Mercury 200 idle and low end power

[VEGAS88]

Sorry in advance for all the history and thanks for any advice. Honestly I have learned everything I know about my rig from reading here on Scream and Fly and the Hydrostream forum. This is my first post.


This 1990 Stock Merc 200 has never had an impressive low end. It is a 2.5 liter and was built in the end 1990 but purchased new in 1991 by me. The motor always has a great cold start and strong top end. It is mounted to a 88 Hydrostream Vegas XT that only used a 24 pitch 4 blade Turbo ski prop for the first for the first 25 years or so. After 2 years in the garage in the mid 90s it would occasionally bog while pulling up a slalom skier on an intermittent basis. After running and sitting in the hot sun it may also be difficult to start on an intermittent basis and have a ruff smoky idle. Revving the engine prior to pulling up a salmon skier seems to help but is not otherwise needed. A few times it has also been known to increase RPM slightly with no change in throttle setting. Yes, this has been going on for over 20 years. The motor has been to a Merc dealer a few times with no change. I personally have recently dip tanked and rebuilt the carbs (even though they looked factory new inside and out), new plugs and wires, fuel filter, etc. It runs the same, very dependable and strong mid and top end even with a recently acquired 27 pitch Mazco RE3. I was thinking of getting the CCM reeds and possibly stuffers to help with the issues. I did pull the air box and check for air puffing out the carbs using a piece of paper at idle and 1500 RPM. The top carbs may pull a bit more but none pushed. I did not notice any fuel spitting but oil does accumulate in the cowl pan below the carbs. I have checked for oil leaks so it must be from evaporated fuel. I will check again under full throttle. The kids are grown up now and I would love to finally get this motor in top form, get a 29 Mazco, and learn to drive. Lower mounts from Bobs will arrive soon.


Anyone with experience regarding the above issues, reeds, and stuffers I would love to hear your thoughts. I can't help thinking there is something else going on but I guess it is time to do the reeds anyway. Really not sure about the stuffers.
Thanks..

[rock]

Might be time to inspect fuel pump diaphragm. They can leak fuel into the crankcase causing some of your issues.

Rock

[Muskoka2]

Might be time to inspect fuel pump diaphragm. They can leak fuel into the crankcase causing some of your issues.

Rock

Possible vapour lock in warm weather/my 2000 225 Johnson sometimes does this!

[coffeeguy]

Try a link & sync following the manual instructions,

[Merc 2.5]

Reeds will help u have better idle and such , also if u can do link and sync , u can put little more timing in it off idle to help out of the hole,

You had carbs off and cleaned well?

[VEGAS88]

Thanks very much for responses. You all have brought some good points.



Yes, the carbs were dip tanked, blown out with compressed air, and completely rebuilt. I believe I did a lync & sync after the rebuild but will do it again for good luck.

Yes, I have been wondering about the fuel pump. I figured since it always starts cold and is really strong in the mid and top end the pump must be OK. I was not considering how internal leakage could impact idle, hole shot, or a hot start. That oil build up in the cowl pan is definitely a clue not to be overlooked. I have just ordered an OEM Fuel pump kit. It is 30 years on the original now so it seems like a good idea.


Regarding vapor lock. Good point. I did some research and the operating temp should be good since I have replaced the thermostats and water pump. The fuel pump rebuild may help. I will also try to be sure and idle for a bit before shutting down. The hot start issue seems to happen when it has been shut off for a while after running on a hot day.


I will start with the link & sync, test for improvement in the ruff idle. Then, report back after the fuel pump is rebuilt and hole shot is tested. It snowed a bit today so I may not see the hot start issue or get to pull up a slalom skier for a bit. I will try to get my son in the water soon for the hole shot /slalom skier test. I will reconsider the reeds after the other tests are complete.

Thanks again.

[Merc 2.5]

Are you runnin a airbox or is it gone?
Reason for this ? Is. If u don't run air box u will most definitely get fuel puddles in cowl pan ,no matter how good your carbs are , the airbox helps this alot but if gasket not so good it will do it also just not as bad

[Mrzip]

Prop

[bullet123]

Bleed lines healthy?

