Johnson 90-HP V4 Lugging

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Posts: 11
Joined: Tue Oct 02, 2018 1:57 pm

Johnson 90-HP V4 Lugging

Postby Wyowanderer » Wed Jun 12, 2019 3:30 pm

[On my 1988 SUPER SPORT 17, the 1988 Johnson 90-HP V4 engine is] lugging under full throttle. When under load [the Johnson 90-HP V4] will only [accelerate] to 3,200-RPM [at proper] trim. A new propeller and new spark plugs [have been installed]. [The 1988 Johnson 90-HP V4] just won't get up and go.

Any suggestions [about the cause of the engine lugging under load and how to remedy it] would be greatly appreciated.

Posts: 6213
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

Re: Johnson 90-HP V4 Lugging

Postby jimh » Wed Jun 12, 2019 8:22 pm

Here are some suggestions for the cause of the engine having difficulty accelerating under load (or lugging) due to electrical problems:

Check the spark plug gap. Spark plug gap too wide seems to cause trouble when accelerating under load.

Use an in-line spark tester to verify all cylinders have spark while under load.

Check for a bad spark coil. A 1988 Johnson spark coil may have developed a short to ground. Visual observation of arcing to ground may be enhanced if viewing the running engine in total darkness. Arcing often leaves visual evidence behind, such as burned or darkened or soft areas in the coil housing.

Check for proper operation of the Power Pack. The Power Pack supplies the spark coil primary windings with an excitation voltage and current. A 1988 Johnson V4 90-HP may be due for a new Power Pack assembly.

Here is another suggestion for the cause of the engine having difficulty accelerating under load (or lugging) that is not in the electrical realm: lack of fuel delivery can also cause poor acceleration under load.

Posts: 158
Joined: Thu Oct 22, 2015 2:58 pm

Re: Johnson 90-HP V4 Lugging

Postby flymo » Thu Jun 13, 2019 6:09 pm

Wyo, it would be helpful to have more context.

Is this a new boat for you? Or was it working fine earlier (maybe last year) and now is unable to get up to speed?

Without more information, your problem could be almost anything - fuel, electrical, wrong prop, etc.

User avatar
Posts: 76
Joined: Sun Nov 29, 2015 4:06 pm

Re: Johnson 90-HP V4 Lugging

Postby dg22 » Fri Jun 14, 2019 10:11 am

If your fuel tank cap has a vent screw, make sure it is open.

If spark is good in each cylinder, check and clean fuel filters

If still a problem, clean the main jet in the carburetors.

If spark is missing on one of the cylinders, try a different spark plug.

If still a problem, a spark coil or Power Pack may need replacing.