Re: 1988 - 175 Mercury - Tune Up Question
Hello,
What parts can I replace to do a tune-up on my Mercury. I replace the plugs every year but last year it was running a little rough at idle and headway/slow speed, stalling, etc.
I assume it is spark related, because when I smash the gas on this thing she goes flat out and runs great.
Should I replace (power pack?), or something like that. Willing to put some money in this engine because it is great.
Thanks
Your assumption if faulty for sure. If it was spark related, it likely would perform poorly when you mash the throttle.
Over time, varnish builds up in the carbs, needles wear, floats sink, etc. That's likely where your problem is. HOWEVER, if you want a good running engine you can trust:
1. Run a compression check on it. If it's a little low, or a little uneven, look up the decarbon procedure here, do it, and re test. If compression is poor, you have major mechanical trouble and no amount of "tune up" will fix it. Either fix it, or run it till it blows and go get another one.
2. Look for the obvious. Is the fuel enricher leaking forward?. If you pump up the primer bulb tight, then give it a firm (not white knuckle) squeeze, does fuel come out of one of the carbs? Is it running cold because there's some frog legs caught in the thermostats? If it still has the "idle stabilizer" module on it, disconnect it and try it without. It's been known to cause this sort of trouble, and the test (disconnect) is free.
3. If compression checks out good, put in a fuel pump kit. It's 20 bucks or so, and should be an annual maintenance item anyway. A leaking diaphragm would cause the symptoms you describe. Don't replace the filter at this time. Do it later if needed after it catches whatever you knocked loose doing the fuel pump.
4. Next step would be to check the link n sync. For this you need the factory manual, a timing light, and a depth gauge (I use a cheep chineese dial indicator), and lots of patience the first time. It's not exactly intuitive at first. Gets easier if you do it a few times. It is, however, well within the shade tree mechanic's realm of doability.
5. Still rough, it's carb overhaul time. Again, go by the book, and look carefully for something that would cause the mixture to be off. Do all 3 at the same time. Carefully clean the gazillion small passages. Use new gaskets, especially the center gasket in the bowl. While the carbs are off, peek into the manifold and look for any obvious reed damage.
6. Still rough, assuming all the above steps have been taken, it's probably reed problems. You have to pull the carbs and reed blocks off, lap the blocks (by hand with a piece of emery paper and a sheet of glass) and install new reeds, might as well be Boyesen reeds, as they aren't any more expensive, and are better.
To have a mechanic do all this would be a couple of grand. It's all within the scope of shade tree mechanics.
hope it helps
John
