Mercury 6-cylinder, 2-stroke SportJet coughing, choking, dying

bluewatersailor

Hi, all -

My recently-bought 1995 Rinker Rocket has the 175xr2 engine in it. The first three or four times that I took the boat out, the engine ran fairly rough - sounded like it was missing once in a while, and kept wanting to stall at idle - but I figured it was just me being unfamiliar with these engines, and maybe it was supposed to sound like that . Today, though, it finally went full bozo on me while I was out on the river; died and refused to restart.

I fiddled with it for a while, checking for spark and fuel (yep, got both), and somehow got it to crank up and stay running - but now it refuses to go above 2,250 rpm or so; in fact, if I push the foot throttle past 1/2, it chokes up and dies. But if I blip the carb fuel lever directly, it'll run up to a good 4000 rpm - without choking. 

So...

I haven't been shipmates with gas engines for a couple of decades or better, so I've forgotten most of what I knew about them. The advice online all seems to point to things like water in the fuel, at which point zapping the half a tank I've got left with SeaFoam sounds like a good general prophylactic. Giving it a fresh set of plugs (and maybe plug wires?) also seems to make sense; I can't get any info on when the last tuneup was done out of the previous owner, so I'm going with a reasonable guess here. But the difference between the "boat" throttle and the carb throttle lever bothers me a bit: it seems to hint that not all is well with timing (which, if I recall correctly, gets advanced when you hit the pedal.)

Anyway: I'd really appreciate any guidance you folks can offer, including ideas on how to tune up this little beastie. I'd really love to get this engine running as well as I can, in addition to making it well again!

zaverin1

Do a fuel sample
plug wires have coils attached to them
 that engine also has two cdi boxes that fail and magnets fail on the flywheel 
stator is also a common item 
all can be checked with a volt meter using different settings.
i would start with fuel,
compression check
and look at plugs 
replace inline fuel
filter and fuel pump screen
if all checks out I would rebuild carbs.
most of the issues are Electrical on those jetS

bluewatersailor

@zaverin1, thanks! I've bought a manual for it, and they've got good diagrams, etc. in it - that's going to be useful - but hearing from someone who knows these things, especially about the bits that have a history of failing, is really great. Much appreciated!

I'm going to see if I can hunt down a set of plugs this morning (an O'Reilly store that's not too far off supposedly has them), and maybe a set of plug wires if I'm lucky enough. The manual doesn't show a screen in the pump, but the inline filter looks generic enough that I should be able to stick one of those little Frams in there and make it happy. Compression... OK, I'll be getting a tester (and a timing light, too.)

It's actually good to hear that most of the problems are electrical; I'm an electrical engineer, so that's a big leg up. In fact, my next major step in restoring this boat to proper function will be rewiring both the engine compartment (which is a horrible, ugly mess right now) as well as the electrical panel (where most of the gauges are either dead, rusty, or showing numbers that I know can't be right.)

Thanks again - it's great having a definite direction to head in!

Willhound

Start with plugs and grab a fuel filter while you're at it. 

zaverin1

If I recall those plug wires have coils on them

bluewatersailor

Willhound said:

Start with plugs and grab a fuel filter while you're at it. 

I pulled the filter; it's totally clear, almost zero resistance to flow, so I've put it back in. Swapped out the plugs - all except for the middle plug on the pump side of the engine; I couldn't get a socket on it (looks like I'll need to get the coil pack off to do that. Sure wish I could get my hands on the "engineer" who designed that layout for just one minute...) This coming week, I'm going to make a "custom" plug socket - as short as possible but still able to grab the plug, and with the sides of the socket top ground to a taper - but until then, that plug gets to stay where it is.

The in-line spark detector from Amazon has turned out to be total crap - only works when it feels like working - and is going right back to them; it's told me nothing that I can base a diagnosis on. Meanwhile, I've bought a nice Bosch timing light that should show me whether I've got good voltage on the plug wire or not... that's going to get put to use tomorrow. I also tossed in 5 gallons of non-ethanol fuel and topped it off with a half a can of SeaFoam; no idea what the previous owner was running in it, but I'm getting the feeling that he wasn't the meticulous type. And that I'm probably going to need to clean out the tank at some point.

I tossed her into the nearby lake today; can't really spend a whole lot of time running this engine with the cowling open at home, the neighbors will start complaining - so I got to do a little more troubleshooting while my sweetie pitched some bait to the local aquatic wildlife. Yep, still the same problem. It's sounding more and more like electrical rather than fuel. No guarantees until I get a meter on the coil packs, switch boxes, and the ECM, but that wiring mess by the engine is ringing all sorts of alarm bells in my brain... a connection could come loose in that junk pile at any time (in fact, the RPM gauge, the bilge pump, and a temp sensor had done exactly that.)
 


Ugh. Some freakin' people's children.

All of that is going to get cleaned up - and I suspect I'm going to find the problem in there. But I'm going to be a good boy for now and troubleshoot properly... first thing tomorrow morning before work.

Wish me luck, folks. If I get lost and disappear without a trace in there, tell my Mama I was brave.

bluewatersailor

More progress -

I built a DVA adapter this morning so I could do dynamic (voltage) as well as static (resistance) tests, and - voila. Clear as day, it's a dead switchbox.

I already suspected it - strongly enough that I went ahead and ordered a pair of switchboxes off Amazon, which should be here tomorrow - but didn't know for sure. The DVA measurement, though, made it obvious: there's a pretty solid partial short across the charge terminals on the box, enough to bring the voltage from ~220V down to 40V. Whoops.

Interestingly (now that I've figured it out, just a bit late!), I remembered another test for switchboxes vs. stators this morning: swapping the stator charge coil lead pairs, blue/red and blue-white/red-white, between the boxes. If the problem moves to the other bank, then you've got a dead stator coil; if it stays where it was, then it's the switchbox. Yep, it stayed in place: 1/3/5 kept on firing nice and hot, while 2/4/6 kept imitating roadkill. The trigger also checked good, both resistance and voltage.

While I was in there, I did a compression test; all the cylinders were at 120-125, which cheered me up immensely.

The new boxes should be here tomorrow...

zaverin1

I agree with swag.
just know that best way to store yours jet is with engine hatch open if possible.
Older jets are known to blow cdi boxes from moisture and pure environment they are in.
specially if it’s salt water 

bluewatersailor

zaverin1 said:

I agree with swag.

Darn, I wish I'd known before. But hey - it's running!!! Spark on all six, what a lovely sound!

just know that best way to store yours jet is with engine hatch open if possible.
Older jets are known to blow cdi boxes from moisture and pure environment they are in.
specially if it’s salt water 

Woah... well, if that happens, then CDI it'll be. But for now - it's been a wonderful learning experience, made me remember things I used to know 30 years ago. Kind like hailing back to my younger days.

Thanks for the help, folks!