1960 Merc 400 not reaching high rpm

[Yugoak]

I just bought my first boat and need some help. I have a 1958 starcraft 15' and it is not even geting to a plane. The first day out on the lake we were able to get boat up to around 30mph then after a few minutes was only able to get up to about 10mph still with WOT. Checked for spark at an idle and found that #2 cylinder didn't drop in rpm with spark plug off. Took home and replaced spark plugs, checked for spark on all 4 cylinder and I have spark checked compression on all 4 cylinder, compression on all four between 120-125. Thought maybe clogged fuel pump diaphram/filter but after inspection, looked good. Spark plug wires are good. I have tried to squeeze the bulb on fuel line while at idle and WOT and didn't find much of a change, bulb was firm. Not sure if my coil would cause this or if maybe a timing problem or a carb problem. It does have two carbs by the way and they are synced together. I find that when i have boat in neutral and use the choke/lever next to my throttle up front it will hit well into the upper 4000's but as soon as i put in gear and WOT boat wont hit upper rpm's. Plz help

 

[coolguy147]

Re: 1960 Merc 400 not reaching high rpm

check spark again changing spark plugs wont do nothing. probably means u need a new wire cause if the rest is sparking good

 

[Yugoak]

Re: 1960 Merc 400 not reaching high rpm

The only thing is that my motor will hit the higher range of rpm with that choke/lever next to the throttle. Only the boat is in neutral. Once I use the throttle and it is in gear the boat wont go above 8-10 mph and rpm sound very low.

 

[coolguy147]

Re: 1960 Merc 400 not reaching high rpm

since u get spark on other cylinders and not the that one. only thing i can think is spark wires/ spring so probably reuse spring unless real bad and replace bad wire. or all of them? but its a magneto system so its all in one system one coil one condensor one point etc etc. possible to be more the one cylinder missing

ur carbs clean?

 

[Yugoak]

Re: 1960 Merc 400 not reaching high rpm

Thank you for your quick response. However I did check for spark on all four cylinders and I have spark now. I just replaced the spark plugs.

 

[coolguy147]

Re: 1960 Merc 400 not reaching high rpm

just reread ur post and since u just bought the boat i would put a new water impeller in there for safety measures no over heat motor for u

compession good

spark if now its working it should get to full rpms

might need to clean the carbs out too and rebuild. i believe these motors had good floats on them so dont think u have change out. get a rebuild kit.

clean fuel filter

change fuel lines

check gear oil for water milky appearence then replace with 85-95 weight gear oil with new gaskets on each screw this motor i believe the one that saids flush is for the water pump and the little screw below the water intake is vent and the screw on way bottom big flat head is drain.

tell me what happens from there

 

[Yugoak]

Re: 1960 Merc 400 not reaching high rpm

Thanks for your insight. Not sure what all is in a rebuild kit however I have taken the carbs off and looked around a bit. Both carbs have a screen above the float which filter crap out and then there are 2 or 3 needle/jets/screws. i was able to blow through the the needle in the float and the float does work to open/close that jet (sorry about my lingo I am a bit new to working on this boat motor). My question is this: If you could possibly tell me which screws adjust what and approx. how far in/out they need to be to get me in the general area for it to run right. i believe that there might be a low and high jet. I also think that the reason I still dont get high rpm is a possible high jet clog or not set at the right depth. Lastly could my timing be off enough to cause loss of high rpm? And if so would my motor idle fine and rev up fine in neutral if my timing were off. Thank you

 

[coolguy147]

Re: 1960 Merc 400 not reaching high rpm

im not terribly familar with 4 cylinders. but im working on a 1961 merc500 myself which is basically same as urs. but if u want to rebuild ur carbs fine with me but just check out the needle and seat if there good'

ill tell u what open of ur magneto. clean and adjust points i think adjustment is .008-.010 again not sure. check coil out not cracks or melting all over. then look at rotor for good condition. basically clean the whole thing up nice and good no oil anywhere etc dust dirt try to keep out