Diagnostic tricks for small motor

[JeffAdams]

Hi Folks,

I posted this on the Mercury/Mariner area, and the suggestion was this might actually be a Tohatsu make. So with apologies, I'm re-posting...

I have an unmarked motor, identified through its serial number as a Mercury Mariner 4/5 sn #09852794 mod #1004211rb year 1995. It used to be on the back of a safety boat at a club many seasons ago.

Cross checking with the parts diagrams for this model suggests a good match.

The motor says 'made in USA', and has a Keihin carb. (But forum Mercury guru suggests made in Belgium or even Japan)

It was starting well, but not holding full power for more than 5 minutes, so it went to the back of my garage for a while (OK - 2 years). I've got round to setting up a test stand, and now - the motor runs very erratically, though always willing to start.

I've tried cleaning the carb and filters (as have others), and it all SEEMS ok. I have a fairly weak looking spark, but at least there is one.

Thoughts turn to the ignition, and more fundamentally (based on motor bike experience), crankcase pressure.

Does anyone have any tricks to diagnose...

Fuel pump
EHT and ignition performance
Crankcase pressure

... that relate to this motor?

There is a few millimetres of a dry sludge in the base of the cowl that just might be interesting, or might just be due to years of careless refueling.

And also, does anyone have any experience with this type to say '15 years old - well that'll be XYZ on that motor...'

Thanks very much

Jeff Adams

 

[pvanv]

Ask Elvin (Tohatsu Guru), as he is both a Merc and Tohatsu dealer, to see if he can help you cross-reference the powerhead to a Tohatsu model. If so, then you can proceed with a Tohatsu parts catalog and service manual. If not, you are back to the local Merc dealer for advice and manuals. In any event, you need to properly diagnose the fuel, ignition, and mechanical systems.

 

[JeffAdams]

Thanks for that Paul,

do you have a username for Elvin here? I can't find him using the search facility

Jeff

 

[pvanv]

Elvin is of course the TOHATSU GURU.

 

[JeffAdams]

Ha - of course. Sorry!

Unfortunately that account won't take private messages so I guess I'll have to hope he catches my posting.

Thanks

Jeff