Questions on Mercarb bowl capacity, running carb dry, and some more related issues

[jack black]

I recently rebuilt my Mercarb after it was badly gunked up after 9 years of using gas with stabil (the boat sits a lot though and I drained over 1 year old gas twice). However, I forgot to measure capacity of the carb when it was apart. When I primed the rebuilt carb, it took ~60-70 cc of gas through the bowl vent before gas started dripping in venturis. I'm guessing the real capacity is lower, maybe 50 cc.

The reason I'm asking is that from now on I decided to run carb dry before storage to avoid future carb mess. The rebuilt was very time consuming, mostly due difficulties removing factory gaskets that were glued with some black sealer to carb and intake.

So, after the test run and idle and mixture adjustments, I shut fuel valve (that I put myself in line) and the engine only ran only under a half of minute before it died. I expected it to run a bit longer on fuel in bowl. How can I know if the bowl was emptied entirely (without taking it apart again)? Too bad there is no bowl drain on Mercarb.

One more idea I wanted to bounce from the smart people here, whether injecting small amount of TWC3 oil into carb bowl before running carb dry would be a good and easy way of fogging engine and carb at the same time. After all, EFI merc engines should be fogged by running 9% TWC3 oil in gas.

Thanks!

BTW, this is a 2003 Bayliner 175 with 3.0L Mercruiser engine.

 

[mpdive]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

You will always have a small pool of fuel left in the bowl. I have never had a problem with a carb when using a stabilizer. Keep in mind that fuel also acts as a lubricant for seals especially the acc. pump seal. Leaving it dry in my opinion is worse than leaving it wet. The bowl will be empty as possible when the acc. pump can no longer charge. I really dont know about injection oil into the carb and would watch for gum issues is left in a dry environment. Never had a problem with the stabilizer though.

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Thanks for the reply. I'm thinking that even if gas is stabilized, it will eventually evaporate leaving impurities behind. It happened to me. I got the running carb dry idea from common advice on web for small engines.

BTW, this is my carb before cleaning:

 

[mpdive]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

You are viewing years of crud and natural deposits from years of running. Keep in mind that the "varnishes" left behind from years of fuel useage are like a glue and attract impurities. What you have is very common for the use. I would not worry about emptying a bowl and would consider maintaining a fuel stabilizer in small amounts throughout the year. Sea Foam is an excellent preventative maintenance item. Good job on the rebuild.

 

[Silvertip]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

If you study the carb a little, you will see only two fuel exists from the float bow. One is in the center which is the power valve and is vacuum actuated. The only other exit is via the accelerator pump. Fuel entering the engine is drawn via the emulsion tubes that sit in the float bowl and are part fo the top cover of the carb. Those tubes do not go to the bottom of the bowl so there is no way to totally empty the bowl. I also agree that the deposits you show are not from stabilized fuel. They are from crude that made its way past the filters. By the way, check the fuel inlet fitting on the carb to make sure there is a filter in there.,

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Yes, you are right, there was some gas left, several squirts of acceleration pump.

There was a filter installed (correctly) in the carb and surprisingly clean. The old gas I drained had green discoloration. I'm positive the green deposit is from evaporated oxidized gas.

 

[achris]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Don't put oil in the petrol. Once oil is added to petrol, the petrol starts going sour. In a hot environment petrol/oil has a life of about 2 months. In a cooler environment the maximum life is 6 months. Fogging a 2 stoke is completely different (and done for different reasons) than a 4 stroke. Use a proper fogging oil...

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Interesting, I found an online article on storing classic cars that talks about my trick of squirting oil into bowl before storage:

One criticism of draining fuel is that the carburetor accelerator pump dries out. This can be remedied by adding a squirt or two of motor oil to the float-bowl vent before the engine expires for the last time before storage. This has the added advantage of misting oil over the valves and combustion chamber for extra corrosion protection during storage. If this is overdone, expect to clean plugs in the spring and clouds of smoke on start-up.

The article also explains that stabil works fine, at least in the lab:

There is a standard test for this called the ASTM D525 “Oxidation Stability Test.” A gasoline sample is put into a container with pure oxygen under 20 atmospheres of pressure. When the sample starts to polymerize (oxidize), the temperature goes up. This is when gum starts forming. Plain gas takes 100 to 200 minutes to start polymerizing, but gas with STA-BIL lasts 1,200 to 1,500 minutes.

from: http://adlersantiqueautos.com/articles/winterstorage.html

 

[achris]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Interesting, I found an online article on storing classic cars that talks about my trick of squirting oil into bowl before storage:

from: http://adlersantiqueautos.com/articles/winterstorage.html

Probably one of the WORST articles I have ever had the misfortune to cast eyes on!!!

The resoundingly unanimous advise for a BOAT is to leave the fuel tank FULL, during storage. As we have been dealing with additives in fuel for a very long time now 'rubber' hoses and the such like are alcohol tolerant and should not leak. Another thing is that an 'empty' tank contains vapour, which is far more explosive than the liquid....

As for the storage life... (as I already stated) petrol has a vastly shortened life WHEN OIL IS ADDED... Pure petrol will stay good for at least 12 months, particularly in a cold environment.

I have stripped and cleaned dozens of outboard carbies and they all have the same problem.... gum and heavy residue FROM THE OIL in the fuel.... I saw the photo of your carbie... That looks great in comparison to the 2 stroke carbies I get to see.

