My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the rest

[CharlieB]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Fab induction pickups on each coil so you can compare RPM on each, if there is any difference then you'll know for sure if any of the CDM's are failing.

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

WITH an additional 200# load it ran 200 RPM above the norm?

PORTING?

What changes had you made before this run?

Porting? Any jetting changes? Float heights?

Have you done a high speed cut off and read the plugs?

I finished a response to this and punched the wrong button and lost it. So here goes again.

The change in performance even with the additional load can only be attributed to the 3 ea 1/4" holes I drilled in the prop. I didn't expect the top end changes I got as a result.

No other changes and no carb work of any kind as I felt that with the performance I was getting at WOT I didn't need to mess with them.

Don't understand the high speed cut off plug read. If it means stop in the middle of a WOT run and read the plugs, no I didn't.

I'm realizing my problems occur at the lower speeds and that is one of the reasons I am suspecting the CDI modules as the problem. The CDI I had to replace several years ago had a thermal problem that affected performance at cold temps...first part of an outing. Even with that bad one, once I got planed out and gave it time to correct itself, it ran flawlessly the remainder of the day and I got my rpms and speed I expected.

Thanks for the inputs,

Mark

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Have you checked to see if a sleeve is moving, thats a common problem with the 3 cyl engines

I don't know how I would check it Laddies, I have no detachable head on this Merc.

Mark

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

I figured you either had a "Double E" or worked with a bunch of Double E propellerheads.

Your still running in the wrong direction!

Well sir, I just pulled up your profile and read it. Speaks well of your capabilities to lead me in the right direction.

Sooooooo what's wrong with my direction and where do you think I should go before I plop dow $300 for all new CDI modules. If I missed the point on one of your comments, would you run it by me again?

Thanks,

Mark

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

There is nothing in my profile that would elude to anything.

I explained the probable cause and fix, and was dismissed.

You seem to have it all figured out. I am gonna just sit back.

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Four stroking

http://www.mopedarmy.com/wiki/Four_Stroking

The condition is called run away. The engine is running on preignition, no spark needed.

Your idle situation sounds like one butterfly is open a little farther than the others. Pull the air box cover and physically look in the throats of the carbs. Insure all the butterflys are closed.

I did and found the top one a few degrees off (detuned) from the others. Fixed it as the first thing in this current troubleshooting effort. Runaway happened later when I had my linkage disconnected and as I said I may have started it when I was at idle and advanced my timing (carb lever disconnected from timing arm).

On the "nothing you said in your profile having to do with the problem"....you said that you were a mechanic, course you didn't say what discipline but if you liked over powered boats than marine is as good a guess as any.

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

I have confidence that you will figure it out..................

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Well sir, I went outside and took the air box cover off again and re-examined the butterflies. Looking closer it appeared that when I was concentrating on the linkage getting the butterflies opened max, I failed to realize that that position caused the butterflies to not close completely at idle. That more that I feel would explain my excessive idle speed which is something I caused myself during this senario, not associated with the original problem I had on the last outing. Rechecking butterflies for uniform convergence, all close together and open the same amount together.

I didn't see anything else you said except for explaining what causes the runaway condition I experienced. What'd I miss?

Mark

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Poof!............. it's gone!

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Profile Fixed................I can has cheezeburger now?

 

[canoemang]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Profile Fixed................I can has cheeseburger now?

ha

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

ha

......

 

[CharlieB]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Have you finished cleaning the carbs yet?

Almost willing to bet #1 float is a bit low and running rich.

I missed that you ported the PROP. Prop venting releases load on initial acceleration, allowing the motor to spool up quicker. It should not make a bit of difference in WOT RPM once the boat is at speed. It will allow the motor to initially rev higher than the 'full speed' WOT RPM.

Strange that your 'at speed' WOT RPM picked up, especially with a 200# increase in load. Although, more fuel additives causing a leaning of the gas can make more power as factory jetting is quite fat to ensure cooler operating temps and well carboned piston domes.

Your fuel mixture may have contributed to the thermal run-away.

 

[capn kurt]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

I'm no certified mechanic, but is it possible that an air leak could be the culprit? Perhaps the carbs aren't tight or something similar? The reason I ask is because of my past experiences with two-stroke motorcycles. I had a bike that had a leak in the crankshaft seal and it had a nearly catastrophic runaway. It would run poorly at low throttle (was hard to keep running) but would rev to max throttle every time you gave it enough gas to get started. I did this twice before finding the problem. This was a single cylinder bike, so perhaps with three cylinders there is enough momentum from the two good cylinders/carbs that it will keep the engine running (roughly) at idle but then wants to runaway at higher throttle positions. It seems if one of the carbs was loose, then you could check the plugs after running a bit and one would be lighter/drier than the others. Just a thought.

capn

 

[capn kurt]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

You know, on second thought - I'll bet anything it's those pesky muffler bearings...or the blinker fluid.