Johnson - no idle and sudden loss of power

[PoorlyJohnson]

I have got an old (early 70's) 85Hp Johnson Powershift II, took it to the sea today and for the first hour (after some initial reluctance to start) the engine was working fine. Then all of a sudden the output went down to 25% of what it was doing. It is now not starting very well if at all, but when it does I can rev it in neutral and it sounds fine as if no problems, achieving max revs. However it will not idle as it stalls when the revs go low. If i quickly go from revving it then into gear it will move, but again at only about 25% of what i know it can do. The fuel is brand new, mixed with new oil 50:1, the plugs are new and all the wires appear to be on. The prop appears to be clear and nothing happened when the power suddenly dropped of (ie hit something).

Can anyone give me some advice on possible causes for this??

Many thanks.

 

[licketdsplit756]

Re: Johnson - no idle and sudden loss of power

im no pro bye no means but in my exsperence. a engine not under a load will rev to hi rpms ounce a load is put on the engine if you have a cycilnder with low compression. is a good cause for your motor to not run under a load. that is how i found out what was wrong with mine..take a compression check on all cyclinders.

 

[iwombat]

Re: Johnson - no idle and sudden loss of power

You're almost certainly not firing on at least one cylinder - either due to spark or fuel.

Drop it to idle and remove one plug wire at a time. If the idle doesn't change that cylinder isn't firing.

Post the results.