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

[Watty]

It seems like you are wasting time, and looking for problems elsewhere. You should do a leak down test on any new/re-assembled engine anyway. Do the test, and THEN start looking for other problems.

Most of my trouble shooting starts with checking spark strength, doing a compression test, and a leak down test. You can rule out a lot of problems quickly and easily this way and then start looking for smaller problems.

The intake area and rear crank seals are notorious for leaking.

 

[retroicon]

Yeah, I know I'm trying to diagnose anything other than a leak first... one because I don't have any way to do a leakdown test, and two because I don't want to have to pull a newly assembled engine back apart with all new gaskets, seals, etc. I figure I should try to eliminate any fuel system issues first, before pulling everything apart.

How can I do a leakdown test without any equipment to do it? Is there a kit somewhere I can buy to do one?

 

[Matt_E]

It's fairly easy to make a kit.

You need a block off plate for the intake manifold and for the exhaust manifold.
Both are very easy to make with some sheet metal and hand tools.
Once you have those, block off intake and exhaust.
Then take the pulse line off the carburetor and connect a cheap pressure gauge (should be able to get this at any home improvement store) plus a hand pump. Pump up the pressure and watch for leak down.

 

[Watty]

You get yourself a sheet of thin rubber. Cut a gasket the same as your header pipe gasket from it, and make another rectangular gasket with the intake manifold stud/bolt holes.

Put the header pipe gasket between the header pipe and the manifold, and the other underneath the carbs, and bolt 'em both down.

Block one of the pulse lines on the cases (if you have two) and that part is done.

Buy yourself a MTB shock pump with a gauge, plug it in to other pulse fitting (may have to get a hose, and a barbed schrader valve fitting), pump it to 10psi and remove it. Spray some soapy water around the engine to find any leaks if the pressure drops. You'll know in about 20 seconds if you have a well sealed engine or a leak.

 

[Watty]

Oop, beat me to it!

 

[retroicon]

Do I have to remove the exhaust manifold, or could I just remove the headpipe and do it there instead? Seems like it'd be easier to make sure I have one hole sealed, rather than 2.

 

[Matt_E]

Yes, head pipe works fine. That's what I did in the past.

 

[FlightPlanDan]

I'm not saying that you don't have an air leak.

But you still have not put fuel to it while running. Have you?
3000-4000 rpm is not a "runaway".
It's Idleing really high. (might be an air leak)

BTW: blowing on the tank check valve won't fill your hull with fuel.

 

[Waternut]

Test plugs/freeze plugs from home depot or the auto store are 10x easier than block off plates, work better, and only cost a couple bucks. Just my experience though...

 

[Matt_E]

Fantastic idea. :biggthumpup:

 

[FlightPlanDan]

Alright, so I didn't get a chance to check it out at all yesterday, but today my wife walks in and asks me if there's any reason the garage should smell like gasoline...

Yeah, not good.

So I go into the garage, and find about 2 gallons of fuel in the bottom of the hull. The last thing I did was blow air into the check valve, and I left the petcock in the reserve position apparently... add to that I didn't have any zip ties on any of the fuel lines because I'd been taking the carbs on, and off, and on, and off ... and apparently all that pressure in the tank sent the fuel to the petcock where it leaked into the hull.

That wasn't fun, but I think I got it all out, flushed the hull with fresh water about 10 times, and everything looks good... even the paint on the engine looks alright... but it got me thinking.

Two things...

First, it seemed like the fuel lines expanded just slightly at the petcock...they slid off VERY easily. There were no zip ties on those lines, and it looked like both the reserve, and the out lines expanded slightly. So the first thought was... could the fuel lines being slightly loose cause a lean condition because they're sucking in a little air? The fuel line is helix racing fuel line... so yes, it's fuel line.

Second thought was, and this is totally random, but I have a temporary ground wire from the battery to the flywheel cover and it's attached to one of the bolts holding that on... I know this is a LONG shot, but could the ground to that spot be throwing something off ignition wise because it's grounding to the flywheel cover, instead of the starter? (I know this is not likely at all, and probably just me grasping for straws, but I'm putting it out there anyway)

The lines to/from your primer are likely reversed.
otherwise, where did all that fuel come from? Needle not seating? Not. It would be choked out when you get it running.
It would bog if it would run at all.

You either love wrenching, or hate riding.
Because you seem to refuse to eliminate the simple stuff first.

 

[retroicon]

The lines to/from your primer are likely reversed.
otherwise, where did all that fuel come from? Needle not seating? Not. It would be choked out when you get it running.
It would bog if it would run at all.

You either love wrenching, or hate riding.
Because you seem to refuse to eliminate the simple stuff first.

