Merc 115 ELPT 1981 - Bogs at 2500 RPM

[Fowl_language]

Hello all,
Thanks for the advice in advance, I usually can fix any problems with the motor in just a few days with your help.

Here is my problem, I have a 1980-1981 Merc 115 on the back of an old fiberform surfrider 15' tri-hull.

I recent had problems with the original mercury throttle control (throttle only button) so I decided to switch out to the Uflex universal throttle control and re-install the original ignition system into the console of the boat. The uflex need some modification to get the nuetral throttle position into neutral on the engine but it seems to be working fine now.

I had to screw out the circular throttle cable retainer all the way though to get idle at 800-900 RPM, I would like idle to be lower but the throttle control has a stronger cable pull than the original.

I have replaced the spark plugs with the NGK at the beginning of this season. I also replaced the lower unit oil with the quicksilver 90w, old oil was slightly grey but not terrible and there were very little shavings on the lower magnetic bolt when I switched the oil.

I suspected some problems due to bad gas so I drained the inboard tank and refueled with super at the right 50:1 mixture and treated with stabil marine, 30 minutes before trip.

Here is the problem:
I took it out last night to 700 ft/above sea level, 40 degrees F, hard start, ball was hard and choke was working, had to throttle only to 75% and hit the carbs with ether to start. After start, boat idled fine for 5 minutes to warm up and shifted into reverse and forward with no problems. WOT to the fishing spot was 4800 for 3 miles and overall speed was 32 mph. (usually get 4800-5100 WOT and 34 MPH). Boat idled for awhile before turning off.

I then trolled for about 5 hours and started again in cold condition, had to ether again which isn't a huge surprise, started better than before, idled for 10 minutes and then tried WOT.

Motor reached 2300 RPM and would not plane (at wot), throttle cable reached full throw. Motor was hid-cupping every once in awhile like it wanted to reach higher RPM.

Initial reaction is stator from what I have seen across the internet, but want other's opinions before I dive into this thing head strong and lose a bunch of money for nothing, i'm a grad student with no cash and the Chinook run this year is at once in a life time numbers! Help please!

 

[Dave1027]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Probably losing spark on 3 cylinders would be my first guess. Go through all electrical wiring and connections first. If that does not fix it then click my sig.

 

[mr 88]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Was it running ok before you switched out the controls ? If so then whatever you did when you were adjusting the throttle for your idle may have messed up the whole idle/acceleration circuit.I would turn out the idle jets a 1/8th of a turn and see if that works or gets better. If it does then continue to turn out the jet one carb at a time and test. As far as the starting goes,do not use ether,use two stroke mixed gas in a spray bottle.Ether will wash away the oil film on your cylinder walls and turn your motor into a "ether baby" Continue to prime the bulb after it gets hard,you are forcing more fuel into the intake which will help the cold starts. See post below this one about being stumped and bogging at WOT with Merc 115,probably same issue and answers.

 

[Fowl_language]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Probably losing spark on 3 cylinders would be my first guess. Go through all electrical wiring and connections first. If that does not fix it then click my sig.

Thanks for the advice I'll check it out as soon as I can, got new plugs today just in case that was some of the problem.

Was it running ok before you switched out the controls ? If so then whatever you did when you were adjusting the throttle for your idle may have messed up the whole idle/acceleration circuit.I would turn out the idle jets a 1/8th of a turn and see if that works or gets better. If it does then continue to turn out the jet one carb at a time and test. As far as the starting goes,do not use ether,use two stroke mixed gas in a spray bottle.Ether will wash away the oil film on your cylinder walls and turn your motor into a "ether baby" Continue to prime the bulb after it gets hard,you are forcing more fuel into the intake which will help the cold starts. See post below this one about being stumped and bogging at WOT with Merc 115,probably same issue and answers.

It was not having nearly as many problems before I switched out the controls. The key start is rewired to the same colors, so if anything I think the throttle cable could be messing it up? Too much throttle at start?

Where are the idle jets? I can't find any diagram for the screw to adjust (haven't done THAT much with the motor)

Thanks for the heads up with the ether I will bring the spray bottle along with some gas/oil mix tonight when I test it.

