Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

Joined
Mar 17, 2010
Messages
17
Hi all,

I'm new and I need help; I have a 1986/7 vintage Yamaha 115 V4 2 stroke engine giving me trouble.

To start at the beginning the engine overheated and as a result I had to be rebuild in one cylinder. At the time I discovered this one cylinder had no compression and when I dug deeper I discovered the cylinder was scored and the rings has become one with the piston.

When rebuilding I honed the cylinder as a re-bore was not necessarily essential. Acting on advice I decided to go with the hone option and fitted a standard piston. Now rebuilt the 3 cylinders that where not rebuilt have a reading of 105 PSI and the cylinder I rebuilt has a reading of 100 PSI which according to my Yamaha manual is ok????

When the boat reaches operational temperature the engine acts as if it is starved of fuel/air and chucks. Once it cools it is fine again so the issue is clearly temperature related. The boat starts on the button every time.

I have replaced:

Big Ends / Small Ends,
All engine seals and gaskets,
Plugs,
Thermostats,
Coils (used),
Fuel Pump,
Heat sensors on block,
All pink wires,
All intake gaskets,
Balanced the carbs,
Replaced the fuel tank and lines,
Fuel Pump,
Power pack box (ECU Box),
Replaced the male/female fuel connection &
other adjustments.

Any suggestions as to what my issue might be are welcome, I am running out of ideas. From what I can gather it is either an intake airflow issue or electrical issue due to heat/pressure.

Hope someone has an idea or two.

Thanks,
Daragh.
 

99yam40

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Messages
8,851
Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

Are you sure it was overheating that caused the piston problem? And what did you do to fix that?
Maybe the problem was a lean fuel problem for that one cylinder and you need to clean carbs,
 
Joined
Mar 17, 2010
Messages
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Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

Hello,

There is a buzzer fitted to the throttle and this sounded at the time to indicate the boat overheated. This happened after the damage was done I think as I would have stopped once the buzzer sounded. I haven't ruled out the carbs, I had them balanced by outboard marine a marine specialist. At the time dirt was found in the carbs and the tank was cleaned, fuel vacuum pump was reconditioned and fuel lines where replaced. I also temporarily ran the fuel straight to the carbs once just to rule out the fuel filters blocking flow and also to test the male female connection which I thought might have been seeping in air.

Do you think it is the carbs, the chucking only occurs when it is at operational temp. It is best described as a starvation of something. What that something is I don't know, Spark, Fuel, Air???
 
Joined
Mar 17, 2010
Messages
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Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

Hello,

There is a buzzer fitted to the throttle and this sounded at the time to indicate the boat overheated. This happened after the damage was done I think as I would have stopped once the buzzer sounded. I haven't ruled out the carbs, I had them balanced by outboard marine a marine specialist. At the time dirt was found in the carbs and the tank was cleaned, fuel vacuum pump was reconditioned and fuel lines where replaced. I also temporarily ran the fuel straight to the carbs once just to rule out the fuel filters blocking flow and also to test the male female connection which I thought might have been seeping in air.

Do you think it is the carbs, the chucking only occurs when it is at operational temp. It is best described as a starvation of something. What that something is I don't know, Spark, Fuel, Air???
 

99yam40

Fleet Admiral
Joined
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Messages
8,851
Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

Your attachment is not any good or at least that is what the web site says when clicking on it.

I have always heard that lean fuel mix will get a piston first and lack of oil will get bearings first.
Overheating would effect more than on cylinder, but that is just my opinion
 
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Mar 17, 2010
Messages
17
Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

It was a diagram of the carb, cant get it to work.

Do you think I have a fuel/air intake issue, its frustrating as the boat runs like a clock until it gets to operational temperature.
 

Bamaman1

Lieutenant Commander
Joined
May 15, 2011
Messages
1,895
Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

You have one of the original Yamaha motors--which started to show up in the U.S. retail market in 1984. The V4 and V6 Yamaha engines made other outboard manufacturers get off their duffs and finally make some positive improvements to their engines. Yamaha ate the competition alive with conservative horsepower and few service problems. It's been said this 115 hp is actually 138 hp at the prop.

You've done an incredible number of steps--at the power head. The 90/10 fuels are quick to break down. Then, an acid that eats anything rubber in the fuel system--including the fuel pump diaphrams. The carbs can be easily cleaned--a total 1 hour job. Carb problems are often sticking needle valves dumping fuel in the engine and trash in the carbs. They're easily cleaned without purchasing any carb kit--if you're careful with the gaskets.

It sounds as if your engine is still overheating--hotter than normal operating temperatures. When you've got an overheating problem, you usually begin to address it at the lower unit. It sounds as if you're getting a high temp. partial seizure in process.

