'95 Merc 5.0L / 2-bbl Runs rich - how to adjust?

[wharfcreek]

I have a 'new to me' 24' boat with a Merc 5.0 - 2bbl / Gen II power set-up, and finally got it launched and run a bit. I've believe it runs a bit too rich overall. When 'up-fitting' for my spring launch, along with all the appropriate filters and oil changes, I also replaced all 8 spark plugs, and they were completely black and carbon-fouled Thinking that might just have been indicative of how it was running when stored last fall in the cold, I simply replaced them and went on to other problems. When I land-started the boat with a hose, it ran a bit rough to start, but being the first spring start I didn't expect perfection. It seemed to clear up, so again, I went on to other issues. When launched this past Wednesday, I noted it was also pretty rough-running when first started, and the idle seemed a bit rough as I left the marina to take the boat home. When running out on the open water it seemed to run OK, but when I got to my creek and had to idle down, I again noted some roughness in the running condition. I'd also noted a tach problem when bringing the boat home, which was simply that it was jumping all over the place, so I replaced it this past Friday, and decided to take it for another 'test' run yesterday. This time it was even harder to start.....and it appeared to flood out almost immediately. Only with the throttle full open and a lot of crank-time was I able to get it running, and again, pretty roughly. I idled out of my creek, out on the Chesapeake Bay for about a 30 minute run, then back home. This time it actually stalled out when I got to my dock. I pulled the top cover and spark arrestor and checked to see if the choke plate was stuck partially closed. It wasn't. I got the engine started again and looked for 'nozzle drip'......and none. So, other than perhaps tweaking the idle mixture screw some (which I"ve not yet done), I'm not sure where to go next. I'm also unsure if this Idle mixture screw is a 'fuel' or 'air' screw.....so not sure if turning it 'in' will lean the idle mixture, or cause it to run more to the rich side. So, if anyone has a clue about that, please let me know. Sorry for being so long-winded, but I just wanted to include as many details as I could. This appears to be the 'original' carb, and I doubt it's ever been off the boat. Being a 'rich' running problem, I don't think dirt or debris in the carb is the issue.....and as I said, it seems to run OK when at cruising speed. So......any help or suggestions would be appreciated. Many thanks, Tom D.

 

[wharfcreek]

PS, not sure if my email notification of a response to this is working properly, so I'll check back here in the next day or so to see if anyone has responded. Again, many thanks!!

 

[harringtondav]

Two thoughts: Idle mixture screws only effect the idle circuit. I don't have my manual now, but normal starting adjustment is to lightly bottom, and back out 1 1/4 turns. Then turn the screws 1/4 turn a time, let the engine stabilize, and continue turning both in an out until you find the "sweet spot".

A bowl float set too high will cause rich operation, even if not high enough to flood the accelerator nozzles. Also dirty air bleed circuits will cause a rich mixture.

My best advice is to buy a carb kit. If you haven't rebuilt a carb, don't sweat it. The kit comes with cookbook instructions. Disassemble and lay out the parts in order. Don't loose the accel. pump check ball. Soak the body in immersion cleaner, follow with an aerosol cleaner, using the straw to purge every passage. Follow with compressed air. Set the float height per instructions.

 

[Rick Stephens]

⇧ What he said. Time to go through the carburetor. Your symptoms indicate improper float height or crud keeping a check valve open. Also, since it is new to you, go over all regular maintenance items - pull the drive off, service the u-joints, change the lube, inspect the impeller, check status of the gimbal bearing.

