Volvo Penta AQ225D: Tuning quadrajet for high elevation. Jets? Metering rods?

I have an AQ225D motor mated to a 280 SP outdrive with 15X19 prop.

I live in Antioch, CA and as a NEW boat owner (new owner, old boat) have enjoyed boating in the Sacramento / San Jauquin Delta. I love to take the family to Lake Tahoe and now that we have a boat we wanted to include it in the fun! BUT... it runs REALLY bad up there!! Had it up there a couple weeks ago and had to advance the timing and mess with the Idle air screws just to get it to run. After messing around for almost an hour, my son and I got it to run "pretty good" but nothing like back home!

At home motor gets up to about 4500RPM wide open. On Tahoe it only gets up to about 4000 and I have to go real easy on the throttle as the motor bogs down... probably drowning in fuel! We all had to move to the front of the boat just to get it to plane and get the RPMs up.

I keep reading about jets and metering rods but can't figure out what to change... is it bigger rods and smaller jets or vice versa? Also, how hard are these to change? can I swap them in and out as I change elevations? Does the carb need to be removed or disassembled? I recently replaced the Quadrajet with a rebuilt one and as I said, it runs great at sea level.

As for the prop... should I get a smaller 3 blade (less pitch) or the same size 4 blade?

So, I guess what I need to know is this: What needs to be done for the boat to run properly at Lake Tahoe?

Thanks.

Re: Volvo Penta AQ225D: What do I need to change to run @ 6000ft

Re: Volvo Penta AQ225D: What do I need to change to run @ 6000ft

If you had to go through all of that to get the baot to start, it sounds like you have other problems as well. Checking all the standard tune-up items sounds like it's in order.

Ive heard that timing changes can go a long way toward improving performance at altitude. Some people discourage those changes since you may forget to change it back when you get back closer to sea level. I would think that's up to you.

Reducing prop pitch will also help. The 4 blade prop will also get you some added lower end performance. I'd definately go at least one pitch number down with a four blade. Don't expect to get full sea level performance, but at only 6000', and with everything in tune, you should still be able to get on plane.

Afraid I don't know much about the carb so will have to wait for others to chime in on that aspect.

Re: Volvo Penta AQ225D: Tuning quadrajet for high elevation. Jets? Metering rods?

Thanks for the prop help!

Anyone have info on jets and metering rods for the quadrajet? I know hwere I can get them... I just don't know which ones to get and how to change them.

Re: Volvo Penta AQ225D: Tuning quadrajet for high elevation. Jets? Metering rods?

You are going to have about a 3% power loss for every 1000' of elevation gain assuming the same temperature. For Tahoe, that will be over 18% loss of power. You might be able to get a little of your power back by leaning up the carb with new jets but it is going to be negligible compared to the power loss due to the lack of oxygen. My suggestion is drop 2 inches of pitch.

I have a house in Tahoe so I am very familiar with your issue. I have a 454 in my 24' boat and I REALLY notice the power loss. I would only rejet for Tahoe if that's the only altitude you will ever boat because if you rejet and take it back to sea level, you will be way lean and could damage your engine.