98 70hp Johnson cutting out

[country_bumpkin]

Just bought this pontoon. We started the motor up in the sellers backyard, fired right up but idled high. We met his mechanic out on the lake the next day and he adjusted the carburetors. We took it out for 20 minutes and it ran smooth, reacted quickly to the throttle control. The next day I took the family out and it ran great again for about 40 minutes, except every once in awhile I felt a 'hicup'. Very quick, it didn't affect the tach speed.

Fast forward two weeks. I took the family out yesterday. Fired right up, idled out past the no wake zone. Pushed the throttle foward, it jump right on it. Got up to about 4500rpms for about 5 minutes and then it cut out. Dead, wouldn't restart. Got towed in.

Back at the house I tried again, and it fired right up, but only idled for a few minutes and cut out again.

The selller did mention that he replaced a "powerpack" (I'm pointing at it) at the end of the season last year.

At first, I thought this was a fuel problem. I bought another fuel tank, bulb and line and hooked it up. The motor ran for about 5 minutes again, and cut out.

I do have a service and repair manual, but haven't dug too deep into it yet.

Any ideas?

Thanks for looking.

CB

 

[tashasdaddy]

Re: 98 70hp Johnson cutting out

please go back edit your post, resize your pictures, most of us will not scan R - L to read a post.

 

[scrampbell]

Re: 98 70hp Johnson cutting out

Disclaimer: consider this a very amateur diagnosis...

How is it pissing? Could it be overheating and have an automatic cutoff? Run the engine for a couple of minutes and then feel the engine block. If it's extremely hot and pissing good, then you may want to try changing the thermostat.

 

[country_bumpkin]

Re: 98 70hp Johnson cutting out

Disclaimer: consider this a very amateur diagnosis...

How is it pissing? Could it be overheating and have an automatic cutoff? Run the engine for a couple of minutes and then feel the engine block. If it's extremely hot and pissing good, then you may want to try changing the thermostat.

peeing like a race horse and keeping cool, thanks!

 

[kybill66]

Re: 98 70hp Johnson cutting out

It is possible that the power pack is going out alot of times when the motor warms up the heat from the motor will make the power pack breakdown. If the motor was getting hot when you ran it alot of times if you just sit there for about 20 min it would start back up. Lets just say i had a customer that as long as he did not go over 5000rpms his boat ran fine but when he did the motor would lock up and then he would sit for about 20 min and then start it back up and off he would go. He didn't have the money to rebuild his motor.

 

[country_bumpkin]

Re: 98 70hp Johnson cutting out

So, I talked to the PO's mechanic today and he claims that they never replaced the 'powerpack', and that the replacement powerpack that the PO handed me in closing the deal was brand new. I switched them out and ran it for about 30 minutes in my driveway, reving it once in awhile....ran flawless and cool.

crossing my fingers, gonna take it back out this weekend a put it through the paces, proly without the gang...

wish me luck