Mercury SportJet 90 Stalling

[jetdriven]

This message was started a couple of weeks ago and was deleted by Steve along with all the other recent posts.<br /><br />I have a 1994 SportJet 90 with the Force 3 cylinder powerhead. After running for approximately 10-15 minutes the engine seems to drop a cylinder and then totally stalls. It will start again and runs fine for only a minute and then stalls again. This goes on and on like this if you take it above 2500 or so rpm unless you let the engine sit until cool. It drops a cylinder and stalls unless you keep it around 2000 rpm. Seems you could drive like that at 2000 rpm all day.<br /><br />I thought it was the fuel system for a long time. It's not. Carbs rebuilt twice, new check valves and diaphragm in fuel pump and in lines.<br /><br />New ignition switch and harness<br />New lanyard kill switch<br />New red stator<br />New red stator adapter<br />New rectifier/regulator<br />Rev limiter is OK. Stalling happens even with it unplugged.<br />New switch box. I thought this was the problem when I last posted on this topic. Well, the new $200 switchbox acts the same as the old one.<br /><br />Compression when engine is cold:<br />Cylinder 1 is 130 psi<br />Cylinder 2 is 90 psi<br />Cylinder 3 is 137 psi<br /><br />Is it the bad compression on cylinder #2 causing me these problems? I can't check the compression with the engine warm, so I don't know if it's dropping when warm. Does compression normally drop when these engines become warmer?

 

[wakataka]

Re: Mercury SportJet 90 Stalling

JetDriven - <br /><br />Sounds like you're having almost as much fun with your SportJet as me! I had a somewhat similar problem a couple of weeks ago. Turned out to be some loose bolts on the reed plate. This is the part to which the carburetors are attached. There are about a dozen small bolts holding this assembly onto the engine block. I had one that was only finger tight, allowing an air leak. <br /><br />I don't think it is your compression causing this problem, although the middle cylinder does seem low. My compression is always better when warm. It's currently running 140, 125 and 140. I put new rings in it last July. My middle cylinder had a broken ring that left some scoring in the bore. I honed it as good as I could, but it is still losing a little compression there. The engine runs fine, though.<br /><br />Do all your plugs look similar, or is one noticibly different? When my engine was acting up, my middle plug was shiny clean, while the other two had the normal brown deposits.<br /><br />It's a long shot that your's has the same problems as mine, but it's probably worth a look.<br /><br />Good Luck - they are fun when they do run!

 

[Capt Ken]

Re: Mercury SportJet 90 Stalling

Had one of my customer's with the same boat drive me crazy last week. Lost bottom cylinder, thought it was carb and did find a plugged vent on the carb. Went to start it and the stator decided to quit and not fire anymore. Replaced the stator and would run fine at the shop but like crap once it hit the water. Finally found a broken reed plate in the lower reed block. You need to find out if its fuel related when you lose a cylinder or ignition.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

RowHome: Thanks for the advice about the reed plate. I will check it out. I have the engine pulled, so as I disassemble it I'll watch for loose bolts. You asked about the plugs. They all looked good. Maybe a little extra oily on the #2 cylinder's plug, but hardly at all.<br />CaptKen: I'll check for a broken reed plate before I tear the block down. Maybe I'll get lucky. I don't think that it's electrical. This running for the first 15 minutes perfectly is really strange. I mean, it runs as good as new until it starts to cut out.<br />What about the fuel recirculation system? Can that cause such behavior? I wouldn't think so.<br />I will post again after I get the reed plate off.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

The reed plate seemed to have good gasket seals when I removed it.<br />The reeds plates seem to be OK. Each one sprung back at about the same force when I gently pulled them up from their seat. I don't see any cracks in the reed body. There is some corrosion on the brackets that hold the reed plates, but the reeds are clean.

 

[wakataka]

Re: Mercury SportJet 90 Stalling

Jetdriven - <br />Your symptoms could be caused by a plugged vent on the fuel tank or a restriction in the fuel line. <br />My Bayliner has some kind of ball check valve in the elbow fitting on top of the fuel tank. It limits the rate at which fuel can be withdrawn from the tank. If you try to pump fuel at a high rate, the check valve closes. I believe this is meant to prevent a rapid loss of fuel if the fuel line breaks. If this valve partially failed, it could restrict the fuel flow so the engine couldn't run at high throttle settings. <br />Put a squeeze bulb on the fuel line near the engine and see if the bulb stays hard while it runs. If the bulb starts to collapse, you've got a restricted fuel line or vent line.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

I thought it was the check valve in the tank that you've suggested. I replaced it with a regular elbow with no check valve. I also had the tank out to make sure that it's clean. The tank is venting, too. It even stalled on me with the gas cap removed from the tank.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

Hey RowHome,<br />What you wrote on Aug. 24th (to the guy having trouble with his SportJet 120) sounds a whole lot like what I'm experiencing. At full throttle your engine wants to die after a while. Then it re-starts, and seems OK at lower throttle. Maybe it is my compression problem then?

