2003 Yamaha 90 hp - low rpm's at WOT

[rduin]

I have a 2003 Yamaha 90 Hp engine with 72 hrs on it and I'm having problems with low rpm's at Wide Open Throttle. I'm only getting 3800 rpm's and reaching 31.7 mph fully trimmed. The owner's manual indicates that the engine should be running between 4500- 5500 rpm's at WOT and running in the mid 40's mph. I did take it in to the dealer and they field tested the boat and also checked the engine and they are baffled. They are not able to locate/correct the problem. Im running a powertech stainless three blade prop (19in pitch) - I thought it might be a prop issue but the dealer tells me it's not. Any suggestions/recommendations would be appreciated.

 

[rodbolt]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

hello<br /> something does not sound right.<br /> where in the owners manual does it state the engine speed and hull speed?<br />when did this problem start? if in fact you took it to a dealer and they are now baffeled you really need to find a better dealer. they make test wheels. use it. it will tell you instantly whether you have a hull/prop issue or a motor issue.<br /> good luck and keep posting

 

[rduin]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

Thanks for the reply. In the manual under "specifications" it states that at Full throttle operating range- the engine needs to be at 4500- 5500r/min. I have a Blue Wave 18 c special and under their performace bulletin a 2003 90 hp ( Johnson) engine should reach the same rpm's as the Yamaha and the top speed be in the the upper 40's. I'm assuming that these engines are comparable in performance. My dealer checked the engine and found no problems. As a matter of fact it will there a week tomorrrow(4/29). I will call and ask for a full report. Could the mounting height on the transom be incorrect? Could this be something that would affect rpm's on the engine due to resistance? Any other ideas would be appreciated. Thanks again.

 

[rodbolt]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

hello<br /> dude<br /> I will tell you once more<br /> TEST WHEEL<br /> you must insure the motor is capeable of making power. use a known good inductive tach as well.<br /> this is where I see to many dealers screw it all up. the best place for the shiney boat spec page is in the trash can<br /> its a sales tool and not a service tool.<br /> you must isolate it from hull to engine.<br /> if the engine will spin the test wheel part #YB1620 to 5100-5300 the motor is doing all it is designed. if it wont you have to correct the motor problems before continuing.<br /> if you cant use the test wheel you cant do this correctly. a 19 pitch on a 90 may or may not be to much on an 18ft boat. but first you must test the engine under load with a test wheel or a dyno to insure its capeable of doing what it was designed to do.<br /> good luck and keep posting

 

[rduin]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

Thanks for the reply dude. A Test wheel/dyno is something that my dealer's service shop should have correct? I will bring this up to them and see if this diagnostics has been done. Seperating the engine from hull is something that I will be bringing up as well. I'm not a mechanic and releatively new to power boating, but learning quickly about the dynamics of it all. Appreciate the suggestions.

 

[rodbolt]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

hello<br /> yes the dealer should have a test wheel at a minimum. if the engine can spin the yamaha test wheel at the proper RPM then you know its a hull/prop problem. if it cant, the engine must be repaired until it will. its very simple but it seems to blast past a lot of dealers.<br /> good luck and try not to have to pay to much for your education as well as a techs

 

[rduin]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

Thanks rodbolt- I will contact the service techs and make sure that this test is done. Is a Dynamometer the same as a wheel? I will post report when I know more.

 

[rduin]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

Well as it turns out the engine checked fine- Dyno test included. Thanks for the tip. The problem was with the prop. The 19 in lugged the engine. After several water test with a 17 and a 15, - the 15 in. brought the rpm's to correct level and speed. This disccovery made me feel much better. Thanks for the suggestions and recommendations. This past week I learned much about engines and diagnostics.

 

[Jake Little]

Re: 2003 Yamaha 90 hp - low rpm's at WOT

When I bought my 2003 Yamaha 90 horse 4 stroke I couldn't get it to go over 3500 RPM's by the tach in the boat. When they disconnected the tach in the boat and connected it to another tach, it worked fine. Once they calibrated the tach in the boat it still didn't work. Then they found there was 2 calibration screws for the boat tach. Works great now.