[firecat1981]

Had an issue last time I was out. When running at WOT after a few seconds a slow pinging starts, then becomes more rapid. If I back off the throttle just a hair it goes away, but the RPM's don't seem to change and my speed stays the same. I am running the same 87 octane with star-tron I have always ran. Thoughts?

 

[Creek Runner]

Motor?

 

[firecat1981]

Yamaha F20 (4-stroke 20hp)

 

[DuckNut]

My Merc 25-4 has done the same thing for 14 years. Cranking on the throttle it will ping; back off 1 mm and gone. Gotta be something other than internals so I live with it.

 

[Brett]

If it's a recent thing, maybe a drop in octane caused by too much ethanol in the last fill up? :-?

 

[DuckNut]

That is a possibility on FC's - mine has never seen ethanol (I am keeping it a secret from it).

But I don't think that is it Brett.  If you smash the throttle wot and then back off say 1 degree it quits.  It is such a small movement that it won't even affect rpm's.  It is strange but like I said I tried to find it but have lived with it and nothing has broke.

edit: almost seems like it might be the throttle cable. If turned too far it might create slack and slap around under the hood. Let off and the slack goes away. Just a guess.

 

[anytide]

need to run some vodka n squirt thru that thing, works for me evry time
-also dries up all the water.......

 

[firecat1981]

Ducknut it seems we have the exact same issue. Maybe I need to get in there and adjust the cables. I'll try filling up with 89 next time I go out and see if that does anything, but I doubt it, something tells me it might not be the fuel.

Tide, you would waste good vodka on a motor?

 

[cutrunner]

Haha Tides bringin the funny!

Ethanol has nothing to do with the detonation. It is actually helping stop it.

My guess is that when your turning the handle all the way wot, your carb link is going wot but stops opening for that last 500rpms or so, but your timing arm is still advancing and that little area is where your detonating.
Honestly, its so finite i would almost have to blame it on how hot it is outside, combined with warm water temps, and the fact that you are a tad (my opinion) underpowered.
I wouldnt worry about it, just try to keep it out of that pinging area or youll have ashtrays for pistons..

 

[DuckNut]

blame it on how hot it is outside

Ha...believe it or not mine is actually ever so slightly louder in zero degree weather. It has a slight change in cadence and I can hear it more through my hats in that weather than I can driving naked in FL.

Cut - your guess is the same as my mechanic said but he was never able to find it even with adjusting some stuff. He even measured the amoumt the little arms would bend when you crank it all the way.

It has never been an issue so I left it. Besides, I get way better mileage when I back off WOT a little.

 

[firecat1981]

Hmm, sounds like it's time to tinker.

It started when I was fishing in the early morning, so heat really wasn't a major issue being it was about 80 degrees or so. I was fishing solo and lightly loaded. I did have my newer prop on so I was spinning more RPM's, maybe about 5500-5700 or so, but haven't tached it yet, I know I'm not over revving. I agree I am underpowered when loaded down, but the 20hp does pretty good when solo.

 

[anytide]

Ducknut it seems we have the exact same issue. Maybe I need to get in there and adjust the cables. I'll try filling up with 89 next time I go out and see if that does anything, but I doubt it, something tells me it might not be the fuel.

Tide, you would waste good vodka on a motor?

didnt say good vodka

 

[firecat1981]

Last time out the pinging got a little worse. Now I have to lower my RMP's by a few hundred in order to avoid it and it doesn't feel like I'm getting full power. This is with 2/3 of a tank of fresh fuel and star-tron so I know that's not the issue.

Does anyone have a link to carb adjustments, it's been a few years? or a diagram of what each linkage does? I mean other then the parts diagram?

Will going to a higher octane gas help? I use 87 now as per the owners manual.

 

[Creek Runner]

I don't think it's fuel related. It's it a ping or a spark knock? Where is it coming from the Cyc? or the Head? How many hours are on your motor? What Rpm's does it do it at? Did you put your old prop back on? and if so did it still do it? Does it do it every time?

 

[firecat1981]

It sounds like a low knock and not a metal pinging, but I could be wrong. I didn't try my old prop since it was lugging the motor keeping it at low rpm's. Maybe the reason I wasn't achieving the rpm's is carb related?
My motor might have 40-50 hours on it. It does it now every time I go to full throttle, no matter if it is recently started or fully warmed up.

If weather permits I'll throw the tiny tach back on and test it out. Any possibility this is it hitting a rev limiter? I doubt it, but I'll consider everything.

 

[Creek Runner]

No you would be able to tell if it hit the rev-limiter, skips not a knock or ping.

What year is the motor?

I had one last month I worked on 2009 F20 that only had 8 hrs on it. It was on a Ribbed Zodiac being used as a dingy for a 68' Sportfish. Anyways it had a knock at anything above 4800RPM's took me for every to figure it out. It ended up being a cracked piston skirt, motor ran fine and had no loss of power just a very faint knock. Not saying that's what yours is but with so little info it could be anything right now. Funny part is I still have the motor I called my client and he said by a new one, and gave me the old one. It's still laying in pecies out in my shop


Get an RPM's reading and also take the old prop just for the heck of it and throw it back on there and see if it does the same thing.

Standing by

 

[firecat1981]

Why wasn't the repair covered under warranty? My motor was purchased in 10/09 so it's still under the 5 year warranty so I may just bring it in and see what happens.

 

[Creek Runner]

At the time when the customer Purchased the engine it only came with a 3 year warranty you must have gotten yours during a promtion of 3+2. Trust me I keep track of all my clients warranties. However I called Yamaha dealer support because of the low hours and I did get them to pay for all the parts, customer pay on Labor (parts are still sitting in the box waiting on me). But my client said buy a new one! We upgraded to the F25 and it only has a 3 year warranty as well.

If your motor is under warranty take it in!!!

 

[firecat1981]

I've got a trip planned for next Wednesday so maybe after that I'll bring it in..
I hooked up the tach and will try, weather permitting to get it out on the lake later today. While the cowling was off I looked over everything really quickly again and noticed a good amount of slack in one of my throttle cables so I tightened it up a little to see if that makes a difference. I also pulled the plugs to see if they were damaged, they looked to be in fairly good condition, the threads were black, but the electrodes and insulator were clean.

 

[Frank_Sebastian]

Could it be a plug not firing every time? I can hear a miss in a two stroke and not feel it, but a 4 stroke?

Frank_S