At a loss on mercury 90! Won't run!

[02merc90]

So i've been having a problem with my mercury 90 4 stroke. It starts but will die immediately under throttle. A few weeks ago i took all the carbs off, cleaned extensively (done by my friend who is a car mechanic). Put everything back together and it ran but only with the idle screw tightened too much and would stall under throttle. Frustrated, i brought it to a boat mechanic. After waiting two weeks for it to just be looked at i went by to check up on it today and they happened to have it out working on it. I asked what was wrong and they said the carbs were dirty...I told them that that can't be because i had just cleaned them and it sounded like a vacuum tube or something was off. They insisted that the carbs must be dirty and it was only running on 2 cylinders...I found that odd since when i took the intake off i saw gas being sent through the first 3 carbs but not the last one (which changed after i cleaned it). The boat mechanic said that the carbs have a bunch of intricate parts and they need to be taken apart (which we did).

Did i miss something? Long story short, when they said carbs i told them to stop what they were doing and i would pick it up tomorrow. They also quoted the carbs at being $1000 worth of work just to clean.

Any thoughts from more experienced boaters? Are boat carbs that much different than carbs on a motorcycle or a car? Is there any special thing to look while cleaning? I made sure to follow the cleaning process in the mercury 90 manual.

The mechanic did say something about balancing...which I do see as being a possibility as to why they aren't running correctly (but i do NOT think they are still dirty). Any thoughts? Can you balance carbs on the assembled engine or do i have to take it apart again?

 

[johnnygjr]

They might be talking about a linc and sinc on assembled engine. Might be in manual,others here on forum will know procedure.

 

[02merc90]

They might be talking about a linc and sinc on assembled engine. Might be in manual,others here on forum will know procedure.

Will the motor not really run if the carbs are out of sync? Does disassembly and re-assembly throw off the sync that much? I looked online on how to make a manometer with a few bottles so i might try that out myself.

 

[galamb]

1000 bucks to clean and rebuild 4 carbs is a little high but not out of the ballpark. For four carbs you are looking at (in general around my way) $750 plus parts.

You said they were cleaned but what about rebuilt? Kit's installed, new needles/seats etc?

And while a carb is pretty much a carb, without knocking your friend, I don't know many mechanics that still see carbs on any kind of regular basis, so it's possible something was missed.

And yes, the synchronization is very important - you are "in essence" trying to get "four" single cylinder motors to work as one - if the sync is off it will run like crap, stall out, surge etc.

And this being a 4 stroke has the valves ever been adjusted? (normally done after the first full season of running) - other maintenance - four strokes don't like to sit and they crave "routine maintenance", unlike grampa's 2 stroke which can be neglected but never fails to fire up.

If you are going to clean them yourself, take off every bit that can be removed - jets, valves etc - replace anything that doesn't look 110%. Make sure the float height is adjusted properly. Make sure the correct jets are installed - they may be different between the different carbs - make sure the number 1 carb is the number 1 carb - again, they may be different and mixing them up could spell "can of worms".

 

[02merc90]

1000 bucks to clean and rebuild 4 carbs is a little high but not out of the ballpark. For four carbs you are looking at (in general around my way) $750 plus parts.

You said they were cleaned but what about rebuilt? Kit's installed, new needles/seats etc?

And while a carb is pretty much a carb, without knocking your friend, I don't know many mechanics that still see carbs on any kind of regular basis, so it's possible something was missed.

And yes, the synchronization is very important - you are "in essence" trying to get "four" single cylinder motors to work as one - if the sync is off it will run like crap, stall out, surge etc.

And this being a 4 stroke has the valves ever been adjusted? (normally done after the first full season of running) - other maintenance - four strokes don't like to sit and they crave "routine maintenance", unlike grampa's 2 stroke which can be neglected but never fails to fire up.

If you are going to clean them yourself, take off every bit that can be removed - jets, valves etc - replace anything that doesn't look 110%. Make sure the float height is adjusted properly. Make sure the correct jets are installed - they may be different between the different carbs - make sure the number 1 carb is the number 1 carb - again, they may be different and mixing them up could spell "can of worms".

Thanks so much for chiming in!

They were cleaned, not rebuilt. one float (number 4 carb) was punctured truing to take out the jet to clean it and i replaced the float, but other than that that's it. Needles/ seats were not replaced. Everything "looked" really clean after tear down but i did not take the floats ect. out of each one. All the jets were cleaned (every carb spit gas except the number 4 before disassembly). The insides were cleaned of any gunk. But no, needles/seats were not taken out and nothing else was replaced in the carb as everything "looked" to be in good condition.

