Idle Fine Tuning, 1988 115 L6

[gregdan24]

Pulled the idle stabilizer box recently and reset the timing - 5 deg primary and 19 deg high speed. I have it idling down to about 600-700 rpm in gear (800 to 900 in neutral). I had to adjust the idle up that far to keep it from dying out. Idle speed screws are turned out 1 3/4 turns. The motor is running real good, hole shots and all, except one thing.

After idling at the slowest speed for a while, the rpms will start to drop down below 600. Once it hits about 500 it will drop off and die unless I give it a goose with the throttle. I know it's not a trolling motor, but I do sometimes find the need to use it for that when out in Lake MI in rougher water.

I suppose I could just adjust the idle speed up, but am wondering if maybe I should maybe advance the timing at idle a couple degrees to compensate for the removed idle stabilizer box. Or is that asking for trouble? Any other suggestions?

Thanks in advance for your ideas, - Greg

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

bump - still wondering about advancing the timing at idle.

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

Sorry - bumping one more time hoping an expert is back from their July 4th vacation.

 

[achris]

Re: Idle Fine Tuning, 1988 115 L6

Try leaning the carbs about 1/8 turn each. Just check that it hasn't leaned them too much to cause a problem on acceleration...

Chris (no expert but I have worked on a few engines over the years).....

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

Try leaning the carbs about 1/8 turn each. Just check that it hasn't leaned them too much to cause a problem on acceleration...

Chris (no expert but I have worked on a few engines over the years).....

Thanks much for the reply Chris! I have them turned out 1 3/4 now and did try with them in 1/8 turn. Didn't seem to make a difference. Bumping up the idle speed doesn't seem to be helping either. It's hard for me to tell if it's loading up or running out of gas. It seems to be better at staying running until it gets warmed up. I may just need to play with the idle mixture screws some more, but like I said it's really good out of the hole right now.

I can keep it going when shifting forward/neutral/reverse, but others have a hard timet. Wife almost smacked a boat when it died on her pulling up to put it on the trailer the other day. So I gotta do something with it so others can use it pulling tubes etc.

Going to check the primary pickup timing again. I may have set it below 5 deg thinking that was "safe". If all else fails I may fix up the rotten wire on the idle stabilizer box and put it back on. It worked fine with it on last year after I put the new powerhead on. Still wondering how much advance I dare set on the primary pickup timing if anyone has info on that.

Thanks again, -Greg

 

[achris]

Re: Idle Fine Tuning, 1988 115 L6

One test you could do while it's starting to die it to just give the choke button a quick press and see what happens. If it kills it quicker, then it's too rich, if it helps maintain the engine running, the idles are set too lean....

Just an easy check....

Chris.........

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

That's one of those "why didn't I think of that" tips Chris. You are an expert and I really appreciate your advice. Thanks! -Greg

 

[Ski'nBlind]

Re: Idle Fine Tuning, 1988 115 L6

gregdan...I have been having the exactly same issue with mine. I have my timing set right in the middle where it's supposed to be at 6 deg ATDC. I have the idle mixture screws set right for holeshot so I don't want to mess with that anymore. This weekend I'm going to try setting initial timing up in 2 deg increments and see if that helps my motor. I don't want to change anything for mid and top range as it screams like a scalded dog.

If this post doesn't get lost too far down the pile I will be sure to tell you the results I had with tweaking the timing a bit for idle.

Make sure you fix those bad wires the right way 1st. I had more than several and I soldered them and finished with heat shrink tubing.

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

I have my timing set right in the middle where it's supposed to be at 6 deg ATDC.

Thanks, it's good to know I'm not the only one chasing this problem. Not that I'm wishing bad running on anyone else....

The Seloc book I have (I know...not the best) says my primary timing is supposed to be 5 deg BTDC. Guess you must have a different motor? I probably won't get mine back in the water now until the weekend, but will report back too.

 

[achris]

Re: Idle Fine Tuning, 1988 115 L6

The Seloc book I have (I know...not the best) .....

Run away!!! Hate those books. What little information is in them is usually wrong!

Here are the 3 pages for the full tuning on your engine, from a proper Merc manual... (If you have trouble reading them, just PM me with your email address and I'll send them to you in full size, 300dpi).

