Lunging motor

[kat-a-tonik]

I have a 1966 20hp Johnson Seahorse that runs great but seems to (for lack of a better word) slightly lunge foreword as you travel across the water at times its barely noticeable at times but it is annoying, does anyone have any ideas as to what might be causing this the prop turns strong and the motor pushes my boat real good

 

[oldboat1]

could be dropping a cylinder (spark cutting in and out). Could be a prop slipping or a gearcase issue. Could be a fuel or carb issue. Does the motor sound differently when it does this? If it's a slight miss, my first guess would be an ignition issue (coil due for replacement, plug wire should be replaced, points should be cleaned and adjusted or replaced.) Done any carb or ignition work on the motor? Fuel fresh with proper oil mix for year?

 

[kat-a-tonik]

The motor doesnt sound any different when it does it,no missing, the carb is in good shape cleaned and rebuilt, fuel is fresh and mixed properly, I havent done any ignition work on the motor yet but I do have points and contacts ordered, if it is a gear case issue what should I look for

 

[oldboat1]

seems like an open question yet. If rebuilt carb, think tweaking the adjustment might help. Need some wisdom from other listers on that carb -- think it's a fixed h.s. jet, but maybe not. If adjustable, would try to lean it out slightly when boat testing. Simple fixes first....

 

[oldboat1]

checked back around -- strikes me it could be a hull issue. Hull is slipping off plane? maybe a weight distribution issue -- need a little more weight forward. might have water in the hull (under floorboards). might be a mounting issue for the motor (anti vent plate about even with the bottom of the hull?) -- maybe need to raise the motor slightly on the transom. may need to change the trim angle.

 

[kat-a-tonik]

Its not water in the boat, doesnt have a floor its just an old tinny V-hull, you may have something with the weight distribution the motor is at the size limit for the little 14 footer, I will try redistributing the weight in the boat, if that doesnt work ill try working with the trim angle, yes its a fixed High speed needle

 

[oldboat1]

yeah, maybe just some tweaking. (I run a '57 18 on a similar hull [open Starcraft 14']. Fun ride -- if running with tiller steering, might move up to center seat and use a tiller extension. I put in a console and controls, so weight -- mostly me -- is forward.)

 

[kat-a-tonik]

It doesnt have a middle seat the guy I bought it from some years back took it out, my wife sits in the front, But we usually have all the equipment and a cooler setting closer to the back with me I will try moving it more to the front

 

[oldboat1]

mmm. might seriously think about putting in that middle seat -- really need it for rigidity, particularly running w/max rated hp. structural issue, if the hull is like mine.

 

[kat-a-tonik]

The missing seat doesnt seem to affect the boat any, I run a 20 horse on it and it does real good, sides of boat are rigid and dont flex, I found out what was causing the lunging, it was weight distribution, I moved more weight towards the front and it solved the problem, thanks for all the tips guys.