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Author Topic:   Mercury OptiMax 135 Throttle Plate Opening
JW_Spencer posted 08-29-2014 11:24 AM ET (US)   Profile for JW_Spencer   Send Email to JW_Spencer  
My 2004 Merucry OptiMax 135 is not achieving full throttle. The butterfly flap on the air intake is only opening maybe 3/4-ths of the way (or 45 to 60 degrees). I can manually move the throttle asssmbly by the air intake an inch or so by hand such that it is vertical and fully open (or 90 degrees). The swing arm linkage assembly on the block atttached at one end to the throttle cable, and at the other end acuates a rod to the throttle body, has a stop screw on both the idle side and the full throttle side. The full throttle stop has a bolt with lock nut, I loosened the lock nut but was unable to unscrew the stop bolt.

Is it the case that the bolt has some kind of thread lock? (It looks clean and spotless.) Should I be able to adjust it? Or is this possibly a factory setting? Seems odd to me for it to be a factory-type setting. But if the same throttle body is used for higher horsepower models, some restriction would be in order such that opening the air flap too much would result in a overly lean supply.

I removed the little rubber tip from the stop bolt and gained about 200 to 300-RPM. It seems there is more in the offing if I can adjust the full throttle stop.

I have read that the 135 is the same block as the 150 and 175. Is this a crude method to govern full throttle on the OptiMax 135? Would it be a bad idea to monkey with it?

jimh posted 09-01-2014 10:50 AM ET (US)     Profile for jimh  Send Email to jimh     
You may be able to get some guidance and perhaps make an informed inference if you have the service manual for the Mercury 135-HP OptiMax engine. There should be a section in the Service Manual for the Mercury 135-HP OptiMax engine that will include a procedure for setting the throttle linkage so that the throttle plate opening is properly set.

If there is a stop or limit on the throttle linkage for input from the remote throttle cable, that is a suggestion that the engine manufacturer doesn't want the throttle plate opening any farther. As you have suggested, perhaps that is a somewhat simple method to limit the horsepower. Another interpretation is that the limit was just improperly set during rigging or perhaps in manufacturing.

Perhaps you can experiment. Run the boat in calm water with the engine cowling removed. Manually open the throttle plate further. See what happens.

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