2 Strokes M5B Inconsistencies.-

[Sea Rider]

1-When all 2 cylinder OB's specifies a 10 hour break in peeriod, this ons being a one cylinder OB specifies just a 5 hour break in period. Why would that be ? is it a 5 hour break in period per cylinder LOL!!

2-All 2 strokes Tohatsu OB's are factory delivered with just one spare plug, this one came with two, not to my joy, wrong heat range plug.

3-Recommended factory plug is : NGK BP7HS-10, what could happen to the engine or its performance if NGK BP8HS10 is used say for summer use. I think there's a 100?C difference per heat range number bwtween 7 and an 8.

Any tech comments for clarification are welcomed.

Happy Boating

 

[tommarvin]

I'm not a tech,if it's under warranty I would do what they say. Five hour break-in great.

Wrong heat range plug doesn't surprise me.

Iv'e read surface gap plugs are best for outboards because of heat. A pro in the Force Forum said very little difference in NGK plugs.100 *C difference seems like a lot. between 7 and 8.

 

[pvanv]

The break-in is 10 hours. Someone grabbed a wrong plug by accident. The 8 plug will foul.

 

[Sea Rider]

Paul, that's what is specified on Owner?s Manual, usually like breaking in engines at 10 hour use, both mentioned heat range plugs were factory delivered along tools, starter rope, prop pin. So an 8 is a colder plug as opposed to a 7, right ?

Happy Boating

 

[pvanv]

Yes.

 

[Sea Rider]

To my content found a full box of NGK BPR7HS-10 plugs, which other Tohatsu model or other brand OB uses BP8HS-10 plugs ? I'm a big fan about installing induction tachs on portable OB's, couldn't go boating without one and this small portable 5 HP is no exception.




As we're experiencing El Ni?o mischiefs, OB will probably see water in some more days to come. As this portable will be powering a small 3.20 mtr light Sib wanted to know once break in process is over what's the max wot rpm that Ob will achieve while lightly loaded. This small sib will be used with 2 up, probably will need to swap prop for one less pitch to pull my revs up. Have already made my mind about that small Sib which is rated for a minimum 15 HP, which has more hull drag compared to a larger one, won't be possible to plane.

Maximizing a 7 lower pitch could bump up + 500 wot revs, which will acccount for a better fast displacement speed than a standard factory delivered 8 with 2 up. Only tach will tell....

Happy Boating

 

[Sea Rider]

Then new Tohatsu 5 HP made it's inaugural outing mounted on a lightly loaded 380 mtr Sib.


Already has 5.5 metered hours, it's fantastic to have an hour/tach unit, can toggle between rpm and hours use by pressing a button. Max rpm was 3.5 K at 10 Km/h. To my content factory delivered prop is a 7 pitch, much better than an 8. Once 10 hour break in period is over, will see if possible to plane with one up, assume that with 2 up will only achieve fast displacement speed...

Happy Boating

 

[Sea Rider]

Was wondering the following : If using ext fuel 3.0 Gal tank, but have a filled internal small tank with shut fuel ****, what would happen if fuel **** is opened along air vent while OB is sucking fuel from ext tank ?

-OB will continue sucking fuel from ext tank ?
-Both tanks will work along till small one is empty, then the larger will follow ?

Question : In order for internal tank to supply fuel to OB properly, ext tank must be disconnected, right ?

Happy Boating

 

[pvanv]

Look at the plumbing. The check valve is there to prevent the internal tank from emptying into the external (if lower). Once the internal tank runs out (by gravity assist to the pump), the fuel pump will draw air through it, and will run out of gas, even though there may be fuel in the external tank.

 

[Sea Rider]

Thanks, will experiment on that one...

Just finished break in 10 hour period,

Some numbers :

380 Mtr Sib as shown above
Just driver sitting at middle deck,
Total weight 220 Kg
Max Speed ; 15 Km/h
WOT Range : 4500-5500 RPM
Max Wot RPM : 5000
Prop : 7 pitch.

5 K is middle wot range, with 2 up and a shorter 320 Mtr Sib which has more hull drag than a 380 will be way less, probably aound 4.5 K (Lug Zone) will combo benefit going for a 6 pitch prop to increase wot revs a bit ? Paul, have you tached your OB on that sailboat of yours while lightly loaded, have you done a prop maximization or still using factory delivered prop ?

Was reading that after break in period is over you need to tach OB and go for a prop that revs inside factory wot range for that given OB, preferably towards max wot rpm range. Factory starter props are usually medium pitched ones. Once best prop is dialed for that application can rev throughout the whole rpm range nicely.

Happy Boating

 

[pvanv]

Luis,

I always re-prop as needed.
My NSF9.8A3 is running a 4-blade 5-pitch HT prop, and runs up to exactly 6,000. Considering that it is a 28-foot displacement hull of over 7,000 pounds, loading of the boat has little effect.
On smaller sailboats running the MFS4/5/6, we still use the 3-blade HT 6-pitch props, which have very large blades.
On my Walker Bay 8, I have an MFS4/5/6, and must both raise the transom height, and lower pitch to accommodate two people. The HT 6-pitch (with the large blades) does not rev as high as the "regular" 6-pitch 3-blade. The WB8 can plane with one, but it struggles to get on step with two. Just too much weight to plane easily.

 

[Sea Rider]

Paul,

Nice to hear that you re prop as needed, regular boaters assumes that factory delivered props should work fine for their current application. Would you recommend going for a 6 pitch, the 320 sib will definitely not plane with 1 up with a 5 HP, is intended for a 15-18 HP OB. Would like to achieve better fast displacement speeds with 2 up and compensate wind cond if the day turns out windy. Would you say that running a 6 pitch should pull my wot revs a bit say + 300-500 rpm to be near max 5.5K range ?

Don't like to demand all the power out of small portsble OB's of that HP, sometimes it's much better to throttle less for boat to smooth slide parallel to water level with less hull drag as opposed to full throttle in which the hull drags at an angle with bow up. Fast displacement and plane speeds are different stories.

Happy Boating

 

[pvanv]

Luis,

If the 7 pitch puts your WOT RPM too low, definitely look for a 6 pitch prop. The RPM Of the HT 6 pitch will be lower than the standard-type 6-pitch, because it shovels more water per revolution. Similar to comparing a 3-blade to a 4-blade of same piych. Bigger blade surface = lower RPM.

 

[Sea Rider]

Paul, was planing going for a standard 6 pitch code 3B2B64513-1

Is 393B64512-1 the High Trust model ? If so, is it a 4 blade prop, or same 3 with larger blades.

Happy Boating

 

[pvanv]

ALUMINUM	HEAVY	8.375	6	3		399B645121	HIGH THRUST
ALUMINUM	HEAVY	7.9	6	3		393B645121

They are both 3-blade props, but the HT prop has big blades.

 

[Sea Rider]

Tested the 320 Sib on flat calm no wind waters with 2 up, passing the rabbit mark achieved 4200 rpm, won't rev any further from rabbit to full wot, useless to demand more power and rpm as the small Sib tends to drag itself due to its shorter size than previous 380 Sib. OB pushes nicely at 10 Km/h boring displacement speed, but better than to be left stranded at terra firme specially at summer.. Will order a standard 6 pitch prop, should pull revs a bit while throttling more.


Happy Boating