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Johnson 90-HP V4 Lugging

Posted: Wed Jun 12, 2019 3:30 pm
by Wyowanderer
[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.

Re: Johnson 90-HP V4 Lugging

Posted: Wed Jun 12, 2019 8:22 pm
by jimh
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.

Re: Johnson 90-HP V4 Lugging

Posted: Thu Jun 13, 2019 6:09 pm
by flymo
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.

Re: Johnson 90-HP V4 Lugging

Posted: Fri Jun 14, 2019 10:11 am
by dg22
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

Re: Johnson 90-HP V4 Lugging

Posted: Wed Jun 19, 2019 2:03 pm
by Wyowanderer
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.

Re: Johnson 90-HP V4 Lugging

Posted: Wed Jun 19, 2019 7:33 pm
by flymo
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.

Re: Johnson 90-HP V4 Lugging

Posted: Wed Jun 19, 2019 10:13 pm
by Acassidy
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

Re: Johnson 90-HP V4 Lugging

Posted: Thu Jun 20, 2019 8:06 am
by jimh
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.

Re: Johnson 90-HP V4 Lugging

Posted: Thu Jun 20, 2019 8:07 am
by jimh
To locate parts try the website

SHOP2.EVINRUDE.COM

Re: Johnson 90-HP V4 Lugging

Posted: Thu Jun 20, 2019 8:09 am
by jimh
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.

Re: Johnson 90-HP V4 Lugging

Posted: Thu Jun 20, 2019 8:19 am
by jimh
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.

Re: Johnson 90-HP V4 Lugging

Posted: Thu Jun 20, 2019 8:22 am
by jimh
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.

Re: Johnson 90-HP V4 Lugging

Posted: Thu Jun 20, 2019 8:20 pm
by flymo
A vent problem is unlikely. It's not consistent with the symptoms described. Sucking air through a busted line isn't really either, but it should be fixed before something catches fire. If fuel flow rate were the cause of the problem, he'd likely still have enough fuel in the carb bowls to get up to speed; it just wouldn't stay there after the fuel was used up.

Re: Johnson 90-HP V4 Lugging

Posted: Mon Jun 24, 2019 8:35 am
by Don SSDD
Marine rubber fuel line is thicker and less likely to collapse when it is being bent, auto rubber fuel line collapses easily when bent, buy marine grade.

Re: Johnson 90-HP V4 Lugging

Posted: Tue Jun 25, 2019 6:45 am
by Don SSDD
On my V4 140, there was a stuck needle [float valve] in one carburetor. On each carburetor there is a drain bowl with a drain screw on the bowl. If one carburetor needle [float valve] is stuck, little or no gasoline will flow out the drain when you open the drain screw of the carburetor with the stuck needle float valve.

Re: Johnson 90-HP V4 Lugging

Posted: Tue Jun 25, 2019 11:11 am
by Wyowanderer
This is the fuel line setup. I am waiting for several new lines but question:
The line from the onboard fuel tank to the filter (bottom left) does not have a pump bulb. The bulb is only on the line from filter to engine and another on the oil line. Is this setup correct? Also I think the fuel line into the fuel tank should be a different setup instead of a direct feed. Thank you all for asssisting me with this, greatly appreciated.

Re: Johnson 90-HP V4 Lugging

Posted: Tue Jun 25, 2019 3:10 pm
by Acassidy
At the time when I owned that same motor, it was 20 years ago, the OMC parts place did not carry replacement fuel hose for under the cowling. Same for the boating supply stores. I live in a big boating community near Kemah Texas. But the only place who did have small fuel lines was the auto parts store like Autozone. They worked and were for the ethanol fuels. Just shared what I had to do, but maybe now 20 years latter those can be ordered online for that motor.

I am not talking about the main fuel hoses from the tank to the motor. I can get them and are very high quality.

I have always put the prime bulb before the big filter not between the filter and motor, this way it is filling the canister when pumped. Always use OEM Yamaha prime bulbs, not the cheap crap that everyone sells. I mount it on the hose so that when I pump it, it is pumping in an up direction, arrow pointing up. This encourages the reverse flow stop valve to fall back down and get a good pumping action.

The oil line bulb is normal and correct. It is used to prime the oil pump on the motor and probably doent need to be pumped until you work on the oil pump and allow air in the line.
Archie