WOT pinging..Merc 228..cause?

[SSSuper83]

Ive got a stock Merc 228/Alpha from 85 in my 82 Sprite. It has a rebuilt 350 Mag carb. Boat runs great at all speeds until I get into the secondaries of the carb, i.e. cruising at 40 and going for WOT. Is this detonation because of a lean or rich condition? I can hear it as soon as the secondaries open. I immediately back off the throttle.

I have 8mm wires, fresh cap and rotor, and run 89 octane fuel with new filters. I installed an aftermarket distributor rotor last year and it seemed like it started then. Not sure. Engine temp is between 140-165 degrees.

Any ideas would be welcomed. Id like to run 55 again occasionally and not be scared of blowing holes in the pistons.

Thanks!

 

[Bondo]

Re: WOT pinging..Merc 228..cause?

Ive got a stock Merc 228/Alpha from 85 in my 82 Sprite. It has a rebuilt 350 Mag carb. Boat runs great at all speeds until I get into the secondaries of the carb, i.e. cruising at 40 and going for WOT. Is this detonation because of a lean or rich condition? I can hear it as soon as the secondaries open. I immediately back off the throttle.

I have 8mm wires, fresh cap and rotor, and run 89 octane fuel with new filters. I installed an aftermarket distributor rotor last year and it seemed like it started then. Not sure. Engine temp is between 140-165 degrees.

Any ideas would be welcomed. Id like to run 55 again occasionally and not be scared of blowing holes in the pistons.

Thanks!

Ayuh,.... Richen the 2ndary circuit,.... She's goin' Lean.....

Check the fuel Filters too, mighta picked up some water...

 

[Don S]

Re: WOT pinging..Merc 228..cause?

Timing could be way off. Did you set it with a timing light?

 

[SSSuper83]

Re: WOT pinging..Merc 228..cause?

Ayuh,.... Richen the 2ndary circuit,.... She's goin' Lean.....

Check the fuel Filters too, mighta picked up some water...

Richening the sec circuit on a Qjet..maybe air valve adjustment? I would have thought this carb would feed more fuel from the get go being off of a 350 Mag. Changed water sep fuel filter three times and carb filter once..no difference.

Does the carb need to come apart to change secondary needles? Cant recall...

 

[SSSuper83]

Re: WOT pinging..Merc 228..cause?

Timing could be way off. Did you set it with a timing light?

No Don I didnt take a light to it yet. The boat ran perfect half the season last year and all of a sudden developed this issue. I am picking her up this weekend since its damn near summer already here in IL. Im just trying to rule out one thing at a time. I will do that first, then chase the fuel system.

 

[SSSuper83]

Re: WOT pinging..Merc 228..cause?

Also I would think if the timing was way off the boat would run bad generally. It doesnt.

 

[picklenjim]

Re: WOT pinging..Merc 228..cause?

Timing doesn't have to be WAY off to get pinging. First thing that came to my mind was timing advanced too far. Timing may be advancing to full advance about the same time that the secondaries are opening. First thing I would check.

 

[missalot]

Re: WOT pinging..Merc 228..cause?

I installed an aftermarket distributor rotor last year and it seemed like it started then.

Check the new distributor's advance curve. Timing might look great at idle, but advancing more or faster than original.

 

[SSSuper83]

Re: WOT pinging..Merc 228..cause?

Check the new distributor's advance curve. Timing might look great at idle, but advancing more or faster than original.

The original distributor is still in it. Just changed the rotor, the Sierra unit I put in has a thinner steel trigger ring. I just wonder if that could be causing the problem. As far as I know the dist has never been out of this engine.