Tohatsu 5 HP Issues.-

[Sea Rider]

Paul, a Tohatsu special for you..

1-My 2 strokes 5 HP engine is only achieving 4700 wot rpm on a 340 mtr small Rib with one up and lightly loaded, prop is a 7 pitch, with 2 up can rev as low as 4300 rpm lugging it. Wot rpm range is 4500-5500.
-Question, should I go for a 3 blade 6 pitch which is the lowest size for better fast displacement speed with 2 up while revving much higher than now ? As the rib is impossible to plane due to size and hull drag for such small engine, will throttle to just 4 K as not to demand much out of that engine.

2-To start engine need to open air valve on fuel tank, prime bulb till firm, pull choke all the way out and throttle grip till both marks align front of each other. Usually pull rope once, engine won't start, close choke to middle setting, pull rope again, engine starts immediately. Owner's manual is very imprecise about cold starting procedures. Would like to know: once engine has started and throttle grip has been returned to idle setting, do you need to warm the engine at middle choke position for some minutes or can push choke fully in and warm engine same ? Which choke position would be best and why ?

3-The engine has already 40 metered worked hours, begun to develop a hesitation like issue when throttling slowly from idle to faster rpm. Have disassembled and cleaned thoroughly all fuel related components tank to carb, now working much smoother, the hesitation has gone. It's advised to adjust idle mixture screw to be on the slight rich side than the lean side, would like to know how much rich is considered too rich and if will foul plug prematurely when warming or idling more than the necessary ?

Thanks in advance,
Happy Boating

 

[pvanv]

Luis,

1- Yes, you can drop down to 6 pitch. If that ends up being too little pitch, you can always go with the 3-blade, 6-pitch "mouse ear" high thrust prop. That would act more like the 7 pitch at speeds (due to large blade area) but may also give better takeoff from idle, again due to "shoveling" water.

2- Every motor will have some differences from others in how to cold start it. The US EPA 4-stroke models often like a little more choke, because they are jetted very lean. The rule of thumb is that once started, you can usually ease off the choke, but if you lean out too far, you will notice right away (and may stall). It's a "feel" that you develop for how that particular motor likes to warm up. Older, loose, worn 2-strokes often want more throttle to start, whether warm or cold. If the water and air are warm, the motor will, of course, warm up faster. After 3 minutes, you can probably have the choke all the way off, unless it's quite cold outside.

3- when adjusting a mixture pilot screw, start with a warm motor on the boat in the water (not just in a test tank) Set the idle stop at specs, then adjust the mixture, then reset stop to specs. repeat several times until you have the best idle at the least amount of idle stop screw. Then richen the pilot screw about 1/8 or maybe 1/4 turn. Remember that the pilot screw has very little effect at higher speeds -- it's primarily for idle and "tip-in" (coming off idle).

 

[Sea Rider]

Paul,

Will order a 6 pprop pitch, should pull my wot revs higher, hopefully 5K as tu push much better at fast displacement speed if encountering choppy windy sea conditions. Luckily that 5 HP didin't come with an 8 pitch. Extreme under lugging for my purposes.

Will try both choke settings, out temp is around 20 C? doesn't need extreme warming up times. One minute will suffice, then opnen the throttle gradually to max 4 K revs at slight passing middle grip to maintain a comfy parallel ride to water level and avoid bow up and more hull drag if throrttle more which is useless.

The throttle transition from idle to faster rpm, is superb. Usually like keeping factory adjustments, but this 5 HP needed a slight pilot adjustment.

Thanks,

Happy Boating