'95 Merc 115 timing issue

[XpressYoSelf]

Recently picked up this 1995 Mercury 115 ELPTO for my 18' xpress and I'm having issues setting it up properly. Starts right up but I can't get the idle down. So far I've adjusted the mixture screws, fast idle screw and checked timing. A big problem of mine is not having an accurate tach to reference when it's running. I just added a tiny tach and think I have too many wraps or something because it's reading around 3000 rpm at idle. Sounds like I'm idling around 800-1000. At this idle my timing can be adjusted from 16-22 degrees BTDC with the spark Advance screw. I've read that it should be at ~2 degrees BTDC at idle, and clearly I'm nowhere close. Does anyone have any advice?

[BIGFLAT]

Pro's are gonna want your motor serial number to assist you...BF

[XpressYoSelf]

Serial Number G176025

[straffordengineer]

Serial number is actually OG176025. The first two digits are always letters. Since you have moved all of the engine adjustment points, I suggest you do a complete Sync'n Link procedure on this engine. I also suspect your timing light or your timing light connection (should be on top spark plug). These engines are supposed to idle around 750 rpm around zero degrees of timing. If you are only getting 16 to 20 degrees at 800 to 1000 then something is definitely wrong. The Sync'n Link on this engines will involve the following:

1) Verify the that all carb butterflys are closed at idle and that they are synchronized to open at the same time.
2) Verify the center of the carb roller is aligned with the mark on the throttle cam (there should be a visible gap about .005 to .010 between the roller and the cam)
3) If this engine has an oil pump, then the oil pump linkage should also be verified to align with the mark on the oil pump while the roller and cam are aligned.
4) Now with the above settings, the timing should be checked to correspond to be around zero (it doesn't really mater if you are at 2 degrees before or after on these engines because once you have this timing set, the next step is to adjust the timing as required to achieve the correct rpm while idling in forward gear in the water)

Is the timing light triggering at times when no marks are on the flywheel or are all the timing marks always present? if yes, could have a trigger problem.

RPMs will be slightly higher while running on a garden hose than in the lake because you don't have any back pressure on the exhaust. Typically the rpms would be around 1000 on the hose and about 750/800 in the lake. Timing with the faster rpms is not affected very much.

These engines only idle on the top two carbs (a 2+2 design engine). Therefore only the top two carbs will have idle mixture adjustment screws. These screws should be adjusted between 1 1/2 and 1 3/4 turns out from a slightly seated position.

I am guessing that one of your carbs is not completely closed or your timing light is not correct. You definitely need a good tach and its sounds like your Tiny Tach is not hooked up correctly.

A factory service manual is really a necessity to set thees engines up correctly.

[XpressYoSelf]

Ok I've checked the alignment of the carb roller and oil pump linkage. As seen in the pictures I think I t looks like they're both lined up. Also the light seems to be functioning properly and shines only when the marks on the flywheel appear in the window. Any suggestions?

[XpressYoSelf]

[XpressYoSelf]

The timing light seems to be functioning properly as it shines only when the timing marks on the flywheel appear in the window

[XpressYoSelf]

Also I've replied with pictures of the linkage alignment, awaiting their approval. But everything seems to be lined up

[straffordengineer]

I don't see any pictures.

[XpressYoSelf]

Straffordengineer you can view the pictures in an album I created on my profile. Thanks again for the help!

[straffordengineer]

Pictures look good and your synchronization should be right provided that there is a slight air gap between the carb roller and the throttle to ensure the throttle cam is not trying to open the carbs, that all 4 carbs have their butterfly closed and operate in unison, and that the timing of #1 plug is basically zero. If you are experiencing higher rpms than around 800 while in the lake in forward gear then I can't help you anymore without physically seeing the outboard. The only thing I can suggest is you have an air leak on one of the top 2 carbs that is allowing air to bypass the butterfly or that there is something wrong with your ignition timing module or trigger. Perhaps Don can offer some advice.

[XpressYoSelf]

Yessir there is an air gap between the cam and roller, and all four carbs are closed and look like they operate in unison. I'll hook her up again tomorrow and see if I can't get the tach to read accurately before posting again. Another question though, at WOT what should my timing look like? (I really do need to acquire a service manual for this thing).

[EuropeanAM]

Let's make sure there are idle air adjustment screws in ONLY the top two carbs (there should NOT be adjustable screws in 3-4).

[XpressYoSelf]

Update: As it turns out, the issue was my base idle timing screw! WOW! The relief and embarrassment are battling it out right now. I had imagined that this adjustment screw was to solely adjust idling RPMs. Once I was linked and sync'ed, I was able to rig up the timing light I bought from Harbor Freight and tune it to 2º BTDC at idle and 22º BTDC at max advance while the boat was still strapped to the trailer. I'm waiting on my new tachometer to arrive tomorrow to see what my WOT RPMs are to get my boat propped right. Currently turning a 4 blade aluminum 19 pitch prop and I hit 40 mph on the GPS, so I'm interested to see the numbers. Hopefully I can get this boat up to 45.

[straffordengineer]

I had imagined that this adjustment screw was to solely adjust idling RPMs.

I am a little confused. The idle speed adjustment screw "is" solely for adjusting idle rpms by adjusting idle timing. I guess I don't understand what you are trying to say.

[EuropeanAM]

It was likely "way" out of whack... and if just one other synchronization adjustment is off, can easily confuse or confound the situation.