Carburetor 90 hp

[bertram3]

Many threads on the topic of rebuilding the 90hp carburetors. Took the challenge and I thought I would share what I learned. The carbs are actually very easy to remove from the motor. After removal, I disassembled them individually as not to mix carb parts. My 90hp is a 2002 model. I purchased the rebuild kit from a Yamaha dealer. Rebuild was easy. Used compressed air, brake cleaner and 1 gl Gunk immersion can. Left all jets intact and did not tamper with the air/fuel screw (I thought). Put carbs back on and bingo, all is running good except I am getting overflow of gas coming out of #1 and #3 carb. Pull them off and find that the set screw that holds the float pin was loose. Tightened them and back on. All is good, take for a test run and start bogging out above 4000 rpms. Read on this great forum about the air/fuel adjustment screw. On my carbs, they are not restricted from the factory. I did find that they were all adjusted differently. Probably during the rebuild. I readjusted them by going clockwise until seated and then backing them out 1 1/4 turn. The idle immediately improved and then the test run was spot on. Achieved 5400 rpms WOT several miles and no issues. Hope this helps..........

[robert graham]

Thanks for sharing your experience...mine is a 1999 Yamaha C90 and feel that eventually may need to go through carbs...but so far, so good!....

[charles90yam]

Great post! I am getting ready to rebuild my 2004 90hp carbs. Have already purchased the 3 kits and only need to find the GUNK now. The whole process seems a little intimidating, so Thank You for posting that it isn't that hard! It gives us rookies hope that we can do it, too!

[bertram3]

Go for it. Pay attention to all your hoses connecting in to the carb. Some of mine had the snap clamps and others had the screw type clamps. I ended up putting all stainless steel screw clamps. The other tip I will offer, leave the linkage rod attached until you remove all bolts holding the carb to manifold as this keep the carbs in place. These are simple carbs to clean. Again, no rush, do one at a time. Another lesson, in your kit you will find little domed plastic caps, almost microscopic. These caps go on top of the needles. I left one off and sure enough, caused the needle to overflow. Once all disassembled, do not be shy about blowing out all orifices with compressed air. Also, the gasket fit is important. While on the bench, I put fuel into the bowl and inverted to ensure all my gaskets were sealing properly. A few times, had to open carbs on the bench and re-adjust gaskets to seal properly. Good luck with these carbs, the job is easy, keep everything organized and CLEAN!!!.....my 2002 90 has never run this great........please do not hesitate to post a question. If I can help, I will..............

[robert graham]

I believe that installation of a fuel/water separator and regular draining of carb float chambers is a good way to avoid the cleaning/rebuilding of carbs....the old "ounce of prevention"....

[charles90yam]

90hp carb rebuild question

For those of you who have already been through the carb rebuild - I just started the first carb and have disassembled it. In the Yamaha kit they provide a new needle valve, and valve seat (brass). How did you remove the old valve seat? It is a 10mm size but with almost no clearance. Best I could measure it looks like about 13mm clearance. I actually ordered 2 different thin wall sockets trying to get to it, but they won't even fit in the space. Is there another tool that I could use? If you have purchased a socket that fits could you tell me where it came from? I have visited hardware stores, auto parts stores, Snap On, etc. That's why I ended up purchasing 2 from the web, to no avail. Thanks - any help is appreciated!

[throrope]

I believe that installation of a fuel/water separator and regular draining of carb float chambers is a good way to avoid the cleaning/rebuilding of carbs....the old "ounce of prevention"....

Ditto on that. I empty the tank, filter, lines, and carbs. For me, no fuel to go bad.

[99yam40]

I took a socket and machined the outside down far enough to get the clearance.

Draining the carbs gets most of the fuel out but not all.
some will remain and as it evaporates it leaves a residue that builds up over time and I am sure there is fuel left in pump and lines that does also.

I think that leaving system full and running often never leaves the residue.
Just my opinion.

