Sanity check before possible rebuild

[mlbinseattle]

Okay, so I purchased an old 15' with a '76 Mercury 850. I figured it would need some attention. I could get it to start (took a while), but it ran bad. It would idle, but dump on me as soon as I put it in gear. After the initial crank, it would take a while to get it started, again.

To begin with, I installed a new set of plugs. After further inspection, it was also obvious the carb needles were shot as it would drip gas out the carbs after pumping the bulb. Floats were shot, also. Rebuilt the carbs and double checked everything. I also installed a new checkvalve kit with diaphragm. Got it going, again, and made an initial adjustment on the Idle Adjust Screws to smooth it out. Then, the impeller appeared to quit working (nothing out of the pee-hole). I waited a minute for it to begin "peeing" after I had started it, again, but nothing. It was obviously getting hot, so I shut it off. After that, it wouldn't crank, and it appears that the cylinders are not getting any gas mixture in the cylinders. The plugs are dry as a bone and so are the top of the pistons. I'm thinking that it got hot one too many times in it's 39 years and the reeds are now shot. (At one point, it was spitting gas back out of the top carb while attempting to crank, and I read that is one indication of bad reeds.)

1) I checked compression on the cylinders (105, 110, 110, 105). I "assumed" these were okay reading seeing everything is within 10%. However, I'd like to get another opinion on these compression readings.
2) I'm debating on whether to replace the reeds and impeller or just go ahead and do a rebuild (rings, bearings, reeds, impeller, and gaskets). If the compression is okay, then I'd like to just replace the reeds and be done with it. (I'm wanting to get this thing out on water before summer is over.)

Thoughts? And thanks in advance for any input.

 

[enginepower]

Compression may be a little low (i don't know specs for it) but it should be enough to stay running at idle in gear. Hopefully somebody can tell you the specs for the mixture screw to help get you started. Spitting out carb could be a bad reed but could also be a timing issue or running too rich or lean as well.

 

[mlbinseattle]

I had to back out the idle mixture screws almost a full turn (total of almost 2 full turns from seated with 1 turn from seated being an initial setting after a carb rebuild according to the service manual). If anything, the mixture should be somewhat rich which it should be and the plugs should be getting wet. No mixture is making it into the combustion chambers. Even the tops of the pistons look dry. That's why I'm thinking the reeds are shot. Yes, IMO, the compression appears to be on the low end, but it should still be good enough to run with some life left. Just my thoughts.

 

[gm280]

:welcome: aboard mlbinseattle. Nice having you join us here on iboats...

When you rebuilt the carb(s), did you totally disassembly them or just spray them with some carb cleaner? There are so many little passages and holes that really need a good cleaning after being disassembled. So I think you need more carb work myself. Buy some carb kits and redo the carb(s). The compressions are livable and really not that bad. And how did you come by the reeds being bad without removing them to see? Post some pictures for us to see what your are seeing. The experts on here will chime in with their opinions for sure... JMHO!

 

[mlbinseattle]

gm20, thank you for the welcome. I'm a "novice" to outboards and 2-cycles having never dealt with them, but I'm no stranger to carb rebuilds and 4-cycle engine overhauls. (Rebuilt a Rochester carb on an 84 Camaro 305 and tuned it. Figured if I can do that, I can deal with these carbs on a Merc 850. lol.) Anyway ... getting back on track ...

I completely took the carbs apart per the service manual for this engine. I replaced the floats, needles/seats, and new gaskets. Set the floats to 11/16" from the base of the carbs to the top of the floats (again, per the service manual). Completely cleaned the airhorns and bowls in carburetor cleaner, rinsed, and blew out with compressed air. After reassembling, I blew into the fuel port with the carbs upside down so the needles would be closed. Couldn't blow into the carbs, so I knew the needles were closing. Flipped those right side up and blew again. Needles were opened. I got it running the first time, and it appeared the bottom carb was dripping after pumping the bulb, so I pulled that carb, removed the bowl, rechecked the needle/seat, and blew it back out with compressed air. That seemed to take care of that problem. After I got it running, again, I had to adjust the idle adjust screws out approx. 1 turn to even the engine out (almost 2 full turns from seated). It ran for a while before I shut it back off. Got it running again, and that's when I noticed that nothing was coming out of the pee-hole. I waited a few minutes to see if anything would happen, and nothing did happen. Fearing that the engine would burn up, I shut it down. I let it cool off, then tried to restart. That's when I noticed the top carb spitting out gas from the front. Figured that I need to do the same thing to the top carb as the bottom, so I pulled it back off, rechecked everything, blew it out with compressed air, put it back together, and tried to fire it back up. Nothing. Before I began any carb work, I had checked the compression, but I decided to check it again after I couldn't get it fired back up. The compression looked the same. Also, I was still getting spark to each cylinder. That's when I noticed that the plugs/piston tops were dry. It just seems that no gas mixture is making it into the cylinders because it's not wanting to fire.

