90 hp mercury

[pat murphy]

Help- I've got a 2000 90hp merc that runs like a rocket on an 18' Pro Weld bass boat but idles like a model A Ford with 2 plug wires off! I've been told by my Merc mechanic that these 3 cyl. engines "just idle rough". It also stumbles till you get to about 1500 rpm then it comes on like gangbusters.<br /> Pat

 

[Kenny Bush]

Re: 90 hp mercury

Check your timing and synchronization......Sounds like your idle timing is off......if the motor runs great once it gains rpm's.

 

[FlyBoyMark]

Re: 90 hp mercury

Boyesen reeds help cure these problems too.... considerably

 

[pmueller]

Re: 90 hp mercury

Same with my 2002 90 Merc. Hesitation on hole shot until higher RPMs. Took it in. Mechanic said one of the carbs was out of adjustment. Lake is still ice, so haven't been able to check it out. On the rough idle, at least on mine, below a certain RPM, it reduces to two cylindars I believe...some gimmick for trolling I think...but does seem to make it a little rough.

 

[bryanredfish]

Re: 90 hp mercury

PJ57:<br /><br />It is only the four cylinder Merc's that drop two cylinders. The 3 cyl. 90 runs on all three at all times. It has been my impression, after talking to numerous mechanics and doing my own adjusting, that it has to do with the timing advance over around 1200 rpm's. These 90's just run like a horse with 3 legs until around 1200 rpm's; after that, they're some of the best running motors out there. This has been my experience with my 2002 Merc 90.

 

[pmueller]

Re: 90 hp mercury

bryan, thanks for the correction!

 

[graddy]

Re: 90 hp mercury

Carb idle screws set as follows. #1- 1/2 turn from seated #2- 1 1/4 turn from seated #3- 1 1/4 <br />Set idle Timing to 0-2 degrees BTDC. The setting is below spec. Throttle cam roller as close to the throttle cam as possible, while still turning freely, try to set .005 or less.<br /><br />install 140 degree thermo(120 from factory) and make sure poppet valve is seating at idle, you can strech the sping a little to increas tension.

 

[jpollman]

Re: 90 hp mercury

My buddy has a 90 Merc 3-cyl that is about the same vintage. It runs FINE at idle and all the way to WOT. I've driven the boat quie a bit and just LOVE it. It's on a 17.5' Starcraft Sportfisher.<br /><br />I think when I'm in the market for a new mill, Merc is going to be the way I go. Although I do like my '61 Evinrude.

 

[KIWI MERCMAN]

Re: 90 hp mercury

pat murphy<br />DTS is spot on.<br />Carb set up on this model makes a huge difference.<br />If you are running in very cold water the 90's only get up to about 90deg's running temp, so change that stat to the 140 deg' and check out that poppet valve seat and valve stem face. We found alot of the valve stem's themselves had a surface that looked like a wave washer. We would turn these down so they were flat and this stops the water bypassing the poppet valve causing the engine to run cold.<br />If you get this done you will not believe the running difference in this model.<br />Dont let them tell you this is the way they are , cause they can be a whole lot better.<br /><br />Kiwi

 

[jpollman]

Re: 90 hp mercury

I agree with Kiwi.<br /><br />My buddy wouldn't put up with that at all. His is smooth as a babys bottom from the time you turn the key. It's a VERY nice motor in my opinion. He runs his from ice-out until early to mid December here in Michigan. So his motor sees a pretty wide spectrum of conditions. I've yet to be out on his rig when it didn't run fine.<br /><br />Good luck !

 

[pat murphy]

Re: 90 hp mercury

well Kiwi, I guess my next question would be what to expect when the water warms up. I'm running in 60 degree water now but it won't be long here in Alabama till we see some pretty warm water temps. I don't want to run this motor too hot in summer temps, but the stumbling is about to drive me to drink. The boat is hard to drive on the trailer because of the stumbling-boggs down and then almost jumps into the bed of the truck! Pat

 

[KIWI MERCMAN]

Re: 90 hp mercury

Pat<br />I would not worry about that at the moment, if the hotter stat fixes your problem right now then thats good right? ( you can always pop the colder stat back in during the summer but i think you'll find that your engine will run fine when your water temp comes up). Just between you and me this engine should of had the 140 deg stat from the start. Where I am in New Zealand it is not as cold as you , our water temp during the winter is down to 5 to 9 deg c (40 to 50 f) and up to 18 to 20c ( 68f) in the summer. With this engine model we change all stats because they just run spot on, the other thing you will notice is less smoke as well, as when they are running hotter at idle they burn your fuel\oil mix a lot better.<br />One last thing, your stat on this engine controls your engine temp at idle and just above , your poppet valve controls your temp from above idle through to WOT. This is why the stat has a great effect on the way your engines runs at idle.<br />Mercury did put out a bulletin on this.<br /><br />Safe Boating<br />Kiwi

 

[puttman]

Re: 90 hp mercury

Pat I have a 2001 90 and here is what happened to it, The oil pump linkage split and the oil was pumping full open, (does yours smoke a bunch) well it was smoking bad (this is after a tune up)so I took it back twice and they said it is ok, normal,runs good well the next time out it started ideling real rough, then stalling.<br />Planning for the next morning I found the broken linkage, I glued and strapped it and replaced it and cleaned the plugs, test ride was good to start but 5 min. and it was back to idleing rough again.<br />This is where im at now. I have been told several different things so I think im going to run it w/fuel additive and new plugs and see it it will clean up.<br />Some say I need a carb job.<br />Some say run it it will clean up.<br />Some say adjust the carb.<br />And mine purred like a kitten until the tune up and broken linkage. wot I lost 3-4 mph and now it is back with the oil set correctly now I think I might be able to blow it out.<br /><br />I guess what im saying is look at your oil linkage<br />Check your plugs<br /><br />Thanks

 

[pat murphy]

Re: 90 hp mercury

well, you are not giong to believe what cured it. My mechanic said rebuild the fuel pump.$11 parts cured the problem, not enough fuel pressure until the vaccum got to really pulling on the diaphram. I hope everybody's problems are this cheap to fix!<br /> Pat

 

[sunray18ft]

Re: 90 hp mercury

i have a 2002 2 sroke 90 hp mercury. it runs idle like a steam engine but works perfect after 1000 rpms. installed new powerhead last year. is ignition timing the problem? please help me guys