Super Jet UPDATED 3/17: SuperJet Running Away/High Revs On Start... Need Help!
- Thread starter retroicon
- Start date
- Location
- jacksonville florida
Dan, like chuckie said, if the throttle plates are closed all the way it should not idle. Make sure you did not get any of the black paint off your carbs in your low speed jets while you were putting them back together. this happened to me one time. maybe you cracked your intake manifold with all that destruction you did to your ski. good luck with the hunt
retroicon
XX-xx-XX-xx-XX
EDIT: See my next post!
Just wanted to come back to this thread to give an update... I hate it when people ask for an answer, then you see 200 posts listing possible solutions, and the guy who had the problem with his machine never comes back. Kind of makes a thread like this pointless if the rest of us on the forum never know what the final solution was.
Anyway, I finally got around to pressure testing the motor just a few minutes ago. I started at 11lbs, and within 4 minutes it was down to 6lbs on the gauge. I'm going to test it again just to make sure there aren't any leaks around the seals where I closed off the carb openings on the intake, and around the exhaust manifold.
But as of right now, it's looking a lot like an air leak is the problem.
-Gary
EDIT: See my next post!
Just wanted to come back to this thread to give an update... I hate it when people ask for an answer, then you see 200 posts listing possible solutions, and the guy who had the problem with his machine never comes back. Kind of makes a thread like this pointless if the rest of us on the forum never know what the final solution was.
Anyway, I finally got around to pressure testing the motor just a few minutes ago. I started at 11lbs, and within 4 minutes it was down to 6lbs on the gauge. I'm going to test it again just to make sure there aren't any leaks around the seals where I closed off the carb openings on the intake, and around the exhaust manifold.
But as of right now, it's looking a lot like an air leak is the problem.
-Gary
EDIT: See my next post!
Last edited:
retroicon
XX-xx-XX-xx-XX
NEW Update: Found a leak around one of the seals where I was pressure testing... I put more soap into the water and really soaked the seals around where I blocked off the carb intake area, and one of them was leaking. I'm using freeze plugs to block off each hole. 1 1/2" freeze plugs for the carb holes, and a 2" freeze plug for the exhaust manifold.
That's the exact kind of plug I'm using.
That's the exact kind of plug I'm using.
retroicon
XX-xx-XX-xx-XX
Alright, yet another update...
So I found the leak around one of those plugs and managed to get the seal nice and tight, then I ran another leakdown test starting a 11lbs, and after 10 minutes I was down to just a little under 7lbs. That doesn't seem like a big leak to me, so I'm going to do a few more 10 minute tests, and then run a few more at 30 minutes... i'll post the results later.
-Gary
So I found the leak around one of those plugs and managed to get the seal nice and tight, then I ran another leakdown test starting a 11lbs, and after 10 minutes I was down to just a little under 7lbs. That doesn't seem like a big leak to me, so I'm going to do a few more 10 minute tests, and then run a few more at 30 minutes... i'll post the results later.
-Gary
- Location
- Maryland
Forgive me if this has been said before but I have not read every post. Have you tried running directly from the tank to the carbs with new hose (Bypassing the fuel selector and filter)? Have you confirmed that the timing is correct?
retroicon
XX-xx-XX-xx-XX
Yes, all the fuel line is brand new, and I've tried with the original selector, with a brand new OEM selector, and direct from the tank.
And as far as I know, timing wouldn't cause a runaway, that said, it's in the original factory position, and since it's running away on every start... there's no real way to check timing anyway.
retroicon
XX-xx-XX-xx-XX
Another update... tested a few times last night, and it was pretty consistent in losing about 5lbs on the leakdown test over a 10-15 minute period. After the 15 minutes, it'd lose pressure more slowly, but it kept losing over the next 2-3 of hours until it got all the way down to 0lbs.
Last edited:
- Location
- Cape Canaveral, Fl
Did you ever figure out what the problem was?
retroicon
XX-xx-XX-xx-XX
Yeah... I did.
