Carb Ice - Continued

[PA1195]

Hey Stu I'm not trying to be critical about the baffling. Here's an example from a quick search of the Forum. There's more from others as well: https://vb.taylorcraft.org/forum/tay...gine-Baffling=

You may be able to just go sideways with baffling and seal against the lower side cowl like Scott CF-CLR did: http://c-fclr.blogspot.com/p/taylorc...d-cowling.html Also see how Scott sealed around his air filter element and why.

There could be air leaks from the carb to induction spider gasket to the intake elbows attached to the cylinders. Gaskets commonly but the rubber sleeves as well. If this were a motorcycle I'd run the engine at idle and flow propane gas via a copper tube on a hose near the joints. Any leak will suck in propane and the rpms will rise.

If it were mine I'd inspect and confirm there's a tight intake system first. The go fly to a safe altitude near the airport and of course apply carb heat if icing is suspected. Then with heat off slowly lean the mixture and see what happens... if it gets better then it's too rich...if it gets worse it's too lean to begin with. My Marvel and C-85 mixture will pull out 1/2 to 1" before falling off due to leanness at 1000 MSL.

Gary

[otrcman]

Regarding the possible lack of baffling to prevent cooling air from going down and out around the valve covers: I don't know what an original baffle set looks like on a side-by-side Taylorcraft, but on the L-2 the baffles out at the heads don't go up to meet the top cowling; they bend outward along the bottom edge of the valve covers and seal to the lower cowling. This accomplishes the same purpose. I can't tell from the photos whether this is the case on your airplane, Gary, but you may be OK with your baffles yet.

Regarding your carb ice problem, sorry to say I'm no help. I flew my L-2M about 200 hours with a 65 and never experienced ice as far as I know. Then installed a C-85 (Stromberg carb) and flew another 1200 hours or so. Still no carb ice AFAIK. I was based at an airport that is 10 miles inland from the Pacific Ocean, so there was plenty of moisture available.

Dick

[PA1195]

Good note on the baffling options Dick...up or sideways. Mine go up but that's not necessarily the only option as my built up cowl fits a -12 with 4" longer motor mount. Most go up in my experience. Scott's cowl testing link above is a valuable read.

Lean or rich or ice or pick two.....the saga continues!

Gary

[N96337]

mmediately pulled carb heat and stumble cleared and I got power back. When I tried to turn carb heat off, the engine saw a decline in power almost immediately and then started to stutter. I flew another 15 mins and was never able to take the carb heat off regardless of RPM unless i started to climb at full throttle. .

That's sounding like a carb mixture problem to me and not carb ice!! I'd be very suspicious of the carb, especially a fresh overhauled one!
John

[3Dreaming]

Gary, if you look at the picture looking down through the 2 cylinders you can see the baffle extend out to the lower cowling. That is the way the stock baffle is for a B series with a closed cowl.

[Kerbs]

The baffling was bugging me how I missed it, because looking at the picture you can't see it... unless you look really close. 3Dreaming is correct, it wraps down and then under. I went through my pictures and here is one showing how the baffling is set up. Gary, thanks for pointing it out though, it's always worth double checking this stuff and a lot of it is still new to me.

Back to the problem at hand, I am going to head out to the hanger today and check sealed/rubber on the induction tubes as well as playing with the mixture. I am thinking there may be something here in one of these. I sincerely appreciate everyone's input and help. Theres such a good cumulative knowledge for our old birds that is just hard to get anywhere else. I will report back when I have more info.

[PA1195]

Hey guys thanks for the correction...on Stu's what I thought was concrete visible below the engine valve covers is actually the aluminum side baffle with felt edging. Airforms https://vb.taylorcraft.org/filedata/fetch?id=156211 is another option like mine. My first Taylorcraft also had vertical baffles and a -4 mount setup.

Make sure you also confirm full travel of the Marvel's mixture control lever lean<>rich. Might also be a good idea to have your mechanic drain the carb bowl via the 1/8" pipe plug in case there's something inside. Sometimes new fuel lines can have internal obstructions at the metal fittings - flap of rubber.

Gary

[Robert Lees]

My (inexpert) instinct, having read and re-read all the very constructive posts here, is that it's not carb ice at all. No-one else (including me, in my C-85 machine in a very humid UK home) has the same problem.

It's a mixture issue...possibly the carb itself.

Kerbs, can you get whomsoever overhauled your Marvel carb to provide a loaner for a flight?

Rob

[otrcman]

Stu, in your very first post for this thread, you said, "Applying full carb heat, stuttering stops and power comes back as the ice clears".

Do you ever see any initial power drop or greater stuttering immediately after pulling the carb heat ? My carb ice experience is admittedly limited, but in the times I have had it, pulling the carb heat first results in increased roughness and power loss. I visualize this as a slug of water going through the engine (melted ice, I presume) and then the engine smooths out and power comes back up.

Pulling carb heat on an engine that doesn't have any ice usually gives a smooth power drop and richer running. From your description, it sure does suggest that you are on the ragged edge of too lean and the carb heat is simply richening up the mixture for you.

