mixture not working

[prkaye]

Bummer. So I took my carb apart and drilled the main jet. I must have messed something up when I reassembled it, because when I started the plane after reassembling everything, the mixture did not work. No leaning, no idle cutoff. I visually verified that the mixture knob was moving the mixture control arm through it's full range of travel, but it was having no effect. So I messed something up internal to the carb.
I've decided it's time to let the pros handle it, and have left the plane with the AME next door.
Any ideas what I might have messed up in my carb that would make the mixture ineffective? Throttle worked fine.

[rvbuilder2002]

Originally Posted by prkaye

Bummer. So I took my carb apart and drilled the main jet. I must have messed something up when I reassembled it, because when I started the plane after reassembling everything, the mixture did not work. No leaning, no idle cutoff. I visually verified that the mixture knob was moving the mixture control arm through it's full range of travel, but it was having no effect. So I messed something up internal to the carb.
I've decided it's time to let the pros handle it, and have left the plane with the AME next door.
Any ideas what I might have messed up in my carb that would make the mixture ineffective? Throttle worked fine.

When you rejoined the two halves of the carb, you most likely didn't get the mixture valve engaged on the valve port at the bottom.

This isn't a jab at you personally, but I feel compelled to mention something that I teach in safety seminars I have done.

In the U.S. our E-AB rules are extremely liberal. We can legally repair or maintain anything on the airplane. The big question is.... should we?

Even though as an A&P, I am certified to work on Certificated aircraft, but I am also required to have type specific training.
Meaning, if Joe Millionair comes knocking on my door and says I am in a hurry, will you quick come change the hydrolic pump on the left engine of my Gulfstream G4 for me? I would have to say no. I have never done that type of work on an aircraft (I have never worked on a corporate jet for that matter). I could gain the type specific training by having another mechanic who is familiar, supervise my work. After that, I would meet the type specific training requirement (for that specific work).

Just because we are home builders, should it be any different?

My opinion is no it should not.
I am not advocating for a change in the rules... I like the level of freedom we have.
What I am suggestion is that if you are about to work on something you have no previous experience with, get someone else involved that does have the knowledge and experience (get your own type specific training).

It worries me on a regular basis, the amount of technical help passed here in the forums, where someone heads off and starts messing around with things that could really get someone hurt (or worse), if the person doing the work, misses an important fact.
No amount of on line help can cover all contingency's. There is still a lot of important details that can fall through the cracks when the people helping aren't actually putting eyes on the project.

In this instance...
I know of engine failures that have occurred because of a messed up mixture valve in a carburetor. You may not know, but because of the way the valve works, it is possible for it to partially function where the valve is only moving through a small portion of its range even though the arm on the carb is moving through its entire range. This can leave you with an engine that runs ok for taxi and run-up, but goes severely lean on climb-out and causes the engine to quit at 200 ft AGL

Ok, off the soap box.....

[prkaye]

I agree... in hindsight I shouldn't have attempted this job myself, but I was lulled into a false sense of confidence because so many other builders have done it themselves. It's with a professional AME now, so he'll get it done right.

[Veetail88]

Oh! I wouldn't turn it over to an Aviation Medical Examiner! Those guys are TERRIBLE with carbs!

[prkaye]

in Canada AME = Aircraft Maintenance Engineer. Equivalent of A&P.

[BillL]

Originally Posted by Veetail88

Oh! I wouldn't turn it over to an Aviation Medical Examiner! Those guys are TERRIBLE with carbs!

I had one tell me to lay off carbs! I had to get an injected engine, so I was ok with that.

[Walt]

Originally Posted by rvbuilder2002

When you rejoined the two halves of the carb, you most likely didn't get the mixture valve engaged on the valve port at the bottom.

This isn't a jab at you personally, but I feel compelled to mention something that I teach in safety seminars I have done.

In the U.S. our E-AB rules are extremely liberal. We can legally repair or maintain anything on the airplane. The big question is.... should we?

Even though as an A&P, I am certified to work on Certificated aircraft, but I am also required to have type specific training.
Meaning, if Joe Millionair comes knocking on my door and says I am in a hurry, will you quick come change the hydrolic pump on the left engine of my Gulfstream G4 for me? I would have to say no. I have never done that type of work on an aircraft (I have never worked on a corporate jet for that matter). I could gain the type specific training by having another mechanic who is familiar, supervise my work. After that, I would meet the type specific training requirement (for that specific work).

Just because we are home builders, should it be any different?

My opinion is no it should not.
I am not advocating for a change in the rules... I like the level of freedom we have.
What I am suggestion is that if you are about to work on something you have no previous experience with, get someone else involved that does have the knowledge and experience (get your own type specific training).

It worries me on a regular basis, the amount of technical help passed here in the forums, where someone heads off and starts messing around with things that could really get someone hurt (or worse), if the person doing the work, misses an important fact.
No amount of on line help can cover all contingency's. There is still a lot of important details that can fall through the cracks when the people helping aren't actually putting eyes on the project.

In this instance...
I know of engine failures that have occurred because of a messed up mixture valve in a carburetor. You may not know, but because of the way the valve works, it is possible for it to partially function where the valve is only moving through a small portion of its range even though the arm on the carb is moving through its entire range. This can leave you with an engine that runs ok for taxi and run-up, but goes severely lean on climb-out and causes the engine to quit at 200 ft AGL

Ok, off the soap box.....

An excellent soap box and I happen to agree 100%. Even though I've been doing this stuff for a long time and am qualified and capable of doing many things, I still let the "experts" do what they are best at. I'm good at general AP work and avionics and have the experience and test equipment to back it up. I don't have a mag shop or a flow bench at my disposal so when it comes to mags and carbs for example I give them to a local shop that specializes it this and that is all they do. If an engine needs a teardown or ovhl I give it to an engine shop that has all the equipment and tools to do the job right, sure I "could" do it but I can't do it as good as the shop that specializes in that work.

I think it important to know ones limitations

[bhester]

Watch the guy that is going to fix it for you, so you will see what the problem is. As you are joining the upper and lower half's you have to insure that the mixture valve goes into the metering sleeve properly.
You can see it near the bottom of this page:
http://www.kellyaerospace.com/articl...essory_AMT.pdf

It is easy for it to get caught on the top of the sleeve, or to slide in on the outside of that sleeve, and not get seated properly.

Easy fix, but it means you need new locking tabs. While your in there make sure your carb has the smurf blue floats.

You can also see the parts I'm talking about in my pictures here:
https://picasaweb.google.com/bobbyhe...88825760545330

[prkaye]

fixed by my AME and working great now. It was just the mixture valve not seated properly as you guys said. Thanks!
It was good getting the FWF looked-over by a professional. He cleaned the engine, identified a few loose fittings, explained a couple of minor oil leaks, and gave me some good advice on my operating procedures to ensure long-term engine health. Well worth the money spent.
With main jet drilled, lower cowl louvers installed, and broken cylinder-wrap repaired, I'm anticipating no more issues with high CHTs. Test flight hopefully tomorrow to confirm.
On a related note - on a recent flight away from my home airport I had to fill with 100LL. I was surprised to observe noticeably lower CHTs on 100LL than I was seeing with 91 auto fuel. My AME recommended blending 100LL with my auto fuel as a better compromise than running straight auto fuel.