He works on motorcycles so that's why i was wondering if those carbs are different than boat carbs.

I saw a tutorial online about how to sync the carbs with a diy bottle manometer which i may try myself after taking the carbs apart yet again and seeing if anything is missed...should i be looking at anything in particular? take every single piece out of the carbs and clean it and just put it back or do i have to adjust things inside the carb?

I don't think the valves have been adjusted, at least not in a while. The boat has been sitting (this will be the third year i believe).

Adjust float height...this may be an issue since i did replace one of the floats (didn't know this needed to be done). How do i adjust the floats? I may have to youtube that one or ask my friend again if he did that or not. i know it wasn't done on the 4th one as i replaced the float. I know the jets are in the correct carbs they came out of though.

 

[galamb]

Youtube is great for "seeing" the process but best to grab a least a Seloc's manual - it will walk you through the cleaning of the carbs, setting the float height etc and step by step sync procedure.

It isn't rocket science by any means but a few too many steps unless the video is following a manual giving step by step instructions.

I usually pull all the (jets) - whether gas jets, air jets, idle jets etc - totally strip the carb down to it's body and soak in carb cleaner (if metal body) or gas line anti-freeze or electrical contact cleaner if it's Marelon (plastic). And then make sure all "channels" are clear by blowing air through (compressor) and the I take a syringe and try forcing fluid (usually gas line anti-freeze which is mostly just alcohol) through the channels/tubes to make sure they are not obstructed.

I check to make sure the jets are correct (again, this is where the manual is priceless) - they could be mixed up, wrong, missing etc (especially if you are not the original owner) - If I take apart a carb I always change the float needle (and seat if replaceable) - also through in new gaskets, o-rings etc - for the cost it saves having to tear things down again.

If upon reassembly if they are adjusted to "initial" spec (and it's usually only the idle jet that you need to adjust) you can't get the motor to at least start and idle then either something was done wrong or the carbs weren't the issue. Synchronizing them will allow them "all idle the same" and to operate as a single unit at all rpms "above" idle - but it should run after initial installation.

If the float height is incorrect you could 1) cause that carb to flood or 2) starve it of fuel turning your 4 cylinder into a 3 cylinder right from the get go - more than one float out of whack and you now have a 2 cylinder or single cylinder motor

 

[02merc90]

Youtube is great for "seeing" the process but best to grab a least a Seloc's manual - it will walk you through the cleaning of the carbs, setting the float height etc and step by step sync procedure.

It isn't rocket science by any means but a few too many steps unless the video is following a manual giving step by step instructions.

I usually pull all the (jets) - whether gas jets, air jets, idle jets etc - totally strip the carb down to it's body and soak in carb cleaner (if metal body) or gas line anti-freeze or electrical contact cleaner if it's Marelon (plastic). And then make sure all "channels" are clear by blowing air through (compressor) and the I take a syringe and try forcing fluid (usually gas line anti-freeze which is mostly just alcohol) through the channels/tubes to make sure they are not obstructed.

I check to make sure the jets are correct (again, this is where the manual is priceless) - they could be mixed up, wrong, missing etc (especially if you are not the original owner) - If I take apart a carb I always change the float needle (and seat if replaceable) - also through in new gaskets, o-rings etc - for the cost it saves having to tear things down again.

If upon reassembly if they are adjusted to "initial" spec (and it's usually only the idle jet that you need to adjust) you can't get the motor to at least start and idle then either something was done wrong or the carbs weren't the issue. Synchronizing them will allow them "all idle the same" and to operate as a single unit at all rpms "above" idle - but it should run after initial installation.

If the float height is incorrect you could 1) cause that carb to flood or 2) starve it of fuel turning your 4 cylinder into a 3 cylinder right from the get go - more than one float out of whack and you now have a 2 cylinder or single cylinder motor

Thanks so much for all the info! I'm definitely going to head to west marine and pick up one of those books. I know the jets are correct anyways as i did use the boat 3ish years ago but i bet the floats are off in 2 of the carbs and that's why the mechanic said it was running on 2 cylinders (come to think of it we put the good float from 1 into 4 so i could more easily attach the new float to one because it is on top...probably both out of whack). The motor does currently idle, just with the idle screw tightened too much. Got the boat back today and will tear is down tomorrow and try to update!