70 hp johnson powerhead???????????

[moored3]

my compression on the 1978 70hp johnson 138-138-140 but the leak down check was very bad does that mean its time for a rebuilt power head. I hear alot about compression but not much on leak down checks. Sure need some advise. How do you know where to for sure get a good one from the internet. They all say theirs are the best. thanks

 

[Robj]

Re: 70 hp johnson powerhead???????????

I am not sure that a leak down test on a 2 stroke is the same as with a four stroke. Maybe the ports were open when you did the test. With those compression numbers, I wouldn't think there is anything wrong. Those numbers look great. What makes you think that there is a problem??

Have a great day,

Rob.

 

[moored3]

Re: 70 hp johnson powerhead???????????

I have been trying to get this engine to idle I have cleaned and rebuilt carbs . link n sync ,new plugs gapped propperly ect.. I have cleaned carbs 3 times just make sure didnt miss anything. still wont idle put each cyl tdc did leak down check per local marine mechanic . The middle cyl was the best the upper and lower could hear air passing by rings, not as hard to hold engine from rotating. Just needed to know the imortance of two cycle leak down thanks any and all advice needed

1978 johnson 70e78c

 

[R.Johnson]

Re: 70 hp johnson powerhead???????????

What were the numbers from the leak down test? It is not uncommon to hear air going past the pistons in the cylinder, after all, you have a ring gap to contend with. If the difference was 10%, or more, I would pull the cylinder head, and take a look. The compression test numbers look good, but I have been fooled more than once with a compression test. My exsperience has been with a leak-down, if the numbers look bad, there is a problem. Most people run a compression test until it reachs the highest number, but don't know how many RPM's to reach that number. A leak-down tester has two guages hooked to a regulator, the pressure applied is constant, so a more accurate indicator. Owwatonna tool's in Minnesota, makes a tester, I made my own.

 

[moored3]

Re: 70 hp johnson powerhead???????????

the compression test was at the ighest rpm the leak down was pretty much 100 percent bad on all cyl. I will pull the head and check for scatches ect ... think you have answered my questions thank you Getting kinda nervous crappie season soon need engine to run well. Think of any thing else im listening

 

[HighTrim]

Re: 70 hp johnson powerhead???????????

What do you have your idle set at, under load in gear?

Also you never mentioned the actual leak down numbers?

 

[moored3]

Re: 70 hp johnson powerhead???????????

I made a mistake on that leak down this is pretty stupid while holding engine kept bumping air off , autual reading were very good with some helpfrom my wife 100psi base1:98 2:96 3:92 thats way good huh I am now putting back together thanks for the help Im redface: