Suzuki DF9.9BS - What prop

Sir.Robin · 14 June 2017, 13:05

So my engine is a Suzuki DF9.9BS (330cc lean burn) wich is basically the same as the DF15A/DF20A but with a restrictor to the air inlet and throttle limited to 5700rpm. Prop is standard Suzuki 9", same as the DF15A comes with i think.

I recently upgraded it to 15hp and it is a pretty big difference in power

With my boat (River 350, 11 feet) fully loaded i cannot use more than approx 75-80% throttle or i will hit the limiter.

Was thinking of a 11", but then i saw that even the DF20A only comes with a 10"... so maybe i should go 10 instead of 11.

Any thoughts?

Fenlander · 14 June 2017, 13:43

Oh that's odd... bit outside my experience. In the UK the DF9.9 is a 208cc based on the 8hp.

Here the 15 & 20HP models are associated both with 327cc and a new Efi unit needed to upgrade 15 to 20hp... and at too great cost to make the upgrade worthwhile.

I think your boat is a hard hull and if so your prop pitch needs will be different to a SIB. I have both 10" and 11" pitch props for my Suzuki 20hp. The 11" is only any use when one up and even then not that great a difference. For a normal load of 2 adults, 1 or 2 light teens and a dog plus equipment the 10" is best.

Sir.Robin · 14 June 2017, 14:00

Yea, we have teh 208cc DF9.9AS (carb) also available here. But the DF9.9B Sport is the same as the DF15A/DF20A.

The 9.9 can also be upped to 20hp, but you will in addition to the restrictor, need to change the ECU (apparantly), wich is expensive.

Upping the 9.9B to 15 however, is cheap. About 16£ for the different restrictor.

See pic for the restrictors... original at the right. Changed to the one at left... more air

I think will trie the 10 first. Too small is better than too big i reckon.

Sir.Robin · 13 July 2017, 19:58

Finally got my prop today! First one i got was wrong and did not fit. Original Suzuki 10" installed and excited to testrun! all them small joys...

Limecc · 14 July 2017, 00:31

I was talking to a guy whilst on holiday in Salcombe who said he purchased the 15hp because he knows where he can get the ecu remapped.

Sir.Robin · 20 July 2017, 22:37

Finally got my new prop tested

Boat with me, mommy and two kids (5 and 9 year old):
9.9Hk & 9" prop: Maximum 4600rpm @ 9knots
Boat with me and 9 year old only:
9.9Hk & 9" prop: Maximum 5300rpm @ 18knots

Boat with me, mommy and two kids (5 and 9 year old):
15Hk & 9" prop: Maximum 5700rpm+ @ 16knots

Boat with me, mommy and 5 year old only:
15Hk & 10" prop: Maximum 5700rpm @ 19knots

This were all in salt water. So it looks to me the 10" is a perfect "allround" prop for us. When having the 9 year old also and a little more baggage, i think the 10 seems perfect.

Sir.Robin · 30 July 2017, 11:44

So got it testet in freshwater too this week.

With the water mirror like (calm) and zero wind, i barely hit the rpm limiter while alone in the boat. Noticeable slower to get up to speed compared to salty water though.

Loaded with kids and mommy, i get max around 5500. With gear and stuff too, 5200-5300 and much slower to get up.

So first thoughts were that the 11" would be better, but after the freshwater experience, i think that would be too heavy.

Running a bit of distance i usually go down on the throttle to about 90% because enigne makes less noise and speed barely drops.

Bikegod66 · 09 August 2019, 02:27

So you changed out the restrictor to the 15 hp one and not the ecu ? Plug check ? Not running lean ?

I have a new 9.9 zuki and would like to perk it up.

Thanks

Sir.Robin · 09 August 2019, 21:38

No need to change ECU for the 15hk restrictor. Only if you want to upgrade to 20hk you will need ECU aswell or engine damage may occour.
Engine will still have the 5700rpm limit though.

Have 100 hours on my engine now, and plugs are looking fine. No wear and grey in colour.

Lean burn? Why wouldn't it?

Just had a 40Km trip (one way) and was travellig at about 5300rpm all the way. Used a little over 6 litres litres one way

Bikegod66 · 09 August 2019, 21:49

Thanks sir robin !

The change to the 15 hp restrictor would probably be a significant boost im guessing. My engine is brand spanking new. 2.7 hrs logged.

It is certainly way less expensive to just do the airbox restrictor.

Thanks

Sir.Robin · 09 August 2019, 21:55

np

That would be correct. The noticeable change of power was larger than i anticipated.

Se my other answers with the different props and loads!

Zuki9er · 11 September 2022, 14:33

Sir. Robin, just wondering how is your motor running after all this time? Any noticeable side affects from not changing the ECU ?

Sir.Robin · 11 September 2022, 18:28

Nope, it runs just as before.

5 years this summer. and pretty precisely 120 hours on it.

Limecc · 11 September 2022, 20:01

Quote:

Originally Posted by Zuki9er

Sir. Robin, just wondering how is your motor running after all this time? Any noticeable side affects from not changing the ECU ?

Martin at West Wales Tuning can clone a DF20 ecu, no need to buy a new one. Contact him for pricing, it will be cheaper. Could optionally have a remap at the same time? Perhaps to 25hp? Can personally recommend!
suzuki-outboard-remapping

Zuki9er · 05 July 2023, 16:31

Quote:

Originally Posted by Sir.Robin

Nope, it runs just as before.

5 years this summer. and pretty precisely 120 hours on it.

How many hours now? Everything still A ok?