Jump to content
John Vance

What is that gunk in my carburetor bowl?

Recommended Posts

After recent engine performance issues, I removed and cleaned my carburetor bowls. It had been 50 hours since annual, during which this would have been checked. I found several different species of gunk:

1.  Grayish black deposits on the bottom of the bowls.  When scraped with a dental pick, tiny flakes of crap came off.

2.  A small (1/16" dia) greasy-looking soft blob stuck on the bottom next to one of the float pins. 

3.  The one I suspect for my engine issues: an approximately 3/16" x 1/8" thin light-tan chunk.  When compressed with a dental pick, it broke up into smaller pieces. 

There's no way item 3 got through a filter, and none of them appeared to be things that were by-products of maintenance activities (e.g. rubber chunks, etc), so I think they sprang into existence right there in the bowls. I use mostly non-ethanol auto gas, but use ethanol auto in the summer for about 4-5 months, and 100LL only when traveling and have no other choice. With 100LL, I usually drop a little decalin in. 

Does anybody know what might cause these contaminants?  More importantly, is there a way to avoid their formation?

Share this post


Link to post
Share on other sites

John, I just don't see any way that sort of stuff could get thru the gascolator screen unless it was in a fine suspension in the fuel.  I'm thinking the tan and the grey crap is something that is very fine and was in suspension in the fuel which got thru the screen then settled out of your fuel and somehow joined together to become an accretion on the bottom of your bowl.  Did you see this in both bowls?  The greasy blob might be a layer of oil or grease that has maybe mixed with some water that might be in your fuel and this congealed inside the bowl.  I've also seen algae growing in fuel.  This occurs at the fuel/water interface if there was water in the fuel.  I think that you might have gotten some fuel from a filling station that may not have a good sumping maintenance program and/or didn't maintain it's final fuel filters.  It appears that you might have found your problem.  My thought is the large, name brand stations that sell a lot of fuel are the ones to buy MoGas fuel from but this isn't always 100%.  Maybe one of the experienced mechanics might have seen what you found.

Share this post


Link to post
Share on other sites
3 hours ago, Runtoeat said:

John, I just don't see any way that sort of stuff could get thru the gascolator screen unless it was in a fine suspension in the fuel.  I'm thinking the tan and the grey crap is something that is very fine and was in suspension in the fuel which got thru the screen then settled out of your fuel and somehow joined together to become an accretion on the bottom of your bowl.  Did you see this in both bowls?  The greasy blob might be a layer of oil or grease that has maybe mixed with some water that might be in your fuel and this congealed inside the bowl.  I've also seen algae growing in fuel.  This occurs at the fuel/water interface if there was water in the fuel.  I think that you might have gotten some fuel from a filling station that may not have a good sumping maintenance program and/or didn't maintain it's final fuel filters.  It appears that you might have found your problem.  My thought is the large, name brand stations that sell a lot of fuel are the ones to buy MoGas fuel from but this isn't always 100%.  Maybe one of the experienced mechanics might have seen what you found.

Hi Dick - The gray/black spots on the bottom were present in both bowls. In one bowl, scraping these spots produced the tiny flakes, but not in the other. The one I couldn't scrape crap from was the one with the big flake in it.  I wondered whether something in the fuel interacted with the aluminum or the anodize layer to spawn the tiny flakes as well as the big one that scared me. The greasy blob was black in color - it obviously wasn't just petroleum grease, or it seems it would have dissolved.  Maybe a watery amalgum, as you proposed. I'm using non-ethanol in NC,  so water would not be absorbed.  What bothers me about all this is the short time frame to creation of this stuff, along with the potential consequences. 

Share this post


Link to post
Share on other sites

Having had my share of questionable stuff in the carb bowls i have come to the conclusion that it has to have come from somewhere between the outlet of the fuel pump and the carb. Anything happening before the fuel pump cant get through the fuel pump filter but after the fuel pump there is no more filtering that goes on. Check the fuel hose on the outlet of the fuel pump. I can't explain what the stuff is that was in your float bowls but must have come from the plumbing downstream from the fuel pump. I am not an expert on the system like some of the mechanics on the forum but that is my take on the issue, for what its worth.

Larry

Share this post


Link to post
Share on other sites
11 minutes ago, Runtoeat said:

Has anyone heard of or considered alodining the float bowls to prevent oxydation?

That might be worth considering, and I don't see how it could hurt.  I'm beginning to think that both the grease ball and the flakes might be Aluminum Hydroxide. I found this on Wiki under Aluminum Hydroxide:

Freshly precipitated aluminium hydroxide forms gels, which are the basis for the application of aluminium salts as flocculants in water purification. This gel crystallizes with time. Aluminium hydroxide gels can be dehydrated (e.g. using water-miscible non-aqueous solvents like ethanol) to form an amorphous aluminium hydroxide powder.....

Any chemists in the house?