The only thing that I can think of that would be causing this is if the reeds weren't opening allowing the suction to pull the gas mixture from the carbs into the cylinders.

In any case, if it is the reeds, I found out from reading the service manual that the reed block is located on the crankshaft for the earlier model powerheads. On the later style engines, the reed blocks are located behind the carbs in the "intake" (if you want to call it that). So, it seems that if the reeds are bad, I'd have to completely tear the powerhead apart which means a rebuild.

If I'm missing something, I'd be glad to hear it. The way I see it, the engine should at least fire if there's a mixture getting into the cylinders, but that's not happening.

Forgot to add that there is gas getting to the carbs. I had replaced the checkvalves/diaphragm on the fuel pump, and that appears to be good. (I don't think anything was wrong with it to begin with, but I wanted to be on the safe side.) The carbs don't drip anymore after pumping the bulb, so I'm sure the needles are shutting off gas flow after the floats rise. I also opened the high speed jet/plugs on the bowls until it started to drip gas, so there is gas getting into the bowls. You can see the the gas on the carbs' venturis, so, there should be something getting sucked into the cylinders.

 

[Dmpaul89]

Did you oil the cylinders before running it? May be the reason for the low comp. I have a 650 merc and its in the 150 range. I bet the rings and all that are gummed. For the water problem you will probley need to replace the impeller anyway but try poking a coat hanger or other wire up in the pee hole. Mine gets clogged up every year may be full of mud. And the carbs... good luck with them.try running it with the choke half on and see what happens may clean em out. If the reeds were bad you would have a heck of a time getting it to do anything. They could be gummed as well... just takes time there are always bugs to fix when ressurecting an old outboard. Dont overthink the carb settings

 

[enginepower]

Just spraying some cleaner and blowing with compressed air is sometimes not enough to clean a carb. Sometimes you have to soak them in solution or use an ultrasonic cleaning machine to get all the gunk out. Some passages are pretty small, especially on the idle circuits, that they are hard to clean. Hope you just have a restricted passage somewhere and that you don't have to tear down to change reeds.

 

[mlbinseattle]

Thanks for the responses Dmpaul89 and enginepower. I soaked the carbs (metal parts only) in Chem-Dip carb cleaner for about an hour and then blew them out with compressed air. I ensured any gunk was gone, and I got into the passage openings the best I could with compressed air. The other pieces were cleaned with carb cleaner spray.

After thinking about it, the only thing I did different before and after the last time it ran was to pull the top carb off, recheck the float setting, and blow it out with compressed air, again. It was spitting out gas prior to this while trying to crank it. It could be that a small speck of something was in one of the passages and loosened up. I didn't think that I ran it long enough (about a minute) for the engine to overheat that bad before I shut it off the last time it did run. I figured it would have taken much more to destroy a set of reeds. It's not like the engine seized or anything. It didn't.

With regards to the impeller, it was shooting water out the pee-hole really good up until it quit doing it. I'll check it again, but if it's clogged, it must have been some crud or something that came off from inside the block.

In any case, I'm going to pull the top carb off one more time and recheck everything. Hopefully, it's just a speck of something that made its way into a passage and is blocking flow.

As far as rings being gummed up, what do you guys think about running Sea-foam or Merc Quickleen? I've heard either is pretty good about getting rid of carbon buildup.

 

[mlbinseattle]

Well, I'm thinking that it is a restricted passage. I took the top carb off, took the bowl off, removed the needle, and blew it out really good, again. Put it back together, and it actually fired up and ran for a few seconds before I shut it down. It's pulling a suction, so I feel safe to say that it's not the reeds. Hallelujah! Right now, I'm letting the battery charge. I'm sure the timing is off like no tomorrow. It calls for a setting of 27 degrees BTDC. I believe that's when it's running at idle, but can I use that while it's cranking, as well? Seems like I'm having a time getting it started, again. Going to look at the carbs some more, and I may let those soak in Chem-Dip overnight. (Doesn't take that long to tear one of these carbs down.) In any case, I feel confident that the reeds are in good shape.

 

[mlbinseattle]

Found out by researching the service manual that the timing for cranking the engine should be at 2-4 degrees BTDC. Also found out (the hard way) that this engine needs a strong 12 VDC from the battery. (They weren't kidding.) Got the initial timing set and jumpered it to my truck battery. It turned over for a bit and then fired right up. I let it run a minute or so to determine if the impeller was, in fact, bad. It is. Nothing coming out of the pee-hole. Going to replace this and see what happens, afterwards. I think I'm on the right track. Carbs are no longer dripping gas everywhere, so the rebuilds seemed to do the trick. Once the water pump kit is installed, I'll see what happens. Hoping that by doing the link and sync takes care of everything. We'll see.

I'll ask, again: Does anyone have an opinion of running Seafoam through the engine to see if it gets rid of any carbon buildup on the rings?

 

[Faztbullet]

: Does anyone have an opinion of running Seafoam through the engine to see if it gets rid of any carbon buildup on the rings?

It will be fine just and follow can instructions and avoid the heavy dose....