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DF300 RPM Question

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Ronyon

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"When I first got my boat with

"When I first got my boat with a single Suzuki DF300, I was able to get 6100 RPM at WOT. When I took it out on Sunday, I could only get to 5400 RPM. Suzuki states that the engine should get between 5700 and 6300 RPM. I would say that it is a prop issue, but it did get 6100 RPM with the same prop when I first got it. The engine runs perfectly, starts right up and idles nicely with no sign of a problem. I have pulled the prop off and inspected the propeller and shaft and all looks good. I did get some fishing line wrapped around the prop on Sunday. I removed most of it in the water and I removed about 8 inches of line wrapped around the inner hub when I removed the prop.

What could cause it to change like this? Any help is greatly appreciated. Could this small amount of fishing line cause the RPM slowdown?"
 
"Not sure what boat you're

"Not sure what boat you're running, but how was it loaded when it turned the high rpm? (fuel, people, gear etc.) Sounds like it was pretty light....Thennnn you filled up with gas/gear.

Is the throttle cable still pulling all the way open?

((Assuming it was yourself driving the first time and you're trimming it out the same as before))

Typically. the engine should "loosen up" after break-in for +100rpm or so.

G"
 
"Ok I tried trimming it out as

"Ok I tried trimming it out as suggested in the previous post and i was able to coax it up to 5600 RPM.This is still below the 5700-6300 recommended and way below what it was getting before at 6100 RPM.

I generally keep the boat about half full of gasoline between 80-90 gallons and it is just me and the family usually. The last time I took it out it was just me and one other person so the load would have been a little lighter overall. The DF300 has electronic shift and has no cables that would cause a problem.

I called the dealer and he suggested trimming it out too, but aside from that, he could not readily explain the drop in RPM. This boat used to get up to 50 MPH with no trimming, now I have to trim it way up just to get to 40 MPH. I fear that this more than a trim/weight issue.

Any suggestions before I take it back to the dealer for inspection?"
 
"One of my df250s on a cat has

"One of my df250s on a cat has just dropped 300rpm on a dry stored boat.55hrs.I am thinking firstly fuel related and will take the easy way out with some fuel injection cleaner and fuel conditioner ,While im out i will probably check the plugs to make sure they have a constant reading ,maybe a good place for you to start."
 
"I went to the dealer to buy S

"I went to the dealer to buy Suzuki fuel conditioner nope,hope about seafoam nope ,Ended up at another shop and buying Starbrite :Startron:added the stuff and enough tools for a full rebuild and went out for arun,Idled away then cruised between 3000-4000rpms for 1 hr ,Then did flat out runs both up and down the river 6100rpm both motors all good.4 strokes are hard to diagnose from the desk and relatively new to the marine industry ,IMO fuel condition in your 4 stroke weather 5hp or 300hp will be the no 1 factor in it performance ,these motors cant be left unloved like a 2 stroke.keep us informed of your progress with your 300
happy.gif
"
 
"J-I-T ,

I wish i could say

"J-I-T ,

I wish i could say i did ,just added the stuff even read the instructions and followed them.I was a bit surprised as im not usually a fan of fix it in a bottle .Im not a Starbrite shareholder ,im a semi retired ,ex boat racer and performance engine builder."
 
"Its doing my head in a bit ,s

"Its doing my head in a bit ,so going out to test again in a day or so ,and will post the results.
I swapped to suzuki 4 stroke because of 5 warranty , and you wouldnt believe how many Mercs i have blown up over the years."
 
"Still good ,did 2 hours today

"Still good ,did 2 hours today ,took enough snap on tools to crew a nascar pit ,absolutely not a cough or splutter and gave it plenty of 6000rpm time.So i pull in to my dock and see my kids towing the neighbours tender with a 6hp 4 stroke "Hey dog can you have a quick look at my motor"Dog is me,After some tinkering i get it to run on the choke, tip the rest of my Starbrite into the tank 20 minutes later ,one happy camper .I sort of get roped into being Mr Fixit where we live ,putting $100k of snap on,on ebay as i am now fix it in a bottle LOL."
 
Update: Boat is in the shop be

Update: Boat is in the shop being checked out. They told me today that they were having some trouble synching up to the Suzuki software program. I will have to wait until Wednesday to see what they find. The mechanic did state that he thinks it may be an electronic adjustment.

Could still be anything at this point. Be back Wednesday.
 
"Got the boat back yesterday f

"Got the boat back yesterday from repair shop. They stated that they were able to get it to connect to the Suzuki software and they made some electronic adjustments. Exact words were " we told the computer to open the throttle all the way at WOT." They also told me that they did not see anything obviously wrong with the engine.

I am now supposed to test the engine to see if the fix worked. I will try to test it this weekend and post the results.

Having never seen the Suzuki computer interface software, I wonder if what the mechanic told me is true. Is it possible to see all of this information and tell the engine to go WOT electronically? I know these are actuators that are controlled electronically, so it sounds possible. I guess I am just skeptical right now."
 
"Ok would love to test boat/en

"Ok would love to test boat/engine, but the wind just keeps blowing on the East Coast.

Maybe Sunday!"
 
"I tested the boat this weeken

"I tested the boat this weekend and I am still unable to achieve over 5400 RPM at WOT. When I trim it up I can get the motor to go higher, but max was 5750 at 50% trimmed. At this point I am thinking it must be fuel related. Should I try the Startron product quoted above? Is there any potential harm in trying it? I will call the service guy this morning and let him know the results too."
 
"Another Update: I changed the

"Another Update: I changed the fuel filter and the water separator this past weekend. The fuel filter (engine) had what looked like foam around the bottom edges. I also emptied the contents of the old water separator into a clear bottle so I could see what the gas looked like. Once the gas settled, I could see some small black particles and a clear sludge/slime in the bottom of the bottle. There was not very much of it, but it was noticeable.

I wonder if this is a result of the gas I have been using? I usually go to the same station to get gas and they have signs up stating that there is 10% ethanol in their gas.

I am going to put the Startron additive in to counter this possibility and hope that it works. The foam like coating on the bottom of the filter concerns me. Any thoughts? Anyone else see this type of thing with a filter?"
 
"Another Update: Have changed

"Another Update: Have changed the engine fuel filter and the fuel/water separator and I added a 16 ounce bottle of Startron fuel additive to just under 100 gallons of gas. Ran the boat all day Sunday for over 6 hours and I see no change in the engine RPM. Perhaps it is a prop issue and I only dreamed about the 6100 RPM I thought I got initially??? At 5500 RPM the boat runs a solid 40MPH, If I start trimming I can get it up to 47ish at 5750 RPM. If it is a prop issue, is that a dealer issue or is this something I will have to pay more for? I would think if the boat is not propped right, the dealer would address it as it is only six months old.
I guess I shouldn't worry about it so much and I am tired of spending money on it. I think I will just fish the rest of Striper season and enjoy the boat for now. If any major revelations pop up, I will update again."
 
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