AQ125A Pinging on partial and full throttle

[Dr. Velocity]

With help from members here, a bit of ingenuity, and new plugs, new plug wires, a new alternator and belt, and a carb rebuilt kit, I finally got our '82 Bayliner Capri running like a top in my driveway. It starts wonderfully and idles great and has decent throttle response.

So, happy with this, I took the boat down to the launch for a test run. Sure enough, it wouldn't start (was on three cylinders again and the needle valve was stuck shut). I took it back home, cleaned the points and rotor and cleaned the needle valve in the carburetor. Started right up and idle great.

I took it back down to the launch, starter her up and got her on the lake. It was running pretty well. I got it up on plane and brought it back down to idle again. Once again, it dies. It'd start up and idle fine, but wouldn't run above 1100 RPM. So, we pointed it back towards launch and started the crawl back to the docks. I got sick of that and took the carb apart in the middle of the lake and cleaned the needle valve once more. Started it up and it was back on plane again.

I had the boat out on Sunday and it was running beautifully... except for the rampant pinging at partial and full throttle, especially when it was getting up on plane. I have a new cap & rotor going on today, but I suspect that the problem may lie elsewhere.

I've ordered a service manual, but it won't be here 'til the end of the week. I don't know if this engine has hydraulic lifters or not (I seriously doubt it), so if it doesn't, I'm guessing I'll be starting out by adjusting the valves. After that, I'm guessing I'm going to need to take a serious look at the timing. I'll be installing a new cap & rotor today, but I have my doubts that their installation will quell the pinging.

I've never adjusted automotive valves before, but I've got the required tools and mechanical ability to do so. I've also never done timing before on engine before, but from what I've read, it's a relatively simple process as long as you're careful and thorough in your procedures.

Does anyone have suggestions, thoughts, or advice as to what is causing the pre-detonation or advice on fixing it?

 

[wire2]

Re: AQ125A Pinging on partial and full throttle

Unless you're getting clatter from the lifters all the time, valve adjustment is not the problem. I'd note and mark the present location of the distributer, then retard the spark by 2-3? (usually ccw) and try it on the water. If it stops pinging, that's it. You may or may not have to loosen the distributer clamp bolt a bit to move it.

 

[Dr. Velocity]

Re: AQ125A Pinging on partial and full throttle

Unless you're getting clatter from the lifters all the time, valve adjustment is not the problem. I'd note and mark the present location of the distributer, then retard the spark by 2-3? (usually ccw) and try it on the water. If it stops pinging, that's it. You may or may not have to loosen the distributer clamp bolt a bit to move it.

I don't see the state of the valves as being a problem, but I'm doubting they've been adjusted in the 583 hours that are on the engine. Preventative maintenance is more of my goal with the valves.

I'll try the retarding the timing on the distributor though.

 

[slia67]

Re: AQ125A Pinging on partial and full throttle

Dr. V,

I am by no means an expert on the Volvo engines, but my '85 AQ125 has an overhead cam and the only means to adjust it is to replace the shims with a different size.

Pinging is normally a sign of incorrect timing. If the boat has been sitting a while you may want to add some octane boost, or add high octane fuel the next time you put fuel in. (As fuel goes stale, the octane ratings lower.)

Do you have a fuel filter between your tank and engine? Mine did not when I bought it. If not, I would put one in to keep particals from getting into your carb.

Doug

 

[Robj]

Re: AQ125A Pinging on partial and full throttle

Pinging is caused by the air fuel mixture firing prematurely. Check your timing, adjust it to spec and use higher octane fuel. If it still pings, retard you timing a bit. May want to also check the condition of the mechanical advance in the distributor. If a spring is broken, it will cause it to advance faster than it should, assuming it has a mechanical distributor.

Good luck and have a great day,

Rob.