Re: 1978 Johnson 70 HP outboard
You need a Service Manual, David.<br /><br />There are three carburetors on that engine and there is not a "low speed screw".<br /><br />It would be illegal to send you a copy of copyrighted material, but you can legally copy from the manual at your local library.<br /><br />You need to do the "link 'n' synch" (carburetor linkage and synchronization) adjustment procedure, which is detailed in the Manual.<br /><br />Good luck.
