I have a 1991 Mariner Mag II 150. The motor starts but idles sort of low. It runs good on the top end. Here is the strange part. When idling or slow trolling, the motor seems like it is not running on all 6 cylinders. When the RPM's hit 1200, it is like there is a power boost and all 6 cylinders begin running. There is also a puff of blue smoke when it feels like all cylinders kick in. I have replaced all of the fuel lines and had the carbs rebuilt. I have also done a decarb on the motor with Seafoam Concentrate. Let me know where I should look next. BASSHAWK

Check valves need to be replaced with ethanol resistant model.

Check the small hoses that run from carbs to the reed block, those are your culprits. Moonshine in todays fuel will lock them up.

If all you have done and has been done right tha idle timing may need ta be looked at a little closer. Lose tha idle stabilizer/advance module. Set idle timing on tha lake, in gear ta where your happy with it. Reset max timing ta 23*. One thing 'bout tha '91 is it should have tha first WMH "pumper" carbs on it. They can be a real pain sometimes. Especially tha idle circuit.......JMO

You may have a needle valve in the carb that is sticking open and it is actually flooding at low speeds.

Thanks for the info guys. Will running the motor for a few hours this weekend blow it up, or will I be okay for a couple of hours?

TLW-How difficult is it to make the adjustments that you are recommending? I don't think I need to idle the engine over 1200 RPM do I? Is'nt this engine supposed to idle around 900 RPM's?

Pat-Where is the best place to get the ethanol resistant hoses that run from the carbs to the reed block? BASSHAWK

I'm thinking ALL fuel lines including tha bleed lines Pat mentioned. If not those could be tha culprit...

If you have never messed with tha link n sync process and don't have an OEM manual I would suggest you take ta someone that knows how ta do it. As far as idle/idle timing, it should be somewhere 'tween 700 ta 850 or so in gear, on tha water. Its what ever blows your dress up and/or whatever tha motor wants.......jmo

Oh yeah, think Pat means from reed plate ta tha block. If not ya need ta change those to.......You can get tha small line from a lawn mower or motorcycle shop. Just make sure ta tell 'em 2 stroke and ethynol resistant.....

Thanks TLW. I am going to change the small lines. I changed everyhting but those smaller lines a few weeks ago. BASSHAWK

Thanks TLW. I am going to change the small lines. I changed everything but those smaller lines a few weeks ago. BASSHAWK