yamaha 40heo 6h4

[imajin14]

1st test in water
hey guys just purcahsed my first boat, its awesome and it has a old 2 stroke 40hp yammi starts first go idles fine but when im in full throttle the power fluctuates every like every 2 seconds not drastically but its noticeable in noise and feel when in the boat...i noticed that one of the fuel lines on the 3rd carb had a slight fuel leak (slow drip) from the hose could this cause that problem?(replacing all fuel lines real soon)....I need help on adjusting the timing and the carbs but i have no clue on where to begin if someone could help me with some info that would be great

2nd test
replaced all fuel lines... started first turn of the key and then died after 15 seconds adjusted each carb half a turn out equally and now it idles smoothly..
in the water it did the same thing from 1st run but while a mate of mine was on full throttle i adjusted the timing slowly and the the problem went away and ran very smoothly at full throttle i locked it off there and adjusted timing aswell for idle and adjusted the carbs its a tad bit shaky on idle and when in gear, might do that tomorrow and work on the idle to get it smooth

can someone help me out on how to adjust timing and adjust the idle properly..

[almetelo]

Fix the fuel lines (leaks)
Dismantle carbs and clean them with compressed air and carburetor cleaner (I use brake cleaner but carefully with rubber parts)

Inspect fuel pump

A/F screw should be +/- 1-1/4 turns out

You must have a service manual for your motor... otherwise probably you donīt know what you are doing...

If you donīt have the SM let me know

[imajin14]

yeah i dont have a SM....but i actually adjusted the screws 1 and half turn out from where it stops i saw it on google somewhere i left it at that...its just the timing i dont have a clue with ive replaced all the lines and the carbs have been rebuilt from previous owner, its just the timing on idle and full throttle thats abit out of whack i did it by ear and feel lol.

so after i did the fuel lines started fine and idled fine but just abit shaky... on full throttle it felt like rpm was fluctuating about 200-300..while my mate was full throttling i was adjusting the timing until it stopped flactuating and ran smooth at full throttle. im abit concerned its a 4.5 meter aluminium boat with a 40 hp it felt like we were going about 20-25 knots i couldnt measure it..but is this normal i would've thought the 40 hp yammi would hit in the 30 knot mark on a light ally boat

[99yam40]

You need to follow the procedures in service manual and set to the specs in there.

I have no idea how old this motor is, how many cylinders or carbs as it is not a motor sold here in the states, but you need to set timing with a light not by ear and I do not see how timing would have been causing RPM to fluctuate at WOT.
most varying of RPM is do not all cylinders are firing and burning the fuel properly. too much or too little fuel can cause this. Check the fuel pump and lines for leaks and set everything to spec
Yes I would think a good running 40 with the correct prop should push the 14 or 15 foot boat 30 with no problems, but you are not measuring RPM or speed just guessing , so start measuring things and report back

[imajin14]

its 3 cylinder triple carb 1987-1989 era with key start ignition it did have oil injection but previous owner bypassed it and just mixes fuel with oil because he doesn't trust the old oil injection in case it failed and the motor seized up..its a very clean motor i will take photos of it tomorrow for you guys...i wish i had a service manual i have no clue on how to check fuel pump on outboards...I have replaced all fuel lines on the outboard no more leaks or tiny cracks. i dont know what rpm i am running at aswell on the side it says yamaha precision blend very similar to this

[99yam40]

You can unbolt the pump from the block while leaving the lines hooked up and pump the bulb to see if fuel leaks out of the pulse port heading to block.

or use a vacuum/pressure gauge to test

I did not know the 40s were 3 cylinders all that far back, thought they were only 2. But this shows what I know about the older ones

[imajin14]

to reinstall the fuel pump will i need a new gasket aswell i don't know where i can source one from

[imajin14]

hey guys when on idle and in neutral when i goto rev the motor with the throttle body lever it stalls and bogs is this normal?

[almetelo]

No, its not normal.
I guess you must adjust A/F screws

SM for your motor:

https://drive.google.com/file/d/0By0...ew?usp=sharing

Hope this can help.