 

[CharlieB]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Stator driven switchbox ignition has a minimum cranking speed of 300 RPM to generate sufficient voltage to operate. This requires a GOOD battery, clean tight connections at both ends of all battery and starter cables. Clean starter brushes and commutator and lightly lubed bushings.

Carbs need to be cleaned, sync'd and properly adjusted.

Edit: Stator voltage on the high speed windings increases with RPM and takes over ignition about 2500 RPM. You need a DVA meter or a DVA adaptor to use with any volt/oh meter and check generation compared to the values listed in the CDI Ignition Guide.

http://issuu.com/cdielectronics/docs/troubleshootingguide?mode=window&backgroundColor=#222222

 

[Fowl_language]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Stator driven switchbox ignition has a minimum cranking speed of 300 RPM to generate sufficient voltage to operate. This requires a GOOD battery, clean tight connections at both ends of all battery and starter cables. Clean starter brushes and commutator and lightly lubed bushings.

Carbs need to be cleaned, sync'd and properly adjusted.

Edit: Stator voltage on the high speed windings increases with RPM and takes over ignition about 2500 RPM. You need a DVA meter or a DVA adaptor to use with any volt/oh meter and check generation compared to the values listed in the CDI Ignition Guide.

ISSUU - CDI Electronics Practical Outboard Ignition Troubleshooting by CDI Electronics

Thanks for the heads up CharlieB, I had a friend back the throttle cable to 500-600 RPM for idle to shift (manually by disconnecting it on the water) then I shifted in gear at low RPM we were able to transition to 4800-5000 and get on plane after that.

Then on the way back we tried it again, shifting in low RPM and then a transition, it worked for about 0.5 miles until we had to throttle down for an obstruction, when we attempted to throttle back up it stayed at 2500 RPM and would not go past again with multiple tries still hidcupping like it wanted to go but could not.

Could the stator cause intermediate problems like this? I always thought that if an electrical part stopped working it just flat STOPPED working.

Thanks for the advice i'll look into getting a DVA!

 

[CharlieB]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Electrical parts can do strange things, it is possible that insulation is flaking off of windings and as they heat and expand the wires touch and loose voltage intermittantly.

The most important thing to remember is there is NO RETURN on electrical parts. You should PROVE the fault before ordering a NON-returnable expensive part.

The first thing I would do is make sure the carbs are clean, and the idle mixture is set correctly. Idle must be overly rich to provide the additional fuel necessary for acceleration, almost 1/4 turn more than 'Best Idle' speed while IN gear and IN the water. I would try opening each idle mixture screw just the width of the screwdriver blade slot and retest acceleration, if that straightens out or even improves the condition then pull the carbs and start cleaning.

Read the CDI Ignition Guide, get a DVA meter or a DVA adaptor for any volt/ohm meter and test your stator. Test it stone cold, then again once well warmed up so you can see if it changes.

ISSUU - CDI Electronics Practical Outboard Ignition Troubleshooting by CDI Electronics

 

[Fowl_language]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Well thanks everyone for the information, I broke down and took it to the shop.

Just got a call from the mechanic he says the compression was acceptable, wasn't great but good enough to keep the motor.

Also said that one of the switchbox's was blown out and that was causing no spark mid range.

Estimated around $500 which I think is acceptable considering the part alone is about $160. I'll keep posting as soon as I get it back and know for sure that was the problem.

 

[CharlieB]

Re: Merc 115 ELPT 1981 - Bogs at 2500 RPM

Make sure you ask for the old parts. While it is possible for a switchbox to fail, they don't usually function correctly again.

A more likely problem is a broken trigger wire, it makes contact then as the wire moves it separates loosing spark on two cyls, as the wire continues to move the broken ends bump together and spark returns.

Wait and see if they call you back and tell you it ALSO needs a trigger.

Too many shops fail to take the few minutes more to properly test, assuming the switchbox is bad, replace it then find it didn't fix it, then change something else until they finally change the defective parts. You end up with a massive parts bill.