Merc 150 High Compression Carb Jetting

[Rush]

Hi,

I hope you can answer my questions. I sure would appreciate it!

First of all, I have a Bastard Black Max B289430 / 2.0 XR-2 150, 1988. I don't know what someone did to it, and I really don't want to start digging into the motor at all. It had no thermos, no poppet when I got it. It has 145-148 psi compression, checked twice with different gauges on different days. I was told that it was an old racing motor? Who Knows? It was a trade in at a dealership and no one can or won't help me with the history.

I installed new thermos and a poppet valve. It has 076 jets on the bottom carb, 074 jets on the middle carb, and the jets on the top carb are screwed up beyond repair. Salt water, salt air, and years of neglect have eaten them up.

My carbs are WH-29's

What jets do I put in this motor to be safe for Carb 1, 2, and 3.

I don't really want to race it and run it wide open very much. I live 1 mile from the Intercoastal Waterway. The water is really bad choppy here most of the time, and it will beat you to death sometimes. I just want it to run good and last as long as it can, without melting a piston. I was told that cylinder 2 and 5 get fatter jets? What do you think?

[hawktuner]

With that kind of compression, I think you need to run 93 octane to ensure you don't have a detonation problem.


On the jetting, I would start rich & work back.

On the 2 & 5 thing, it depends on the carb and motor, but my manual shows WH-29's having the 2 & 5 jets one size bigger than the rest.

Use the search function to search the forum for "jetting" or jets, etc. There should be several good messages explaining how to "tune" your jets to be correct posted
by experienced people.

Good Luck :D

[Rush]

I contacted T-Rex, and he said to start with 78's. I have been through all of the carb and jetting posts here for days, but until I contacted him, I didn't find out about my specific engine type and problem.

Thanks for your help!