1986 Johnson 70HP - a couple of issues

[HugoB]

Hello,

I'd would appreciate some help with a couple of issues I've been having.

- First issue - when starting the motor after it's been sitting for a week or two, it starts ok, but for the first while (up to 5-10 minutes) it has no power. What I mean is that I put the boat in gear and throttle to the max, and the motor only reacts as if I put the throttle at 20%. After the above mentioned period of time, while running around at low speed, it seems to clear an everything is ok. This doesn't happen when I start the boat up after a shorter break (a couple of days).

- Second issue - When the engine is hot (been running for a while on full speed), it dies as soon as I put it down to idle. Have to be careful docking the boat, because if I come in too fast the engine will die and I won't have the option to reverse.

Thanks in advance.

P.S. I am using 87 octane gas, if that matters.

 

[tashasdaddy]

Re: 1986 Johnson 70HP - a couple of issues

check your spark and compression first. report back. when and what was the last service done to it. is this a new motor to you? how long have you had the problem?

 

[HugoB]

Re: 1986 Johnson 70HP - a couple of issues

I replaced the sparkplugs this year. This was my father in laws boat that I took over this year. The second issue has always kind of been there, the first issue is a new development this year.
It was serviced (basic tune-up from what I gather) a couple of years ago, so not this winter, when I had it in my garage.

I assume to check compression I need to take it to a shop.

 

[Brew2]

Re: 1986 Johnson 70HP - a couple of issues

You can check compression yourself, but you need a compression tester gauge. You can purchase one at any automotive supply store (or borrow one from a neighbour!).

Basically, it looks like your typically air pressure gauge except it has a hose and fitting that screws into the spark plug hole. In a nutshell, you remove all the plugs, screw the gauge into one of the holes, turn the motor over 3-4 times, and check the gauge for the pressure. Repeat with other cylinders. The pressure should be above 100 psi and within 10% on all cylinders. Note that the plug wires will still be sparking so make sure they are grounded or no where near the open sparkplug hole. Gas vapour can exit the hole and if it gets to the spark from the wire....Kaboom!!

You can do a search on "Compression Test" and get more details or better yet, look in your manual. If you don't have a manual yet, buy one. Best $$ you'll ever spend if you are going to do any of your own work on the motor!

The basic starting point with almost any outboard problem is...do you have good spark, compression and fuel delivery. If you eliminate compression as a potential source of the problem, you can start concentrating on the other two.

Good luck!

 

[Brew2]

Re: 1986 Johnson 70HP - a couple of issues

Oh yeah..... and welcome to iboats!!