Johnson Service Bulletin SB-966 - Loss of Engine Performance Due to Clogged Fuel Filter

SUBJECT:  Loss of Engine Performance Due to Clogged Fuel Filter.

MODELS AFFECTED:  All Engines Using "Tea Bag" Type Filter.

Reports that an engine is starving for gas are occasionally received from the field. We have noted that in some instances, the problem was remedied by merely replacing the "Tea Bag" fuel filter, even though the original filter did not appear to be clogged. While this is apart from other fuel volume deficiencies as caused by faulty fuel pumps, inoperative tank vents or pinched gas lines, it is nevertheless a very realistic problem with outboard motors. As a result, we now suggest yearly replacement of the "Tea Bag" filter as a preventative measure.

The specific condition mentioned above will usually occur after prolonged storage. During the storage period, volatile agents evaporate from gasoline in the fuel filter bowl. Anti gum and varnish agents that are blended into the gasoline to inhibit the formation of such, also diminish themselves in a month or more, generally speaking. The result is then a formation of gum and varnish on the fuel filter mesh which clogs the fuel filter.

Since gasoline gums or varnish are nearly the same color as gasoline itself, it is hard to distinguish between the two. Filters clogged in this manner certainly impede fuel flow to the carburetor, however, and eventually show up in a customer complaint of power loss, speed loss, or top R.P.M. loss.

Gasoline is not a suitable solvent for its own gum and varnish residue, and, since other commercially available solvents might themselves lead to filter element deterioration in time (small particles falling off and being carried into carburetor), the only practical way to cure this problem is to replace the filter element.

We therefore suggest that the "Tea Bag" filter be replaced at the start of each season. Don't replace it at the time the yearly prestorage tune up is performed for reasons mentioned in paragraph #2. The cost of this filter for any engine, 5 through 75 h.p. is around $.60, which is quite nominal when considering the aggravation and spoiled outings that its annual replacement might eliminate.

Keep in mind that this problem is not solved by merely redesigning the filter element, (bigger holes). It has a definite purpose to not only trap dirt but prevent moisture (water) from entering the carburetor and engine. The ability of this filter to impede the passage of moisture is determined by the minute openings (holes) formed by its mesh.

Extra copies of this bulletin are available for posting in the showroom so that your customers also have a chance to recognize one of the problems that result from prolonged storage periods.