 

[wakataka]

Re: Mercury SportJet 90 Stalling

JetDriven - <br /><br />My earlier problems were due to the engine seizing up from the timing being advanced to about 40 degrees BTDC by the idiot I bought it from who was trying to hot-rod the boat. He had even fabricated a longer timing link because the factory link wouldn't allow the timing to be advanced this far. He must have been running it on racing fuel. Of course he didn't mention this when I bought it and I didn't think to check the timing before running it. When I ran it on regular fuel, it seized, complete with melted piston crown and broken rings. After the seizure, it started and ran OK for maybe another hour. What finally caused it to stop was when a piece of the broken piston ring got on top of the #2 piston and pounded the spark plug gap shut.<br /><br />The fact that my engine was running OK, at least for awhile, with broken rings in #2 leads me to belive that low compression would not cause the problems you are having. Mine still has somewhat low compression in #2 due to the scoring of the bore, but it runs OK.<br /><br />Have you checked to see if your engine is running hot? I suppose if you had blocked water passages or a bad thermostat you could be overheating it and causing it to lose power. Mine does not get very warm to the touch. Even when running hard you can lay your hand on the cylinder head. If your's is getting too hot, this could possibly cause it to run bad or partially seize up. I hope that's not the problem, because it means that you've probably got some internal damage by now. <br /><br />By the way, if you're going to put new rings in it and don't need to bore it, it is possible to do this without splitting the crankcase. There is just enough room to get the rod caps off working through the intake ports on the "bottom" of the engine. It's a bit of a trick keeping all the needle bearings in place when you reassemble it. I used some grease to hold them in their cages while I set the rod cap back on. <br /><br />Good luck<br /><br />RowHome

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

RowHome,<br />About the needle bearings: how did you get them out of the block when you removed the rod end caps? Will they hang in there without falling into the case?<br />My engine runs nice and cool, like it should. Thanks for the advice about removing a piston without splitting the case. You have saved me a lot of work here. I'm going to re-ring and hone that bad cylinder and then see if that fixes the problem. I agree with you that 90 psi compression probably shouldn't cause the problems that I'm having. I don't know what else to try though. Thanks again and I'll post when I get the new rings in.

 

[wakataka]

Re: Mercury SportJet 90 Stalling

JetDriven - <br /><br />Remove the carbs and the reed plate. You can see the rod ends through the ports in the bottom of the crankcase. Set the motor on it's cylinder head and carefully remove the rod cap. You'll need a 1/4 inch 12 point socket. The needle bearings are captured in a two piece cage. On my engine,the needle bearings stayed in the cage after I lifted off the cap. Pick the needle bearings out of the cage. You can then push down on the connecting rod, moving it away from the crank throw, and get at the other half of the needle bearings. The manual says not to use a magnet on the needles. Not sure why. A q-tip with vaseline on it can substitute as a grabber if you drop one. I marked the cages so they would go back in in the same orientation as they came out, although they are symetrical and will fit either way.<br /><br />Reassemble by inserting the piston into the bore. You'll need a ring compressor. It's a bit of a trick to get the rod end to meet up with the crank throw, but you can work a screwdriver through the exhaust ports and push it into place. <br /><br />Once the piston is in, turn the engine back on it's top and move the crank throw out of the way. I put a wadded up rag in the bore before turning the enging on it's head to keep the piston from coming out. Put the half the needles into the upper half of the cage with some grease. I used regular general purpose whell bearing grease, althouth there is probably something better, this didn't seem to cause any problems. Use only as much as you need to keep the needles from falling out. Once the bottom cage and bearings are sitting in the rod cap, move the crank throw into place over top of them. Then insert the two needles that go on either end of the cage. These two aren't captured until both halves of the cage come together. <br /><br />Put the other half of the cage on in the same fashion, then put on the rod cap, using new bolts with red locktite. BE SURE THE ROD CAP LINES UP WITH THE ROD. There are no indexing pins or grooves on it, and it can slip out of allgnment and ruin the crank. There is a small patch on the rod that is ground smooth before they split the cap off at the factory. You should not be able to feel any ridge when dragging a pencil or a scribe across this smooth patch when you put it back together. Mine went fairly easily. Just don't torque the bolts down until you get it lined up, or you can ruin it.<br /><br />I hope you've got a manual for the other bits. I used the Clymer one, which was adequate for this job. If you hit any snags, you can e-mail me at XYZwakataka@charter.net Remove the capital letters from the e-mail address. I disguised it to prevent spam.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

