Super Jet UPDATED 3/17: SuperJet Running Away/High Revs On Start... Need Help!

[retroicon]

So I've been having all kinds of problems with the fresh rebuild of my superjet motor. It's running the stock dual 38's with 145 mains, 75 pilots, and the stock 1.5 needle and seat. The carbs just underwent a complete rebuild, with new diaphrams, and the needle/seats are new too. It's at 1.25 turns out on the low, and 1 on the high.

First I ran into an electrical problem, the connector on the start/stop switch was bad... not the switch, but the connector from the switch to the ebox. Replaced that with a weatherpack, and now it fires... but, now I have a new problem.

When I start the ski, it revs to what seems like 3,000 - 4,000 RPM and it stays constant until I press the stop button. I've only let it do this for 5 seconds or so because I'm not in the water, and not wanting to run anything into the motor using a flush kit until it actually runs right...

The other odd thing is, sometimes it wouldn't fire unless I took the flame arrestors off, and choked one carb with my hand...

So I was thinking air leak maybe (fresh motor build, all new gaskets) until I read this...

This is not a big deal at the moment. I'm kinda looking for confirmation.

The ski is running good. But lately when I fire it up, after it sits for a day or two, it revs up significantly for 30 seconds or so. Then will idle normally. (as if there was plenty of fuel in there prior to starting)

I'm guessing that one of the needles is not seating properly. And, because I store it outside, the pressure builds through the day from the sun.

What else could it be?

Thanx,
Dan

Perfectly fine, all our skis are that way, we do tend to run up our idle screws for a faster than normal hot idle, so when we start them cold they're just a bit lean, as long as you keep one finger on the stop button and one on the throttle in case you get a runaway engine...pin the throttle wide open and keep pressing the stop button as fast as you can and that will stop a runaway engine, or like some say, if you don't have dual exhaust, plug up the exhaust outlet with your foot and smother it out.

That was from this thread... http://www.x-h2o.com/threads/86426-Needle-quot-not-seating-quot&highlight=revs

Does anyone else's ski do that? Revs up to the point where it seems like a runaway on start when it's cold? And, how the hell do you let it run that fast for 30 seconds without cooling to see if that's what's really going on?

I mean, I trust Chuck's advice because he knows what he's talking about... but this just sounds crazy to me. It runs lean, so it revs up for 30 seconds before getting to normal idle?

Can someone help me understand what's going on, and maybe get this fixed so I can get out on the water?

Just so we're on the same page.

Stop/Start switch is Ok. Checked that. Fuel lines are in the right spots, brand new OEM fuel selector switch, brand new fuel lines. It's basically all new... new ADA head, new 83mm pistons, new fresh bore and hone, new fresh freeride porting (by LPW).

What could be going on? Is it likely the lean condition... if so, how the hell do I stop it from doing that on start? And if you don't think it's the lean condition, got anything else for me to check?

-G

 

[retroicon]

SuperJet Running Away/High Revs On Start... Need Help!

Just wanted to add to this... it's from another thread. (yes, I use the search. )

It sounds like your ski is running lean...but that does NOT necessarily mean an air leak. It could also be starving for fuel.

- do you have any pinched fuel lines?
- is the check valve on the tank working correctly (letting air into the tank)?
- did you recently open your carbs, and forget to put the clear diaphragm back into the fuel pump?
- are the jets clear?
- is the fuel petcock clogged?
- if you can get it to idle at all, did you try spraying a bit of ether near the crank seal and see if the ski revs up?

Those are the easy, quick things to try that I would do first...

Fuel lines not pinched.

Check Valve appears to be working. If I blow through the line, air gets into the tank...

Clear pieces are in the carbs, and new during the rebuild.

Jets are clear, pulled the carbs 2 days ago and checked that, and checked the screens too.

Petcock is brand new OEM just removed from the package, and not clogged.

As for the last one, spraying something near the base gasket while it's running... if it's already at 3k-4k rpm... without cooling... how would I leave it running long enough to test? And, that sounds like a dangerous test... spray a flammable gas at a running motor that could have an airleak?

 

[BruceSki]

check the sync on the carbs. If one butterfly is slightly open it will run away.

Edit: Another thing i usually do when I put new fuel lines, empty carbs, and a new fuel selector is remove the return lines and blow through the one way valve on the tank to create fuel pressure and prime the fuel system and the carb. Then you know you have consistent fuel flow and air in the fuel lines is not the reason for the runaway.


did you double check your fuel line hookup as well? I know it sounds stupid but its easy to mix up.

I did this on the last motor i built and felt like a jackass once i realized i had to supply and return lines hooked up backwards. It would start on the primer then lean out and run away on me with no more fuel.

 

[waterfreak]

lower your idle and manually choke the carbs on cold starts till they are primed and engine is idling normally

 

[retroicon]

check the sync on the carbs. If one butterfly is slightly open it will run away.

Edit: Another thing i usually do when I put new fuel lines, empty carbs, and a new fuel selector is remove the return lines and blow through the one way valve on the tank to create fuel pressure and prime the fuel system and the carb. Then you know you have consistent fuel flow and air in the fuel lines is not the reason for the runaway.

I am seeing a ton of air in the lines, it's definitely not full of fuel...

did you double check your fuel line hookup as well? I know it sounds stupid but its easy to mix up.

I did this on the last motor i built and felt like a jackass once i realized i had to supply and return lines hooked up backwards. It would start on the primer then lean out and run away on me with no more fuel.

