CONTINUOUSWAVE

Q1: what is the function of a crankcase lower drain fitting on a Johnson 90-HP engine?

Q2: what hose connects to this fitting?

A description of where the fitting is located or a picture would be a huge help for us to suggest what it connects to.

If the fitting is small for a 1/8-inch ID tubing and on the forward facing part of the lower unit it may be the attachment point for the speed sensor tubing which runs to the helm speedometer.

Based on the description, I suspect that the hose barb fitting you are asking about on a two-stroke-power-cycle engine and located at the bottom of the crankcase is probably part of the oil-recirculation system of the engine. An engine service manual will show you what hose connects to this hose barb and where that hose routes to.

The oil recirculation system on a two-stroke typically attempt to collect oil that has come out of suspension in the fuel-air mixture and has fallen to the the lower end of the crankcase. This oil puddles there. The drain and hose recirculate the oil to the top of the crankcase. The fitting typically includes a check valve so that the pressure pulses in the crankcase push the oil uphill in the hose and deliver it to a similar fitting on the top of the crankcase.

Without having the service manual that provides an illustration of the routing of the oil recirculation hoses and fittings, there is no way to be certain if my guess is correct. If you plan to perform work on an engine other than the routine maintenance described in the owner's manual or operating guide, having the factory service manual is a must. Therefore, you need to get the engine service manual for this particular 2000 Johnson 90-HP engine and see if my guess was correct.

Another guess: the air pump that operates the fuel lift pump on many classic two-stroke-power-cycle engine is drive by pressure or vacuum pulses from the crankcase. A fitting on the crankcase with a check valve routes the pressure pulses to an air motor. The movement of the air motor operates a fuel lift pump. The air motor and fuel lift pump are usually in one assembly referred to generically as "the fuel pump."

ASIDE: the scope of the REPAIRS and MODIFICATION forum is mainly on the hulls of Boston Whaler boats, and the forum cannot offer advice on repairs to engines other than in a general manner or perhaps for some very well-known and documented tendencies of failure.

MarkCz wrote:If the fitting is small for a 1/8-inch ID tubing and on the forward facing part of the lower unit it may be the attachment point for the speed sensor tubing which runs to the helm speedometer.

Based on the description in the first post of the location of the fitting as being on the lower part of the engine crankcase, I do not agree with your assessment that it might part of a Pitot tube speedometer rigging, but if the fitting has been improperly described and is actually located on the engine gear case and if the engine gear case has a Pitot tube opening, then the fitting could be part of a Pitot tube speedometer system. However, for that to occur this particular model-year 2000 Johnson engine would need to have provided such a system. I do not think that all older 90-HP two-stroke-power-cycle engines would inherently have a Pitot tube and hose barb fitting on their gear case.

The owner of Johnson became the Bombardier Recreational Products company or BRP. BRP has been outstanding in their publication of very detailed lists of parts for their engines, including very precise diagrams illustrating all the parts, their location on the engine, and including hoses.

You can easily find a detailed drawing of a 2000 Johnson 90-HP engine that will show you the fitting you are asking about by visiting the BRP website for parts. You can begin at

https://epc.brp.com/

From that URL above you enter the appropriate data to locate the engine model of interest. I was able to find detailed drawings associated with a 2000 Johnson 90-HP engine there. Curiously, some part descriptions were in French. Most were in English. Canada is a bilingual nation, particularly in Quebec, where BRP is located.

Good luck with your inquiry.

Jimh--thanks for the response, appreciated.
Figure 1 below shows the drain nipple on the immediate right side where the shift rod enters the rubber guide at the crankcase. The screw holding the nipple in place can be seen and just above is the male barbed fitting on the nipple.