Need help with motor

[narvlebenoit]

I have a probleum with my 1991 Mercury 90 horsepower 6 cylinder motor. I would appreciate any help anyone might be able to give me. When the motor is cold it wants to bog down and not run wide open as if it is not getting feul but i rebuilt the feul pump, changed the gas hoses and put new spark plugs , cleaned the tank of all trash. Once the motor warms up it runs great. Next time I put it in the water it will do the same thing until it warms up again. What should be the top RPM of motor when running at full throttle?

 

[fish 4 life]

Re: Need help with motor

According to piranha.com the min WOT RPM should be 5000 and max WOT RPM should be 5500.


Motor Specs
Manufacturer: Mercury
Year: 1991
Horsepower: 90.0
Cylinders: 3
Type: 2 stroke
Gear Ratio: 2.30:1
Min WOT RPM: 5000
Max WOT RPM: 5500
Spline Count: 15
Drive Type: Outboard

 

[Bob_VT]

Re: Need help with motor

The inline 6 is a great motor. Welcome to iboats.

I feel your frustration and yes the I-6 do not like to be run hard cold.

The two most critical things you did not mention in your original post were carbs and if you did a link and synch? Those carbs are picky and MUST be balanced to operate in unison.

This is a set of directions to an older model and for the newer model I would consult a manual. http://forums.iboats.com/showthread.php?t=168855

I will move this post to the mercury outboard section where it belongs.

 

[narvlebenoit]

Re: Need help with motor

The carbs have been rebuilt about a year ago, do you think they would have to be rebuit again or adjusted, or maybe use some kind of cleaner through them? thanks for the help!

 

[Bob_VT]

Re: Need help with motor

Well..... depends..... it only takes a tiny bit of crud to block passages in a carb and it really depends on storage and fuel quality. One of the primary reasons for using stabil in fuel is so it will not brag down and sludge up the carbs. The old inline 6 was a cold hearted beast.

Couple of questions have you used the Mercury power tune on the carbs and motor to make sure the cylinders are de-carbed? Have you checked your compression? How does it run after the "bogging" ??? I would put money on link and sync being your cure. When you do that proceedure you are making sure the timing is set properly, the carbs are adjusted properly and balanced with each other.

Just food for thought ..... if one carb dumps too much fuel it will throw the engine out of balance.

 

[narvlebenoit]

Re: Need help with motor

I got the compression checked, it was fine. What Mercury Power tune is?
I will give it a shot if not will go to lync and sync, which i don't really know either exactly what that is. Thanks for the help Bob.......Narvle

 

[Bob_VT]

Re: Need help with motor

Most Mercury dealers sell a Mercury Tuner spray which is sprayed into a carb while the engine is running ....... it is the Mercury brand decarb spray and many here have used seafoam for the same purpose..... I was told by a VERY reliable mercury guy to use the mercury spray and I listened..... it worked best.

If you are not familiar with link and sync I would recruit a fellow mechanic. It is a critical part of getting everything to work perfect and it is a MUST to be exactly accurate on the timing marks. You have a private message.

 

[narvlebenoit]

Re: Need help with motor

did not find merc tune but tried some seafoam and it seams like it did some good.itstarted comming out of the hole real good today .idle really smooth today i will try to go out tomorrow for a ride and see how she runs THANKs....again Bob .

 

[emckelvy]

Re: Need help with motor

Narvle, it sounds like your carbs could be a touch lean, you might try richening up the idle mixture and see if that helps.

Each carb has a mixture screw, pointing out of the front top side of the carb, to your right as you're looking at the carbs. Turn each screw about 1/8 of a turn CCW and see if that helps. If there's an improvement, you know you're going in the right direction.

Once you get in the water and all warmed up in gear, you can 'tweak' in the idle mixture by adjusting one carb at a time. Go lean (CW) and rich (CCW), finding the points where the motor speeds up then slows down again. Wherever the idle speed is highest and smoothest is the midrange of your mixture adjustment.

Now, with each idle mixture needle adjusted to that midrange, you'll probably find you have a nice, smooth idle but when you put it in gear and try to accelerate she'll probably die. And likely be cranky when starting cold.

This is because Inline Sixes don't have an accelerator pump like a carbureted car engine. So, you do have to go a bit rich on each carb to make the Ol' Gal happy.

Try 1/8 turn rich (CCW) on each idle mixture screw. Then check your acceleration. Adjust again if the motor bogs at takeoff. Repeat again if necessary. If you can't find a range of adjustment that cures the acceleration bog, you'll need to look at other areas as suggested.

But I'm thinking that since it only does it when cold (which is when you need to be a bit more on the rich side) and it's better when warm, sure sounds like a mixture thing. These are quite sensitive and I can recall on my old 1350 and 100 Mercs that any time I thought I was flooding them out on the cold start, they proved me wrong by wanting more gas!!!