Excellent procedure. I really appreciate it. I have the factory Merc manual for the boat, but it does not say anything about aligning the connecting rod end cap. I'm glad that you brought that up.<br />I pulled piston #2 and it has two broken rings and a big slice on the edge of the crown of the piston. The cylinder escaped damage, somehow. The top compression ring broke and part of it entered the exhaust port. On the stroke back up it cut into the piston and through the second ring. There are no dings in the head or on the top of the piston. The exhaust port is a little beat up inside, but the bore is OK. I'm going to hone it and put in a new stock size piston. I'll let you know how it runs when I get it back together.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

Thanks to everyone who offered advice. Especially to RowHome for telling me how to replace a piston without splitting the case. That saved me a lot of work.<br />The boat runs fine now. Cylinder #2 has the new piston in it. The compression is:<br />cylinder #1 = 127<br />cylinder #2 = 135<br />cylinder #3 = 125<br />The boat is running fine now.

 

[rudeafrican]

Re: Mercury SportJet 90 Stalling

I'm glad you got the problem licked. If I was you, I would've honed the other 2 cylinders and replaced their rings as well. Saves on labor down the road.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

Yeah rudeafrican, I had the same thought as I was reinstalling the powerhead. If I were doing it all over again, I would have replaced all of the rings.

 

[wakataka]

Re: Mercury SportJet 90 Stalling

JetDriven - <br />Glad to hear you're back on the water. I'm just curious, what type of boat do you have and do you know what the top speed is? I'm trying to figure out if I should be getting more than about 39 mph (GPS) out of my '93 Bayliner Jazz. I'm turning about 5100 rpms at that speed.

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

My boat is a 14 foot 1994 Stinger made by Classic Boats of Austin (TX). I bought it new from a dealer in 1998. I have never seen another one like it, although they must be out there. I think it may be heavier than your Bayliner. Top speed is about 38 mph at 5200 rpm on calm water according to the speedometer. I don't have a GPS. <br />I think that your boat is moving along pretty well. Kenimpzoom has a 1994 Jazz and I don't think he's ever hit 40 mph in it. <br />I hope this is of help to you.

 

[kenimpzoom]

Re: Mercury SportJet 90 Stalling

Nope never hitten 40 MPH.<br /><br />I get about 34 MPH with 3 people or 37 MPH with just my self (240 lbs).<br /><br />Ken<br /><br />www.sportjetworld.com

 

[wakataka]

Re: Mercury SportJet 90 Stalling

Sounds like my boat is right in the ballpark. I wasn't sure how good of shape the pump was in, but it must not be too bad. <br /><br />I've put some washers under the back of the ride plate to keep it from porpoising. I think it cost me a couple of mph on top end but made the boat a lot more stable in choppy water. I've not seen this trick documented in the manuals anywhere, but Mercury clearly designed the ride plate to be adjustable. Just put washers under the rearmost screws to deflect the rear portion of the plate downwards and it acts like a trim tab. Wonder if that's why they call it a "ride" plate? <br />

 

[jetdriven]

Re: Mercury SportJet 90 Stalling

Yeah, I've done that washer trick, too. It never helped me much on my hole shot, though. I bought a set of SmartTabs trim tabs from Overton's for $159 that uses gas-charged cartridges...no wiring and they're self-adjusting. You might want to try these. They let me stay on plane at about 12 mph when I am alone....used to be about 20 mph was minimum planing speed. And, to get on plane, I had to get my rpms up to at least 4800 or it would never plane with me alone. Now it planes at about 4400 rpm with 2 people in it. Also, with two people before the trim tabs, I could never get on plane, even at 5200 rpm, unless the passenger went up to the front of the boat. I even had a new wear ring in the jet drive and couldn't get it on plane. I used to porpoise a lot, like unbearably for some people. These tabs make it ride smoother then my friend's 16 foot runabout. Sorry for the long post, but these stern-heavy boats should have come with these. At least some of the sea-doo guys caught on a little sooner when it comes to tabs.