90 Johnson 120hp V4 Loses Power at full throttle

[petryshyn]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Kmoonster <br />maybe you do have something floating around in the carbs plugging the main jet now and then........wouldn't hurt to pull carbs and check.

 

[lakerunner]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

I was having the same trouble I replace all the fuel line,clamps,filters,and blub also drained the carb bowls and so far the engine has run great. Just something to check.

 

[Digdug]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Kmoonster,<br />I just had the exact same problem on my 1994 120 Evinrude. I was totally convinced it was an electrical problem because it would not happen until I ran the boat at 3/4 to full throttle for a few minutes and engine was warm. Engine would idle and rev just fine. After 5 trips to the lake and doing all the electrical and compression checks before and after power loss I finally decided to look at the fuel system. I drained the gas tank and added fresh gas and oil (VRO is disconnected). I disconnected the fuel line at engine and pumped fresh gas through line and re-attached. Pulled carbs and cleaned them using a can of OMC carb cleaner with the little red straw (spray through jets). Engine now runs perfect. I never would have guessed it to be a fuel problem? Looks like Lake Runner and Jack B had similar problems that turned out to be carbs. I am interested to see what happens...please post.

 

[Kmoonster]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Well I'm back,,got a hold of a retired OMC outboard mechanic. He looked at it and found that my starboard side cylinders were not firing after a while. plugs looked clean, not firing on that side. used his test equipment and said that the power pack was faulty. Had 125 psi on all cylinders (compression checks) he said it was not a gas problem or compression problem. I have the power pack on order and waiting for it to come in I'll keep u posted.

 

[Digdug]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Kmoonster,<br />Is there any good information you can share about how you finally figured out the cylinders had quit firing. Did you try a spark tester after the engine had warmed up?

 

[Kmoonster]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Yep ran it a while and then went over there and the right hand side plugs were not burning,,it had cooled down and we put it on a spark tester,,they were firing good after the motor had cooled back down, Still can't expain why It's going thru that many power packs,,,all other ignitions parts check out good...

 

[seahorse5]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Several things can cause repeated powerpack failures. The most common is a poor or intermittent ground. Make sure there is a toothed lockwasher under the ground terminal. Cracked or shorted coils can backfeed high voltage into the pack and weaken the components, as can non-suppressor sparkplugs. Use only the Champion QL78YC style or the QL82YC if you troll a lot.<br /><br />In some situations, a timerbase (sensors) can affect a pack even though it tests OK. That one is very hard to find! Make sure the pack is not rubbing against the inside of the motor cover. Usually you will see a white residue on the pack if that is the case.

 

[Kmoonster]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

UPDATE<br />Well I'm still waiting on my power pack to come in. UPS should have it here tomorrow. plan on putting it in this weekend. I went ahead a used a can of Engine Tuner on my moter and I could tell a difference in the way it idled. all kinds of carbon came out the exhust,,,made me a believer...Just want to keep yall up to date. I'll post the results after power pac replacement,,,hope it warms up for test run this weekend....later and thanks again for the help

 

[Kmoonster]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Got the power pack in today plan on puting it in this weekend. I looked at the wiring diagram in my manual boy did it confuse me, it shows more wires than what's on my new Pac, I'm going to compare it to the one on my boat now. The wiring diagram covers 88-90 so that might explain it. I'll let yall know the results<br />

 

[clanton]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

In the 8th post from the top, charge coil test, if the test numbers and meter are good,<br />the charge coil is shorted.

 

[tdenton2]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

I have a very similar problem with a 1977 Johnson 85. When I am running at full throttle, about 5,000 RPM, it will intermittingly start hesitating. We have not used the boat over the last couple of years, but it was doing this the last time I used it. Before I took it out this year, rebuilt the carburators, replaced the fuel pump, replaced all the fuel lines, and relaced both fuel tanks. I did all of this more a as precaution than anything else because all of these parts were original, and the fuel tanks had a small amount of rust on the inside. The problem is still there though. The last time I had the problem, I stopped and took the engine cover off, and then immediatly went back to full throttle and the problem did not come back. This leads me to believe like several others have noted, that it is an overheating problem. I suspect it is a power-pack problem, but I hate to replace it on without knowing for sure. I have checked it out according to the Johnson manuel, and it checks out o.k., but with it being an intermitent problem I am still not confident it is good. I am anxious to see how Kmoonster's problem works out.

 

[Kmoonster]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

HEY Guys,<br />Yesterday, I replace the power pack and spark plugs. I took it out today, man that thing runs like a scalled dawg. It ran better than it has in a while. I was a little worried about the fuel but it ran good. PROBLEMED SOLVED Thanks so much for all the help..I also added a new trolling moter, the boat worked great but my performance was awful, I lost a $60 reel over the side and I was in such a hurry I unloaded the boat and forgot to put the plug in,,ouch. I was just fixxing to blast off and I noticed both bildge pumps were on and the boat was sitting a little low,,luckyly I backed the truck back in ad pulled it out and put the plug in but the boat was fine,,,,,wheee, what a close one. Well thanks again for all the help. Keith

 

[Digdug]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Moon, you and I have same boat and motor. Glad to see things have worked out well. How much speed are you getting with the 22 pitch prop. I am running a 20 and it is a good mix between speed and hole shot. My speedometer reads about 58 mph and my rps are at 5800-5900. Cavitation plate on my motor is 3 inches above bottom of hull. I am thinking about getting a jack plate to maximize efficiency. How do you like your jack plate? Do you think it helps??

 

[tdenton2]

Re: 90 Johnson 120hp V4 Loses Power at full throttle

Well, I replaced the power pack last weekend and the motor now runs like a top. Sounds like power packs are a real problem with Johnson motors. Oh well, that is the second problem with this engine since 1977, I guess that is not bad.