Cessna 150 creeping mixture control

[Gerald K4NHN]

My son flies a 182 and recently bought a 150 H. On his 182 the mixture control has a friction type and stays put where he puts it. On the 150 it's just a pull and push control. Did the 150 H come with just a push and pull or did it come with a friction type. With the push-pull it doesn't want to stay in the rich position, it will slowly move back to the center position with the motor running. The carburetor was just rebuilt and the engine runs supper smooth and has a great idle. I checked to see if the cable was in a bend and it looks to be an almost straight movement and not like so much that I have read about and also seen on U-tube about bending so much where it comes out of the shield... The mixture arm goes to full body stop in the rich and lean positions. Should we look for another control that has a friction adjustment on the cable or is this a normal operation on the 150 H?

 

[Tom-D]

My son flies a 182 and recently bought a 150 H. On his 182 the mixture control has a friction type and stays put where he puts it. On the 150 it's just a pull and push control. Did the 150 H come with just a push and pull or did it come with a friction type. With the push-pull it doesn't want to stay in the rich position, it will slowly move back to the center position with the motor running. The carburetor was just rebuilt and the engine runs supper smooth and has a great idle. I checked to see if the cable was in a bend and it looks to be an almost straight movement and not like so much that I have read about and also seen on U-tube about bending so much where it comes out of the shield... The mixture arm goes to full body stop in the rich and lean positions. Should we look for another control that has a friction adjustment on the cable or is this a normal operation on the 150 H?

Disconnect the inner wire of the cable, pull it out about half way put a kink in it and replace.

 

[peerlesscowboy]

Shouldn't it have a little spring loaded gizmo on the control to prevent it from working out?

 

[Henning]

Shouldn't it have a little spring loaded gizmo on the control to prevent it from working out?

Yep, they wear out after 40 years though. Tom has the right solution, just add some friction in the cable. The kink works really well because most of those cables don't have a liner in the spiral casing, so you get little detents even.

 

[Witmo]

Or, replace it with a vernier control.

 

[3393RP]

Disconnect the inner wire of the cable, pull it out about half way put a kink in it and replace.

Free.

Or, replace it with a vernier control.

Not free.

I know which method I would use.

 

[tinerj]

Or, replace it with a vernier control.

Yes! The only time I managed to kill the C150 engine was when I was adjusting mixture in flight and hit unexpected turblance with a push pull original equipment one.

 

[Henning]

Yes! The only time I managed to kill the C150 engine was when I was adjusting mixture in flight and hit unexpected turblance with a push pull original equipment one.

Oh big deal, it started back up again, didn't it? People can spend their money as they please, don't get me wrong, but there is no way I would buy a Verneer cable to replace it with. Between the cost and installation hassle, the value just isn't there in my mind. Now if I had a broken cable and had a Verneer lying around that wasn't going to cost me, yeah, then it's worth the hassle.

 

[Tom-D]

Free.



Not free.

I know which method I would use.

Me too. There is nothing wrong in upgrading to a vernier, they are not cheap, and it requires about 3-4 hours to install one. But they last for ever. but so does the push pull.

 

[Dan Thomas]

Me too. There is nothing wrong in upgrading to a vernier, they are not cheap, and it requires about 3-4 hours to install one. But they last for ever. but so does the push pull.

They'll last longer if they have the teflon liner, but those cables without the liners suffer from vibration causing the cable sheath to chafe little grooves into the wire. Those little grooves weaken the wire and it will eventually fail. When at the flight school I saw a throttle cable and two carb heat cables fail due to that. We started replacing all the engine controls at engine change. Too many thousands of hours on old cables.

Cables with nylon liners have had their own issues. The nylon can melt onto the wire if the control is too close the exhaust, and in a descent, when things get cool, it can seize the control.

Dan

 

[Henning]

Morse cables aren't completely problem free either, but they are close. They do fail in corrosion mode though. They all work a long time, make your choice, if you have to replace it you'll do it once regardless the choice.

