Johnson 90-HP V4 Lugging

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Wyowanderer
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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.

jimh
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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.

flymo
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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.

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dg22
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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.

Dave

Wyowanderer
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Re: Johnson 90-HP V4 Lugging

Postby Wyowanderer » Wed Jun 19, 2019 2:03 pm

Changed the fuel filters, did notice the fuel hose snapped to engine has a leak going to replace the head of fuel line.

Checked the spark plug QL77JC4 @ 0.030" and spark.

Onboard installed fuel tank does not have a vent screw.

Will research how to check the spark coil and power pack.

Running the TWCIII oil thru the VRO 2 system.

The prop Keller is 13x7/8 11.

The engine runs smooth, but lugs at full throttle, feels like it needs to plane but can't.

This engine had not been run in over 10 years, but seems to have been well taken care of.

Also, the connector for the shift linkage inside the upper unit came off and I can't seem to find the part to purchase to keep it together, it looks like a small pinch type washer. Need a suggestion.

Thanks to each of you for assistanting with my questions.

flymo
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Re: Johnson 90-HP V4 Lugging

Postby flymo » Wed Jun 19, 2019 7:33 pm

By all means replace any leaking fuel lines - if it's sucking air it's not going to run right.

If that does not fix it, not having run in 10 years, you're likely to be looking at a fuel problem. If it were my motor, I'd rebuild the carbs and do a link and sync as a first step. Likely you'll find the high speed jet in one carb is plugged. You do not want to continue to run the motor in this condition - running lean will fry it pretty quickly.

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Acassidy
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Re: Johnson 90-HP V4 Lugging

Postby Acassidy » Wed Jun 19, 2019 10:13 pm

I agree with flymo: the carburetors need to be rebuilt before running again.

Also, replace all fuel lines on the engine because since it is leaking they are probably all bad.

While at it, replace any inline filters.

Inspect all the fuel hoses coming from the tank to make sure they are not deteriorated also.

You can get replacement hose for that engine by pulling off a hose and going to auto parts store and get a replacement hose the same size. Then cut for length for the engine. I did this on that exact engine years ago.

Running lean is not good for that engine.

Archie

jimh
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Re: Johnson 90-HP V4 Lugging

Postby jimh » Thu Jun 20, 2019 8:06 am

Rubber fuel hose for use with gasoline on a boat must meet USCG ratings. That such fuel hose can be found at an auto part store may be speculative.

jimh
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Re: Johnson 90-HP V4 Lugging

Postby jimh » Thu Jun 20, 2019 8:07 am

To locate parts try the website

SHOP2.EVINRUDE.COM

jimh
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Re: Johnson 90-HP V4 Lugging

Postby jimh » Thu Jun 20, 2019 8:09 am

If fuel leaks OUT of a hose, air will leak INTO the hose.

The hose to the engine from the fuel tank on a boat is under negative pressure (vacuum) and could easily be sucking in air. The leak should be repaired as the next step in the process of remedy of the apparent lack of fuel at high throttle setting.

jimh
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Re: Johnson 90-HP V4 Lugging

Postby jimh » Thu Jun 20, 2019 8:19 am

An engine that has not been run in ten years could have residues in the fuel system where the gasoline evaporated and left behind the oil mixed with it.

jimh
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Re: Johnson 90-HP V4 Lugging

Postby jimh » Thu Jun 20, 2019 8:22 am

Wyowanderer wrote:Onboard installed fuel tank does not have a vent screw.


Below-deck fuel tanks have a vent, usually on the hull side and high above the waterline, connected to the tank by a hose. Mud wasps like to build nests in the vent fittings, which blocks the vent.