[tlwjkw]

don't know if you are one of 'em are not? most folks put way to much in "manual" idle timing numbers.. works ok with very few pre cdm mercs.. after you do tha link and sync make sure there is a slight gap (this can vary ta suit what you want tha launch ta do) between tha carb roller and throttle linkage throttle cam.. then to get tha idle rpm/idle speed right it needs ta be done in tha water, in gear under a load with idle timin' screw only.. manual numbers don't mater with a happy idling motor and owner...... jmo.

[VEGAS88]

Bleeder hoses look good (no cracks) and air box is always on during normal running.


I did link & sync adjustment with some testing yesterday and more is planned today. Prior to link & sync I had a quarter inch gap between the carb roller and throttle linkage throttle cam. Following the instructions I had to adjust the idle stop screw significantly to "align throttle cam with center of roller". I then used an index card (doubled over) to set a slight gap between the throttle cam and roller before tightening the cam roller screw. This gave me an idle RPM of about 1800 at start up in neutral (in driveway with water flush on). I understand idle adjustment should be done in gear in the water but I needed to get it down low enough to shift. This is where old memories of last time came flooding back. I now needed to make significant changes to the primary pickup to get the idle RPM down between 900 and 1000. The engine idle became ruff and eventually stalled. I then remembered going through this years ago on the water and needing to adjust the primary timing pickup for a happy idle and then adjusting the idle stop screw to bring the RPM down (a reverse of the manual instructions). I may need to break out the timing light today just to see where I am. More work is needed, thoughts are welcome. A few questions and comments are below.

1. I have not touched the maximum spark advance adjustment screw. The engine was running great in the mid and top end. Did my changing the primary pickup impact the maximum advance setting? I guess I should verify with a timing light. I want to avoid the risk of predetonation.


2. Regarding the fuel dripping into the cowl pan. Carbs are rebuilt and airbox is always on unless I am testing. Gaskets are good. During idle, gas is dripping off the bottom of the top carb and possibly others. I will try to determine if it is all carbs or one today and find a more exact origin. I ran it with the airbox cover off and did not notice fuel coming out the throat opening. Thoughts are welcome. This newly found carb leak may need to be a separate post.

[tlwjkw]

if you need ta adjust tha 1/4 20 idle stop screw ta bring down idle ya got something outta whack..... tha absolute only thing that should change idle AFTER ALL LINK N SYNC things are done is tha idle timing.....

[tlwjkw]

idle timing has 0 effect ta max... after you set max at crankin' speed you really don't need a timing light anymore... your carbs may be tha main problem if ya gotta leak in any one of 'em...

"before tightening the cam roller screw"..... don't know what ya mean here?.. tha cam only turns at one end of tha linkage.. it doesn't "tighten"..

one other thing that "might" effect tha way it starts out ok but gradually gets worse at idle is mech fuel pump.. it can have a leaky diaphragm that effects idle and lower speeds............

[VEGAS88]

I know what you mean when you say" if you need to adjust tha 1/4 20 idle stop screw to bring down idle ya got something outta whack". I agree, I am just not sure what is out of adjustment. Prior to Carburetor synchronization, section 2 C in the manual says to loosen the cam follower screw and allow the cam roller to rest against the cam. Then, adjust the Throttle Cam using the Idle Stop Screw on the throttle arm "to align mark on throttle cam with center of the cam roller". It is this throttle cam adjustment that raises my idle RPM to 1800 and therefore requires too much adjustment to the primary pickup timing to bring the idle RPM back down enough to shift.


Would it help to remove the control cables and do the Throttle Cam Adjustment again and then follow through with the idle speed adjustment using the primary pickup/idle timing adjustment?


My fuel pump rebuild kit arrived but I would like to get the idle back to baseline before messing with something else. Ideally, I should test the boat in the water before doing the fuel pump.

Thanks!

[tlwjkw]

yes on throttle cable.. it needs ta be disconnected till ya get everything else right.. you adjust tha throttle cable (barrel nut) to fit tha throttle arm AFTER ya get tha idle timing and stop set.. i always do what i call "pre-load" tha cable.. when barrel nut is put in place it should be puttin' slight pressure on tha arm makin' sure its all tha way against tha stop.....

look at tha "linkage" between throttle arm and cam.. you will see its threaded on both ends.. barrel nut in cam and barrel nut in linkage.. you can use this adjustment to get cam where ya want it after you get timin'/speed where ya want it.. then you can adjust tha stop...