Mariner 115...PLEASE HELP!!!

wycough

Cadet
Joined
Jul 8, 2007
Messages
18
O.K. here it is.
1996 Mariner 115 that stalls/stumbles when in the holeshot from idle to 2100 rpm's when the #3 and #4 carbs kick in and it then it runs awesome.

It stalls and stumbles all over itself. Idle seems a bit rough and uneven. I'm mechanical. This one has me and the boat mechanic(2 of them) stumped. It's like the #1 and #2 carb are not doing their job properly. The boat runs great after all four carbs are kicked in.

Recent work.

new regulator
new impeller
prop pulled and hub checked
carbs cleaned
link and sync
throttle cable adjusted for WOT

this is when the problem started

now everything to fix problem

fuel sample taken = good
carbs re-built with new gaskets and needles
floats checked for proper measurement
new link and sync including dyno
oil pump adjusted(was a bit rich)
fuel accelerator new and gap checked
fuel pump rebuilt
compression good and even
1/2" spark
new plugs NGK and gapped .0400
new fuel filters
thermastat replaced(running kinda cool, but continues to do so w/ new part)
the carbs don't seem to hold adjustments very well. Each time the motor is turned off the carbs seem to need new adjustments after motor cools. Minor adjustments not major.

It's not really a holeshot problem, so please don't blame it on the prop. It's from idle to 2100prm's which just happens to include the holeshot. It's any acceleration up to 2100rpms.

Boat info: 1996 Champion 171 with Mariner 115. Great holeshot before. Trophy 24P stainless prop. Runs 48mph @ 5000 rpm's at 17-19 water psi. 5 or 5.5 inches below pad. (I think it needs to be 3.5 inches) Will address this after this problem here gets fixed. Motor has been in great shape since new. Very clean and maintained.

There may be more just can't remember right now. Any ideas? Thanks
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Mariner 115...PLEASE HELP!!!

Have the carb been adjusted in the water in gear and float levers checked, if so then have you tried to run with the jets from bowl vents removed. If they get alittle crud in them they will give you a fit.
 

wycough

Cadet
Joined
Jul 8, 2007
Messages
18
Re: Mariner 115...PLEASE HELP!!!

Have the carb been adjusted in the water in gear and float levers checked, if so then have you tried to run with the jets from bowl vents removed. If they get alittle crud in them they will give you a fit.


Carbs have been adjusted in the water in gear. As stated, the floats are right on the money. The jets were soaked in carb cleaner for 24hrs then compressed air blown.
 

wycough

Cadet
Joined
Jul 8, 2007
Messages
18
Re: Mariner 115...PLEASE HELP!!!

If they the jets had any crud in there wouldn't it run like crap thru out the rpm range? Mercury doesn't sell jus the jets separate.
 

MercGuy

Petty Officer 2nd Class
Joined
Jul 20, 2006
Messages
195
Re: Mariner 115...PLEASE HELP!!!

I recently went through some of the same issues with my 1998 Merc 115 (basically the same engine, I think).

I can only point to 2 things that you haven't already mentioned.

1) I re- propped so that I was running at the max rpm at wot (actually a little over @ 5300). However, if you were running OK before with the same prop we can probably forget that one.

2) I decarbed with SeaFoam. There is a link on this procedure that details running a dedicated tank of 3/4 gallon, then adding a bottle of Seafoam. Mine smoked like nobody's business, so I actually did it a 2nd time.

Really made a difference for me, hope it can help you also.
 

wycough

Cadet
Joined
Jul 8, 2007
Messages
18
Re: Mariner 115...PLEASE HELP!!!

Engine was Seafoamed prior to link and sync.
 

ChgoEnforcer

Recruit
Joined
Aug 4, 2007
Messages
2
Re: Mariner 115...PLEASE HELP!!!

wycough,
i have a 1994 mercury 115 hp that had the same problem,i figured it out today. when i rebuilt carbs the bowls got mixed up i had a bigger jet on #1 and a smaller jet on #3. #1 .056 #2 .056 #3 .050 #4 .060 when it should of been #1 .050 #2 .056 #3 .056 #4 .060. decided to pull the carbs today to recheck float level and check out the jets.with the bowl removed and the drain plugs out you car see the # of the jet on it. let me know if this helps


Chuck
 

wycough

Cadet
Joined
Jul 8, 2007
Messages
18
Re: Mariner 115...PLEASE HELP!!!

I did one carb at a time. Never two carbs apart at the same time.
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Mariner 115...PLEASE HELP!!!

Close up the plug gap to .032

fatten the idle mixture on 1 & 2 not even an eighth turn

try again and repost

I have same unit on a Pro Craft 180 SS22P 5900WOT, NO hesitation
 

jmburock

Petty Officer 2nd Class
Joined
Aug 25, 2005
Messages
174
Re: Mariner 115...PLEASE HELP!!!

Just a thought, but could it be your stator low speed windings. I'm not sure if your particular motor has both low and high speed windings. Worth a check since you've done almost everything fuel related. Would consider ignition next on the list, checking for spark on all cylinders/ checking ohms on stator/ ? switchbox..
 

Redneck Yacht Club

Seaman Apprentice
Joined
Aug 13, 2007
Messages
37
Re: Mariner 115...PLEASE HELP!!!

Hmmm...check valves?
Pinch the one hose at a time with pilers. See what happens.
Merc. has updated check valves or clean them with Power Tune.
Those check valves will dump extar fuel into cyclinders and mess with your air/fuel mix if not working propely. And I think there was a Parts bultlin on them to.
 

MercGuy

Petty Officer 2nd Class
Joined
Jul 20, 2006
Messages
195
Re: Mariner 115...PLEASE HELP!!!

Close up the plug gap to .032

fatten the idle mixture on 1 & 2 not even an eighth turn

try again and repost

I have same unit on a Pro Craft 180 SS22P 5900WOT, NO hesitation

I'm curious as to how you arrived at the .032 gap recommendation. As I posted above, I've got basically the same engine (1998 Merc 115). Do these engines run better at .032 ?

I'm due for a set of plugs, so I could try that gap and see how she does.

Also, if I'm reading your post correctly, are you running 5900 rpm at WOT ? Isn't max rpm for this engine 5250 ? If your propped that low, it would certainly help reduce any stumble & hesitation.

My engine runs pretty good, but does stumble occasionally, so I am interested in any little trick to perfect it.

Thanks !!
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Mariner 115...PLEASE HELP!!!

Nothing wrong with your set up that a lil carb adj won't clear up

It's a 2 stroke, the idle MUST BE a lil fat to accelerate, adj the idle mixture screws on the top 2 fatter til the slight bog is gone.

Make sure that the accel pump is set BY THE BOOK

I run NGK BPR7HS 10 at 135 compression, someday I may mill the head to raise the compression to 140 -145 and change plugs to BPR8HS 10, they work well and don't cost near is much as the precious metal plugs, at this price the slightest degradation in performance, I change them again.

Hopefully your prop is vented/ported.

My Quicksilver Lazer II came with the boat (used) he pulled skiers, I should replace it with a 24, but it cost $$$ so I only WOT just to get it up then run @ 4900
 
Top