HTH & let us know how it goes............ed

 

[narvlebenoit]

Re: Need help with motor

Finally had nice weather to go out and now I have another problem. Is it possible for 3 coilsto go out at once because 1, 3 and 5 guit firing. Motor runs but just on 3 cylinders, could it be the power pack? Thanks for any help you could offer me, Happy New Year ....Narvle

 

[emckelvy]

Re: Need help with motor

Power pack is likely but best to troubleshoot before replacing $$$ parts.

Check this out, item #8 should help:

http://outboardparts.com/mercury/troubleshooting/troubleshooting10.htm

Another good link with resistance values for the stator trigger etc:

http://www.boatpartstore.com/mercreadings.asp

You should be able to find replacement parts here at the iboats store.

I like "CDI" brand replacements and I get them here:

http://www.boatfix.com/searchcdi.asp

HTH..........ed

 

[narvlebenoit]

Re: Need help with motor

Thanks for the info ED. this crazy Louisiana weather got me on hold but i will still try to get started latter today .I check on part prices @i see what you mean.and i think that was some of my other problems with the bogging down when she was cold.

 

[Selcorunner]

Re: Need help with motor

Finally had nice weather to go out and now I have another problem. Is it possible for 3 coilsto go out at once because 1, 3 and 5 guit firing. Motor runs but just on 3 cylinders, could it be the power pack? Thanks for any help you could offer me, Happy New Year ....Narvle

I strongly believe that the power cut on 3 sylinders is due to the stator in need for replacement. It has actually happened to me twice, with both the in-line 6 115 hp i have owned ( 85 and 86 models). I still have the 86. Both times it happened when reducing planing speed down to trolling.
A wire failure in the stator results in the loss of ignition to 3 sylinders.

Another comment regarding the first problem of enginge bogging when cold:
On my merc 50 hp 1981, I experienced the same problem. After carb cleaning etc. I finally found out why it would run ok at high speed after 15 minutes at low speed. Old grease lubricating the plate adjusting the ignition timing, prevented the spring from pulling the plate when the carbs were opened up. 15 min. at low speed created enough heating to "melt" the old grease and the spring was able to turn the plate and adjust the ignition to proper timing! I still need to spray it annually with CRC to prevent the problem.

Regards
Selcorunner
Oslo, Norway

 

[narvlebenoit]

Re: Need help with motor

hey guys I,am buying new switch boxes for my 91 inline six and a friend told me after putting them on i should run the motor easey for a while is that a fact or just talk .

 

[narvlebenoit]

Re: Need help with motor

I have a 91 iline six put new switch boxes and before new boxes I would get 53000 RPM at WOT and now with new ones I only turn 4000 at WOT dont have a clue whats wrong.I played with carbs ran seafoam and then cleaned the plugs real good does anyone have a secggestion on what to try now . )O yes it runs perffect at 3000 RPMS thanks Narvle

 

[narvlebenoit]

Re: Need help with motor

was checking out spark plugs an two of them look real clean what does this and what could the prolbem be......Thanks Narvle

 

[emckelvy]

Re: Need help with motor

The clean plugs might not be firing. Also check for droplets of water. If no water, just fuel-washed, one thing you might try is to put a timing light on each spark plug wire and make sure each one is sparking.

If you have someone helping you, you can even check this underway with a load.

Sounds like a bit more ignition troubleshooting is in order! I think we've discussed a bit more in P.M.s but I'd reiterate the O.P.'s suggestion of checking (or re-checking) the stator just to rule it out. These things can go at any time, so you could potentially be chasing other problems around while the stator is giving you fits.

HTH..........ed

 

[narvlebenoit]

Re: Need help with motor

put timming light on each plug wire and spark looks fine at 800 and 1500 RPMs so I guess its off to the stator switch boxes are new coils all firing is their anything else that may stop it from turing at full RPMs because before new switch boxes it would turn 5300 RPMs all i did was switch boxes thank again Narvle

 

[achris]

Re: Need help with motor

What's wrong with this statement?

[size=+1]"1991, in-line 6, 90 hp"[/size]

Did none of you see it? Inline 6s finished completely in 1988. (90hp inline 6 finished in 1986). Please post you engine serial number so we know what we are looking at.

Ok... run slow at first with new switchboxes... Someone's pulling your chain... Total BS.

Was pulling 5300, now only 4000... recheck your wiring... A couple of crossed wires (switchbox to coil, or trigger to switchboxes) will have it running ok but not making full rpm at WOT.

There needs to be no connection between the stator and ground. The stator coils are isolated from ground. You could put a layer of rubber under it and it would still work perfectly.

Which 2 plugs look clean? This could be water getting into the cylinders and steam cleaning the plugs, or a clue as to which wires are crossed.

Max revs should be 4500-5000rpm. If you're pulling 5300, great, don't worry about it.. Less load on those engines is better. For your bogging at cold (Personally I don't rev a cold engine hard, causes more engine wear), try opening the mixture screws (richening) 1/8 turn.

Chris...........

 

[narvlebenoit]

Re: Need help with motor

I bought the boat about a year ago the guy told me it was a91.the S#5672739. Thanks Chirs if you could give me the right year Narvle.Oh and the wires when I change the switch boxes I did one wire at a time an they were color coded with the boxes.