outboard modification

[andyc]

I have a current model Suzuki 4 hp 4 stroke outboard, I got with a dingy package and it wont plane the dingy with 4 people.
I dont suppose anyone knows how to modify the engine so it is more powerful.I know there are a 5hp and possibly a 6hp modal that look identical.
Is it a carb jets mod or any ideas?????

 

[LadyInBed]

Hard to mod the O/B
Try getting the four people to loose weight!

 

[tobble]

I think I might have read somewhere that those engines are all based on the same block, presumeably machined out as appropriate to create the different bores/strokes etc. So short of stripping it down, boring out bigger, getting new cylinder heads, con rods, etc etc...

On the other hand I may have dreamt that and someone will come along and tell us otherwise!

 

[dsw]

change the prop might help .

 

[VicS]

It is true that the 4, 5 & 6 hp models are all based on the same 138cc single cylinder engine. They have the same gear ratios and fit the same range (6" - 7" pitch ) props, however the power is produced at different rpm ranges.

They may have the same carbs differently jetted, or have different carbs. They may merely have a restrictor plate between carb and engine. The porting may be different so may be the camshaft profiles. There may be differences in the ignition systems to allow the higher rpm ranges in the higher power ones. You will have to look into all these matters in detail in order to determine if it is reasonable to uprate a 4hp. If its only a question of removing a restrictor plate and/or changing a carb jet the uprating may be feasible otherwise it is not likely to be worth it.

You do not say what dinghy you have but I notice that only the 2.3 and 2,7 metre models are offered with a 4 hp engine and they only have a maximum capacity of 2 & 3 persons respectively. The 2.9 metre version has a capacity of 4 persons, however, and that is offered with 5, 6 or 9.9hp engines. That has an aluminium floor as opposed to an air cushion floor.

Clearly if you want to carry 4 persons you need at least the 2.9m dinghy and I would think the 9.9 hp engine to plane with only 2 persons on board. If you want it to plane with 4 persons on board you will, I suspect need an even larger dinghy and a much more powerful engine. Curiously Suzuki do not seem to specify a maximum engine size for their dinghies though!

 

[graham]

I had one of these .To increase the revs/hp Order the throttle restrictor plate for the relevant horsepower as a replacement part.

Its the only difference.

Its an L shaped piece of stainless steel that is longer for the 4 than the 6.

To locate it take the cover off,operate the throttle watch for the throttle arm moving on the carb ,the metal plate it hits at full throttle is held on with a bolt.Yours will have a 4 stamped on it you need one with a 6 stamped on it.

My son pointing it out with a bit of metal rod.

 

[VicS]

[ QUOTE ]
Its the only difference.

[/ QUOTE ] Thats sorted that then . Not what i meant by restrictor plate just a limiter. Sounds as though all one needs to do is file the plate down until it allows the throttle valve to open fully. However 6hp is not going to get a dinghy with 4 on board to plane is it?

 

[graham]

You couldnt file it down as its bent up at the end to provide a surface for the throttle arm to come against. You could cut and weld it if you knew the exact length it had to be. Replacement part is about £15.

Wether it achieves the performance he is looking for is doubtfull but he will get a third more horsepower for 5 minutes work.

 

[jwilson]

Fascinating - even more interesting is the several hundred pounds RRP difference between the 4 and 6 on Suzuki's price list !

 

[andyc]

Thanks for the help chaps.

 

[Clyde_Wanderer]

What size dingy is it?
Why do you want to plane a dingy with 4 people in it anyway, are you not setisfied with just getting from a to b without having to rip the sh*t out of things? or is that a stupid question to a mobo? /forums/images/graemlins/laugh.gif

 

[Clyde_Wanderer]

[ QUOTE ]
I had one of these .To increase the revs/hp Order the throttle restrictor plate for the relevant horsepower as a replacement part.

Its the only difference.

Its an L shaped piece of stainless steel that is longer for the 4 than the 6.

To locate it take the cover off,operate the throttle watch for the throttle arm moving on the carb ,the metal plate it hits at full throttle is held on with a bolt.Yours will have a 4 stamped on it you need one with a 6 stamped on it.

My son pointing it out with a bit of metal rod.

[/ QUOTE ]
Can he not just remove it allowing him to do 80kts with 8 people on board and make his dingy fly? /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

 

[andyc]

Now we are talking,If I wanted to go slow I would row.
I dont need it to get 100yds to me boat, I need it to do a few miles 4up quick as pos, on one tank,besides,flat out at displacement uses a s load of fuel..so much so that we keep ran out and had to row 3 miles back against tide which is imposible..At planning speed it is economocal and less painful.