1992 Johnson Evinrude 120 hp

[littlemac]

I took the boat out a few days ago and it was topping out at 60mp. Today I took it out and it would not go past 40mp. It also used a lot of gas. Could it be too much oil in the gas? Or could it be the spark plugs?

[littlemac]

I took my 1992 johnson 120 hp boat out a few days ago and it was topping out at 60mph. Today I took it out and it would not go past 40mph. It also used a lot of gas. Could it be too much oil in the gas? Or could it be the spark plugs?

[ed/il]

I have a 1990 120. What boat is yours on, 60 is fast for that motor. Change the plugs and see if that helps. Are you mixing your oil? If so get one of those calibrated measuring canisters and you will get it right every time. Do you have a fuel water seperator? If not you should get one. Someone will coe along and post an expert reply. Good luck on your motor.

[littlemac]

15 foot Ray Craft Bass Boat. Thank you for the information that you have given me. If you can think of anything else, please let me know.

[Walker]

Does it idle good? If so you might be dropping a coil under load. Pull all the coils and clean the grounding straps and where they bolt to the block.

[littlemac]

Walker, Thank you very much, I will try that first thing in the morning. Thanks, littlemac

[littlemac]

I have a 120HP Johnson every time I take it out it runs good for about 20 minutes then it files out the plugs. help!

[ob]

Tell us what sparkplugs you are using.Engine calls for QL77JC4 gapped at .030" or for continual high speed operation QL16V surface gap.Both are Champions.Otherwise check what Walker mentioned.The fact that it used more gas than normal could point to a carburetor related issue.A rich fuel mixture would lead to wet/oil fouling of sparkplugs.

[littlemac]

I used the L78YC champion plug. Took the boat out yesterday it ran good for about 45 minutes with the new plugs at the speed at 45 & 50mph. Took it out today ran good for about 10 minutes then it started filing the plugs out. It will run but only about 38mph. It takes for ever to plane off. Help!Thanks, littlemac

[littlemac]

I used the L78YC champion plug. Took the boat out yesterday it ran good for about 45 minutes with the new plugs at the speed at 45 & 50mph. Took it out today ran good for about 10 minutes then it started filing the plugs out. It will run but only about 38mph. It takes for ever to plane off. Help!Thanks, littlemac

[ob]

For starters,if your engine is indeed a 1992 120 hp John/Rude ,the L78YC plug is not the correct plug for your engine.Post the model number of your engine so we can be sure what you have.

[ezeke]

No matter what else you do, get the thermostats and the spark plugs right first.

[littlemac]

The model no. is j120tlend.I appreciate all the help....

[ob]

The "EN" in the model number denotes that the engine is indeed a 1992 model.Unless my sources are incorrect,the L78YC sparkplug is not the correct plug for the engine.I listed the other two plugs in an above post that correspond to the 92' 120 horse motor.The YC plug is a protruding nose plug and will fire at a different combustion chamber location than the QL77JC4 or the QL16V surface gap.Install the right plugs and test run engine.If they foul out,then look elsewhere for your problem.

[alden135]

Check to make sure your timer base advances fully and isn't sticking. That was one of the problems I had with my 1990 120.

[littlemac]

back again 1992 120hp johnson cleaned coils had carbarators rebuild put new oil&fuel .motor still runs great with a new set of plugs for about 10 minutes then it starts losing speed.it cranks and idles good. help im desperate.i can/t find amechanic that can figure it out little mac...

[marysboats]

What would really help here would be to make a running test on the entire ignition system with a peak reading volt meter. Did you do a compression test? You could also have a fuel restriction. Try squeezing the primer bulb when the engine slow's down.

[littlemac]

ran a compression test all cyc.were 155 lbs.could it be a weak power pack. It cranks very easy never even have to choke it. the engine does not miss it just loses speed&hard to plane off after a little time on new plugs.thanks alot....

[Dhadley]

Whoa hoss! 155? Come on....How did you do the test? Put the gauge in one cylinder and then start the motor? I can tell you how to get a true 155 but I doubt it's been done to that motor.

[littlemac]

took all plugs out put compression gauge in one clc. at time and spun the engine. If thats wrong please tell me how to do it. thank you very much.

[ezeke]

Did you replace the thermostats yet?Have you tested the recirculation check valves?Someone asked before if you are pre-mixing fuel??What is RPM at planing? Top RPM? How long since the last De-carb?What size and pitch propeller?Can you post a picture showing how the motor is set in relationship to the transom?

[littlemac]

I have not replaced the thermostats yet. The machanic that i am using said he did not think it was the thermostat. I can't get the RPM because my tach. is not working. I am pre'mixing the fuel. What size propeller does it carry? I can post a picture of how the motor is set on the transom tomorrow. I do have a jack plate. Where are the recirculation check valves? I have given up on my machanic. Thanks very much, littlemac

[ob]

I'm still interested in knowing whether the last plugs that fouled were the QL77JC4 or the L78YC.

[marysboats]

If the engine is in sound condition, you could do as I discribed. A voltage running test would tell what component in the ignition system is breaking down if that is the problem. Doing cranking test's on the trailer may very well not show the problem. This test would show what component is failing, sensor, charge coil, power pak. You could then narrow it down to the ignition coils, or a faulty connection. If the ignition check's out, do a pressure, vacuam test on the fuel system. This is going to take the proper equipment, but without, you are groping in the dark. Tool's can get exspensive, but so can needless part's.

[littlemac]

Its fouled out both types of plugs I/ve bought nine sets of plugs since Feb.