2000 Merc 40 / 4 stroke crappy idle

[Angler Don]

3 cylinders , 3 carbs, bigfoot.<br /> Idles rough. <br /> seems to be loading up, running excessively<br /> rich at idle. One cylinder dropping out,<br /> quite repetetive, rough, smooth, rough.<br /> Carbs have been cleaned & sync'd, no change.<br /> Idle mix is not adjustable, they have an<br /> internal idle jet. I don't think this is<br /> supposed to 'cut out ' cylinders at idle<br /> like the larger engines, is it ??<br /> Auto enrichener, thermostat, tests ok.<br /> Runs well in all other respects.<br /> Help, any thoughts ??<br /> Thanks !<br /> Don

 

[Wellcraft 89]

Re: 2000 Merc 40 / 4 stroke crappy idle

What do the plugs look like ?all the same ?<br />Maybe the floats are set too high!drawing excess fuel in.<br />I don't think these models cut cylinders out.<br />Its not overheating is it,i thought they would do that if it detected an overheat situation.<br /><br />Just some thoughts<br />Rich

 

[Angler Don]

Re: 2000 Merc 40 / 4 stroke crappy idle

thanks, Rich.<br /> plugs all look pretty wet & black, <br /> gas fouled. I have changed them twice this <br /> season. Changed the oil as well, it gets<br /> black & contaminated as well. When idling<br /> there is a lot of sooty exhaust under the hood from running so poorly. That probably affects all cylinders then, they are running on exhaust fumes. Clears out and runs<br /> great off idle and above. Never overheats, pulled stat & checked in hot water against specs, it was right on . Thanks for the ideas, maybe a float problem ?? <br /> Thanks,<br /> Don

 

[Angler Don]

Re: 2000 Merc 40 / 4 stroke crappy idle

so, today I,m back into the carbs. Look the same as before. Floats are plastic and not adjustable, but the level checks perfect, according to my Merc manual. Needle tips are perfect. One thing I am curious about is the manual specifies a # 42<br />idle jet, those in the carbs are stamped 35.<br />Is this number the jet size ? Is it the wrong size ?<br />Would a # 42 be larger or smaller diameter than a # 35 ? Richer or leaner at idle ?

 

[laser51]

Re: 2000 Merc 40 / 4 stroke crappy idle

I have recently purchased a 1999 mercury 90 hp 3 cylinder. The motor only has about 30 hours on it. However it is doing the exact same thing your engine is doing. Have you come up with any answers?

 

[outboard tech]

Re: 2000 Merc 40 / 4 stroke crappy idle

Well we moaned to get this 4 stroke junk, now we got it. I believe your carbs do indeed have idle air screws--they are covered with welch plugs and drilling them out requires extreme care. Not a job for rookies. Also these carbs have to be balanced with a mannometer to equalize vaccuum or you're wasting your time. The reason the adjustment screws are covered--(not sure about the 40, but absolutely the 50/60 version has them) is an EPA requirement--you're breaking the law if you change them, and it won't idle unless you do. The mannometer only costs about a grand! Good luck!

 

[Angler Don]

Re: 2000 Merc 40 / 4 stroke crappy idle

to this point, I have checked and tried everything I can with this carb setup. The fact is this, it runs too rich at idle. The idle mixture is not adjustable. After 2 seasons of research, try this, check that, I spoke with two people who were willing to enlighten me a little, or rather support my theory. This carb setup has some inherent problems in it's design which cannot be changed or repaired. Period. This is a known issue to those on the inside. There never was a recall or service bulletin issued in regards to this issue.<br />Two different senior level technicians from two different local Mercury dealers each confirmed this, but not willingly, of course. Kind of like I'll tell you the answer after you figure it out. I asked them straight out, is there something wrong with these carbs ?? Something that can't be fixed ??<br />Now they say "Yup, best off getting the new version carbs, that 'll fix it" Hey, it's not like all the secrets of the world, here. Just want my boat to run right. Not trying to get anything free. Not trying to sue anyone. Anyway, the 2001 & 2002 model years had a couple design changes, addressing these issues, including adjustable idle mix, and perform much better than the originals.<br />I ordered the "kit". It includes three new design carbs, plates, linkages etc. Everything needed for an easy, bolt on repair. $624.00<br /> Knowing what I do now, I am confident of a successful repair. I'll post the results after I get them here and installed. Thanks for listening to my rantings.<br /> Don

 

[Angler Don]

Re: 2000 Merc 40 / 4 stroke crappy idle

hey outboard tech, <br />the replacements I have coming do have mix adjustments behind a welch plug. The setup I have now has no provisions for an idle mix screw. The hole bottom is cast shut, the hole isn't even threaded. Rather, under the top cover, in the idle circuit is a # 42 air bleed, no other size is available to correct / change the mixture. Someday during the engines life you may have to compensate for internal wear, age, altitude etc. You can't ! Completely foolish. Probably had to pacify the EPA by issuing a number of tamper proof models to insure compliance. Or something.<br />These are found on 30/40hp 1999/2000 3/cyl/3 carb 4 stroke engines serial number OT178499 & below.<br />Some of Mercury dealers parts updated software doesn't even recognize them in the parts lookup anymore.<br />Like some dirty family secret. Check Mercury marine website parts express for serial # OG993964. Look at the exploded view. Part # 8 is the idle jet.<br /> I have used a mercury type manometer from my friend he uses on his 6 cyl Honda Valkyrie, I also have a non-mercury type of my own. I had the Mercury dealer sync with their electronic type. All yielded similar readings. Like I said, the thing runs perfect, except for idle. I need idle to troll. If I can't troll, I can't fish. If I can't fish, life has no meaning . OOOOOOO<br />Gloom, despair ....

 

[outboard tech]

Re: 2000 Merc 40 / 4 stroke crappy idle

Don; 'glad you got some insight on the carb situation; we seldom see the "smaller" 4 stokes, so I was a bit unsure about the air screws; but have cursed plenty of the bigger ones. The real "dirty family secret" is the actual manufacturer of those nightmares. I'll give you a hint,until recently, most of that motor arrived in the US in a container ship and got painted black. The carb situation is pretty much moot now as the new motors are EFI, but there's still the motors in the field. I've done thousands of carb jobs to date, and the only two times I've ever had to install new carbs--were Japanese 4 stroke design. I hope your repair works out, and thanks again EPA for ruining a great domestic product. Ya could always do what the 4 stoke Yamaha owners do when they won't idle; tie off a couple cinderblocks overboard for some drag and throttle up a little bit 'til she quits snortin!!!

 

[Wellcraft 89]

Re: 2000 Merc 40 / 4 stroke crappy idle

Don ,glad you got somewhere with this.<br />If all works out for you.This info should be put somewhere for future owners to see!<br /><br />Rich

 

[Angler Don]

Re: 2000 Merc 40 / 4 stroke crappy idle

Update<br /> the repair was a complete success ! She runs as she should again, and needless to say, I am quite pleased. Trolled at idle for 90 minutes, smooth as silk. Still sucks to put $624.00 into it to make it work as it should.<br /> Installation was rather simple, one small modification required. The new carbs have bowl vent tubes, which vent down through the adapter plate. This requires drilling a 9/16" hole through the adapter plate to accomodate this.<br />Bolt 'em on, sync 'em up. <br /> Quicksilver part # 883313A5 carb kit. <br />Something to keep in mind, should you ever run across the same carb set up, you know what to do.<br /> <br /> Thanks to all who listened and offered advice and comments. <br /> Don