With a Stromberg carb, you would know the mixture was too lean because it would stumble as you add throttle. But on a Marvel, this is masked by the accelerator pump.

I'm beginning to agree with the other guys. Time to investigate mixture, and not a moment too soon. You don't want to cook your new engine with an overly lean mixture.

[PA1195]

I had a PA-12-180 that quit during winter in flight. Cruising over frozen ground on skis after recent maintenance. It was a little rough at startup (it was preheated well) from the cold below zero air, but took off at what felt like full power and climbed to 2500'. The 4-point CHT's were normal but the EGT's were a bit higher but then they tend to be leaner in winter in dense cold air with fixed fuel flow.

About 45 minutes later one second running ok and then quiet. Pulled carb heat - the plane had a real heater system - nothing. Switched tanks - nothing. Switched mags from Both to L to R and back - nothing. Headed for a frozen oxbow lake off a river at best glide. Just in case recent maintenance had messed with the mixture control and it may have come loose or the carb arm had slipped on the cable I pulled the mixture full lean then back rich - Vroooom! Climbed and finished my trip to a remote cabin.

Edit: I now recall pumping the throttle after the stoppage and the engine would briefly respond then die. Same for activating and pumping the 4-point primer. The engine wouldn't stay running with the primer unlocked but the combo of the accelerator pump and primer made me consider a fuel stoppage somewhere in the carb. Then I went to the mixture control cycling.

Next day mechanic flew out and we drained ice crystals from the carb. Moving the mixture had broken up some of the icein the float bowl near the main jet and reestablished fuel flow to the engine. During maintenance there was nothing in the gascolator or finger screen so the carb wasn't drained. Now I have a quick drain valve on all my Marvel carbs.

Gary

[Kerbs]

Well I didn't get to fly yesterday like I hoped, got stuck choring. I got out today and flew for an hour and collected a lot of good data. Another similar dry high pressure day like the previous.

Before flight, I pulled the cowl and check the intake tube rubbers. Everything looks in place and correct. I checked all the hose clamps and everything was tight. I also checked the primer into the manifold, manifold to carb and carb to airbox. Everything looks good.

I spent quite a bit more time experimenting and here is what I found. The engine is running great at 2,400 rpm or better. The engine is also running great (without carb heat) at 1,900 rpm and lower. I could vary the power within this lower range without a problem, no hesitation or ice. What is puzzling me is that the engine starts to stutter really bad in the 1950-2350 rpm range unless carb heat is on, in which it smooths out, power increases slightly and I run fine. If I am at 1,900 rpm and advance the throttle slowly, it will get to about 1,950 then just continue to stutter and run worse as i continue to slowly advance it until I either pull carb heat or advance the throttle hard. That was another reason I am starting to think it is not ice. When the engine is in this 1950-2350 range and running poorly, if I apply full power suddenly, it seems to clear up. I don't think that would be the case with ice. I could not find a power setting within this range where the engine ran smooth, only above or below. Within the range, it starts to stutter and continues to get worse fast until I take corrective action.

I did try leaning it with the mixture when it started to run poorly and it only made it worse. In my testing, I never let it continue when it started to stutter as I did not want to lose the engine, in all cases i either advanced the throttle or pulled carb heat. I spent about 15 mins today flying in the lower 1,900 rpm and below range doing slow flight, varying throttle without carb heat and it ran perfectly smooth. Its just that prime cruise range that is giving me a fit.

Again, I am stumped, but at least feel a little better having got some more data on it. I'd love any ideas or feedback.

[Kerbs]

Robert - good idea on the carb. I ordered mine form Air Power. I dont think they will give me a loaner but I will check with our museum and see if they have anything. They are loaning me a prop to try the pitch right now and are pretty good about that stuff.

[sully]

That's beginning to sound like a valve spring problem.

Sully

[sully]

Robert - good idea on the carb. I ordered mine form Air Power. I dont think they will give me a loaner but I will check with our museum and see if they have anything. They are loaning me a prop to try the pitch right now and are pretty good about that stuff.

Call Marvel direct. They took my carb and rechecked it even though I didn't get it from them. Cost me shipping only.
BTW, they found nothing wrong but it ran much better afterwards.

Sully

[PA1195]

Stu review these for your 10-4240-1 carb:

http://www.insightavionics.com/pdf%2...b%20Manual.pdf

https://msacarbs.com/carburetor-troubleshooting/

Before you send it in for reexamination make sure the intake system is tight. You said above you checked everything - how about the intake elbows to cylinder gaskets and hardware? A primer can leak when closed - if it leaks fuel it'll run rich - if it leaks air at the primer line fitting to primer or in the line before the spider it'll run lean. Check for leaks with a shot of brake cleaner while idling looking for rpm rise.

I'd drain the carb via the float bowl plug into a container with the mixture full rich. If there's any obstructions in there they may escape. If the troubleshooting chart or further service doesn't help get it looked at. One more - does changing mags when rough make any difference like Both-L-R?

Gary