 

[wharfcreek]

Rick, done, done, and done! Before I even saw the boat! Actually, I purchased the boat in February, covered in shrink wrap and sitting on blocks in a local marina. It's prior owner claimed it had 3 known problems; it overheated, the tilt/trim didn't work, and the trim tabs were non-functional. Beyond that, he claimed all was good as far as he knew. I had the marina cut a door into the back of the shrink wrap, and started on the engine issues. Removed exhaust manifolds and risers, and replaced same along with new water tubes and riser spacers. Did the spark plug replacement at the same time, along with inspecting everything, replacing the fuel filter, and of course, oil and filter change. Manifolds and risers; completely plugged!! I then had at the tilt/trim. Cylinders locked up. Obtained a rebuilt set, installed, flushed and refiled fluid reservoir, all good! Then, removed outdrive and had at the gimble. Found all bellows to be OK, but stiff. All replaced. Found that the main gimble housing (or 'helmet' as it's often called) had a problem; the area around the water intake had eaten away from electrolysis. Found 'O' ring plugging output port. Had to replace outer housing. Done. Also found water hose between transom plate and main gimble housing had kinked. Replaced that with OE 'molded' type. All bellows were replaced as well, reassembled and all bolts and fasteners 'torqued' to manufacturer's specs! Then had at the outdrive. Replaced water pump impeller (distorted and bent), and replaced outer pump housing. Checked "U" joints, OK, and greased appropriately. Checked main gimble bearing, OK, and re-greased it as well. Reinstalled everything, did a 'test' start on engine to check for leaks and general running. All seemed OK. Note: Also replaced shift cable to outdrive. For not having yet seen my boat, I did quite a bit of work. BTW, I fixed the trim tabs too! All this, a new prop, and a new battery. Checked charging system, steering, even checked to make sure bilge pumps and fire extinguishers all were functional! Then, finally, last week arrived, I removed the shrink wrap, and saw the boat for the first time. To my delight, it looked good!!

Dav, I'm going to take your advice and just do a complete overhaul on the carb. Actually, I'd planned to try that before replacing it....but I was hoping to find someone that sold Jets for the thing before I actually started. I'm pretty good with carbs. I spent 33 years in the auto industry.....and at one point held an ASE 'MasterTech' certification. I spent a good bit of my career in the Service Division of a US Auto Maker.....so I know my way around a car motor pretty well, as well as being old enough that my early experience rather predates the onset of fuel injection. At one point I could take apart a Thermo-quad and rebuild it blind-folded. I'm still pretty handy with motorcycle carbs, though most bikes are now EFI as well. So, I guess my 'experience' is what is pointing it's finger at jetting.....not an actual problem with the carb itself. Although, that said, I'm well aware that a partially sunken float will make for a richer mixture....where a full sunken one will lead to nozzle drip and serious flooding! So, I'll do the rebuild....just for drill......and see what happens. I'd just like to make note of the jets I pull out of it, and be able to find some smaller ones (if need be) for down the road. If you've got any info on who might sell them, that would be a real help. Please PM me with that.

Anyway, thanks to both of you for the comments and contributions. Hopefully I'll get this sorted out and then get into some serious travel with the boat. I'd like to pretty well cover the entire Chesapeake this summer, particularly if gas prices stay to the lower side of things. That would be a real 'plus'! But, I don't expect to hang on to this boat much past this summer. I'm really more of a 'fisherman'.....and my little 17' Key West with my new 115 Merc OB is really 'boat enough' for me! This was a lark.....and hopefully one that will work out OK in the long run. At one point I was worried that I was maybe spending good money after bad. But, hearing the engine start and run....that was a big relief. And, in actually seeing the boat for the first time and finding it to be in really nice physical shape, that put my mind at rest. So, if I can just get this engine running as I think it should, it will be all over but the travel! So, again, thanks guys!!

Sincerely,

Tom D.

 

[Rick Stephens]

Sounds like you have it covered... indeed. My bet the carb was jetted properly. Of course, not a lot of art in that from the factory. They do em all the same. I don't know what the jet sizes are, but like you, I'd have zero issue with finding the proper ones to calibrate the carb if that should prove necessary. Enjoy your boating!

Rick

 

[wharfcreek]

Rick / Dave,

If either of you are still here, can you tell me who this 'Mercarb' is manufactured by? I've heard both Rochester and Carter. I'd like to see if I can find a Jet source, but need to get the proper manufacturer first.

Many thanks,

Tom D.

 

[Rick Stephens]

No idea. I bet Bt Doctur would know tho.