Share this post


Link to post
Share on other sites

Don't.

The bowls will out live you as they are. I do a lot of carbs from around the country. I have only seen one set that needed replacement because they had been filled with water and left to sit. They had come from Florida and had sat outside most of their life and they were 12 - 15 years old. The little tiny marks some of you see from a drop of water is nothing.

Share this post


Link to post
Share on other sites

The three words that popped out for me in that Wiki post were "Gels", "Crystalizes", and "Ethanol".  Made me go hmmmm.  I'm not worried about the black spots, but I don't care much for the flakes. 

Share this post


Link to post
Share on other sites

Has anyone else found stuff that flakes off like John sees?  John, I'm thinking this is not from a reaction with the aluminum bowl.  I think it's something that was suspended in the fuel and precipitated out.  I have not noticed this in my carbs and I use 100% ethanol MoGas.  The weird thing is that the fuel in the bowl would need to sit unused for extended periods in order to form this scale.  Your fuel doesn't sit in the bowl long enough to do this  Do you think this scale might have been there but not flaked off when your carbs were inspected and it wasn't noticed?  Maybe this has been there before you bought the plane and formed due to the plane sitting unused? 

Share this post


Link to post
Share on other sites

I've seen it.

It caused power loss and severe engine roughness on a CTSW I worked on. I found a flake floating around at the bottom of the bowl right where the main jet is. At high power settings, it would suddenly drop in power and get extremely rough. Reducing throttle to idle resolved, and then advancing again up until a certain point would be smooth.

Removed the flake, no more problem.

I do see particles in the bowls from time to time. I also have one bowl that has some discoloration in an area, which I thought might be water damage. So far though, years later, it's still the same spot with no change. Maybe it would flake off if I scraped it... but I am going to leave it alone!

Share this post


Link to post
Share on other sites

My carbs were torn down during the "hose job" at Lockwood in late 2006, and should have been during the last annual in August 2017.  My airplane did sit for a month last summer, another thing that makes me go "hmmm".  I spent several hours today googling things like 'carburetor corrosion with ethanol gas' and there are lots of stories out there, with photos, mostly relating to old carbureted cars, but also some stuff on the Van's site. I'm all but convinced that what I saw was Aluminum Hydroxide in two different forms (gel and crystaline).  I think it's very possible that it could be missed during inspection because it's either still adhering or because it's just not obvious unless you look closely.  I missed it at first glance.  Obviously, lots of people are using ethanol gas all the time with no problems, but I think people should be aware of the possibilities.  I plan to limit ethanol as much as possible. There are several suppliers of Swift fuel near my home in Indiana, so I might be flying for gas this summer, not just hamburgers. 

Share this post


Link to post
Share on other sites
7 minutes ago, John Vance said:

My carbs were torn down during the "hose job" at Lockwood in late 2006, and should have been during the last annual in August 2017.  My airplane did sit for a month last summer, another thing that makes me go "hmmm".  I spent several hours today googling things like 'carburetor corrosion with ethanol gas' and there are lots of stories out there, with photos, mostly relating to old carbureted cars, but also some stuff on the Van's site. I'm all but convinced that what I saw was Aluminum Hydroxide in two different forms (gel and crystaline).  I think it's very possible that it could be missed during inspection because it's either still adhering or because it's just not obvious unless you look closely.  I missed it at first glance.  Obviously, lots of people are using ethanol gas all the time with no problems, but I think people should be aware of the possibilities.  I plan to limit ethanol as much as possible. There are several suppliers of Swift fuel near my home in Indiana, so I might be flying for gas this summer, not just hamburgers. 

Oops- the Lockwood work was done in 2016, not 2006. 

Share this post


Link to post
Share on other sites
4 minutes ago, Anticept said:

If your plane is going to sit, drain the bowls!

Yes, I came to that conclusion today as well. 

Share this post


Link to post
Share on other sites

Do the float guide pins have a sealer applied during assembly at the factoty?  I would have to pull a bowl off to look.

Share this post


Link to post
Share on other sites

This is interesting.  Now, with your chemical detective work and Corey's comments, I'm in the corrosion camp John.  I still think there's a argument made for alodining here if it is corrosion.  Or, how about sloshing with creme weiss like our wings?  Coating with Imron? (waiting to get Roger's response :eyebrow-1057:).  I have drilled and installed drain screws on the carbs for my lawn and generator equipment.  Wouldn't do on the Rotax but a point well taken about draining the carbs.

What did you find on Van's website?  Were there comments specifically made about finding flaked off debris?

Share this post


Link to post
Share on other sites

I have seen mild corrosion in a float bowl, but it was not black and flakey, it was white and powdery.  I could rub most of it out with my fingernail.  I then used a white Scotchbrite pad and some Corrosion-X to clean out the bowl.  This seemed to work.  I use ethanol gas.

