1981 Johnson 70hp no power under load

[tkartmazov]

Hi All,

I've been reading lots, finally registered to post

A formerly mentioned motor (J70ELCIM) came my way, been sitting for 2 years. Starts on 1/2 turn every time, idles fine after I adjusted the big idle screw, has a nice solid stream out of the pee hole, no visible leaks of any kind, all grease and lube seems normal. However, when under load, it seems to choke. If i throttle up without engaging the drive, the motor spools up beautifully to any rpm desired.

Spark is good, compression around 120 in all three, carbs look brand new compared to the rest of the motor (although i haven't taken them apart yet).

My question is: other than the carbs (i just ordered the parts for a rebuild of all three), could there be anything else causing this? And if so, is there anything I can potentially diagnose while waiting for parts?

Thanks in advance for your help; this is a great site with lots of very useful info!

 

[Solittle]

Re: 1981 Johnson 70hp no power under load

If your engine is starting that easily I wouldn't touch a thing other than do the carbs. You could easily mess up somthin that ain't messed up.

 

[tkartmazov]

Re: 1981 Johnson 70hp no power under load

thanks, i will patiently wait for the parts to arrive then... hopefully that'll do'er

 

[Toddo1]

Re: 1981 Johnson 70hp no power under load

I have that exact same motor. When you clean those carbs, make sure to remove the welch plugs before soaking them. Real important to get inside those passages.

If you need link n sync instructions, I have them in .pdf form.

 

[Isaacm1986]

Re: 1981 Johnson 70hp no power under load

have you tried running some seafoam through it? I had a 65hp merc that did the same thing, ran seafoam in a tank and it was good as new.

might be worth a shot.

 

[kenmyfam]

Re: 1981 Johnson 70hp no power under load

have you tried running some seafoam through it? I had a 65hp merc that did the same thing, ran seafoam in a tank and it was good as new.

might be worth a shot.

A decarb is never a bad idea if you do not know when it was last done or if you know it has not.
Just my 2 cents though.

 

[tkartmazov]

Re: 1981 Johnson 70hp no power under load

I have that exact same motor. When you clean those carbs, make sure to remove the welch plugs before soaking them. Real important to get inside those passages.

If you need link n sync instructions, I have them in .pdf form.

Thanks for the note -- pardon my ignorance, but what are the welch plugs? I would definitely like to take you up on the link and sync .pdf!

seafoam added to the shopping list for decarbing

 

[Toddo1]

Re: 1981 Johnson 70hp no power under load

The welch plugs are the things in your carb kit that look like little bottle caps. You need to drill a small hole in the center of each one and pop them out before soaking. I emailed you that pdf.

 

[orbea1313]

Re: 1981 Johnson 70hp no power under load

I recently purchased and older 1981 Johnson 70 hp J70ELCIM that has no power under load, although this problem comes and goes. The carbs are new, as well as the fuel lines. Checked the jets and they look new and don't seem to have any sign of blockage. I have fouled out 2 sets of plugs since running the engine, only about an hour of run time total. Basically the motor seems to run OK until it is fully warmed up (after about a couple of minutes at WOT ) then the no power under load will start. Compression on the motor is good, at 140 psi per cylinder. Visually the motor looks to be in very good condition, but since the motor was installed on the boat, there has not been a link n sync done on it. I know from reading the forums that the butterflies should all be closed at idle, and that the idle rpm is controlled by the advance arm linkage that has the large idle screw on it.
There is a slight gap between the roller and the cam at idle as well, and the advance is coming in slightly before the throttle cam starts to move. Does anyone have any suggestions other than the link n sync to check. Toddo1 (or anyone else) do you still have the instructions in PDF form that you could send to me? Trying to save some money and not buy a service manual just yet.

 

[Slife2]

Re: 1981 Johnson 70hp no power under load

I have a 1979 50hp johnson and it runs fine when hooked up to the garden hose. But we take it to the lake and once we get it the water under a load it doesn't want to stay running. I took the carbs off and cleaned them and I changed all the fuel lines, and it still dies and runs like crap under a load. If anyone could tell me what to do now to fix the motor that would be awesome. Thanks