i think what is meant is "lean condition". a lean condition can happen from an air leak in a gasket or seal but its not always the case. your internal fuel filter (inside the carb) could be clogged. if you have dual carbs, they could be out of sync. if you have a single carb, the idle could be set too high. your on/res valve could be clogged. ive even seen the fuel pickup pushed to far down in the boot on the tank causing the bottom of the pickup to hit the bottom of the tank and restrict fuel.

 

[keefer]

I have replaced the stock Yamaha fuel filter / water seperators with the Purolator #20004. I have found these Advance auto parts for about $3 as opposed to $15 at Riva or stock Yamaha units. They look identical inside and out and will fit into the stock bracket holder. You might also check the filters inside the carb on the fuel pump side. I have seen these get clogged also.

Sounds like an air leak to me also. I didn't even pull a muscle either.

 

[surfjunkie]

essefel, and they are probably right 9 out of 10 times but i'm just lazy and cheap enough to want to make sure i've checked all the small/easy stuff before i try to bust open the bottom half. i just dont know all the small/easy stuff to check and you just gave me a couple more to add to the list. thanks

 

[Robert]

Don't worry, you don't have to take the motor back out to perform the leak down test. You just have to take it out if there is a leak found in the cases or crank seals.
I took Friday off b/c the seaside fiesta is tonight on Flagler.

 

[SkiDaddy]

Did you check the throttle shaft bushings to see if they were all worn out?

Robert is right, you need to leak test it.

BTW I'm DITW, ignition probs - intermittent spark.:banghead: :banghead: :banghead: :banghead:

 

[surfjunkie]

didnt realize i never updated this thread.

put different carbs on and it never did it again so i guess i'm glad i didn't tear down the whole friggin engine chasing some phantom air leak.