 

[Silvaire]

May as well go whole hog and put a vernier throttle cable on too, make it one fancy-a$$ 150

 

[tinerj]

There was a significant fuel improvement when I switched to vernier for the finer control on the 150 HP on the C150. And the cost was far less that the amounts I am hearing beingvquoted here.

 

[Henning]

There was a significant fuel improvement when I switched to vernier for the finer control on the 150 HP on the C150. And the cost was far less that the amounts I am hearing beingvquoted here.

5 times the price minimum. Granted the number is not in the 4 digits when done, pilots are cheap and tend not to spend $5 more than they have to. In this case they would spend at least $400 in a shop. Whether they can get that back in 5 years of fuel consumption or not is typically not a consideration.

 

[peerlesscowboy]

Doesn't your C150 have the same thing as my '53 C170B?
Note the little rectangular metal deal around the mixture control up next to the panel, there's supposed to be a spring that makes this gizmo lock the control from backing out unless you push the bottom of it while you're pulling out, it should slide freely going in.

 

[Silvaire]

That's what I thought too There are also the ones that have notched serrations that keep them from creeping in either direction. A vernier is a bit overkill for a little O-200 but if the modest price isn't gonna kill you, by all means....

 

[Pilawt]

Doesn't your C150 have the same thing as my '53 C170B?
Note the little rectangular metal deal around the mixture control up next to the panel, there's supposed to be a spring that makes this gizmo lock the control from backing out unless you push the bottom of it while you're pulling out, it should slide freely going in.

150s up through the 1967 150G had that. But the 1968 150H, like the OP's airplane, switched to what they called a "ratchet-type" mixture control. Serrated sides of the mixture shaft rubbed against a hasp behind the panel, creating a little bit of a ratchet feel as the mixture control was moved, but not much additional friction. There was no other way to secure the mixture control, and as the airplane aged, the serrations wore down and the "ratchet" effect lessened, leading to "mixture creep" like the OP described.

The '68 150H brochure touted, "The mixture control provides positive, locked mixture setting from idle cut-off to full rich."

I remember these differences vividly. I soloed in a '67 150G and took my PPL checkride in '68 150H, when they were brand new. The sketches below are from the 1967 and 1968 owner's manuals, respectively. Naturally, those skimpy manuals didn't describe their operation in any more detail.

I've seen the mixture controls of several '68 and later 150s modified with spring locks like John's.

 

[Gerald K4NHN]

Hi all
It'll be another week before we'll be able to get back on the 150. All of you have been a great help on how we go from here. I'll keep the group informed as we go forward. I have enjoyed every posting from you guys.

Gerald K4NHN
Cayce, SC

 

[petrolero]

I had a 1966 C172G with one of those old style mixture controls. It uses a piece of metal bent into a V shape that was supposed to keep it in place. It is an exceedingly cheapo solution. The metal works most of the time at keeping the mixture in place. But I could only make gross adjustments and since that control was sticky and tended not to slide smoothly, several times I over- or underadjusted the mixture. It was super distracting and infuriating.

So even if the aforementioned "kink" method worked for keeping it in position he'll still have trouble fine-tuning the mixture. Given that the mixture setting is pretty important and can theoretically end up killing the engine (yeah I know), I'd kick that sorry ancient control to the curb.

The very first modification I did on my 172G was to replace that mixture control with a Vernier. Just sayin'.

 

[peerlesscowboy]

I had a 1966 C172G with one of those old style mixture controls. It uses a piece of metal bent into a V shape that was supposed to keep it in place. It is an exceedingly cheapo solution.

Actually the one I pictured is 2 pieces of metal that pivot on the top held apart by a V shaped flat spring. Trouble is that over time and cycles the spring loses it's "spring" and it doesn't hold the shaft anymore. Not a bad design really but it should'a had a better spring