Johnson 70HP Running Problems

So here is the problem. The engine runs for a couple of minutes then after a while it begins to rev up then die. As it is about to stall out it picks up and revs up to speed again. It repeats this quite violently untill i kill it. If I wait for 5mins or so it starts up fine and starts to do the same again. I have done the following:
Changed the head gasket,
Cleaned the carbs - although I may not have done this well enough they seemed very clean.

It was doing this before both of the above were done, and after I had changed the head gasket I ran it on muffs for 30minutes so I could re torque with NO problems at all. Took it down to the coast and the problem returned after I had put it in gear to sort out the idle etc on the throttle,

Any ideas would be appreciated
Thanks

Re: Johnson 70HP Running Problems

Have you tried pumping the primer bulb when it does this? If this helps, rebuild your fuel pump. But first check all your fuel lines and especially the primer bulb for cracks. They should all be soft and pliable. Make sure the fuel tank vent is clear.

Re: Johnson 70HP Running Problems

is you bulb going flat?

Re: Johnson 70HP Running Problems

Hey guys, thanks for the fast response. The bulb doesn't get flat. I had tried pumping when running but no joy still persisted.
A freind of mine just said that some Johnson/Evinrudes had a function where they would rev on and off if they were overheating so they would get you back to shore ok. I have noticed it starts when you would expect te thermostat to open. It is I think a 1985 model did these have that function built in?

Could it be the CDI or a coil?

Re: Johnson 70HP Running Problems

some of the models had a bushing that went bad, and cause play in the throttle linkage, causing this problem.. it has a black center and a white outer. $10 parts clik on picture to enlarge.