early 80s Johnson 70 boggs under load...!

[manoverboard2]

Hi All,

New to the forum...thank goodness I found it! Just got a used boat and have fixed many things so far. The latest test has popped up in the acceleration of the motor. Here's where things are...

The motor will start perfectly. It will idle great. It will idle great really fast (with the "fast idle" lever up). I put the lever back down and put it in gear...it idles perfectly...pushes the boat about 5 mph. As soon as I press the throtle past idle, it wants to die. I let up...it runs fine, I press down too far or too long, it boggs down and dies.

I have found the if I run the fast idle for about 3 minutes or longer, put the lever back down to normal idle and then throttle it, it will hestitate for just a second, but then take off to full power. If I stop it and then resume in just a few seconds or minute or so...it will take right off again only with a slight hesitation.

I'm running 50:1 gasil and 87 octane pump gas. The water temperature is 41 degrees F. 5000 feet elevation.

Any thoughts or suggestions or 2-cycle wisdom will be greatly appreciated!!!

 

[tashasdaddy]

Re: early 80s Johnson 70 boggs under load...!

i'm going to say dirty highspeed jets, also was this a sea level engine you took to 5000 ft. if so you might need to check with a local shop as to what jets they are running in the region.

 

[manoverboard2]

Re: early 80s Johnson 70 boggs under load...!

It's not the jets. Took the carbs off yesterday and cleaned them all out...no residue of any kind in them. Blew all the jets out with cleaner and compressed air. Still ran like crap. Idles fine. Goes about 5-7 mph fine. Giving more gas above that speed kills it. I CAN'T FIGURE THIS OUT! HELP!

What I know:
1) The carbs are clean.
2) Nothing is clogging the air filter.
3) It's not the fuel pump...I tried the "squeeze the bulb" method when trying to run it faster...squeezing the bulb didn't make it any better.
4) It's not the gas mixture...checked and checked again.
5) No water in the gas.
6) Spark plugs are getting fire.

Someone on one of the other threads mentioned a "timing plate" being frozen. Could this be the cause on my engine? Where is the "timing plate" and how can I check it?

Thanks!!!!!!!!!

 

[Brew2]

Re: early 80s Johnson 70 boggs under load...!

If you "bump" the primer (ie. push in the key) when trying to accelerate, does the motor recover? If so, then you're likely still looking for a fuel delivery problem such as an air leak.

You could try a new fuel line attached to a remote gas tank and see if things change. If things improve you've narrowed the problem to an air leak in the hose/fittings and/or a tank venting issue. If they don't improve, you've eliminated those things and will have to have a closer look at the fuel pump and/or carbs.

Good luck!

 

[manoverboard2]

Re: early 80s Johnson 70 boggs under load...!

Figured it out. Got new plugs...the old ones were at least a 1/2 inch shorter than the new ones...on the inside part of the plug. I guess the extra room in the cylinder head screwed stuff up. Fixed!