Yamaha Carburetor Swap

[boscoe99]

Someone probably paid 100's more for the F50 not knowing this. If it ever quits raining I am going to bolt these on and try it.

They do it all of the time with the Offshore models. Buy the F300XCA. For the decals. Then run the motor on 87 octane gasoline such that the motor more than likely won't be able to produce 300 HP. But they can tell their buddies about how big their johnson is.

[ChuckB1954]

They do it all of the time with the Offshore models. Buy the F300XCA. For the decals. Then run the motor on 87 octane gasoline such that the motor more than likely won't be able to produce 300 HP. But they can tell their buddies about how big their johnson is.

Thanks for all the help. Got 'em mounted.. won't be long!

[ChuckB1954]

Got it running.. Doesn't idle properly. The linkage is not working right. I didn't realize by bending the tab to let the throttle go full open, that same bent tab would affect the idling when it makes contact with a roller when the throttle is fully closed! . I am pulling the carbs back off, removing the #4 and installing the butterfly and shaft from my old carb. What was I thinking? I could have saved myself a lot of work. Would have taken me 15 minutes had I known.


From my old carb:
20190817_204816small.JPG

I bought the flywheel cover that was missing and also the idle diaphragm:

20190817_171249small.JPG
20190817_171244small.JPG

A crying shame to have to take this apart again! Lesson learned.

20190817_171329small.JPG

[99yam40]

do not let the motor eat the screws holding the throttle plate to the shaft

[zenoahphobic]

Got it running.. Doesn't idle properly. The linkage is not working right. I didn't realize by bending the tab to let the throttle go full open, that same bent tab would affect the idling when it makes contact with a roller when the throttle is fully closed! . I am pulling the carbs back off, removing the #4 and installing the butterfly and shaft from my old carb. What was I thinking? I could have saved myself a lot of work. Would have taken me 15 minutes had I known.


From my old carb:
20190817_204816small.JPG

I bought the flywheel cover that was missing and also the idle diaphragm:

20190817_171249small.JPG
20190817_171244small.JPG

A crying shame to have to take this apart again! Lesson learned.

20190817_171329small.JPG

Ofcourse Yamaha don't want it to be too easy to change from one horsepower to another!

This "provision of a range of horsepowers" was driven by the limitation or maximum horsepower rating that boat builders had to put on their hulls. And presumably consumers liked their boats to be categorised, with insurance premiums varying accordingly.

It used to be that engines went up "linearly" between Hp and weight, and therefore often physically it didn't work to add a bigger motor. That is, the stern of the boat not only needed to be stronger but needed more buoyancy; an overpowered boat was obvious by its attitude in the water.

But these days engines are far more lighter per Hp, and boats are more accomodating in stern buoyancy.

I often wonder how this categorisation by Hp came about, as cars and motorcycles were/are categorised by capacity. Aspecially as a large increase in Hp often only returned a small increase in speed.

[zenoahphobic]

do not let the motor eat the screws holding the throttle plate to the shaft

Good point. Perhaps they may be pressed or deformed to stay in place, so removal may damage the thread. In any case Loctite essential.

[ChuckB1954]

Good point. Perhaps they may be pressed or deformed to stay in place, so removal may damage the thread. In any case Loctite essential.

The screws came out and threaded in clean.. I used brake cleaner and a very slight amount of red Loctite on the tip of a tooth pick.

[almetelo]

as posted before the only diference beside the stickers is the throttle linkage (about 2cm shorter on the F40) not allowing the butterfly to completely open
Can post pics of both linkages later if you want.
The F45 (not sold in US) had diferent carbs and diferent CDI with retard ignition timing (the only 2 diferences on the F45 to F50)

I have a F60AET 69W and the only diference to the F40C 6K0 (not sold in US) is also the throttle linkage

On similar motors most of the time the small HP motor is a detune from the high HP motor EX: F80 is a detune of F100, F50efi is a detune of F60efi etc etc

[ChuckB1954]

Went outside last night and while battling the rain and mosquitoes I pulled the carb asy off. I took it in my garage, loosened the top three carbs and took the bolts out of #4 and slid it out. The shaft/linkage was fairly easy to remove and reinstall. Spring tension is critical. I had it back together in 15 minutes.. quite proud of myself. I was carrying it back in the house to match it with pictures on my computer to make sure I had the linkages right.. Then I realized.. Damn! I had removed the 40HP parts and then reinstalled the same parts!! Started the process over and soon it was back together with the right parts. The wife wasn't too pleased when I brought it in the house to verify the linkages. 3AM.. stopped for the night, leaving it on the front porch.

This morning after checking/adjusting the valves I got everything together. Runs good, but I still have some adjustments to make. Had to stop.. got rained out again. Can't wait to finish and try it out!

The little slide locks for the throttle linkage still needs to be installed. I am going to ty wrap them then apply heat to reshape so they fit tighter


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[99yam40]

we have lucked out on the skeeters so far this year, but I know that will not hold up when a storm heads this way with high tides and rain