Motor and trim tabs

[jjhjrcmh]

I have a 1998 E200TXECM and have several questions. One is when I get on plane the engine surges after 3800RPMs. It idles good and runs good with all good compression. I had another question before about prop and found the pinion nut sheared off and broke the shaft. Replaced with a rebuilt lower gear case but problem was before this. I checed idle rpms and they are 6-700 and in gear at 5-700rpms She starts fine. Getting on plane is no problem but as it trims out I have to back off to 35-3700rpms or she jumps around.

I have hydraulic trim tabs could the create this problem? What is there purpose? can the create cavitation at motor by robbing water? I have run them up and down left and right and cant seem to correct problem. I have a 23 foot Sunbird Neptune center console.

 

[Chris1956]

Re: Motor and trim tabs

Generally trim tabs will not cause ventilation. Have someone observe the motor whaile at planning speed. See if the antiventilation plate is at the surface of the water, while underway, or above the water. If it is above the water by an inch or two, you might see if you can lower the motor on the transom some.