Carb Magic

[petehowell]

I've had the original carb on my O-320 for 3040+ hours now. It was talking to me. Harder to start, mixture distribution doing funny things (cylinder 3 was running lean), when it was really hot, it liked to diesel when shutting down, and just last week it would leak some gas after shutdown (sticking float). It was time. This 10-5217 Carb had served me well.

I found a nice deal on a nearly new 10-3678-32, made sure it was pickled as described, then transferred over the pretty blue epoxy float. Used the new gaskets and washers and buttoned her all up.

Swapping the carb is pretty quick on the 9A and a good excuse to clean the airbox and filter, so I did. A few ground runs verified fuel was atomizing, so I asked for laps above the airport to be safe, and it was. Landed, dropped the cowl and inspected everything - all good. Now it was time to get some real data. I was a bit worried b/c the 5217 had a pepperbox(holey) main nozzle and the 3278 just has a straight tube - what would I find??

5217 Nozzle- Pepperboxed

3278 - Non-pepperboxed (yet)

I was, however, very pleasantly surprised - the 3278 provided remarkably even, FI-like mixture distribution!

Full boat ROP climb out- as I passed 5K ft the temps came down a bit. Yikes, that's a lot of Gas!

GAMI lean-test at 8000 ft - 0.1 GPH spread! Noice!

8000 ft LOP cruise with a nice CHT range and great economy - I will try a bigger blocker in front of #2 to try to get more air back to #4

Low 2300ft JFA LOP cruise with great temp spreads on 5GPH (slight dive here - 5GPH will get me 130KTAS dead level)

More tests to come, but I'm really happy so far! I have spare nozzle that we might modify with a pepperbox design as others have done here, and get some comparison data.

#3 is no longer lean and the other cylinders are right in line. Starting is back to dead-simple and no leaks after shutdown. Good stuff!

 

[Walt]

Just FYI for others, recommended OH for carbs is 10yrs or TBO. Why wait for it to fail or leave you stranded somewhere.

 

[Dan 57]

Thanks for the report @petehowell.
These excellent results demonstrate one more time, if needs be, that the carb ain't dead. Folks around here are almost exclusively hooked to FI, but the benefits, if any, are really small.
My "old" Lyco is now being replaced by a brand new TB variant, and I juggled for quite some time weighing in the pro and cons of each system. Ordered a brand new carb to fit that nice looking red Thundie...

Trouble is that mechanical piece of art sure shines like a statue, and I'm now hesitant to install it on my steed. Might re-install the old engine, and take that beauty home and display it in the living... ok, might have to ask wifey beforehand.

 

[MacCool]

Ah! The rest of the story . Glad to hear that that was a successful project, Pete. Your GAMI spread is way better than my IO320.

 

[uk_figs]

Just FYI for others, recommended OH for carbs is 10yrs or TBO. Why wait for it to fail or leave you stranded somewhere.

Walt, what does a carb overhaul entail?
Figs

 

[Walt]

Walt, what does a carb overhaul entail?
Figs

You know me, I prefer to lets the folks who OH carbs everyday do it. Factory rebuilt units are my choice, gave up using local shop after some issues.

 

[rv6builder]

When I first finished my carb'd -6, I would get a split second hesitation out of the engine after leveling off in cruise and pulling the power back. