Help me troubleshoot my Merc 20hp 2 stroke

[DaubsNU1]

It's a 1974 Mercury 200 / 20hp two stroke.

 

• Carburetor rebuilt this spring.

• Last two times on the water the initial start and run have been great, normal as usual.
• After sitting for a while, motor refused to start...and leaking fuel in to the water.
• Fished yesterday, same thing...ran great off the dock...then refused to start, leaking fuel.
• Got home a pulled the cover...fuel sitting in bottom, leaking out of motor.

 

I am thinking the float has a small hole...making the boat run good off the dock...but as fuel sits in the carb...floods out and leaks.

 

Am I wrong?

[Kirtley Howe]

I am not sure how mechanical you are, so I will word this like you know very little.  If you are mechanically inclined/knowledgeable please don't be offended.

Bad float. Or bad needle jet. Or float is sticking, or needle jet is sticking. The carbs on 2 strokes are pretty simple. Open it up and check for a sticking float (does the float move easily through its' entire range, both up and down?). If not, look for bent or damaged parts.

Your float could be leaking, as you mentioned. Take the float off and shake it....do you hear or feel any sloshing? If yes, you need a new float...it is possible to fix a leaking float but is usually not worth it. Just get a new one. Even if you don't hear sloshing, your float could still be leaking. Take the float and submerge it into water and watch for very small bubbles. If you see any, your float is bad.

Your float needle could be worn...it is located under the float, and all it really is, is a stopper, kind of like a sink stopper. As the float moves up and down, the needle can move to allow more or less fuel to the carb. If it is sticking or worn, it will "leak" allowing the carb to flood. Could work fine on initial start up. Motor runs fine. Then you stop and shut off motor, but the needle jet does not seat into the closed position which allow the carb to flood. Replace the needle jet.

What knowledge I have comes from working on 2 stroke motorcycles, but the same things should apply to a 2 stroke boat motor.

[DaubsNU1]

Great information @Kirtley Howe! I really appreciate you taking the time.

 

I'm sort-of-familiar with 2 stroke carbs after diving in to my 1979 Lawn Boy many, many times(!)

 

Marine mechanic did say the needle was sticking a little when he did the carb kit earlier this spring.

 

I will dive in to the carb next week.

[TnRiver46]

I got a buddy selling one, late 70s 20 hp 

[airshot]

Use an actual factory rebuild kit for your carb !!  They have all new gaskets, needles, seats etc, plus they will tell you howvto set up the carb for proper operation !!  Just cleaning rarely works well.  Also check you hose from the tank and the fittings as they do wear out and need replaced every so often.  From your description you need a real rebuild kit for that carb to do it right !!

[DaubsNU1]

18 minutes ago, airshot said:

Use an actual factory rebuild kit for your carb !!  They have all new gaskets, needles, seats etc, plus they will tell you howvto set up the carb for proper operation !!  Just cleaning rarely works well.  Also check you hose from the tank and the fittings as they do wear out and need replaced every so often.  From your description you need a real rebuild kit for that carb to do it right !!

 

Yep, purchased factory rebuild kit...and had my local Mercury mechanic install that kit this spring (along with new seals in lower unit).

 

 

[Way2slow]

Sounds like someone needs to find a mechanic.  I would be p****d if I paid someone (which will never happen) to rebuild a carburetor and they told me the needle seems to still be sticking after they were done with it.  That's one of the main things the dumb*** is supposed fix.  That's another one of those cases where they don't know how to rebuild a carburetor, which there are tons of "mechanics" (I use that term loosely) that don't.  They know how to take it apart, put a few new parts in it and put it back together, a 10-year-old can do that.  There's a whole lot more to rebuilding one that.  The first thing is knowing how it actually works, which orifices do what and how to clean and inspect each.  There's a whole more to one than air just passing through the venturi and pulling some gas through with it.  I actually heard one of those dealer "mechanics" telling a customer the fuel pump pressure squirted the gas through the jets into the engine, and it was squirting too much and flooding it out.

[Kirtley Howe]

34 minutes ago, Way2slow said:

Sounds like someone needs to find a mechanic.  I would be p****d if I paid someone (which will never happen) to rebuild a carburetor and they told me the needle seems to still be sticking after they were done with it.  That's one of the main things the dumb*** is supposed fix.  That's another one of those cases where they don't know how to rebuild a carburetor, which there are tons of "mechanics" (I use that term loosely) that don't.  They know how to take it apart, put a few new parts in it and put it back together, a 10-year-old can do that.  There's a whole lot more to rebuilding one that.  The first thing is knowing how it actually works, which orifices do what and how to clean and inspect each.  There's a whole more to one than air just passing through the venturi and pulling some gas through with it.  I actually heard one of those dealer "mechanics" telling a customer the fuel pump pressure squirted the gas through the jets into the engine, and it was squirting too much and flooding it out.

Well, he would be "sorta' right" if it was a fuel injected motor. <G> I also agree with the idea that there is a lot more to a carb than just the float and needle. But since OP said that the motor would start fine first thing, and run fine until shut off, I think that the venturi and orifices are clean and working as they should. Since the carb only floods after initial use, I strongly suspect either the needle or float....especially as the "mechanic" stated that the needle was still sticking (sometimes?) after the rebuild. I don't think I would use that mechanic again. It would be one thing if he just missed that the needle was sticking and was willing to fix it (again) for free, but it is something else indeed that he KNEW it was a problem and didn't fix it before giving the motor back to the owner. What ever happened to pride in workmanship?

[DaubsNU1]

It was the first time I have used this marine mechanic...however, sister and brother have taken several boats his way, and good experiences.

 

That is why I was thinking leaky / bad float....that is probably original to the engine. I may end up taking it back to him...not sure at this point. 

 

I really like figuring things out for myself. Especially if I can work on the Merc during the week...I would hate to have my boat sitting at the mechanic for a few weeks : ) 

 

I will keep you posted. Headed to South Dakota with my brother's Alaskan this weekend...should be a fun time chasing smallies and eyes. 

[DaubsNU1]

Pulled the carb off today. Sank the old float in water...one or two tiny bubbles developed on the float...I don't think enough to make a difference, but I replaced it anyway.  

 

Manual calls for .280 to .320 measurement from top of float to carb. I did not have the proper tool, so measured old float, and got it close. 

 

Surprisingly easy to take the engine apart and carb off. Whew!

 

Here is where it gets interesting...I attach the fuel line....and soon fuel comes spilling out of the carb(!!!)? 

 

There was pressure building up in the 3 gallon fuel cell. That may have been my problem all along. 

 

I loosened the cap...hooked up the garden hose...and it runs great!  Started, stopped...started again...let sit for a while...started again.  Good to go! So for now, problem solved. 

 

I'll be on the water tomorrow morning to make sure. 

[TnRiver46]

How’d it go @DaubsNU1? 

[DaubsNU1]

50 minutes ago, TnRiver46 said:

How’d it go @DaubsNU1? 

 

Changed plans...fished with my brother. I'll run it next weekend.

 

[DaubsNU1]

Got the boat on water this morning. 

 

Ran GREAT!  

 

Four or five pulls to get started first thing in the morning (standard). 

 

After that, it was one pull to get the old Merc fired back up. 

 

No issues. Problem solved!