Hello, newbie to the forum here.
I have a 1986 Mirage 217 Intruder with a 350 and an alpha. I got the boat for free from the friend of a neighbor with a blown motor and a bad drive, so i replaced the motor and put a stern drive engineering alpha on the back. The problem is, even since then the performance of the boat has seemed to suffer. I understand that this boat is heavy and won't be winning any races with only a small block, but my neighbor insists that the performance was significantly better before the motor was replaced, and for some reason i believe him. When the motor is cold i can put the throttle down and the boat planes off no problem. I have never had a problem planing off when first leaving the launch, but later on when the motor is a little warmer its like the boat hits a wall at 3000 rpm. If we don't move everybody to the front of the boat it won't plane off. After it planes it has no problem staying up and will run up to about 45 mph without any problems. I am fairly certain that the carb is tuned decently well and the timing is set good as well. My dad thinks that the timing might not be advancing properly, which is possible but i haven't looked into yet. It has the stock Merc ignition, which I'm looking for an excuse to swap over to MSD anyway. I'm wondering if anybody has experienced this before or might have any idea what the problem could be before i go spending money on new ignition parts. I just can't quite wrap my head around why it would perform so well when cold, yet struggle so much when warm.
Thanks,
Jarrett

Does the engine stumble or act like a miss when it's warm?

Sometimes, yes. Do you think the timing is too far advanced?

This is a carb problem not timing. Does it have an electric choke. What is the base timing.. Should be around 10

Chris

punch the designer in the face



JUST JOKING!!!!!!!!!!!!!!

Trust me, I would if I could.

As for this being a carb issue, it has one of those goofy Holley Quadrajet replacents with a manual choke. I thought my carb tuning was in pretty good shape, but I could be entirely wrong. What do you think the problem is?

I was in a boat that did that. Drop the boat in the water and go. Later on, the motor didn't miss, but it would take forever to get on plane, then shortly after go back to normal speed.

It was the bellows + shift cable boot. Let in so much water while off plane and sitting for a bit, his crappy bilge pump couldn't keep up...until of course....the boat was finally on plane and belows was out of the water.

Anyway - I don't like that style Holley much but should be easy to tune. Wonder if you have some slight vapor lock going on.

Hard to help without more diagnostics. Your boat is old. Could be multitude of things.

BTW: No reason to spend money on the MSD vs normal replacement stuff on your motor.

I don't think that's the problem because my pump almost never kicks on and I never get much water in the bilge when toodling around. I'm not a huge fan of that style carb either. It seemed like a good idea at the time, but in hindsight I would go with something else.

Try another coil. Could be breaking down when hot.

I have a hot ignition issue with me 350 with Thunderbolt IV ignition. I have a good used module, but still couldn't accelerate past 3500 rpms without a miss. I can pull out of the whole and hear the secondaries opening up. I also have a new fuel pump. The miss will hit hard, then I can't refire it. I will be replacing the distributor pickup and coil, then I feel I'll be ok.

You might have a similar issue.