So contrary to what everyone wanted me to believe with the carbs, or timing, or having the lines hooked up backwards, or the petcock, or whatever else... it was an airleak.
No one ever seems to want to believe you on a forum when you say you know what you're doing, or what you've done, when putting an engine back together, or that you've already checked, re-checked, and triple checked your work on the easy stuff. ( stuff like making sure the fuel lines are hooked up right, or that the carbs were put back together properly )
I know everyone is just trying to be helpful, and I always appreciate that... but when you've said 10 times in a row that you've checked something... give the poster the benefit of the doubt, and eliminate that as a possible problem.
Anyway... rant over, and here's the deal...
The reason for the slow airleak was a bad front crank seal, and all of my initial tests were done with the flywheel/stator cover still on the motor because I'd just put on new gaskets and seals all the way around. Every seal and gasket was replaced with a new, OEM Yamaha part... including the front flywheel gasket, which I seal with 1211 because I ride in salt 99% of the time, and I want to be sure everything is sealed up TIGHT.
I didn't want to pull the motor, and take everything back apart again because I knew my gaskets were all new, OEM, and I used a new, OEM front crank seal too... the problem was, the new front crank seal had a small slit in it which was causing the slow air leak...
It looked like someone had put the end of a box cutter through it at some point... maybe when a box was opened, or maybe it was just bad from the factory. Either way, it was a bad seal.
Now the slow air leak on initial testing... down from 11lbs, to 6lbs or so over that 10 minutes time is because the seal had just a small leak, and that leak was behind a well sealed front flywheel cover. It was a slow leak from the crankseal itself, and it appeared even slower with the flywheel cover still on.
I think that also explains why I never got a full on runaway, and why it seemed to take a couple of seconds to get up to about mid-throttle and never further in my testing... I think the leak wasn't big enough to draw in enough air to go lean enough to cause a full on runaway... but it was big enough to cause enough air to escape, causing a middle of the road lean condition. ( that's me guessing, but seems logical to me based on what I know about motors )
Basically, enough air leaking in to cause the RPMs to go up, but not enough to cause full on runaway immediately. I'm sure that had I kept it running or water tested it, that the leak would have gotten bigger and bigger, and that the heat would have gotten high enough to cause that lean condition to be worse... but, because I never had it running for more than 10-15 seconds at time, the leak never let in enough air to go full runaway.
I'm sure a lot of guys here have had the same experience with OEM parts that I have... sometimes the outer semi-clear plastic isn't in the best condition when you get your stuff. I'm saying that because it didn't seem odd to me at all to get a new, OEM part, with a plastic wrapper that wasn't in the best condition. I've had that from Riva, Greater, Wamilton's, Blowsion, and plenty of other very reputable dealers over the years. So, when the wrapper had a nick in it, I didn't think twice... ( yes, I still had the wrapper in my box o' parts )
It's just a guess, but like I said, it looks like someone got the seal with a box cutter at some point, and the blade probably went through it causing a slit that was hard to see, but big enough to cause a small air leak in the one damn spot that required a total motor teardown...
Awesome.
So contrary to what everyone wanted me to believe with the carbs, or timing, or having the lines hooked up backwards, or the petcock, or whatever else... it was an airleak.
No one ever seems to want to believe you on a forum when you say you know what you're doing, or what you've done, when putting an engine back together, or that you've already checked, re-checked, and triple checked your work on the easy stuff. ( stuff like making sure the fuel lines are hooked up right, or that the carbs were put back together properly )
I know everyone is just trying to be helpful, and I always appreciate that... but when you've said 10 times in a row that you've checked something... give the poster the benefit of the doubt, and eliminate that as a possible problem.
Anyway... rant over, and here's the deal...
