Yamaha 2003 F 90 - low RPMs

[Kanadakid]

Rod / JB others,<br /><br />My 2003 F90 / 65 jet max RPm is 4900 maybe 5000.<br />Took it back to the dealer who ran it and said it was running fine. The manual says it should get up to 6000 RPMs.<br /><br />I puching about 2000 lbs boat and gear. Dealer said he was goinf to get me a different impeller<br />( Jet no prop).<br /><br />WOT speed about 33 mph on speed stick. The engine sounds fine.<br /><br />Just for info....do you think it is OK to run these 4 strokes at WOT while running. Do you think they will last years provided I change oil <br />(Mobile 1) every 25 hours or so.<br /><br />#3......manual reccomends valve adjustments at 2 years ??? How expensive is that. I'd prefer not to do it because I don't want to have the engine cracked open and monkey'ed around with.<br /><br />Value your honest opinions.<br /><br />Thanks<br /><br />Kid

 

[bigbrownbuku]

Re: Yamaha 2003 F 90 - low RPMs

there is a clearance, impellor to housing spec, try moving washers "up"(bottom of impellor to top) to play with wot rpm otherwise the impellor is wrong/gimped. no motor will last forever, for longest life run the engine at "cruising" about 3/4 wot max. the valve adjustment on that engine is very simple and requires removing only a few minor external parts and the valve cover. the cover gasket is reusable and the valve to cam clearance easy to check. all the valces i have checked since the advent of 4strokes i have only come across 1 or 2 that required adjustment.

 

[rodbolt]

Re: Yamaha 2003 F 90 - low RPMs

I am with BenC<br /> check the impeller to wear ring and maybe try a smaller impeller. but if you run it at max it wont last as long as 3/4 throttle. however even at 5k it will last a long time. its amazing. but do check the valves. its easy to check and the gasket is reusable. but you do want an impeller that will allow it to turn 6 k or slightly above with a medium load. they dont like lugging.

 

[Kanadakid]

Re: Yamaha 2003 F 90 - low RPMs

Ben / Rod,<br /><br />Thanks for the advice. its nice having you guys on here to help. Ben what does Gimped mean? The engine was bought last Feb 2004 , it was a 2003 leftover. <br /><br /> It doesn't have to many hours on it. The impeller is very tight, just a hair between impeller and ring.<br /><br />How many hours do you think F 90 4 stroke can reasonably expect ? I am a stickler for changing my oil.<br /><br />Are you guys technicians ? <br /><br />Thanks Again,<br /><br />Kid

 

[bigbrownbuku]

Re: Yamaha 2003 F 90 - low RPMs

hours im not sure. gimped means "perhaps the wrong one" loosely....<br />yeah a tech.<br />if it was new in 04 you still have a few years left. as with any outboard lack of use is your enemy. a 25 hour service interval might help with that however.

 

[rodbolt]

Re: Yamaha 2003 F 90 - low RPMs

I have been accused of worse myself.<br /> follow the service guide. always remember the block at the top states hours OR montly,semi annually, yearly etc etc. follow the guide, do the maint on the jet. it requires maint as well. periodically check the wear ring clearence.<br /> if you try to adjust the engine speed by dinking with the washers your screwing up. the "washers" are actually shims that seat the impeller higher or lower in the wear ring, that is how you maintain the correct impeller to ring clearence. by moving the impeller up on the shaft your increasing the clearence therby inducing a cavitation. hard on engine cooling systems and hard on impellers. best to use the correct impeller at the correct clearences. it can also lead to uncontrollable cavitation at speeds.

 

[Kanadakid]

Re: Yamaha 2003 F 90 - low RPMs

Rod,<br /><br />The impeller clearance is good so I left it alone as it is within spec. Where are the hours stated ? Somewhere on the top of the block ? <br /><br />Do you think the low RPMs is the result of the impeller or the engine itself. <br /><br />The dealer said it is just the way the engine runs on this rig. They checked everything else <br />and said it is set correctly.<br /><br />He did order a new 7 3/16 impeller for me to try. Said that would give me an extra 300 to 400 RPM.<br /><br />Holeshot will probably be slower with this but top end will add 3 -4 mpg ?<br /><br />Rod / Ben, nice having you guys on here. If you get to NJ or eastern Pa. please let me know. Owe you a nice steak.<br /><br />Thanks,<br /><br /><br />Kid

 

[rodbolt]

Re: Yamaha 2003 F 90 - low RPMs

hello<br /> the impeller loads the engine just like a prop. lower pitch = more RPM due to less water moved. your hole shot may improve. I was not talking about engine hours. I was refering to the service intravel. its broken into hours OR dates whichever occurs first. the 25 hours oil change, while it wont hurt, is a waste of money. just be aware that as the impeller wears RPM will increase. thrust will decrease by a proportional amount until the wear becomes excessive.