Have you checked the lower unit for any obstructions in the cooling passages? Is the impeller good?
 
Joined
Mar 17, 2010
Messages
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Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

Hi there,

You learn something everyday!

I am in Ireland and its the winter here now so I have a few months to work on her.

Funny you mention the gaskets, I have a complete set of intake gaskets on order. I also service the boat every winter which includes an impeller. This was also changed last year, but I didn't inspect passage for grime and blockages. Ill do that this weekend. I think we might be in the right area.

Do you think the differentiation between compression in the cylinders combined with carbon build up is now adding to the original issue that caused the boat to overhead to create the current problem???

If I examine spark strength, timing, fuel/air mix and the follow the two steps above i.e. clean carbs and replace impeller and see if there is any blockages - in theory I should be on the road to recovery????????????
 

roccochiodo

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Nov 25, 2011
Messages
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Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

hey did you buy the boat with the problems i had very similar issue with my 1985 yamaha 140hp it was getting hot so ended up completly pulling powerhead exhaust plates heads full rebuild to clean all the salt build up out of the engine put it back together and guess wat did the exactly the same thing almost commited suicuide over it.ended up finding out it was the prop may i arsk wat prop your running coz even tho mine never hit rev limiter or struggled alot it was the wrong pitch and type for my motor witch caused it to get hot around 5000rpm then the buzzer would go off then would go into limp mode witch makes the motor jerk and drop the revs down. i never would have though a prop could do that. but a old skool boat machanic gave me the advice checked it out and havent had a problem since. buy the way i would have atleast re ringed the other cylinders coz 100psi is pretty bad even if all cylinders are even. mine is at 165psi at all four
 
Joined
Mar 17, 2010
Messages
17
Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

That's interesting. I didn't think a prop would make any odds particularly if it was working fine on the motor previously? I wonder could it be off balance or worn out? Any Ideas?

It was an old school boat mechanic who originally suggested not to do a re bore on the other 3 cylinders. As it happened they had another 115 in for re-pare its compression was similar. Over the years they have come across low pressure 2 strokes that still work perfectly fine. I had to run 10 hours on her before I pushed it we also added additional oil in with the fuel at the time. I find your solution interesting. Mine is not overheating no buss-er sounds but this motor does have a "limp home" feature which is designed switch the engine to 2 cylinders and run @ low revs to get you home. I think this is kicking in slightly which is causing my problem. When I disconnect the pink wires this still occurs. As above I also changes the ECU unit on the boat. I ordered a new water pump I think this will help, it needs to be getting good water to stay cool. I don's have any salt issues as it runs in fresh water.
 

roccochiodo

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Nov 25, 2011
Messages
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Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

does your motor say precision blend on the motor cover? the 140hp was rare that i have only come out in some places.the 115hp is identical eccept the inner and outer exhaust plates and carbs thats how they got the extra power.if its a precision blend i have the exact same motor. i dont think its your prop thats causing you problems seeing it was running fine before. i bought my boat with the problem the boat had a 13 x 19k on it witch was causing the over heat issue i changed to a 13 1/2 19k and problem solved bill witch is a boat machanic i no said if the motor does it too easy it will overheat aswell thats wat was happening. i would have thought maybe if was reving too hard yea but it wasent so i never thought of the prop o well motor fully cleaned out now and fresh so wasent a complete waste of time i surpose.all i can say getting the f---ing powerhead off jusus friken christ ended up getting another mid section piece after i had to sharpen my biggest chisel and bash it in between the power head and mid section to get off i hope i never do a job like that again!
 

roccochiodo

Recruit
Joined
Nov 25, 2011
Messages
3
Re: Yamaha 115 V4 2 Stroke 1980's era - Issue at operating tempature

does your motor say precision blend on the motor cover? the 140hp was rare that i have only come out in some places.the 115hp is identical eccept the inner and outer exhaust plates and carbs thats how they got the extra power.if its a precision blend i have the exact same motor. i dont think its your prop thats causing you problems seeing it was running fine before. i bought my boat with the problem the boat had a 13 x 19k on it witch was causing the over heat issue i changed to a 13 1/2 19k and problem solved bill witch is a boat machanic i no said if the motor does it too easy it will overheat aswell thats wat was happening. i would have thought maybe if was reving too hard yea but it wasent so i never thought of the prop o well motor fully cleaned out now and fresh so wasent a complete waste of time i surpose.all i can say getting the f---ing powerhead off jusus friken christ ended up getting another mid section piece after i had to sharpen my biggest chisel and bash it in between the power head and mid section to get off i hope i never do a job like that again!
 
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