The reason for the slow airleak was a bad front crank seal, and all of my initial tests were done with the flywheel/stator cover still on the motor because I'd just put on new gaskets and seals all the way around. Every seal and gasket was replaced with a new, OEM Yamaha part... including the front flywheel gasket, which I seal with 1211 because I ride in salt 99% of the time, and I want to be sure everything is sealed up TIGHT.
I didn't want to pull the motor, and take everything back apart again because I knew my gaskets were all new, OEM, and I used a new, OEM front crank seal too... the problem was, the new front crank seal had a small slit in it which was causing the slow air leak...
It looked like someone had put the end of a box cutter through it at some point... maybe when a box was opened, or maybe it was just bad from the factory. Either way, it was a bad seal.
Now the slow air leak on initial testing... down from 11lbs, to 6lbs or so over that 10 minutes time is because the seal had just a small leak, and that leak was behind a well sealed front flywheel cover. It was a slow leak from the crankseal itself, and it appeared even slower with the flywheel cover still on.
I think that also explains why I never got a full on runaway, and why it seemed to take a couple of seconds to get up to about mid-throttle and never further in my testing... I think the leak wasn't big enough to draw in enough air to go lean enough to cause a full on runaway... but it was big enough to cause enough air to escape, causing a middle of the road lean condition. ( that's me guessing, but seems logical to me based on what I know about motors )
Basically, enough air leaking in to cause the RPMs to go up, but not enough to cause full on runaway immediately. I'm sure that had I kept it running or water tested it, that the leak would have gotten bigger and bigger, and that the heat would have gotten high enough to cause that lean condition to be worse... but, because I never had it running for more than 10-15 seconds at time, the leak never let in enough air to go full runaway.
I'm sure a lot of guys here have had the same experience with OEM parts that I have... sometimes the outer semi-clear plastic isn't in the best condition when you get your stuff. I'm saying that because it didn't seem odd to me at all to get a new, OEM part, with a plastic wrapper that wasn't in the best condition. I've had that from Riva, Greater, Wamilton's, Blowsion, and plenty of other very reputable dealers over the years. So, when the wrapper had a nick in it, I didn't think twice... ( yes, I still had the wrapper in my box o' parts )
It's just a guess, but like I said, it looks like someone got the seal with a box cutter at some point, and the blade probably went through it causing a slit that was hard to see, but big enough to cause a small air leak in the one damn spot that required a total motor teardown...
Awesome.
Leaking cases or crank seals will cause motor to run rich , not lean .
Air leak would have to be between reeds and carbs to cause lean running .
Air leak would have to be between reeds and carbs to cause lean running .
JT_Freeride
John Tetenes @Jtetenes
- Location
- Long Island
If you have an air leak in your case you have a lean condition not rich. More air than fuel equals lean.
Only reason I bothered to reply is I hate to see bad information posted. It is a myth that crank seal leak will cause lean running. That is all I will say.
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
That makes sense. As the pressure builds in the cases from the down stroke it is going to force the air out. This would increase the fuel to air ratio due to less air. Now someone is going to say "But it will suck air in". Not really. There is 0 pressure outside the the cases. Any suction created is so minimal. Unlike the High Pressure area you have inside the case where it is going to try and force the pressure out.
Thank you to everyone who put in their two cents on this post, I was having what seemed to be the same problem but eliminated an air leak off the back (it's not always a air leak) after a lot of hair pulling, turns out it was one butterfly slightly open causing the same symptoms originally disturbed. Thanks to all that replied to this thread for helping me get back on the water again!
i know this post is super old . BUT i aquired a SJ. my question is this 1 out of the 2 carbs i had from OEM was not in great shape. so i bought a nice used one off ebay . i pulled the jets and pop spring and needle out of the oem one and swapped into the new one along with rebuilding both with mikuni kits. with that being said when i was swapping parts over the old High / low parts where a different thread on the one off ebay vs my oem SJ . my ski currently when starting trys to rev to the moon i think i have both oem and ebay one 1 1/4 turns . so i think i need to set the non oem one to 2 1/4 turns on the L, what should i set the High at one the ebay carb.