I mentioned where the fuel came from... I blew pressure into the check valve, that sent fuel through the lines and up to the petcock, the petcock didn't have any zip ties holding the fuel lines on and it was in the reserve position, and the fuel was leaking from the loose lines, at the petcock. I'm 100% positive this is where the fuel came from because I had the petcock sitting in a plastic cup on top of the head, and that plastic cup was full, overflowing, and leaking the fuel down into the hull.

The plan was to start it today, but when I walked outside to a hull full of fuel that kind of changed the plan...

And no, I don't like wrenching... at all. I spend about 3 times the amount of time most people spend putting things together so that stuff like this doesn't happen. The last time this ski ran for 3 years without an issue, and before that it was 5 years without an issue. Not a single fuse, wire, line, or gasket of any kind changed... and this is in 99% salt and surf riding.

The only reason this engine was out in the first place was because I broke all 4 motor mounts, and my midshaft housing had the rubber come loose in Daytona... while it was out I figured I'd get a fresh bore, new pistons/rings/clips, and freeride porting to give it a little more power. It was running fine when I took it out... so no, I don't like wrenching, and I do like riding, which is exactly why I was trying to find the REAL reason the ski revs up to 4,000 RPM for 5-10 seconds when I fire it up.

I've been riding a superjet since 1992, and have never had that happen on any of the 4 I've owned... not even a single time. That's why I immediately though airleak, but figured I'd check the easy stuff first, before tearing the engine down again.

And yes, checking the carbs, fuel lines, routing is the easy stuff...

 

[retroicon]

I'm not saying that you don't have an air leak.

But you still have not put fuel to it while running. Have you?
3000-4000 rpm is not a "runaway".
It's Idleing really high. (might be an air leak)

BTW: blowing on the tank check valve won't fill your hull with fuel.

See below... it sure will.

And I wouldn't call 4,000 RPM a high idle, that's more than half throttle on a stocker, and right at half throttle for most 701's... no, it's not a full on runaway, it's not getting hot enough for something other than the spark plugs to ignite the fuel, and the stop button is working fine to kill it... but it's not a high idle either.

 

[retroicon]

Test plugs/freeze plugs from home depot or the auto store are 10x easier than block off plates, work better, and only cost a couple bucks. Just my experience though...

I'll check this out tomorrow. Looks like a trip to Home Depot to put together a pressure testing kit. On that note, if i had a pop-off pressure guage... that'd work to test the pressure, right?

 

[FlightPlanDan]

have you pushed fuel into it while it's running?
Have you run it on the garden hose, to see what the idle woud do with more fuel?
have you put it in the water to see if the same happens?

I'm only trying to help.
I'm no F'ing idiot.

You may very well have air leaks.

But a sain person would rule out all other possibilities b4 tearing the engine down again.

 

[FlightPlanDan]

do you think that the hull filled with fuel because everything is hooked up properly?

C'mon man.

 

[retroicon]

I agree Dan, but it seems we're in the minority... most everyone else is saying "Airleak dude, check that first". I think check everything outside of pulling it apart myself.

And no, I'm not putting it on the hose or running any water through it until I know what it is. If it is a leak, then I just filled my motor with water, maybe just a little, while it's running, and I'm not doing that during break-in on a fresh build. I did that maybe 15 years ago on a fresh rebuild, and that ski never ran the same until I changed the rings, and gave it a fresh hone... (long story, not worth posting unless asked)

P.S. I'm no idiot either. I've been riding a Yamaha for almost 20 years, and kawi's before that... I've been the only wrench on any of them.

 

[retroicon]

do you think that the hull filled with fuel because everything is hooked up properly?

C'mon man.

You don't have to agree with me, but I was the one in the garage and saw it with my own eyes. I blew air into the check valve and the pressure was really up... I was blowing into the lines to clear all the air out, so I blew into the check valve until I couldn't blow into it any more. The pressure was really up.

Picture a balloon... you blow into it, and the air is going to come out somewhere. In this case, I blew into the tank, the air had to escape, so it was pushing the fuel through the out line, into the petcock, and leaking from the loose lines... it happened exactly that way, whether you agree that's what happened or not.

Also, no primer was on the system at this time. The petcock was sitting in a cup, that cup was full of fuel, and both fuel lines were nearly off of the petcock... the fuel was running down the side of the cup, over the head, and into the hull... you could see the streams of fuel running down the head, cylinders, and down into the hull.

 

[FlightPlanDan]

Where are you located?
pm if you don't want to say.
Like Chuckie said, another set of eyes is needed.

 

[SUPERTUNE]

Pull the carb bank off, and air filter top to remove screens (leave air cleaner base on) make sure idle screw is completely out and on the workbench, then hold them up to light (outside or inside) look up from the bottom of carbs up through the throttle plates and see it you can see any light, no light, then an air leak somewhere, light coming through...find out why.
Are the shafts stiff from corrosion in the bushing and preventing closure? Do the throttle plates have air gaps at each side of the throttle plates by the throttle shaft?
This is a problem that occurs when the throttle shafts have too much end play in them.