Mystery 115

[wavrider]

Hello Board,

First time posting but been reading the boards and gathering lots of usefull info here.

I have a 115 (maybe?) model # 115etl78g according to the plate.
compression is 110 on all 4 cylinders more or less , all in specs.

Timing is set at 24 WOT, L77jc4 plugs gapped at .40, sea foamed the engine.
I have not tested the spark but starts pretty easy every time.

I can get it to idle lower than around 700 to 750 RPM, WOT at the ramp not in gear is 4000 rpm at best, under power with a 13 1/4" RH 17" Michigan prop I get roughly 2800 RPM at best.

I had the carbs replaced right after I got the engine as the old ones were full of junk and corroded beyond repair.

After trying everything I knew of to get the idle better I researched the part numbers on the carbs. top carb is 393769, bottom is 393770, these part numbers cross to a 90 hp engine, I do not know what year they are.

The question is, can I find a part number or casting number on the block that will let me know if I have a 90hp power head or if I have a 115 powerhead with 90 hp carbs on it?

That way I will know what manual to purchase for the engine I have.
thanks in advance for any replies, enjoy n be safe,WAV

 

[HighTrim]

Re: Mystery 115

Look for the "welch plug". It is located on the top , rear of the motor and will contain the model and serial number. Im assuming this motor is new to you, and has ran like this since you aquired it or did this just start? Who rebuilt the carbs?

 

[wavrider]

Re: Mystery 115

Thanks for the fast reply, getting the flashlight and heading to the back 40 now. Wav

 

[HighTrim]

Re: Mystery 115

Sorry it will be about the size of a quarter and shiny

 

[wavrider]

Re: Mystery 115

Welch plug states 15etl78g.

Looks like it is time to get the correct carbs and start from there, thanks again for the reply.

 

[Solittle]

Re: Mystery 115

Not a good idea to run it at WOT in neutral even in the water. Idling at 700-750 is OK but you should be turning 5500 rpm at WOT in forward gear of course.

 

[wavrider]

Re: Mystery 115

Thanks for the replies. I will post back when I locate a pair of carbs and start tweaking them in.

 

[tschamp20]

Re: Mystery 115

its a 1978 115hp according to the first # in your post.15hp according to the second number.probably 115 though. does it have 4 cylinders? if so its a 115hp

 

[steelespike]

Re: Mystery 115

Lack of speed could be a spark problem.You could be losing one or more cylinders.While it might not run right with those carbs I would think it would
at least run like a 90.When trying to get wot you might try a little choke or
CAREFULLY squirt some fuel mix into the carbs.

 

[wavrider]

Re: Mystery 115

Different carbs were put on from the previous owner. My nephew originally gotr the boat then I helped him get it to fire but carbs were shot, so my nephew went and had rebuilt carbs installed from the guy he bought it from.
then I later purchased the boat from my nephew, he lost interest when he could not get it to run correctly.

I took the carbs off yesterday and cleaned them real well. Had some small debris in the bottem carb high speed jets. Not enough daylight left to install them yesterday so I will try to get them on today after I leave the office if enough time and daylight permits.

I will venture to the local auto store and see if they have a spark tester to check the spark on the ignition side of the house.

Thanks for all the replies and I will post whatever results I end up with. enjoy and be safe,WAV.

 

[wavrider]

Re: Mystery 115

Installed carbs, filled the barrel with water, hit the solenoid primer only twice, left the throttle in the idle position. Turned the ignition, started up and idled at 700 rpm just as smooth as a kitten purring.

Let it idle for ten mins or so to see if it would "burp" or "sneeze".
Idled wonderful. Ran the throttle up to roughly 3500, still had alot of throttle to go but did not want to WOT if not in the water as per advice from recent posts. Quickly brought throttle back to an idle, usually the engine stopped at quick decellaration but this time just idled wonderfully.

