Using this post http://mastercraft.com/teamtalk/show...highlight=lt-1
I also suspected problems with my bleed tubes after taking the boat out a few weeks ago. The temp was spiking after coming off of plane and only quickly revving the motor out of gear would bring the temp back down. No problems with temp during cruise, only when coming off plane. My bleed/crossover tube was still connected to the heads at the rear of the motor so I unbolted it with the intention of moving it to the front. Turns out the tube was clogged badly, the banjo bolts and tubing both had enough crud in them to completely block the flow.
A quick way to check for flow in the tube is to feel the small hose that dumps the bleed water into the drivers side riser. If the motor is up to temp the hose should be quite warm because it dumps a small portion of the cylinder head flow overboard. If the small bleed hose is blocked the hose will not be warm and you need to investigate. I swapped the bleed tube from the rear of the motor to the front but I only used the Banjo fittings and cut off all tubing except about an inch remaining on each banjo fitting. I had to use some wire and a very small screwdriver to clean out the banjo bolts which were full of rust and crud. The rest of the tubing was full of rust/crud so I just cut it off and replaced with small water hose and clamps. I will post a picture in the morning of the hose routing I used.
I took the boat out tonight and had no temp spikes at all so it looks like the fix worked.
I always flush my motor out after every use but I have only owned it for 4 years. I guess over the years the steel lines start to rust inside and any dirt just makes it worse. If your bleed tubes are on the back of the motor it is made worse because the crud can settle down inside the banjo bolts and clogs the small passages inside the bolts when the boat is stored.