I've seen this mentioned a few times, and think I have it right, so let me just confirm...

On the 1st carb, the one towards the rear of the ski, there are three nipples. The first one is on the pulse plate, and that has the pulse line going to it from the intake manifold. The second nipple is on the center of the carb body, facing the rear of the ski, and that has the fuel line coming to it, from the petcock... the 3rd nipple I'm sure is right.

2nd carb has both fittings on the pulse plate, one in, one out.

-G

 

[retroicon]

lower your idle and manually choke the carbs on cold starts till they are primed and engine is idling normally

The idle is already as low as it goes, neither of the adjuster screws are touching the stop plate, and both butterflies are closed as far as they'll go... I confirmed this with the throttle cable taken off too, just in case it was keeping the butterflies open a little.

As for manually choking the carbs, got a suggestion on doing both at once? I can do one with my hand while hitting the start switch, but not both at the same time. Maybe put a towel over the top of each?

 

[retroicon]

And just adding my own question here...

If it's a lean condition, would opening up the low speed screws to something like 3 turns, just temporarily, be a decent test to see if this is the problem? I'm thinking that should make it go way rich, being so far open... am I right?

 

[BruceSki]

The bottom nipple should be the fuel inlet/supply.

The one on the part of the carb closest to the cylinder should be your pulse. It is the middle line.

The top line should be your return to the tank.

 

[BruceSki]

The second carb does not have a fuel pump. The carb closest to the rear of the motor has your fuel pump (middle nipple) and the pulse from the crankcase makes the diaphragm in turn control the needle to allow fuel into the carbs.


I would make sure those lines are connected correctly before you start turning screws and messing with jetting. It should run with that jetting.

 

[retroicon]

Right, 2nd carb has no fuel pump... just the slave.

On the picture attached, the line coming out of the fuel filter, and into the carb... which would be closest to the outside of the hull... that's the fuel intake line, right? Or said another way... the pulse line goes into the fuel pump/pulse plate, and the fuel line from the petcock goes into the fuel filter, and then out of the fuel filter into the carb into the nipple that is lowest on the carb. (in your picture, it's the one furthest to the right)

 

[BruceSki]

Correct

 

[retroicon]

Then I've had it right all along. There's another thing to check off the list...

 

[BruceSki]

okay. next step make sure the lines are primed. Pull the return line off the tank and blow into the check valve. If fuel comes out of the return you know you have fuel pressure through the fuel circuit.

After this you can continue to diagnose

 

[Waternut]

If you're running at 3-4000 rpms consistently, I wouldn't think you have a problem at all. If your idle screw isn't touching the adjustment plate, then your throttle cable isn't adjusted properly and you need to loosen it so that the carbs can close more.

Your fuel lines can't be mixed up or it would die after a second or two. It's totally common for an engine to run away when you first crank it up. The air in the fuel lines is going into the carb and causing less fuel and more air and that creates what seems like an air leak. Once you have enough fuel in the lines, it'll clear up. Priming the carbs by placing your hand over them is like choking it and works if you aren't using a primer. A run away engine will start up and immediately shoot up to max rpms. Doesn't sound like you're having that problem.

 

[waterfreak]

The idle is already as low as it goes, neither of the adjuster screws are touching the stop plate, and both butterflies are closed as far as they'll go... I confirmed this with the throttle cable taken off too, just in case it was keeping the butterflies open a little.

As for manually choking the carbs, got a suggestion on doing both at once? I can do one with my hand while hitting the start switch, but not both at the same time. Maybe put a towel over the top of each?

If your throttle plates are fully closed and the engine is still idling high then you have an air leak somewhere!
If that's the case, you may want to do a pressure test on the engine.

Also, make sure you inspect your pulse line carefully (no cracks or tear)

 

[augustaf]

Have you considered deleting your choke and installing a primer? With the carb throttle plates closed and a primer squirting gas you would experience a nice slow idle.

 

[retroicon]

If you're running at 3-4000 rpms consistently, I wouldn't think you have a problem at all. If your idle screw isn't touching the adjustment plate, then your throttle cable isn't adjusted properly and you need to loosen it so that the carbs can close more.

It does the revving, even with the throttle cable off of the carb... I thought of that too.

Your fuel lines can't be mixed up or it would die after a second or two. It's totally common for an engine to run away when you first crank it up. The air in the fuel lines is going into the carb and causing less fuel and more air and that creates what seems like an air leak. Once you have enough fuel in the lines, it'll clear up. Priming the carbs by placing your hand over them is like choking it and works if you aren't using a primer. A run away engine will start up and immediately shoot up to max rpms. Doesn't sound like you're having that problem.

I have a primer, no choke... but even still, if I'm not choking one of the two carbs by placing my hand over it, it won't start...

 

[retroicon]

Have you considered deleting your choke and installing a primer? With the carb throttle plates closed and a primer squirting gas you would experience a nice slow idle.

I have a primer... when I prime to start, that's when this is happening. I can't start at all without priming.

 

[retroicon]

And just to re-confirm... the check valve has the word "tank" and an arrow on it. I'm assuming that the arrow actually point to the tank, so that when you're looking at the check valve, the word "tank" is upside-down, and the arrow points to the gas tank... correct?

 

[jaxrider]

I dont see how it could rev like that if the throttle plates are closed. I think you should pressure test your engine.