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97 Yamaha 115 2 Stroke issues

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Old 01-12-2018, 04:54 PM
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Default 97 Yamaha 115 2 Stroke issues

Working on some issues with this engine hoping to get some help from some of you Yami experts.

18' Action Craft Flats Boat (1250 Lbs with gas and a fat guy) Prop: 13 3/8 x 15 Alum

ISSUES:
Hard starting cold
idles @ 7-800 RPM once you get it started and 8-900 RPM warmed up
Only getting about 33-34 MPH @ 4700 RPM WOT Trimmed out

WHAT I HAVE DONE:
Running on a separate Fuel tank and changed the fuel filter at the motor.
Changed all the plugs
Checked compression (all 120psi)
Checked for spark on all Cyl. OK using a inline spark tester
Check to see a difference in idle by pulling plug wire off 1 cyl. at a time

Cyl 1-2-3 make a noticeable difference (Rough idle and drop in RPM) while 4 is barely noticeable.

Verified visually for spark on the spark plug on No. 4 (BTW no.4 plug looked brand new)
Verified with inline spark tester that there is a spark

Swapped no. 2 and 4 coils and CDI connections. No. 4 still makes no noticeable difference in RPM and idle while disconnected.

So I am left with the assumption that something is up with the fuel delivery to that No. 4 Cylinder?

Clogged Carburetor Jet or possibly stuck/clogged reed valve?

What do you all think? TIA!
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Old 01-12-2018, 05:44 PM
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You found the suspect carb
Test fuel pump
If you have a quick fuel disconnect I would rid of it
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Old 01-12-2018, 05:55 PM
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Originally Posted by wetneck View Post
You found the suspect carb
Test fuel pump
If you have a quick fuel disconnect I would rid of it
If it where the lift pump I would think it would effect the engine to the point it would hardly run.
I suspect the lower carb. I am going to decarb/power tune the cylinders and carbs overnight before pulling the carbs.
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Old 01-12-2018, 06:22 PM
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Can't clean carbs with miracle additives, it needs to be pulled to bits and cleaned.
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Old 01-12-2018, 06:28 PM
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change the plugs first.

then pull the main jets and inspect.

I had a 115 giving me the same issue, ended up being a bad plug that would't arc under pressure
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Old 01-12-2018, 07:26 PM
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Originally Posted by aplusmiami View Post
Working on some issues with this engine hoping to get some help from some of you Yami experts.

18' Action Craft Flats Boat (1250 Lbs with gas and a fat guy) Prop: 13 3/8 x 15 Alum

ISSUES:
Hard starting cold
idles @ 7-800 RPM once you get it started and 8-900 RPM warmed up
Only getting about 33-34 MPH @ 4700 RPM WOT Trimmed out

WHAT I HAVE DONE:
Running on a separate Fuel tank and changed the fuel filter at the motor.
Changed all the plugs
Checked compression (all 120psi)
Checked for spark on all Cyl. OK using a inline spark tester
Check to see a difference in idle by pulling plug wire off 1 cyl. at a time

Cyl 1-2-3 make a noticeable difference (Rough idle and drop in RPM) while 4 is barely noticeable.

Verified visually for spark on the spark plug on No. 4 (BTW no.4 plug looked brand new)
Verified with inline spark tester that there is a spark

Swapped no. 2 and 4 coils and CDI connections. No. 4 still makes no noticeable difference in RPM and idle while disconnected.

So I am left with the assumption that something is up with the fuel delivery to that No. 4 Cylinder?

Clogged Carburetor Jet or possibly stuck/clogged reed valve?

What do you all think? TIA!
I'm no expert in any way but i think WOT should be around 5500 RPM
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Old 01-12-2018, 07:54 PM
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Originally Posted by noelm View Post
Can't clean carbs with miracle additives, it needs to be pulled to bits and cleaned.
Actually I have used Merc Power Tune in the past and it has performed time saving miracles.

Brought back 5 psi per cylinder on 2 optimax motors a few months ago. Used it on a Johnson 115 carbs, and the motor afterwards ran perfect!

