Float drop down adjustment

[marts99ss]

I took off the carbs to check and adjust. I blew in the carb inlet and it was holding pressure. I shook the carb and now it was not. When I was taking off the float cover and the floats dropped and it sealed again. I adjusted the tangs behind the floats restricting the drop down and now they don’t stick anymore. The floats were dropping so much that they touched the float cover. I know because I tested the dissents of travel, shook the carbs without the float cover and they didn’t stick open. Does anyone know the drop down distance? I know adjustment level height is 16mm, but I don’t know the drop down level? Is it ok not let them hit the float cover? I think the main nozzle channel in the center of cover is the part that contact with the float. I've attached photos.
I have a 1989 Yamaha 150 Pro-v with 3 nikki carbs. Any advise will be appreciated

Thank you

[boscoe99]

The only specification is for float height. Who cares about drop since the float will normally be floating in fuel? If there is no fuel in the float bowl then the motor will not be running so what does the float drop mean?

Not sure what a float cover is. The float sits in the float bowl and the bowl is attached to the carburetor body.

[marts99ss]

Thanks for the reply. This happened to me a couple of times. One the lake when I was pumping the primer bulb, I saw fuel drip down out of the carbs. The bulb didn’t get hard. The other time it flooded the engine and it didn’t start. So if there is no specification it’s ok for me to close the tangs behind the float in order to stop the excess movement? It wouldn’t cause any problem with engine drivability? If I don’t close the tangs the floats will make contact with the float chamber (the part that covers the floats not part of the carbs main body).

[marts99ss]

Can I ask you a different question? How can a float cause the needle to leak? I have this float that it’s adjusted to 16mm but the needle is not sealing. I’m checking with a hand pressure pump. I changed the needle with the same float it doesn’t seal. I changed the float and it sealed. I don’t get it. How is this possible? I’m thinking the tang is damaged.

[TownsendsFJR1300]

If its still leaking, the needle is NOT seating fully. Either the needle or the seat is worn. The needle should be nice and smooth with NO grooves in it. Make sure there's absolutly no grit before or after the seat as that will allow leaking. **If the needle seat/seat is rubber(or a flexible part), it may have hardened up over time/ethonol, etc, and isn't sealing like a new one would.


You can easily perform this test on the bench with the float bowl off, carb in the correct upright, running position.

If you have a small auxilary fuel tank, simply supply fuel to the carb and push the float gently upwards(closed), (as if you had a full float bowl). Obviously, it should not allow liquid to flow.

One other possibility(not likely) is to check the float itself for leaks. If its allowing fuel to seep into it, it won't float, and will stay open 100% of the time. Simply setting it under water(maybe in a cup, held down with something) and looking for bubbles. Shaking the float and hearing fluid sloshing around inside shows it leaks and needs replacement as well..

Re the drop down tab, as you noted, the float (or any other part of the carb)
should NOT be touching/binding the float. You can confirm this simply by turning the carb upside down and right side up while YOU blow into the fuel nozzle. Air will flow in the upright position(as it should) and NOT flow when flipped upside down(simulating a full, fuel bowl-needle is CLOSED).

It goes without saying, if your needle has a thin "hook" spring, make sure its wrapped properly around the FLOAT TANG. This is to make sure the float pulls open the needle (should the needle stick). In Boscoes picture, specifically area #1... If its not installed correctly, all bets are off...

As Boscoe noted, take your float measurement W/O the gasket on.

Lastly, I would measure the bowl depth itself and compare it to the drop down, float level. As shown in your pic's, those floats are formed to fit around that "higher drain casting". I would adjust the drop down level to be just inside or NOT touching the bowls themselves. Again, just re-test by flipping the carb upside down/right side up and blow, by mouth, air into them to confirm their NOT sticking open and closing when appropriate.

