Yamaha 150 TXRC: Lot of black specks in carb bowls

[Psalm 99]

This is puzzling: For the third time in a month, my engine has lost either an entire carb or one side of a two-barrel carb. Engine slows to 1600 - 2500 rpm and I limp in at 8 mph. Entire fuel system is new and clean up to the carbs. In an attempt to solve the problem, I've totally replaced the small on-board fuel filter, fuel lines (right up to carbs), primer bulb, fuel/water separator and fuel pumps. Installed a new fuel/water separator (10 micron, entire unit) with-in the last month. Now, trying to isolate the source of junk in my fuel system and using a clean white cup, I first sucked about a pint of fuel out of tank (clean), then thru fuel/water separator (clean), then through the entire system past the fuel pumps and into the clean, white container. There was no junk from the tank thru the new fuel/water separator but past this to the fuel pump discharge there were specks from 'just visible' to particles about 2-5x the size of the period at the end of this sentence. This happened with the first cup pumped but the system remained clean in subsequent (4) cups. Draining carbs directly into a clean cup resulted in quite a bit of black specks showing up. Removed top carb and removed bowls. A few good sized black specks in bowl even after draining. The only thing that looks like a contributor are the black plastic floats. Removed both floats and put them clean white container then through a sonic cleaner with 100% Simple Green bath (heated). Result showed appreciable black specks from ''dust' to about 10x the size of a period. The floats all still work but it sure appears that they are shedding junk which is fouling the jets. Fuel back-flows through the system when the engine is shut down and I figure this is the reason junk was in the engine fuel lines. I got this engine with 325 hours and have put another 300 hrs on since purchase. Having the engine lose a carb has been an on-going problem. Carbs delivered fuel to only two cylinders when I first got the boat. The local Yamaha mechanic initially put the carbs through his sonic cleaner and I've done the same (disassembled). Additionally, I've put some pretty strong solutions of Ring-Free through the carbs as well as the recommended dose each time I fuel up. I'm ordering new floats (6) but in 50 years of amateur engine work, I've never had a float shed junk. Any comments and further recommendations sure would be appreciated.

[pstephens46]

Avoiding a bunch of speculation, I wonder if Rodbolt has seen this before?

If the float was shedding pieces I would guess the float surface would look strange. How do they look?

[99yam40]

I would also look at the fuel lines.
they have had problems in the past.

and do not forget to look in the fuel pumps for junk hiding in there or what ever that will come out and plug things up

[Psalm 99]

Thanks for the responses! Floats have a rough exterior. Best similarity would be to about 800 grit surface but plastic. Fuel lines are brand new (about 3 wks old). I replaced them all with Yamaha parts via this website. Fuel pumps are less than a year old. I've flushed them by disconnecting the fuel pump discharge lines and, with the primer bulb, squirting fuel into a plastic cup. When I do this after the engine has run, there will be junk in the lines and also in the carb bowls. However, subsequent flushing from the fuel pump discharges produces clean fuel. When the engine is shut off, the fuel drains from the carb bowls back into the fuel lines. I know its sort of reversed from normal but it sure appears that the black specks and produced in the carbs and backflow into the fuel system when the engine is shut off. Some of the specks are certainly large enough to foul a jet.

[panasonic]

Perhaps someone replaced the floats with cheap aftermarket copies and the plastic they are made from is not up to the task over a long period of time. Or someone ran something in the fuel, an additive, that has attacked the plastic. Only speculation now.. I think you are on the right track by replacing the floats.

I have to agree that it is strange problem...I have never seen a plastic float fall apart like that, seen them split open or Crack on a rare occasion.

Good luck.

[Psalm 99]

Carbs had definitely been worked on before I got the boat. Needle valves leaked and the floats had been bent way down from spec, I guess to obtain a seal at the needle valves. Cleaning valve orifice and correctly adjusting floats helped greatly. Real possible that the floats are not genuine Yamaha parts. Engine has low operating hours but I suspect that ethanol-laced fuel was left for an extended period in the system. Engine has a good reputation and I'm hoping that with this last fix, I will have solved the problem.

[rodbolt17]

I have never seen the Yamaha floats fail.
I have seen fuel lines and pump diaphrams fail.
that junk is coming from somewhere.

[pstephens46]

If you were to rub or scrape the existing floats with your fingernail is there a black residue?

[TownsendsFJR1300]

Plus 1 on changing out the floats.

You don't where they came from (cheap Chinese knock offs?) and from the description sound like junk.

While you have them out, why not put them in a small, see thru sealed container of fuel overnight.
Does anything fall off them in that container?

Also the fuel lines.. You did use MARINE GRADE fuel lines correct?

I've had the internal liner of a Mercury fuel line disintegrate and get caught up in the under cowl filter...

[Psalm 99]

The fuel line from tank to engine was originally about 14' long which was necessary to get to the enclosed fuel/water separator and back to the engine. I relocated the separator and reduced the fuel line to about 4' (new, good marine quality). I did put a new Yamaha primer bulb in but got lazy and did not replace and internal fuel lines. When this problem surfaced, I bought all the little fuel line pieces via this website for installation inside the cowling. I did split lengthwise the removed longer feed line to check the interior surface which look new. Just fished the original lines out ot the trash as it appears this was not the problem. I will try soaking the existing floats in gas overnight but after putting a few through a sonic cleaner and seeing the appreciable amount of black junk left in the clean white plastic cup I used, it seemed that the floats were the problem. Before checking the floats, I was thinking of putting small, in-line filters right at the fuel line connection to each carb as I couldn't find where the black specks were coming from. New floats were ordered from this website. I've sure been wrong before but, except for the floats, I've run out of options.

[robert graham]

Maybe the inside of primer bulb is deteriorating?....

[TownsendsFJR1300]

The fuel line from tank to engine was originally about 14' long which was necessary to get to the enclosed fuel/water separator and back to the engine. I relocated the separator and reduced the fuel line to about 4' (new, good marine quality). I did put a new Yamaha primer bulb in but got lazy and did not replace and internal fuel lines. .

When I posted the "internal liner", that was in ref to your main (say 3/8's or 5/16") fuel line.

The INSIDE of my 3/8's line actually separated, turned to mush, came loose and got caught in the engine filter. It WAS the short line from the transom filter to the engine (thus-nothing inside the transom filter)... The outside looked normal

[Psalm 99]

Primer bulb is new and Yamaha part. 'Internal' fuel lines refer to the lines with-in the engine cowling including the line from the internal fuel filter and out to the primer bulb. This amounted to about 7-8 small pre-cut pieces of fuel hose and one long section which replaced the fuel hose from the engine-mounted fuel filter to the new primer bulb (about 3' in length. I did notice that where all the interior short pieces had a light grey color like the lines which were being replaced, the final long line (3 footer) was standard black fuel line. All these were purchased from this website and are 5/16" ID. The new fuel line from the primer bulb to the exterior fuel/water separator and then to the fuel tank is 3/8" ID. Using a separate primer bulb to dump fuel into a clean container, there is no visible specks in the fuel coming from the fuel tank up to the fuel/water separator nor from this point to the engine-mounted fuel filter.

[99yam40]

anything before the filters will get caught in the filters, so all of that should not be the problem.
sounds like you found the problem(floats).
hope all goes well once you get the new ones to install

[Psalm 99]

Sure appreciate all the help ( as always!). I'll post once the new floats have been installed and tested.