The key is to let it sit overnight and turn the flywheel manually (without plugs) before letting it sit inside the block.

But I agree - Nothing beats pulling the carbs and spraying them out.
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Old 01-12-2018, 07:55 PM
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Originally Posted by midcap View Post
change the plugs first.

then pull the main jets and inspect.

I had a 115 giving me the same issue, ended up being a bad plug that would't arc under pressure
OP - already did that.
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Old 01-12-2018, 07:56 PM
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Originally Posted by 101grunts View Post
I'm no expert in any way but i think WOT should be around 5500 RPM
This is the exact issue. WOT only 4700-4800... Needs to be 5+
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Old 01-12-2018, 09:01 PM
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My 97 130 HP, had a pink thread sealant in the carb bowls, it would plug up the Needle and Seat.

A clean plug sounds suspicious, so I would check Compression on that Cylinder, and replace all of the plugs, before cleaning the carbs.

Oh and there are Carb Bowl Drain Plugs on all 4 bowls. 10mm Bolts, pull #4 and pump the bulb.
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Old 01-12-2018, 11:38 PM
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Originally Posted by aplusmiami View Post
Actually I have used Merc Power Tune in the past and it has performed time saving miracles.

Brought back 5 psi per cylinder on 2 optimax motors a few months ago. Used it on a Johnson 115 carbs, and the motor afterwards ran perfect!

The key is to let it sit overnight and turn the flywheel manually (without plugs) before letting it sit inside the block.

But I agree - Nothing beats pulling the carbs and spraying them out.
Actually, nothing beats pulling the carbs and CLEANING them, and not with spray, wonder why we need tools and mechanics when all you need to do is spray stuff or put stuff in your fuel!
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Old 01-13-2018, 01:12 AM
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If you pull those carbs you need to get them spotless and used high pressure compressed air to blow them out after cleaning. Do a half assed job and you will probably be pulling them a 2nd time.
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Old 01-13-2018, 05:27 AM
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I assume this motor has 4 carbs. I owned one but it has been a while. I agree you have found the bad cylinder/carb. Also agree that you will probably have to take it off and completely clean all the jets and passages with a thin wire and some spray.

One thing to try is take off the air box and with the boat under load either with another person running it or better yet on a lift with the bow up and stern down. Take a clean rag and choke the bad carb. It will not bog down much as that cylinder is not doing much now.

Quickly remove the rag after a second or so. Sometimes that blast of air will unblock the jet that is causing the problem. This can also be done to each carb one at a time to find the problem cylinder.
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Old 01-13-2018, 07:05 AM
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That #4 is getting steam cleaned, water coming from somewhere.
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Old 01-13-2018, 08:20 AM
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Originally Posted by hevysrf View Post
That #4 is getting steam cleaned, water coming from somewhere.
If it was sucking water you see a lotta water vapor on the exhaust
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Old 01-13-2018, 09:40 AM
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Remove the #4 carb and make sure the main jet tube is clean and that the float isn't stuck closed.

your plug is telling you it's lean
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Old 01-13-2018, 10:12 AM
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Originally Posted by aplusmiami View Post
If it was sucking water you see a lotta water vapor on the exhaust
I have to disagree from my own experience. Bottom cylinder starboard?
YMMV.

Last edited by hevysrf; 01-13-2018 at 10:19 AM.
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Old 01-13-2018, 10:45 AM
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Originally Posted by hevysrf View Post
I have to disagree from my own experience. Bottom cylinder starboard?
YMMV.
Bottom Port. Carbs coming off on a bit. Will post followup.
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Old 01-13-2018, 02:23 PM
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Please post. The most frustrating thing I experience on "help" threads is that the OP never follows thru.

Hope your fix is simple and cheap.
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Old 01-13-2018, 02:38 PM
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There's still things we don't know, only thing for certain is one cylinder appears to be not working, could be many things causing this, from water leak, spark failing, carb blockage plus other possibilities, no positive trouble shooting has been done, just "reasons" why suggestions are not the issue.
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