[marts99ss]

Thank you Bosco and Townsend. You have given me great information. Measuring without the gasket was a good idea. Yamaha manual notes to measure with the gasket to 16mm. I measured 17mm without gasket since the gasket is 1mm. Is that OK. I checked every carb to 15 PSI with a MityVac. It was holding. Before I put on the air cover when I was pumping the primer bulb I check in the carbs there was not fuel spilling out so I guessed everything was good. Started the engine everything was fine it didn’t pop curing the crank. I took it to the lake today and it poped during the start. It was not running right when it was cold. It stalled a couple of times. It never did that before. It was running a little rough. It didn’t have good power. I don’t know what I did wrong. I want to open the carbs again. How can I adjust the carbs to run rich. When holding the carbs upside down on the table the floats should be adjusted less than 16mm? As per Yamaha manual? What else have I overlooked? I also would like to do the bench test with the fuel primer bulb.

[TownsendsFJR1300]

You can change the float level 1 mm but that won't make it run richer. Spec's allow +/- .5mm. I'd go to 16.5mm W/O THE GASKET as Boscoe posted. I'd measure W/O the gasket just to be as accurate as possible. (gaskets flatten out where pressed and so where not pressed). Most carbs are measured W/O the gasket for that reason, its just more accurate.

Re the 15 PSI, I'm not sure what your fuel pump pressure is, however testing at 15PSI is WAY more than doing it by mouth. (I have a pressure Mity Vac as well but doesn't measure output pressure, just sucking)


Looking at the parts fisch, you simply have butterflys for the choking system.

1989 PROV150LF Yamaha Outboard CARBURETOR Diagram and Parts

It sounds like a lean sneeze while still cold and just needs more choke (or see below).

Did you re-sync the carbs after re-assembly?

NOT mentioned and really important, did you pull the idle and main jets out? They need to be removed, inspected and cleaned if necessary. That wouldn't cause the initial overflow you mentioned, however it would affect if the carbs function properly. A clogged jet WILL CAUSE a LEAN condition(sneezing or worst case, no running at all).

**Their NOT clean UNLESS you can visually see thru ALL THE orifices. Spraying carb cleaner into the carb body with the jets installed DO NOT CUT IT.

And lastly, if the engine, short of this new issue and fuel overflow, is running crappy NOW and it ran good before, IMO, DO NOT RE-jet the carb.
There's still an issue, wether it be a clogged jet, misadjustment(sync), leaking needle, leaky float, etc..

Good luck

[marts99ss]

Sync and link is dead on. I did this last time. I'm 100% sure this is not it. I will hold the chock more to see if that will get read of Pop at cold start. I will try to make some changes to the pilot screw to see if it runes better. I'll try to see if it's running lean. If it does help good. If not I will pull the carbs and clean it one more time and all the jets. Mityvac has one with vacuum and pressure pump.
The funny thing is that I think the pop during crank start is kind of fixed. I don't think the valve needles are leaking anymore like before. Before It would pop at cold and every time the engine was off for more than half an hour. Yesterday it only popped in the morning and started to act up and stall a couple of time in the morning. It didn't pop after that after being off for one hour and it didn't stall. It just didn't feel right. I think it lacked power. One think I think I noticed was when I was driving at slow at around 15 mph the engine sometime got this boost of power and pushed the boat forward. It was very small kind of push to the boat. I'm thinking maybe a dirty or old fuel?

[TownsendsFJR1300]

I think most, myself included, assume your doing this with fresh fuel.

A previously good running engine, with old stale fuel (fuel will go bad in as quickly as a month) will NOT run right. Your just introducing crap back into the system

A stabilizer and Yamaha's Ringfree, IMO, is a no brainer and WELL worth the money.

Most of my fuel (built in 50 or 60 gallon tank) is probably a year old now and still looks new, smells new and is NOT cloudy(engine runs great!!). (I use K100 and will swear by it).

If its surging, the Ringfree may very well help with cleaning it out...It certainly can't hurt..

If the fuel is old and un-treated, dump it...