99 115 2-stroke vibrates/runs rough midrange **FIXED!**

[lugnutz426]

This Started The End Of Last Season. Shakes And Runs Rough Off Idle And Up Worst At Around 3000 Rpm. Starts And Idles Okay. Will Run 5300 Rpm. Smoother At High Rpm. Prop Good, Carbs Rebuilt, Fuel Pump Rebuilt. 140-145 Compression In All 4. I Kill Each Cylinder Individually And It Runs Worse Equally So I Know All 4 Are Firing.
Only 200 Hours In Fresh Water. Block Cool When Running. Plugs All Look Same/good . ....any Ideas?

Thanking You In Advance.

Joe

 

[porkchopper]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

Joe, my 96 mariner 115 2-stroke is doing the same thing also.I'm going to check out the fuel system from the tank to the fuel pump and see if there's any air leaks, and then look for the fuel filter and clean or replace, then onto the fuel pump and see what kind of vacuum it has. I just bought this boat this spring and need help also.
Stan

 

[lugnutz426]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

My Primer Bulb Stays Full. I Pump It While It Is Happening And It Does Not Help. Carbs Are Full Of Fuel. Can't Be A Supply Problem. I Can
Pump With Engine Off Until Floats Shut Off. Start It Up Put In Gear And It Is Shaking Immediatly. Fuel Filter Always Full Of Fuel Too.

I Am Beginning To Think It Is A Trigger Or Mechanical Balance Issue.

A Few Folks Recommend To De-carbonize Will Try Today To See If That Helps

Joe

 

[MercGuy]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

You might want to check to see that all your exhaust plate cover bolts are torqued to 18ft/lbs.

Tighten them up and report back.

 

[lugnutz426]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

Thanks, I Will Check Them. They Have Never Been Off. Do They Tend To Loosen Up? How Would That Effect The Running/shaking?

Joe

 

[MercGuy]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

Thanks, I Will Check Them. They Have Never Been Off. Do They Tend To Loosen Up? How Would That Effect The Running/shaking?

Joe

Mine were very loose (about 3/4 of a turn). Some bolts showed signs of water leaking out of them.

The cover plates and their gaskets form a seal on the side of the cylinders. When you take the plates off you can actually see the sides of the pistons.

If the gaskets are leaking, it will affect compression on the power stroke, and crankcase vacuum on the intake stroke. Crankcase vacuum and pressure are what drive the fuel pump. So many problems can result.

I'm curious to know what you find because in my case I changed several things at the same time and then my engine ran much better. Therefore I don't really know if it was tightening the exhaust cover bolts, or one of the other things that I did that fixed it up.

 

[lugnutz426]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

mine were tight. decarbonizing did not help either. she does not vibrate in
neutral. I AM NOW THINKING BENT DRIVESHAFT?? what other things did you
change?

joe

 

[MercGuy]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

mine were tight. decarbonizing did not help either. she does not vibrate in
neutral. I AM NOW THINKING BENT DRIVESHAFT?? what other things did you
change?

joe

I replaced every bit of the fuel line from what was inside the tank all the way to the engine. I didn't see anything bad, except that the strainer screen on the end in the tank looked awfully fine to me. I removed it since I can't see the point of plugging up a fuel line in a place that you can't get to while on the water. I'm relying on my inline fuel filter instead.

I rebuild the fuel pump for the 2nd time. Didn't see anything wrong with it.

I replaced the vacuum/Pressure hose from the crank case to the fuel pump. Didn't see anything wrong with the old one.

As I said, I tightened up the exhaust cover bolts.

Afterwards it ran better than it ever has.

 

[sschefer]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

There's a lot of things that can cause this but most commonly it seems to be the stator.

 

[lugnutz426]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

Thanks

 

[CharlieB]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

I'm surprised that no one mentioned carb synch. Critical to get a smooth pulling motor while under load, not near as noticeable in Neutral without the aid of a carb synch stick (multiple vacuum gauges).

 

[sschefer]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

I'm surprised that no one mentioned carb synch. Critical to get a smooth pulling motor while under load, not near as noticeable in Neutral without the aid of a carb synch stick (multiple vacuum gauges).

