2004 115hp Suzuki 4 stroke

[jimmy.hardy@ymail.com]

Motor runs great at 90% throttle, very, but when I go full throttle it starts stalling out. (bogging) So I back off and it runs fine. New fuel line, filter, fuel pump. Pleases help.

[Harper]

90% throttle? What RPM at that "90%"?

[jimmy.hardy@ymail.com]

5700 rpm's give or take. When it hits 6000 it starts bogging. To be clear, it runs strong @5700 rpms but as soon as it hits 6000 is when it starts bogging.

[Moonlighter]

Jimmy, it always helps if you give 100% maximum info and all recent history when asking for assistance. So the more you can tell us, the better....

So, is this a new problem?

Would it previously run at 6000 with no issues?

Was anything at all done or changed immediately before this problem happened?

Has the tacho been reliable to date? Ie are you sure it isnt just hitting the rev limiter?

Is the fuel fresh?

Do you run a water separating fuel filter in the main fuel line? If so, any signs of water in fuel?

Was there any trash or water in the filters youve already changed? Have you done anything else to try to fix the problem?

Let us know.

[jimmy.hardy@ymail.com]

Boat sat for two years before I purched it. I cleaned out the fuel tank, replaced all the fuel lines replaced the Fuel vapor separator, fuel pump and new gaskets, plugs and plugs. The rev limiter was broken so I replaced it. Motor started with no issues but this promblem presists! It does act as if it is trying to go into limp mode but the switch is disingauged when it's in gear. It acts as if it's starving for fuel. No sign of water in fuel. Thanks for the advise!!!

[Moonlighter]

It sounds very much like it is hitting the rev limiter to me. I think that they normally kick in at about 6400rpm, spark and fuel are cut when limiter cuts in as you probably know.

The tach may be under-reading the revs, its not unheard of for that to be the case.

I have never messed with the rev limiter?? I am pretty sure it is built into the ecu, rather than a separate part?? Can you check the parts list for your motor in the "purchase Suzuki parts" section at top of this forum and advise which part you replaced? Sure it wasnt something else like the neutral throttle switch??

Heres a link to the parts page for your motor:
http://www.boats.net/parts/search/Su...115/parts.html

Is there any way you can verify by a separate tach as to the rpm's actually being achieved?

Another option is if you can find a Suzuki dealer nearby with the Suzuki SDS diagnostic system, they will be able to connect it up, and any over-revs will show up on the engine readout report, and this would verify that its hitting the limiter.

Any details on the boat its on? Size, weight etc, and the prop size? Could be under-propped?

Report back when able.

[jimmy.hardy@ymail.com]

So what your saying is that the rev limiter is doing it's job? My tac could just be off by a few digits? It starts boggin, like I said at 6000 rpms. (Give or take) so i could adjust my throttle box to stop at that point? Because it runs beautiful just short of 6000 and a speed of around 42 to 45 mph for hours.

[Nayna32]

It is definately a possibility. I run both a Suzuki Tach /Monitor and a C10 color gauge. At WOT the tach is reading 5900-6000 rpm, and the digital C10 reads 6300-6400 rpm.

[Moonlighter]

Yes, it could easily just be the rev limiter doing its job.

See the previous reply from Nanya, who explained how much his analogue tach is out compared to the true data from the ecu which is showing on his digital gauge.

If you are indeed hitting the rev limiter quite easily, then it would mean that you are "under-propped". Meaning that your current propellor hasnt got enough pitch. The engine is thus not performing to optimum.

You dont fix over-revving by adjusting the throttle box - you fix it by changing propellors to one that is more suitable!

I guess what we dont know is how the previous owner used the boat - if he was always carrying a very heavy load, then possibly he ran a lower pitch prop so the engine still reached its optimum rev range - or, he may have changed the prop to an old cheap one before selling the boat for some reason - we just dont know.

Thats why I asked about your boat (model length, weight etc) and what your current prop size is - its diameter and pitch. It should be stamped on the hub - likely on the inside, so you will probably have to remove the prop to see it, but check the outside first. Also tell us if the prop is stainless steel or alloy.

Normally a 115 would run a 14" diameter prop.

One thing I would say is that since you just said your boat speed currently is 42-45mph, i am theorising that your boat is quite light, maybe only 16-17ft long, and easily pushed - that is pretty fast for a 115hp motor! Is that GPS speed??

If they have always just run a standard sized prop (say a 20" pitch) then it would not be surprising to find that such a light easily pushed boat is under-propped.

So give us all known boat details so we know a bit more.

Also check to see if you can find anything that identifies the prop maker too - if its a Suzuki or some after-market brand, that would help.

Once we have that info we will have more info to help gauge if the engine is likey to be truly over-revving, or not.

FYI, the rule of thumb is that every extra inch of pitch in the prop will reduce revs by 150-200rpm - assuming that the same make, model and diameter prop is used.

Report back with that info and we will see where we go from there.

[jimmy.hardy@ymail.com]

Locking it up on line, my Carolina Skiff weights 950 lbs. The prop is a 3x14x19. fyi

[Moonlighter]

Yes, with a very light boat like that, in all probability you are under-propped.

What length?

You could try the next size up, 14 x 21", that would take about 300-400revs out of it, should be below rev limiter and give you some more top end speed.

[jimmy.hardy@ymail.com]

19' V Series 950 lb's. Aluminum aftermarket prop.