2000 f25 elry problem

[bradwsm1]

Hello all. New here with a question on a 2000 yamaha f25. I will try to give all the info i can to see if we can solve this riddle. I have a 14' 1958 lone star Malibu with the f25 on it. the boat is very light, 300 lbs give or take. the motor runs great, starts easily, gets on plane quickly but has zero top end. with a 10p solas aluminum prop the best i can turn is 20mph at 4800 rpm. I went as far as to buy a yamaha 8p prop wich netted 15mph at 5200 rpm. so here is all the info, i have installed new (correct spec and gap) spark plugs, fresh oil and filter+ lower oil, checked valve lash, had the timing checked and the carb cleaned with new feul filter. checked that the linkage was set up correctly and achieves full throttle. Still no change in performance. The carb has the correct main jet #112 and the spark plugs look normal. Compression test showed 210 psi even. I only run non ethanol fuel with a little seafoam. the motor is mounted at the correct height ( cav plate abot .25 in above boat bottom). I originaly put the motor on my 1957 12' crestliner ( runs 22mph at 5500rpm) with a 2003 15 hp 4 stroke mercury with a 9x 10p prop. With the f25 it ran 22mph at 4500 rpm with a 13p prop and 4800 with the 10p. I just assumed it was the added weight that was responsible for the lack of performance. After I installed it on the 14' and had the same resaults i can only conclude there is a issue. Performance resaults from other boats running the same motor seems to back that up. Any thoughts at all would be great.

[TownsendsFJR1300]

You would like to get to 6,000RPM's WOT, with that engine, fully loaded.

Sounds like you may be over propped just a bit..

[rodbolt17]

do yourself a favor.
find a dealership with test wheel YB-1621.

put it on, back it down the ramp.
spin it up.
if it wont turn 4200-4400 with yb-1621. fix the engine issue.

if it will spin the test wheel fix the hull/propping issue.

yep its that simple.

[bradwsm1]

Thanks for the info. It is at a certified yamaha repair shop now. I will find out if they have the tool.

[rodbolt17]

trust me, that test wheel is a wonderful tool.

it quickly seperates hull/rigging issues from engine issues by providing a known load and a specified RPM for that load from the Yamaha engineering dept.

and it can be used for troubleshooting under a known load.

[bradwsm1]

Couldn't find anyone with the test wheel. So got the boat back, they said that it was running lean. I am not sure why, and since there are no mixture screws for adjusting the carb I am not sure what they could have done. But now the motor runs worse! At the last bit to get to wot it bogs and the spark plugs are looking dark, not wet, just flat dark brown. At least they didn't charge me anything.

[TownsendsFJR1300]

When was the last time the carb(s) were checked /cleaned?

I would at least drain them, catch what comes out in a clean small container. Look for water, debris, etc. It should smell fresh.

If the engine sat for awhile, especially without fuel stabilizer, that would make it worse...

You still have main and idle jets as you noted. If the engine ran good for years, it likley does NOT need re-jetting.

Logically, if its running lean now, tells me the carbs have crap in them... You must be able to see light thru the jets. Just blowing air does NOT count. Some of the orifices are extremly small..

[bradwsm1]

They actualy cleaned the carb! I saw it apart. They said they took care of it running lean. And it was cleaned two weeks before by another local shop, chasing the same problem. Ran the same the first go around, this time it is worse. Spark plugs say it's rich now.

[99yam40]

maybe you have a bunch of junk in tank, lines, and pump that keeps hitting the cleaned carbs if they were cleaned properly

[bradwsm1]

That's what is so frustrating, tank, primer and lines are brand new, replaced the under cowl fuel lines, as well.

[TownsendsFJR1300]

Well, if they haven't, as noted above, remove the drain plugs in the carb's and pump the primer. Catch the fuel in a CLEAN container. Keep going until fuel comes out clean.

I have, on my own boat, had ethonol eat the inside of 3/8" fuel line (marine grade) and the under cowl filter caught it. It was the short piece between the transom filter and the under cowl line that failed.

If you have small spec's of fuel line (broke down) in the system clogging up the system, you'll be chasing your tail....

I gather you've never been on a carb or comfy tackling one?