'88 Mercury 150 XR4 Beeping and Cutting Out - Need Help!

[achilles555]

Hello all. For the past several months, I've been restoring a 1985 Charger Foxfire with a 1988 Mercury 150 XR4 on it. I finally had a chance to get it out on the water today (for the first time), and ran into some problems. I have done the following to this motor to date:

• Replaced water pump.
• Rebuilt fuel pump.
• Replaced the oil lines.
• Replaced 1 switch box.
• Drained and replaced lower unit oil.

When I got her out on the water, I ran into some trouble. The motor starts fine, and idles beautifully. The boat comes out of the hole quickly, and rides great. The problem begins when I get her going past about 1/4 throttle. Once on plane, and at about 1/4 throttle, it runs perfectly and purrs like a kitten.

Once I push it to about 1/2 throttle, the throttle control/housing starts intermittently beeping beep - beep - beeeeep - beep, and the motor begins to run rough. There is no pattern to the beeping, but it doesn't stop. The motor itself stops running smoothly at about 1/2 throttle, and the prop in the water starts to make a "garble" sound, like the prop is not running in clean water. The further I push the throttle, the higher the RPM's go, but the boat does not pick-up any speed. It just runs really rough, and won't go any faster.

I tried giving it gas around a corner to see if cavitation was the problem, but it didn't change anything. I'm really at a loss as to what the problem might be. Can anyone out there help me figure this out? Thanks so much ac.