Just bear in mind... You are working with a BOAT, that article is for CARS....

0.02,

Chris........

 

[GA_Boater]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

The article also explains that stabil works fine, at least in the lab:



from: http://adlersantiqueautos.com/articles/winterstorage.html

I always store cars and boats too in a pure oxygen environment at 20 atmospheres. Right.

That belongs in the archives along with the lab test of feeding lab rats 200 gallons of diet Pepsi sweetened with saccharin killed them with bladder cancer.

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

I always store cars and boats too in a pure oxygen environment at 20 atmospheres. Right.

That belongs in the archives along with the lab test of feeding lab rats 200 gallons of diet Pepsi sweetened with saccharin killed them with bladder cancer.

This is why I said "at least in the lab". Notice, it was Stabil's own lab. When Pri-G (a competitor) did a similar study (ASTM D-525-98), Stabil was only marginally better than untreated Chevron 87 fuel: http://www.kansaswindpower.net/PRI lab_tests.htm

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

I reviving this thread as I still have 2 unanswered questions:

1. bowl capacity of Mercarb in the 3.0L mercruiser I/O
2. a way to completely drain the carb as "running dry" doesn't do the trick

Thanks!

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Another bump. I did a little study on Stabil and left it in a small jar. It evaporated in 2 weeks leaving thin solid film inside the jar.

I think this is what is happening in my carb when left sitting for several months.

This discussion supports it: http://www.mtfca.com/cgi-bin/discus/show.cgi?tpc=118802&post=278496

So, my idea is to stop using Stabil, start using TWC3 oil and consider plugging bowl vent before storage.

Anyone tried plugging bowl vent?

 

[achris]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Don't use TCW-3, it will be even worst. If you are leaving it over winter, add nothing to the fuel. Straight petrol has a life of about 12 months in average temperatures, with the cold of winters that will be even longer.

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Don't use TCW-3, it will be even worst. If you are leaving it over winter, add nothing to the fuel. Straight petrol has a life of about 12 months in average temperatures, with the cold of winters that will be even longer.

The straight gas idea is not bad. Actually I'm testing aliquots of gas spiked with various additives (including TCW3) in some glass jars. I should have some results in a month or two. The results so far suggest gas spiked with MMO is corrosive to brass.

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

Don't use TCW-3, it will be even worst.

BTW, the link I provided above states this:

Patrick Martin posted about this recently in the Methanol thread.

His experience is that Sta-Bil will, if the carb dries out of gasoline in, say, six months, leave a hard varnish/goo that necessitates disassembly and cleaning of the carb before use.

As an alternative, he uses a shot of 2-cycle oil in the gas tank before storage — apparently it too stabilizes the fuel and if said fuel should evaporate from the carb over time, the oil residue left behind will readily mix with the gas once the fuel shutoff valve is opened up.

If 2-cycle oil works as gas stabilizer in Model T cars, why wouldn't it work in a boat? I'm sure there are lots of people on this forum who use 2-cycle engines with TWC3/gasoline mixture and have some good ideas about it. This subforum may not be the best one to ask this question though.

Finally, if Seafoam does stabilize gas as it claims and many people agree, its major ingredient is mineral oil, just like TWC3.

 

[Jmunk]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

I've been using Startron as a fuel additive, not sure if it's better then Stabil, but I haven't had any issues with any engines that I've used it in.

On a side note, I do add a quart of TWC3 oiil to my diesel from time to time. It's suppose to be ash-less and will not leave deposits in the combustion chamber like normal two stroke oils.

 

[mpdive]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

I'm kind of under the impression that you are determined to add something to your fuel regardless. I have used stabilizers for years and dont fret about small deposits as they are a natural byproduct of raw fuel. To worry about the small downtime of the boat would be like constantly being worried about buildup in your vehicle. Carb rebuilds are a common maintenance upkeep and is just part of the boat ownership lifestyle. Again, I would not worry about it and would not be concerned about the small amount of buildup you noticed after years of service. As Achris mentioned, fuel life does well all on it's own for short time spans with no help from us.

 

[achris]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

BTW, the link I provided above states this:



If 2-cycle oil works as gas stabilizer in Model T cars, why wouldn't it work in a boat? I'm sure there are lots of people on this forum who use 2-cycle engines with TWC3/gasoline mixture and have some good ideas about it. This subforum may not be the best one to ask this question though.

Finally, if Seafoam does stabilize gas as it claims and many people agree, its major ingredient is mineral oil, just like TWC3.

It doesn't... That guy is completely misinformed, and just plain wrong. Go talk to someone with an outboard in a hot climate... Ask him how long his fuel lasts...

Some people put 2 stroke oil in the fuel as an upper cylinder lubricate, which is is very good at. But it is NOT, and never will be, a fuel stabiliser.

And Seafoam is NOT like TCW-3....

 

[jack black]

Re: Questions on Mercarb bowl capacity, running carb dry, and some more related issu

And Seafoam is NOT like TCW-3....

Yes and no.
Seafoam Ingredients/CAS #/Wt.%
Pale Oil/64742-54-7/40.00 - 60.00%
Naphtha/64742-49-0/25.00 - 35.00%
IPA/67-63-0/10.00 - 20.00%

If one googles for pale oil CAS# 64742-54-7, a lot of things show up, including popular TCW3 oils: http://msds.walmartstores.com/cache/623587.pdf