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  Fuel filter & prop pitch change

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Author Topic:   Fuel filter & prop pitch change
mustang7nh posted 07-10-2004 10:00 AM ET (US)   Profile for mustang7nh   Send Email to mustang7nh  
How often should one change the fuel filter in that clear bowl under the cowling? 1995 Yam 250 carb. Thanks

Also, would this ever increase your WOT rpm if you were not getting enough flow (although it runs smooth without a hiccup at all rpms currently)?

I'm only getting 5000-5100 on my 1991 Outrage 22 with the engine trimmed up high, mounted up on third hole, and just me on board. Runs smooth, turning a 19 Stilletto pitch. I would just think that it should be able to spin that on this rig without a problem to a higher rpm.

What performance changes do you get if you drop pitch but increase rpm? mpg, cruise or wot speed?

jimh posted 07-10-2004 11:02 AM ET (US)     Profile for jimh  Send Email to jimh     
Fuel filter elements should be replaced when the filter becomes clogged.

If a fuel system restriction was limiting the amount of fuel available at wide open throttle (WOT), this could limit your engine speed.

It is hard to predict how changes in propeller pitch will affect things like boat speed and engine fuel economy without testing. It is generally accepted that as propeller pitch is decreased, engine speed at WOT will increase. Whether this will also cause a boat speed increase is difficult or impossible to predict.

In order to assess fuel economy, a real-time fuel flow measurement is needed.

Sal DiMercurio posted 07-10-2004 06:50 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Mustang, that 250 should twist that 19p prop close to 5800 rpms.
5000 rpms is UN-acceptable.
You may not be getting full throttle because of sinc & link.
Do you by any chance have plates on the boat?
If your running with the engine trimmed up & the plates in the down position, your defeating the pupose of tilt & trim.
If in fact you do have plates, put them in the up position & then trim the engine out.
If you don't see at least 5700 - 5800 rpms, better have the engine checked out.
Sal
mustang7nh posted 07-11-2004 09:00 AM ET (US)     Profile for mustang7nh  Send Email to mustang7nh     
Sal-
The trim tabs are new, but the 5000-5100 is both pre and post tabs. WOT runs are with tabs retracted and engine trimmed up. I got 5200 with no bottom paint and 48mph per handheld gps. I've wrestled with this because one would think that with a 250 it would fly. Not that 46-47 is slow, but I've heard of others with 225s getting 51. But the engine runs very smooth and doesn't seem to be giving any indication that it is malfunctioning at all. Your suggestion of the sync-link is a good one and I'll have it checked out when I get a chance. Are tachs every wrong? Its the Yam digital tach that came with the engine.
Sal DiMercurio posted 07-11-2004 10:28 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Is that the 3rd hole down from the top, or 3rd hole up from the bottom of the bracket?
If it's the 3rd down from the top, something is definitly wrong with your setup.
Sal
mustang7nh posted 07-11-2004 11:44 AM ET (US)     Profile for mustang7nh  Send Email to mustang7nh     
Third hole down from the top, as in it is mounting higher than lower.
Peter posted 07-11-2004 06:15 PM ET (US)     Profile for Peter  Send Email to Peter     
Sal - Redline on a Yamaha 250 is 5500 RPM and it twists the propeller through slightly lower 1.81:1 gears. 48 MPH at 5000 to 5100 RPM with a 19 inch propeller indicates to me a 9 year old Yamaha 250 that is working properly.

Mustang - Having had a Revenge with a 225, I am of the opinion that reports of 51 MPH with a 225 are overly optimistic. Given that it is a 9 year old motor, you might consider dropping down to a 17P propeller which would put you right at 5500 RPM. Otherwise, I wouldn't touch anything.

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