how do you set up carb(s) on mercruise 120 1978?

[shakespear]

have recently purchased a boat with a 120 mer. inboard it had been sat for 2 years have done loads to it but had to strip down carb (a Whinchester 2 barrel single choke version).<br />now need to set it back up, have access to a gas analizer but need to know if there is a plug on the manifold that lets you get to the exhaust gases before they mix with cooling water as i dont think my mate wuold appreciate his £15000 analizer filled with water!!!<br />and if there is what should the Co2 % reading be.<br /><br />Thanks for any help!!!

 

[trevorcday]

Re: how do you set up carb(s) on mercruise 120 1978?

I think you mean a Rochester carb. If that is the case setting it up is really simple. Follow the guideline in your service manual or the spec that came in the carb. rebuild kit for float height. Set the idle mixture screws at 1.5 turns out from a lightly seated position then re-instal the carb. You will need to put the boat in the water to set-up the idle speed and mixture so that the motor sees the correct back pressure. With the boat in the water start the motor and warm it up. adjust the idle stop screw to give about 900 rpm. Next adjust the idle mixture screws 1/8 of a turn at a time, first out until the motor begins to stumble a little (call this point a) then trun them in making note of how far you have turned them. When the engine begins to stumble a little turn the idle mixture screws out unitl you are half way back to point a. Re-adjust the idle speed and you are done.<br /><br />There is no provision to use a gas analyzer to perform these adjustments.

 

[petryshyn]

Re: how do you set up carb(s) on mercruise 120 1978?

Little tip on adjusting with an analyzer.......adjust idle mixture until O2 = CO2. That will give you stoichiometeric and as close to 14.7/1 as you can get.<br /><br />As mrmerc says, in your case, adjust each mixture screw equally, and adjust for best idle quality....

 

[shakespear]

Re: how do you set up carb(s) on mercruise 120 1978?

thanks all will try it tommarro