Just helped my brother clean his carbs on a C60 .
He has worked way too many hours the last year and did not have much of a chance to take the boat out.
There was a thick residue on the bottom of the bowls and #1 & #3 were not hitting

[rodbolt17]

take a standard 1/4 drive 10mm socket and simply grind the OD till it fits.
DO NOT use worm screw clamps especially on plastic T's and pump fittings.
either use the wire spring clamp or a 4" wire tie.

I do several sets of inline carbs a month and rarely see issues.
remove all jets, carefully clean the parts and reassemble.
its rare I use kits.
be aware that not all inline 3cyl carb kits contain the small oring that's located under the needle seat.
use of the wrong oring will lead to leakage.
if the fuel bowl gasket isn't damaged and the float,needle and seat are ok I typically just change the top cover gasket and the needle seat oring.

if your kit contains 3 small orings and 3 really small orings your ok.
if it only contains 3 orings then most likely you will need to buy the seat orings seperatly.

[a387673]

Carbs/Rebuild, Rodbolt

Rodbolt, .... just curious.... why do you replace the gasket on the top cover but not on the fuel bowl? I also gather that you don't bother with pilot or lo-speed needles unless visibly worn.....?

Echoing Bertram, I just did a rebuild and had to reseat gaskets on two of the three float bowls after reassembly. Small remnants of "chalky" build up around old gaskets must have interfered with the seal of the new gaskets, had to clean on them a little more.

Re: the 10mm socket....... I have one for 3/8- drive, Craftsman, I think, tapered, that will just barely get in there and grab that needle seat... wouldn't reach if it had to go another 1 mm....

[TownsendsFJR1300]

Most carb issues (IME), are due to clogged jets / varnish from sitting with un-treated (no fuel stabilizer). IMO, stabilizer is a MUST....

Its rare to see the needle and seat worn and if the bowl gasket doesn't get destroyed (stick to both the bowl and carb body) can usually get used again.

Getting to the idle and main jets (preferably removing) and cleaning is the key. I literally look thru each jet for sun-light coming thru evenly.

As noted above, I also hook up a spare/bench fuel tank (old mower gas tank with an on/off fuel valve) once the carbs re-assembled to check for leaks before re-assembling on the engine..

You can also get a visual on the actual float level height by attaching a clear hose to the bowl drain nipple, holding the hose verticle and then opening the drain screw. The fuel will fill the hose and you can visably see the actual level.

The above applies to mower carbs, motorcycle carbs (especially when not used often), outboard carbs, etc..

[Sepeteus]

Can I install the main jet needle in the wrong direction? My repair manual says that "Position the series of holes in the nozzle to face port and starboard when installed."
The problem is that the nozzle has a total four sets of holes. What holes am I supposed to get towards port and starboard?
Does the position of the holes even matter?
My outboard is 70HP (1990), with a Keihin BCK carburetor.

[TownsendsFJR1300]

Can I install the main jet needle in the wrong direction? My repair manual says that "Position the series of holes in the nozzle to face port and starboard when installed."
The problem is that the nozzle has a total four sets of holes. What holes am I supposed to get towards port and starboard?
Does the position of the holes even matter?
My outboard is 70HP (1990), with a Keihin BCK carburetor.

The only thing I can think of is for better atomization of the fuel as air gets pulled thru.

If there's 4 sets of holes, it shouldn't make a difference. That nozzle is pulling fuel from the bowl. Its not like its coming from somewhere else..

Unless there's someway of locking that jet (as noted above) they usually just snug down. It'll still suck fuel thru the nozzel, maybe just not as efficient.

IMO, unless you can even see the direction(of the holes), and get it snug as noted, it shouldn't be an issue..

[Sepeteus]

Okay, I thought so too. I just wanted to make sure that I would have to dismantle carbs again.
Thank you very much!

[TownsendsFJR1300]

Please post how it works out.. Good luck..