1978 85 hp !!!!!!!!!!!!!!!

[solidwaste75]

I have a 78 v4 85hp javalyn took it out for the first time yesterday and it ran fine but I dont know much about these engines. When I would put throtle all the way down the motor would run for a couple of seconds at low rpms then all the sudden it would just start to pick up rpms and run like a banshee..It was like opening up a 4 barrel on an old carb..It was predictable and happened every time..So I dont know if that is supposed to happen like that or not..I have this motor on a 16.5ft 72 larson tri hull and when I got it wide open the boat would bounce up and down like a bucken bronco any way to stop this??<br />Oh yea I dont have a tach so I dont know for sure what the rpms were but at wot sounded like around 5k...Thanks for any input

 

[Goodoleboy]

Re: 1978 85 hp !!!!!!!!!!!!!!!

Sounds like you may have your motor trimed up to high. Look at the rod that goes into the holes at bottom of motor mount bracket.<br /><br />Try it on the first hole setting. If it stops (porporseing). Then try second hole. Play around with diffrent settings until you are satisfied.<br /><br />Engine hesetating is not suposed to happen. You may need to do a link and sync. May also need to clean carbs. <br /><br />Should also check timeing. If your only turning 5000 its two low. Should be 5500 to 6000. The only way to know for sure is with a tach.<br /><br />Ofcourse you knew that already. But you really do need one to geter fine tuned.<br /><br />Good luck!

 

[solidwaste75]

Re: 1978 85 hp !!!!!!!!!!!!!!!

Im sorry I dont know what a link and sink is??Can you explain? And I was trying different posisions with the trim all day with it to try to counter act porpusing to no effect the cavitation plate lines up with bottom of hull when completly down I herd those smart tabs help stop that but i dont know for sure.. Thanks for youre help

 

[Goodoleboy]

Re: 1978 85 hp !!!!!!!!!!!!!!!

You cant do a link and sync. without a manual. Mabey someone will come along that has an engine like yours and will be abel to help you do this.<br /><br />I dont know what to tell you about the porpuseing problem. Mabey its to much pitch in the prop.<br /><br />Theirs some guys on here that can whop uh fix on ya tho. not to worry.<br /><br />Good luck!

 

[solidwaste75]

Re: 1978 85 hp !!!!!!!!!!!!!!!

Thanks gooodoleboy hope so..

 

[solidwaste75]

Re: 1978 85 hp !!!!!!!!!!!!!!!

lil help please

 

[Basscat 1]

Re: 1978 85 hp !!!!!!!!!!!!!!!

I think Goodoleboy hit it right on the head. For the porpouse problem try changing the tilt pin it the first or second hole. You have to experiment with this since every boat is different.<br />The carbs will need to be rebuilt too. Clean and soak them.<br />You need to get a service manual, and also a tach.

 

[solidwaste75]

Re: 1978 85 hp !!!!!!!!!!!!!!!

my tilt pin is on the first hole and I have tilt trim on it and tried many different pos lil effect..so you think the hesitation is due to carbs needing rebulit??Thanks for help..

 

[Jdeagro]

Re: 1978 85 hp !!!!!!!!!!!!!!!

Using the tilt / trim on the motor to stop the porpoising sometimes works, but even then it is a compromise. You would be running the prop at an angle to lift the stern and push the bow down. The problem is that the prop is then running at an inefficient angle. You will loose speed and fuel efficiency. If this has not corrected the porpoising issue then the best thing yo can do is add trim tabs. Of course this will provide a host of other benefits as well. If you choose Smart Tabs use the ST980-40.