I don't think an airplane sitting for a month is a problem.  I think 4-6 months might be the timeframe to start thinking about issues.

Share this post


Link to post
Share on other sites
4 hours ago, Runtoeat said:

This is interesting.  Now, with your chemical detective work and Corey's comments, I'm in the corrosion camp John.  I still think there's a argument made for alodining here if it is corrosion.  Or, how about sloshing with creme weiss like our wings?  Coating with Imron? (waiting to get Roger's response :eyebrow-1057:).  I have drilled and installed drain screws on the carbs for my lawn and generator equipment.  Wouldn't do on the Rotax but a point well taken about draining the carbs.

What did you find on Van's website?  Were there comments specifically made about finding flaked off debris?

I'll leave it to the experts, but it seems alodine might help where the anodize has been compromised.  I don't think it would pose another contamination risk, since it's a chemical conversion process, not a coating.  I don't think I'd try to apply any sort of coating, though.  The post I found on the Van's site did not talk specifically about flaking, but did refer to corrosion, and seemed to come from a credible source:

http://www.vansairforce.com/community/archive/index.php?t-82539.html

I'm not going to get too crazy about all of this, but I do plan to limit ethanol where feasible, and check the bowls myself every time I do the between-annual oil changes.

Share this post


Link to post
Share on other sites
3 hours ago, FlyingMonkey said:

I have seen mild corrosion in a float bowl, but it was not black and flakey, it was white and powdery.  I could rub most of it out with my fingernail.  I then used a white Scotchbrite pad and some Corrosion-X to clean out the bowl.  This seemed to work.  I use ethanol gas.

I don't think an airplane sitting for a month is a problem.  I think 4-6 months might be the timeframe to start thinking about issues.

Andy - the flakes I found looked off-white or light tan, but I must admit I was looking at them through 3/4" of fuel.  The spots on the bottom of the bowl were very dark, though, and localized, covering a small percentage of the area.  Does CorrosionX help limit corrosion on metals immersed in fuel?

Share this post


Link to post
Share on other sites

Mr Vance,   i too have had exactly what you described above.   I could not figure out what/ where it came from.    

I have also had corrosion on the floats bowls.  This was a big concern to me so I replaced the bowls only to have the same thing happen on the new ones within the first few months.     I make it a habit now to check the bowls every month.   (using non ethanol mogas)

image.png.1934ddd5d5bbe82c5a8d55cb451f03

Share this post


Link to post
Share on other sites
27 minutes ago, cdarza said:

Mr Vance,   i too have had exactly what you described above.   I could not figure out what/ where it came from.    

I have also had corrosion on the floats bowls.  This was a big concern to me so I replaced the bowls only to have the same thing happen on the new ones within the first few months.     I make it a habit now to check the bowls every month.   (using non ethanol mogas)

Thank you, cdarza  - it's very interesting that you're getting this with non-ethanol.  Maybe I need to look a little deeper, and inspect more often, as you are doing. 

Share this post


Link to post
Share on other sites
9 hours ago, John Vance said:

Andy - the flakes I found looked off-white or light tan, but I must admit I was looking at them through 3/4" of fuel.  The spots on the bottom of the bowl were very dark, though, and localized, covering a small percentage of the area.  Does CorrosionX help limit corrosion on metals immersed in fuel?

Corrosion-X is a metal penetrant and corrosion inhibitor.  So it does prevent corrosion from starting or progressing. I don't know how well it continues working in the presence of fuel, but it should help at least get the existing corrosion out.

Share this post


Link to post
Share on other sites

Fuel will clean Corrosion-X off.

Hi Cdarza,

That little bit of corrosion isn't a big deal. Clean the bowl and put it back on. I see this in almost all bowls.

 

If you have a couple of spots of discoloration or corrosion it is not a big deal. There is no need to replace bowls.

Share this post


Link to post
Share on other sites
1 hour ago, Roger Lee said:

Fuel will clean Corrosion-X off.

Hi Cdarza,

That little bit of corrosion isn't a big deal. Clean the bowl and put it back on. I see this in almost all bowls.

 

If you have a couple of spots of discoloration or corrosion it is not a big deal. There is no need to replace bowls.

Hi Roger - It looks like Cdarza had some debris, in addition to the discoloration.  It's much smaller than the largest chunk I found, and might make it through the main jet & needle without causing any performance issues.  Has that been you experience?  

Share this post


Link to post
Share on other sites

The main jet orifice is fairly large and yes if the debris is small enough it passes right through and you'd never know it. If it is too big then usually when you are flying a round 5200 rpm the engine reduces rpm down to around 4000-4200 rpm. You could still fly. Then time to land push the carb back out of the socket, drop the bowl, toss the garbage out, replace the bowl and you're on your way without being stranded. That's called self rescue. It would pay to double check the other bowl to. This takes me about 30 minutes to pop the top cowl, do both bowls and put the cowl back on. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×