99 Yamaha t9.9exhx carb flooding out when throttle applied

[sunbirdneptune]

I have a 1999 Yamaha t9.9exhx as a kicker motor on a 23' Sunbird Neptune that I am restoring for my Dad. The motor idles great but the carburetor loads up and is obviously flooding when you increase the throttle. I took it apart and did not find much residue, blew through all jets, and ran fine wire through them. Float appeared to be in good shape and needle valve looked clean and did not appear to be sticking. I am by no means an outboard mechanic, but I am usually pretty decent at other small motors. However, I don't know anything about this carburetor and don't know how to proceed. Should I order a kit for $50.000 that only replaces parts that I have already inspected? Order a new carb for $384.00? Or is there a specific item in the carburetor I should check? Any help is appreciated. Thanks and God bless

[ausnoelm]

How do you know it's flooding? Seeing as it idles OK, I suggest pulling the carb to bits and cleaning properly, do some basic trouble shooting, you say you're OK with other engines, just because this one has a propellor doesn't make trouble shooting/repairing any different.

[rodbolt17]

I really really doubt it is flooding only when opening the throttle.
I mean think mon think.
what is flooding?
flooding means it is very rich.
by the act of opening the throttle plate your making it lean.

my guess would be it cant flow enough fuel to run.

[99yam40]

I see that carb has a diaphragm for something, could it be an accelerator pump that adds extra fuel when the throttle is pushed.

something to look into if the compression, spark, timing and all the jets and passages are clean

[sunbirdneptune]

Yes it is definitely flooding. Blows black smoke when applying throttle as if you were trying to run a typical small engine with the choke on. The accelerator pump is working. Nothing is leaking fuel anywhere. I see that it has a small check valve for the accelerator pump - could that have something to do with it? Or possibly float setting? I can't understand why it does not flood when idling - it idles beautifully, but apply throttle and it bogs down blowing black smoke like it is getting way too much fuel.

[sunbirdneptune]

Also, could the "enrichment device" / starter set be causing this? or would it also do it at idle?

[99yam40]

carb has idle jets and main jets it gets fuel from

main jets being too large or something restricting air flow are the only things I can think off off hand.

I guess the enrichment system could be dumping too much fuel also, but like you I would think at idle it would also be too rich if it was that

[sunbirdneptune]

I will pull it apart again and recheck jets - this outboard sat up for a few years without being ran more than once or twice a year for a few minutes. To my knowledge it ran fine before sitting.

[sunbirdneptune]

Also I can't find any air flow restrictions - intake is clean and runs like this with the hood off.

[sunbirdneptune]

I replaced float, needle, gasket, cleaned everything well, removed all jets and ran wire through them, found nothing. Still have exact same problem. Can't find any air restriction, exhaust does not seem to be retricted, I am out of things I know how to check. Engine will idle fine, but apply throttle and it bogs, sputters and blows black smoke. Pulled plugs and they were black gasoline fouled. Cleaned plugs and no difference. Any ideas anyone????? Enrichment device??? Should I quit now and buy a new carburetor?

[cpostis]

Grasping at straws!!!
Not familiar with this small engine.
Guys, how does the fuel pump operate on this small 4 stroke engine? Does it run off crankcase pressure/vacuum? If he had a leaking fuel pump diaphragm could gas enter the crankcase diluting the oil? could diluted oil/gas mix pass the rings and causing rich running and fouled plugs?

I know I'm reaching, but enquiring minds want to know!

sunbirdneptune, can you smell gas in your oil?

[ausnoelm]

Don't think the idea of a crankcase vacuum/pressure fuel pump would be a big hit on a 4 stroke?? Did you check all the small air passages in the carb?, not just the jets.

[sunbirdneptune]

Fuel pump is pumping and oil has no gasoline smell... Could a weak power pack / coilset cause this? or would it not idle correctly?

[sunbirdneptune]

And yes, I blew through and or ran fine wire through every passage. If something were stopped up it would seem to me that it should starve for fuel and die when giving it throttle. Instead it keeps running very roughly and blows black smoke as if you had the choke on (but it has no choke) never will throttle up completely and has no power.

[cpostis]

Don't think the idea of a crankcase vacuum/pressure fuel pump would be a big hit on a 4 stroke?? Did you check all the small air passages in the carb?, not just the jets.

Didn't think so.
I guess it's operated off a cam or crank lobe?

Can someone answer my curiosity?