tune up help '82 rude 115

[thehermit]

Greetings,<br /><br />Just performed a compresion check...all cylinders @ 120 except #3 is @ 110! One book tells me this is OK the other one says >5 diff is bad....what does the board think??? <br /><br />I also asked my mechanic about the theromstat (hasnt been done since I've owned it 6yrs). He said if it hasnt been done to just run the motor. Is there any way for a backyard mech to test this tstat to see what its doing (I removed one of the hoses and it dosnt look that cruddy for a salt water boat)? I can touch and hold the block while idleing on the muffs in yard. I guess I am gearing up to tackle this!<br /><br />and timing...I have read all the posts on timing...this motor runs good now and if it aint broke...can I just check for peace of mind?<br /><br />Thanks...this is a great source for info!!!<br /><br />Cape Cod Hermit

 

[rickdb1boat]

Re: tune up help '82 rude 115

Hi Hermit<br />110 PSI is OK on the one cylinder. Still within 10% of the others. Might try a decarb once and see if that helps bring it up a little. If the boat has been used in saltwater, just change the thermostat out. They are cheap enough not to mess with. Plus if it's stuck open, your motor will run cooler and carbon up faster, not to mention running below par due to cooler cylinder temps. If the motor runs good now, there's not much else to do. I don't know the timing specs off-hand right now. It's easy to check though. A manual will tell the specs you how check it.<br /><br /> <br /><br />decarb<br /><br /> <br />Parts And Diagrams

 

[thehermit]

Re: tune up help '82 rude 115

Hey Rick,<br /><br />Yea decarb is also on the horizon (along with the tstats i guess) thanks for the weigh in on compresion! seems like its ok for the old goat

 

[ledgefinder]

Re: tune up help '82 rude 115

If a good decarb doesn't help, I'd continue to poke around for the root of that compression difference - it could be that you have a carb running lean and are beginning to toast that cylinder. <br /><br />You have two thermostats, one for each side. Both sides of the block should be (if I remember right) aound 140 degrees F - so you can rest your hand on the block for about 5 seconds. If one side is a good deal cooler than that, about the same temp as the ocean water, you've got a stuck thermostat. The thermostats are a BEAR to change on this motor (or an interesting mechanical puzzle, depending on your viewpoint), you can search the archives here for discussions and advice on that point. I'd leave them be if the temps are OK. <br /><br />Opinions differ on the seriousness of a stuck thermostat. It's worth mentioning that Mercs had no thermostats up until the mid-1980s(?). Others feel a thermostat stuck open is as bad as one stuck closed. Clearly the motor will run more efficiently and idle better with the thermostats functioning.

 

[thehermit]

Re: tune up help '82 rude 115

ledgefinder and folks,<br /><br />can you apply the touch test (5 second rule) on the block above 1 and 3 when running in the yard on muffs or do I need to be running the motor for a bit in the water and then try this? <br /><br />I did search the tstat archives and it seems if I hit trouble I will be drilling holes in the cowling to access the bolts (which I thought of and also saw mentioned.<br /><br />Also I did do the carbs with a rebuild kit a couple of years ago and plan on taking them off again this year soon to go through again. If I can remember there was no real needle valve adjusting screw to "lean" it like on small engines....thats why I stuck to swapping gaskets ect....<br /><br />after I do decarb...tstats and biannual water pump I was going to bring it in to the pros for a sychronize and timing check...I just dont get all that stuff in the maunual....hey and I dont want to burn up anything like a cylinder...<br /><br />WILL DECARB FREE A STUCK THERMOSTAT?

 

[ledgefinder]

Re: tune up help '82 rude 115

The motor should come up to operating temp OK on just the muffs - takes maybe 2-3 minutes. <br /><br />Didn't mean to worry you about the 110psi. As long as you've been careful about off-season storage, fresh gas, etc. since the last carb clean, you're probably fine. I run one of those $2 inline fuel filters on mine, and always use portable tanks that I can reliably clean offseason. Not a big fan of permanent tanks for 2stroke outboards - just seen too many cases of gummy and/or watery gas - though I know a big boat going a ways offshore needs to carry a lot of gas. <br /><br />Timing & synch won't move on their own on these motors (not like the old days when points would wear).

 

[ledgefinder]

Re: tune up help '82 rude 115

Decarb isn't related to the thermostats (just kind of an oven-cleaning for your combustion chambers).

 

[thehermit]

Re: tune up help '82 rude 115

ledgefinder,<br /><br />decrab a thermostat....what was I thinking OK got my head back on now...<br /><br />I do have a perm tank (18gal) but aslo have a fuel water seprator installed...are you recomending a cheap (auto type) inline filter in addition to the seperator? <br /><br />I will try the hand temp 5 sec test tommorow I will have the boat in the water then....