Lack of power on AQ125B - pinging and dieseling

[Alan Lloys]

I am working on a 1985 Bayliner Capri 1950 bow rider with the AQ125B engine.
This is twin the the current 1985 capri cuddy I have with the same engine.

When I bought it the timing belt was broken and the sea water pump was worn out.
I replaced the timing belt, adjusted tension and then went through all the standard tune up procedure
I set the cam and car per the instructions. I have done this before so I feel pretty good that I got it right.
Adjusted carb (it was supposedly rebuilt last year from previous owner - it looks very clean), set dwell on points and adjusted timing. I verified that the mechanical advance worked.
Tested compression and having all in the 140 psi range - great for this age engine.

I can get it to run great in the driveway in a tub of water but at higher RPM range I am getting some pinging. When I turn the engine off it will diesel for 10 sec or more.
I verified that ignition is off as I tried stopping the engine with the ignition kill switch and it still dieseled.

Anyway today I finally was able to take it on the water. It ran great at lower RPM but it maxed at 3500 RPM and approx. 25 mph. This is with the standard 14x19 prop. Based on my cuddy it should be able to get around 4800 RPM with that prop and just shy of 35 mph. I messed around the timing and it really did not have any effect at all at high RPM.

I am a bit stomped at this point. I am considering if I just got a bad tank of gas with the boat. It came with the tank full when I bought it used.

Any and all suggestions are appreciated.

I am considering trying it out tomorrow in the driveway running it from a gas can and see if it takes care of the dieseling. If it does then I will have to figure out a way to drain the tank. Not sure if that would impact the high RPM performance too.

 

[jerryjerry05]

Re: Lack of power on AQ125B - pinging and dieseling

Sounds like the belt might be off by a tooth?

 

[Alan Lloys]

Re: Lack of power on AQ125B - pinging and dieseling

That was my first thought. I have checked and double checked and all the marks line up on the shafts.
I will will triple check to make sure.

What I don' understand is why that would make the engine diesel.

Also just thought about the carb. These ones have a high speed jet - wonder if it is plugged which would make the engine run too lean at high speed and starve it.

 

[Alan Lloys]

Re: Lack of power on AQ125B - pinging and dieseling

Update: I think JerryJerry05 was correct.
3rd time must be a charm for the timing belt.
I had recently put a new timing belt on a 125A engine which has a mark on the cam cover used to line up the cam timing.
The 125B does not have the same shroud on the cover but I used something I thought was a mark. Well turns out it was not.

Once I completely removed the timing belt and re-installed it using the marks on the belt as guide it solved the dieseling.
I am optimistic that this will also solve the lack of power.
I will update next time I have time to get it on the water.

 

[jerryjerry05]

Re: Lack of power on AQ125B - pinging and dieseling

Right for once,YEA!!!
These Volvos can be tricky.
Had a friend ask to check out his 125 after it sopped running the way it should.
Checked EVERYTHING twice.
Found nothing.
Then noticed a new prop on the drive.
It was an aftermarket and it was shaped different.
Asked when it started to perform bad and the owner said right after he changed props.
Not smart enough to figure that out by himself.
Changed prop and the performance came right back.
The aftermarket was the same pitch but the blades were a completely different shape.

 

[cptbill]

Re: Lack of power on AQ125B - pinging and dieseling

could be off by a tooth but sounds like you have a burnt valve or another problem in the head, I would start with compression test

 

[Walt T]

Re: Lack of power on AQ125B - pinging and dieseling

Had a guy who swore up and down he had the belt on right, so I took one look and it was so obvious it was way off I had to ask how he aligned it. He said "Whut?" Said he put it on exactly how it came off.

 

[Alan Lloys]

Re: Lack of power on AQ125B - pinging and dieseling

could be off by a tooth but sounds like you have a burnt valve or another problem in the head, I would start with compression test

Compression is good and even at 140+ on all cylinders.
I feel pretty confident that the it was just the timing. My mistake thinking I knew what I was doing (on the 125A) and not realizing that it was a bit different on the 125B as you have to use the belt marks.