Yamaha 50hp 4 stroke carb problems..

[Tailwalker]

I've got a 2000 Yamaha F50 that has developed carb problems for the 3rd time since I've owned it. This is really getting ridiculous. I am fanatical about making sure the gas never gets old, etc. I use it within 3 months or I get rid of it. Racor fuel/water separator, changed regularly, used to keep fuel stabalizer in it and leave the gas in the carbs until the second time around with trash in the carbs so my mechanic agreed w/me that running them dry would be better which I've been doing for the past 2 years with no problems. Then this weekend I was fishing. Had been running fine all morning. The only issue I noticed the last couple times was hard starting when cold. It was definately flooding and you'd have to crank multiple times to clear the gas before it would start. Then no other issues but I knew this was the start of something.

After fishing and restarting numerous times going to different areas I ran about 6 miles at about 5000rpms and the motor was running great. I then pulled it back to come off the plane and the motor starting vibrating violently and running rough. This is a small boat and the seas were running about 2-3 feet so I did not want to have it cut off and leave me stranded so I wound it back up and ran it all the way back in. It ran fine at high speed but again when I got back to the no wake zone the motor did the same thing and then cut off. I got it to restart and had to jockey the throttle all the way back to the ramp. Then the motor would just not idle.

Pulled the cover and I could smell the gas. You can see some seepage on two of the carbs so my thinking is the bowls are either coated with shellac or have developed pinholes flooding out the carbs. I pulled the plugs and 1 and 3 were fine but 2 and 4 were completely black with a ton of carbon. I think clearly those carbs are dumping far too much gas and causing the rich running problem. I put new plugs in, bypassed my fuel system with a 3 gallon tank and fresh gas to see if any change, nothing. I then sprayed carbs with carb cleaner and did this to each bowl by pulling the drain screw on each. Made it idle a little better but still runs rough and from idle to about 2500 when you give it any gas from idle it starts to bog until you get it over 2500 and it runs fine then.

I've got good spark on each cylinder so I think its the floats.

Anyone else that knows carbs and 4 stroke motors think it's something else?

I've done all I am going to do. It goes to the shop this week and I fear I'm looking at a total rebuild of all 4 carbs to the tune of at least $300.00.

Love the motor but I'll never buy another carbed 4 stroke. I don't know why it took Yamaha til this year to come out with fuel injection in their smaller motors.

If anyone can think of some other issues you think it could be let me know.

Thanks.

[chris V]

good motor and good carbs, just very sensitive to debris. you havent mentioned anything about a fuel water seperator. It stops alot of junk from getting to the carbs
before you take it to the shop, get some "seafoam" and treat it, it make clean out your problem, and if not, you are out less than $10

[Tailwalker]

Thanks. Look at the first paragraph. I've got a racor fuel water/separator on it. It's definately a carb problem. Everything obvious has been done including running sea foam through it, etc. I dropped it off at the shop today. I'm certain that it's going to need a carb rebuild as number 2 and 4 are definately flooding the cylinders at anything under 2500 rpms. That's also why the plugs are completely black and horribly fouled.

[Mac25]

have seen them get to points that they had to be replaced,could not be cleaned,add to that 4 carbs and its time to throw the it away.

passages just to small to be cleaned,never a small 4 stroke in my ownership,i guess when small 2 strokes are no longer avail everyone will be happy.

[JackB]

When I purchased my used boat with a Honda 4 stroke I found out that buying a several year old boat with only 36 hours on it was not as great as I first thought. The net result, due to gummed up carbs, was a $1200 expenditure to have the 4 of them replaced. At first I was sure they could be cleaned like other carbs but after speaking with factory and mechanics found that is not the case. Orifices are too small and if soaked the nitrile used for chokes swells up and creates other problems. It was sad to see 4 carbs end up in the trash bin but it solved the problem.