1975 70hp johnson problem

mfrat22 · Feb 27, 2013

Hey guys first time user. I have a 1975 70hp johnson ob and it runs good out of water and will throttle up a little slow but it does but when I put it in the water as soon as I throttle up it dies. NOTE: I alredy pulled apart the carbs and soaked cleaned and sprayed with carb cleaner to ensure I get all the jets and valves can anybody help much appreciated thank you.

fireman57 · Feb 27, 2013

Re: 1975 70hp johnson problem

Hi. Welcome to iboats. If you are positive that you have them all squeaky clean then you need to make sure that they are synced. The throttle plates must all open evenly and at the same time. You might want to consider getting rebuild kits for them and make sure that you take the little silver caps off the carb body and clean under them well you get new ones in the kits. Just tap the new ones in with a flat punch carefully. I put clear fingernail polish over them after I change them to make sure that the circuit is sealed. Also check when you move the throttle forward that your timer base under your flywheel moves freely and all the way. Check that and let us know.

mfrat22 · Feb 27, 2013

Re: 1975 70hp johnson problem

Thank you I will check all that tomorrow and ill get back with you thanks again

fireman57 · Feb 27, 2013

Re: 1975 70hp johnson problem

The little silver caps I was talking about are called welch plugs. Sorry, couldn't remember the name of them when I was typing.

BonairII · Feb 27, 2013

Re: 1975 70hp johnson problem

My vote is that it has something to do with the timer base(spark not advancing). Probably time for a "link and sync".

BUY AN OEM MANUAL FOR YOUR MOTOR! Best money you'll ever spend.

mfrat22 · Feb 28, 2013

Re: 1975 70hp johnson problem

Im new at workin on boats what does link and sink mean exactly

fireman57 · Feb 28, 2013

Re: 1975 70hp johnson problem

It is a procedure that ensures that the carb throttle plates open at the same rate and the same time when the timing is advanced so the air/fuel ratio is optimized. If you do a search for it on here the procedure will pop up. It sounds more involved than it really is. Simple to do.

mfrat22 · Feb 28, 2013

Re: 1975 70hp johnson problem

Took it out today and other than havin to pump the ball a few times while runnin it was good

fireman57 · Feb 28, 2013

Re: 1975 70hp johnson problem

If you have to pump the bulb to keep it running that means that your fuel pump is weak. Time for a rebuild or buy a new one.

mfrat22 · Mar 1, 2013

Re: 1975 70hp johnson problem

Just got back takin it out was runnin good and all of a sudden full throttle it was barily runnin adjusted some of the cables last night with the black turn peice maybe that was it dont know and have gas leakin out of the carb

fireman57 · Mar 1, 2013

Re: 1975 70hp johnson problem

Sounds like you have a float stuck in a carb. Take it off and reclean it and reset the float. It should be level when turned upside down.

BonairII · Mar 1, 2013

Re: 1975 70hp johnson problem

Def sounds like a weak fuel pump. A rebuild kit is cheap.

Check ur float level. Also inspect the needle/seat for wear. If either of them are worn they won't seal properly and can cause a flooding condition.

mfrat22 · Mar 4, 2013

Re: 1975 70hp johnson problem

Ok took the carb apart replaced all needle seats and o rings new gaskets for carb and put back together after another soak and spray with cleaner. Also measured from carb to top of float at 3/4 of an inch sits level when upside down and gas is still comin out of carb runs great in gear now though with hose hooked up

BonairII · Mar 4, 2013

Re: 1975 70hp johnson problem

Are all of your carb gaskets good? Where is the fuel coming out?

fireman57 · Mar 4, 2013

Re: 1975 70hp johnson problem

when you had your carbs off did you happen to take a flashlight and shine it in the opening behind each carb? That is to see if there is wandering bolt or some other trash that found it's way against the reed valves. I had a carb bolt get sucked in and it laid against the reeds and it spewed fuel out and it ran like, well, let's just say bad. Otherwise what Bonair says.

mfrat22 · Mar 5, 2013

Re: 1975 70hp johnson problem

I did look and there was a bolt and took it out dont know where it came from though and the but other than that they are clean gas is still drippin out the top carb

mfrat22 · Mar 5, 2013

Re: 1975 70hp johnson problem

Are the carbs supposed to hang 3/4 of an inch from the bottom of the carb

BonairII · Mar 5, 2013

Re: 1975 70hp johnson problem

When you flip carb body over...the float should run parallel to the carb body. Prob 1/8"-1/4" gap between float and body(if I remember correctly)

idonthaveaname · Mar 5, 2013

Re: 1975 70hp johnson problem

Had a similar motor. It was the stator. Not saying yours is, but you can check it.

mfrat22 · Mar 5, 2013

Re: 1975 70hp johnson problem

Ok I have the carb hangin 3/4 of inch when held right side up ill fix that thank u for the info much appreciated will the vent on gas tank being closed stop the gas flow enough to make engine run bad and to idonthaveaname I will check that thank you

1975 70hp johnson problem

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