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Low max rpm's AQ 125

J

justboughtaboat

Member
I have a 1984 18 foot cimmaron boat with the AQ125 with the penta 270 outdrive. Long story short, It's my opinion that when I bought it, it had not been in water for atleast 2 years.
What I have done:
New plugs
New wires
New cap,rotor and points.
Carb was also rebuilt.
timing set to 10 BTDC @ 600 rpm
I cannot get a full check on the advance. But the damper is marked to 30BTDC and it does advance a few degrees beyond that.
Dwell is at 59 degrees, assuming my old dwell meter is accurate.
My AQ125 will not rev beyond 2100 rpm when on the lake. At 2100 rpm the engine purrs like a well fed kitten. Aside from a small stumble and occasional carb back fire, it revs smoothly and quickly. And MPH speeds seem to be around 25mph I guess. But 2100 rpm is all I can get from her. As a result the boat NEVER planes out. I do not know of the pitch of the prop. I can only assume it is the original prop. It seems impossible for a wrong prop to cut 2000 rpms off of an engines max revs but, I know very little about boats. And I don't think the fine tuning I need to do to get rid of the stumble could be the issue either? Any suggestions would be greatly appreciated.
 
Check the prop size (diameter & pitch) and let us know. I expect it to be around 14x17 or even 14x19 depending on the boat's weight. Also, check the position of the trim pin. The default position is in the middle, that is #2 hole (there are 3 possibilities).
 
I actually just ran out and checked the prop. On the prop it is stamped 14x19. And I actually did change the trim pin position after getting back from the lake. Thought that might help it plane out better lol. I put it in the lowest hole. It was in the highest hole. I'll move it up to the middle hole before going back out.
 
Today, while running in a large tub of water. The engine did in fact reach 3200 rpm, I backed off at that point. So is it really possible that the trim position could hinder it that much? The boat was digging one hellova deep hole in the water when trying to speed up. Pushing the rear of the boat down hard into the water. Boat acted as though it weighed ten tons when trying to cruise. I won't have time till probably next weekend to put her back on a lake to see if changing the trim position has helped.
 
There is no substitute for doing a WOT RPM test and while under load and in the water in order to determine if the prop is correct.
Engine must be in full tune.
Your advancing system must offer the correct progressive curve and the correct TA. This requires strobing the timing marks as you increase RPM.
The drive ratio must also be correct (2.15:1 for you).
The hull must also be clean.

If not, you can't prop the boat correctly.
 
Well I bought a new mechanics meter. Dwell test and RPM and what not. My Dwell was way off. It is now 62.5 degrees. Timing advances to 35Degrees smoothly and without fail. Accelerator pump does fire a shot of fuel. No idea if it's enough? But on the lake yesterday the boat planed out nicely but I never got above 4000 rpm. Not sure I need it to. Felt like I was going way to fast haha. Electronic ignition is my next buy.
 
Couple of things you may want to check. Can you still move forward the speed lever after you reach the 4000 RPM? If not, it may be a cable adjustment problem. And is your trim pin in #2 hole? Also, how heavy is your boat? You may want to try a 14 x 17 propeller, maybe you are overpropped.

Yes, one shot of fuel from the accelerator pump is fine.

And buying electronic ignition will be a wise move. You will notice quite an improvement, especially regarding smooth idling and starting. :)
 
It hesitates when I try to throttle up slowly. If I just ram the throttle forward, no problem lol. I am going to try the pertronix before I mess with the carb much more.
 
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