Put the cowl on and started engine, coughing, missing at idle and would not get to 3000 rpm even if 3/4 throttle?

Take cowling off and back to purring like a kitten and easily 3000 rpm with a lot of throttle left to give?

Engine smelled rich like it was being ran with choke on, I have no choke just a solenoid primer. Open for suggestions on the cause. Can not see me running down the river with the cowl off, but if the bite gets going good I sure would be tempted to. thanks , WAV

 

[guy74]

Re: Mystery 115

My guess is you either have an exaust leak under the hood, or you have spark plug wires that are grounding to the latches when you put the hood on.

 

[wavrider]

Re: Mystery 115

Update on mystery 115.

Took boat down to the lake today. Started fine, idled fine, ran it at idle in gear, then midrange around 1750 to 2000 RPM, smooth acceleration throughtout the range. Everything good so far. Accelerated to 3/4 throttle, run 3500 RPM at 34 mph or so the 23 year old speed gauge registered.

Went to WOT and it increased RPM to 3750 -3800 for a few seconds then heard the engine come back down 3500 according to tach. Ido not trust the tach either as it si 23 years old also. 1984 bayliner and I can only assume all the gauiges are original equipment. throttled back down to 3/4 throttle and maintained 3500 RPM. Ran around the lake several times with various throttle configurations and never a burp or sneeze.

I think I have it almost correct. I will order a new tach so I can be confident of the RPM's as engine sounds like it rev's more that 3500. could be a rectifer or regulator problem as my volt meter says 16V at more than 1/4 throttle so perhaps a bad diode on one leg of the bridge rectifier?

I think the eccessive smoke while in the "barrel" was mostly from the de-card still burning off carbon as at the lake she did not smoke excessively, with the cowl on for all test runs.

I have a 13 1/4-17 prop. I may need to reduce the pith to get the correct rpm range out of the engine once I establish the corrrect RPM displayed on the tach.

Thanks for all the responses to my never ending questions. It never hurts to get another opinion and the members here have been absolutely fantastic.

Enjoy and be safe,WAV

 

[HighTrim]

Re: Mystery 115

I agree, your RPMs are much too low for WOT.

 

[wavrider]

Re: Mystery 115

Sorry to bump a thread so old but I have been working on my 1970 33hp and sort of let the 1979 115 set to the side. I never followed up on the 1979 115 tach problem.

Finally got around to installing a new tach on the 1979 115, took it out for a spin and fishing trip to vilano beach yesterday.

The problem was the old tach, I get a little over 5500 rpm at wot, around 5700 to be exact on an uncalibrated (i guess) new from factory tach. Looks like I am getting around 37 mph top speed.

Idles at 500 rpms and runs smooth through all the acceleration.
Thank all of you who replied to the questions and the 115 on the Bayliner Marlin Trophy model is running great.

Did I forget to mention she likes gas? Alot of gas? (grin)

Next project is replace all the cooling system in the 115.

Merry Christmas to all and thanks again,WAV.

 

[DJ]

Re: Mystery 115

Sorry to bump a thread so old but I have been working on my 1970 33hp and sort of let the 1979 115 set to the side. I never followed up on the 1979 115 tach problem.

Finally got around to installing a new tach on the 1979 115, took it out for a spin and fishing trip to vilano beach yesterday.

The problem was the old tach, I get a little over 5500 rpm at wot, around 5700 to be exact on an uncalibrated (i guess) new from factory tach. Looks like I am getting around 37 mph top speed.

Idles at 500 rpms and runs smooth through all the acceleration.
Thank all of you who replied to the questions and the 115 on the Bayliner Marlin Trophy model is running great.

Did I forget to mention she likes gas? Alot of gas? (grin)

Next project is replace all the cooling system in the 115.


Merry Christmas to all and thanks again,WAV.

Wave,

5700 is PERFECT. That engine will use a lot less gas if you run it 3/4 throttle as opposed to WOT.

Glad everything worked out. Good job!