1977 johnson 70 hp not running fast.

[mabonk84]

Several years ago I bought this boat to going fishing on weekends. Due to schedules I have probably used this boat 5 times in 5 years. This year I go to take the boat out and it runs only about 10 mph it used to go 45 mph. I have completely ran the tank until it is dry. I have put oil in to the specified 50:1 compression and have even added some carb cleaner to the tank. I probably should have never messed with any of the linkages, but I did to try figuring out what controlled what. I do the routine maintence like adding oil to the lower unit. Most recently I have discovered that the fuel pump is spitting out gas out of the back of the fuel pump. Can this small thing cause this much loss in power? Also I have attached a picture to the linkages I have moved around and circled in colors If someone could please explain what these control it would be greatly appreciated. I am going through the manual and have only been able to figure out that the green circle controls the idle at start up. PLEASE HELP!!! I would love to get her going fast because I found a nice lake near the house but all the good fish are on the opposite side of the lake where I launch it takes me 15 mins just to get where i want to fish.

 

[kenmyfam]

Re: 1977 johnson 70 hp not running fast.

If fuel is spitting out then something is wrong and potentially dangerous. You need to investigate and fix this first. While you are at it do a carb service and clean out. Decarb the motor and if you are using the motor infrequently then use fuel stabiliser in your mix.
You should also do a basic health check on your motor. Compression, spark, fuel delivery (spitting issue to begin with) and spark plug condition.
Post your results for all to review and discuss.

 

[tashasdaddy]

Re: 1977 johnson 70 hp not running fast.

99% clogged jets. read ethanol and carb cleaning. http://forums.iboats.com/showthread.php?t=299680 you need to start these motors atleast once a month on muffs, or properly prepare them for storage, if they are going to sit.

 

[mabonk84]

Re: 1977 johnson 70 hp not running fast.

Recently bought a inline spark checker, and compression tester. I put the inline spark checker on all three cylinders and found the spark to be incredibly rapid. Spark is good. I did a compression test on all three cylinders and found two at 120 and one at 110. I did also take apart the control box and greased everything. I took the black cover that covers all three carbs off and noticed when i have the throttle all the way down that the carbs were only a quarter of the way opened, so I made the adjustment and took it out on the lake. It starts up fine, and shifts into both forward and reverse fine but just will not go. I know she's heart but just isn't reaching her potential. Can the fuel pump really hold back this much power. I'd hate to spend $100 on the fuel pump and that's not it. I've taken the fuel pump apart and do not notice any rips in the gaskets it's really strange.

Your thoughts are much appreciated.

 

[billy4hp]

Re: 1977 johnson 70 hp not running fast.

Recently bought a inline spark checker, and compression tester. I put the inline spark checker on all three cylinders and found the spark to be incredibly rapid. Spark is good. I did a compression test on all three cylinders and found two at 120 and one at 110. I did also take apart the control box and greased everything. I took the black cover that covers all three carbs off and noticed when i have the throttle all the way down that the carbs were only a quarter of the way opened, so I made the adjustment and took it out on the lake. It starts up fine, and shifts into both forward and reverse fine but just will not go. I know she's heart but just isn't reaching her potential. Can the fuel pump really hold back this much power. I'd hate to spend $100 on the fuel pump and that's not it. I've taken the fuel pump apart and do not notice any rips in the gaskets it's really strange.

Your thoughts are much appreciated.

If the fuel pump is leaking then it needs to be either rebuilt or replaced... But if it has sat for a long time just plan on biting the bullet and rebuilding the carbs with kits (don't just plan on taking them apart without putting in new gaskets, needle/seat assembly, etc)....

The thing with 2 cycle outboards is the fuel is both fuel and lubrication so if the fuel pump is weak and or the carbs are plugged you are risking not only a bad running engine but a potentially damaged one if it's not getting enough lubrication via the fuel charge...

Good luck....

 

[Lion hunter]

Re: 1977 johnson 70 hp not running fast.

The pump is a big issue. It's a pulse pump so if it's spitting it's also drawing air into the lines. Did you adjust the throttle plates to open all the way while in gear. Most motors have a stop that prevents the throttle from going fully open while in the start or nuetral position. Do what others have said, rebuild carbs, fuel pump (these do have rebuild kits available so unless the body is cracked don't buy a new one), replace all lines, filters. I don't ever use carb cleaner in the tank. These carbs are to easy to take apart and clean and I have never known an in the tank cleaner to work very well. Might try some seafoam in the tank to decarb the cylinders.

 

[tashasdaddy]

Re: 1977 johnson 70 hp not running fast.

it sounds like you need to check timing, and then do a link n sinc. it did wonders for my 77 70hp, so good i blew a head gasket, because of a bad tstat. http://forums.iboats.com/showthread.php?t=299680

 

[mabonk84]

Re: 1977 johnson 70 hp not running fast.

Turns out one of the plugs was actually ruined, so I replaced all three and cleaned out all the carbs. The boat is flying now, and actually plains quite well. Fuel pump still spits up a little bit, and will need to replaced down the road. Thanks for all the help everyone.

 

[Big Bubba]

Re: 1977 johnson 70 hp not running fast.

Mabonk84,
Sounds to me after reading your thread that your fuel pump diaphram inside the fule pump is bad. Basically the diaphram that works off your #2 cylinder pulse pressure/compression will not pump right if that diaphram is cracked or has a hole in it. I am learning myself and have a 1983, 70 horse Johnson outbaord but what I have learned on this GREAT!!! forum is that if fuel is leaking out of that small hole on the back of the fuel pump your rubber diaphram is bascally shot and you need to either #1 rebuild the fuel pump or basically replace it. Take care, Bob

 

[Lion hunter]

Re: 1977 johnson 70 hp not running fast.

Not to be condesending mabon but you may not have to worry about replacing it down the road if it catches fire. There are alot of things under that hood passing spark. You are runnng under a very dangerous situation.

 

[kenmyfam]

Re: 1977 johnson 70 hp not running fast.

Not to be condesending mabon but you may not have to worry about replacing it down the road if it catches fire. There are alot of things under that hood passing spark. You are runnng under a very dangerous situation.

Agree completely. Sort out the spitting issue.