antique johnson backfiring

[tgissel]

I have what I believe to be a 1956 Johnson Sea-Horse 35hp mounted on 1956 Feathercraft Vagabond.<br />Model# RDE-19 Serial#1550100<br />Motor will run wide open, but anything other motor backfires and shakes violently. Any suggestions?

 

[Paul Moir]

Re: antique johnson backfiring

Welcome to Iboats, tgissel!<br />RD-19 is in fact a 1957 35hp. In '56 there was only a 30hp (which was based on the 35.7CID engine rather than your 40.5CID).<br />Other helpful facts:<br />Spark plugs: Champion J4C (were J4J's, now discontinued) gapped at .030"<br />Fuel/oil mixture: 24:1 87 octane gas to TCW-3 rated outboard oil.<br />WOT RPMS: 4500<br /><br />Backfiring through the exhaust is symptomatic of bad timing. Make sure the armature plate underneath the flywheel is free to swivel with the throttle, but is not loose and shaking. Failing that, pull the flywheel and adjust the points to open .020" max.<br />To remove the flywheel, you must use a puller that acts on the three bolt holes near the hub of the flywheel. A beefy automotive harmonic balancer puller equipped with 1/4"-20TPI Grade 8 bolts about 3" long will work. When the flywheel is reinstalled, the flywheel nut must be torqued to exactly 105 ft/lbs, or the flywheel key will shear.<br />If it's backfiring through the carburetor, that is an indication of lean running. Diagnose the fuel system - and rebuild the carb.<br /><br />Obtain a manual. It's worth it's weight in gold, and having one is manditory for wrenching your engine. Iboats sells aftermarket ones. Your local library may also carry one. Reprints of the orginal OEM repair manual can be obtained from one of the following places:<br />TheOutboardWizard<br />Mastertech<br />Marine Engine<br />Ken Cook <br /><br /><br />Hope this gets you started! <br /><br />PS - we're not allowed to call a '59 engine antique around here, since that's younger than JB. Just call it experienced instead.

 

[tgissel]

Re: antique johnson backfiring

Thanks Paul. I have a manual and have pulled the flywheel off, checked the points and done a compression check. How do you determine if one of the coils is "breaking down"? Thanks for the engine year!

 

[rwise]

Re: antique johnson backfiring

A visual check is if it has any cracks in it replace it, the coil that is. Should be able to get a replacement at NAPA or your johnyrude dealer.

 

[Chinewalker]

Re: antique johnson backfiring

I have VERY rarely seen a non-cracked coil fail, so if the coils aren't cracked, more than likely they're fine. If your motor is backfiring, check the flywheel key to make sure it's not sheared. Also, where are your needle valves set? High speed (bottom screw) should start out around 1-full turn from closed position. Low speed should start our around 1.5 turns from closed. The backfiring/sneezing could be from a lean condition on the low speed needle...<br />- Scott

 

[tgissel]

Re: antique johnson backfiring

Thank you Chinewalker, I think that may be the key to my problems, the High speed needle is bent as well as the low speed. Am I correct in think that air can pass where it is bent and mess with the needle settings.