15 hp Johnson Top plug fouling, runs 1/2 speed on btm. plug.

[Jim Barnes]

It ran OK except for occasional light sputtering and was a little hard starting. Then it<br />started on one cylinder and ran fairly smooth at 1/2 speed and we noticed a strong<br />fuel odor. Checked plugs, top one was fouled and bottom one looked fine. Replaced <br />old plugs with proper new plugs-- did same thing. Checked fuel, no obvious problem.<br />Is the coil or other related part the problem? Does anybody have ideas? Model # is<br />15R78B, (I guess it's a 1978), SN E-4852084. Thanks for any help, Jim.

 

[Hooty]

Re: 15 hp Johnson Top plug fouling, runs 1/2 speed on btm. plug.

If you've got a manual, the next thing ya need is a spark gap tester. NAPA will have one and they're not expensive. Get that and follow your manual for testing ignition stuff.<br /><br />c/6<br /><br />Hooty

 

[DJ]

Re: 15 hp Johnson Top plug fouling, runs 1/2 speed on btm. plug.

Don't know what year your engine is? Suspect-coil.

 

[Boatist]

Re: 15 hp Johnson Top plug fouling, runs 1/2 speed on btm. plug.

Could be Points, condenser, or coil.<br />Pull the plug wire and see if spark will jump one inch. should get a good strong spark. If you do then need to check compression. I think your engine is like mine where you can swapp coils without unbolting anything. On my 75 15 hp can swapp plug wires and input plug to coils without unbolting anything so easy to elminate the coil. after that if no spark need to check points and condenser under flywheel.