The only thing I would do differently to the book is to use NGK BUHW plugs, not the chumps. It also says the primary throttle pick up for your engine is 5*-7* ATDC, not before (as your seloc says). That would explain your problem very neatly....

Chris.......

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

Run away!!! Hate those books. What little information is in them is usually wrong!

Well ain't that just great! I went and looked again and sure enough the Seloc says BTDC....what a POS. The pics you sent are readable, so really appreciate that. Can't wait to see what happens when it's set right! Thanks again Chris.

 

[Ski'nBlind]

Re: Idle Fine Tuning, 1988 115 L6

Yep....happened to me too. Checked that book 3 times when I was setting the initial timing at 5 BTDC. It idled so darn bad you could tell it wasn't right. A nice forum member pointed that out to me also that the Seloc is WRONG.

Good bunch of folks here!

 

[arsenalpsu]

Re: Idle Fine Tuning, 1988 115 L6

you'll need to re-do your link and sync onces you've fixed your primary pickup to ATDC.

 

[Ski'nBlind]

Re: Idle Fine Tuning, 1988 115 L6

I suppose I could just adjust the idle speed up, but am wondering if maybe I should maybe advance the timing at idle a couple degrees to compensate for the removed idle stabilizer box. Or is that asking for trouble? Any other suggestions?



Greg
I worked on my boat this morning and advanced the initial timing +2 deg's so now it's set at 4 deg ATDC. Double checked linc and sync and set the rpm to 750 under load, 850 in nuetral. Took the boat out on the lake for 4 hrs and most of a tank of fuel. Never died on me anymore. Wouldn't even die trimming the motor way up to beach the boat. No hesitation problems...no holeshot problems.

Hope it helps

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

Ski'nBlind - glad to hear you got it dialed in. Readjusted mine to 5 deg ATDC and redid the link and sync yesterday but haven't got it in the water yet to reset the carbs and idle speed. The suspense is killin' me, so probably tomorrow. - Greg

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

Finally got mine in the water yesterday and pretty much dialed in. The thing that has me wondering a little is when the motor is warmed up good, it idles at 600-650 in gear and 800-900 in neutral. That's as low as I can get it without having it die when shifting into forward or reverse. Idle screws are all 1 3/4 out - that's where it seems to do best all around. Even then, if I try to idle in gear, it will eventually have a hard time staying running. I've decided it ain't no trolling motor without some trolling bags/socks over the side. Or better yet a 9.9 kicker...

The thing that gets me is when it's cold, it idles between 1000 and 1200 and about 800 in gear. I don't remember this being the case with the original powerhead, but it's been a few years since that one ran right, so I don't recall for sure. Is that kind of difference to be expected between a cold and warm engine?

Thanks again you guys for being a great help in getting my 115 adjusted right. It's running like a new motor

Greg

 

[achris]

Re: Idle Fine Tuning, 1988 115 L6

Sounds like the idle mixtures are set too rich. Try winding them in 1/4 turn.

That 1 3/4 turns is just a preliminary set point. Just to get the engine running. You need to tune them once everything else is set. Adjust the mixtures so the engine is running right, then 1/8 out. Check that it doesn't hesitate on acceleration and you're good to go. If it does hesitate, then turn them another 1/8 turn put and try again....

Chris........

 

[Ski'nBlind]

Re: Idle Fine Tuning, 1988 115 L6

Just curious
Did you set the timing with the throttle cable connected and in neutral or with the cable dis-connected and lined up the arrows (marks) on the throttle cam?

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

Sounds like the idle mixtures are set too rich. Try winding them in 1/4 turn.
Chris........

I probably haven't been methodical enough with the idle mixture screw adjustments, although I have tried turning them in to get it to idle right in gear. I'll just have to go at it with more of a purpose I guess. Thanks Chris.

 

[gregdan24]

Re: Idle Fine Tuning, 1988 115 L6

Just curious
Did you set the timing with the throttle cable connected and in neutral or with the cable dis-connected and lined up the arrows (marks) on the throttle cam?

I disconnected the throttle, lined up the marks with the idle at the stop, and held it there with a bungee. Then redid the link and sync and checked the timing again. Surprised me a bit how much that 10 deg retard dropped the idle speed - had to adjust the idle stop screw out quite a ways from where it was before.

Does your idle drop a couple hundred rpm when hot compared to cold or is it the same no matter what the engine temp is?