O'reily's has one that sits on the carb throat works pretty slick. It will find a leaky float needle or a bad gasket in a heartbeat! You just need one good carb as a reference.

 

[CharlieB]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

The 115 4 cyl 2 + 2 is a unique creature, idle circuits only on the top two carbs, the lower two cyls do not receive fuel to fire until the throttle is moved OFF idle, this is why the carb synch is so critical to the smooth transition, acceleration, and operation of this motor.

Get a copy of the FACTORY service manual, it does seem expensive but you get what you pay for, the factory SPELLS everything out quite well, the aftermarket books are lacking a lot of details, all very important.

Clean carbs are critical at ALL RPM ranges, a leanness on any cyl greatly contributes to rough running and vibration. A lean cyl can, and will, melt a piston. Address this problem immediately.

A bent propshaft or blade will cause a vibration only in gear. Take a close look at the prop, with the engine OFF, of course, turn it around and notice if it 'wavers' from a slightly bent shaft. A submerged log can bend a blade or shaft very easily.

 

[lugnutz426]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

thanks

prop and prop shaft good. carbs linkages were adjusted/synced as per factory manual when they were rebuilt.

 

[CharlieB]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

This Started The End Of Last Season. Shakes And Runs Rough Off Idle And Up Worst At Around 3000 Rpm. Starts And Idles Okay. Will Run 5300 Rpm. Smoother At High Rpm. Prop Good, Carbs Rebuilt, Fuel Pump Rebuilt. 140-145 Compression In All 4. I Kill Each Cylinder Individually And It Runs Worse Equally So I Know All 4 Are Firing.
Only 200 Hours In Fresh Water. Block Cool When Running. Plugs All Look Same/good . ....any Ideas?

Thanking You In Advance.

Joe

On 2+2 pulling a plug wire on the lower two cyls at idle should NOT make any difference in the engine speed or smoothness.

OFF idle and in gear all cyl's fire and would make a difference.

My question at what speed and conditions did you kill each cyl as a test?

A weak low speed stator winding causing an orange or yellow spark at cranking speed will cause a lot of low speed problems until motor speed increases and the high speed windings generate sufficient voltage to carry the ignition system, then the motor would smooth out.

Use an adjustable gap spark tester set to 7/16 inch, crank the motor and observe the spark quality, it should be a sharp crack, bright blue, any less is a problem.

 

[lugnutz426]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

At 3500 Rpm All Cyl Disconnect Individually Will Make It Run Worse.

At Idle Speed I Just Discovered That Number One Is Weaker Than Number 2. It Will Stall When Number 2 Is Off. Number One Off Will

Make It Run A Little Slower. Carb Needle Adjustment Will Not Correct Imbalance. Throttle Plates Are Both Closed At Idle

I Switched Coils On 1 And 2 . No Effect.

Disconnected Both 3 And 4....did Not Effect 1 And 2 At Idle.

I Will Do Spark Jump Test, But How Can Stator Output Effect One Cyl And Not The Other?.

I'm Losing It!!!

Joe

 

[CharlieB]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

Stator has low speed and high speed windings, transition is around 2000 RPM

Ignition module stores the charge voltage

Triggers tell the module which coil to route the charge to.

 

[lugnutz426]

Re: 99 115 2-stroke vibrates/runs rough midrange

Re: 99 115 2-stroke vibrates/runs rough midrange

Fixed. Prop Was Not Good. Is A Propulse Variable Pitch. On First Inspection All Blades Were Good. Has A Solid Hub. Turns Out One Blade Out Of Index ( Indexing Tab Cracked Decreasing Pitch On One Blade. Idle Was Poor Due To Carbs Shaking From Prop. Changed The Bad Blade And Vibration Gone (18 Bucks) Idle Improved And Number One Firing Good After 1/2 Hour
Running Smooth At Cruising Speed And Minor Adjustments.

With The Carbs And Fuel Pump Rebuilt And All Adjustments Done "by The Book" This Engine Now. Runs Better Than It Did When It Was New!

Thanks To All That Offered Help

Joe

 

[sschefer]

Re: 99 115 2-stroke vibrates/runs rough midrange **FIXED!**

That's great news. Congrats!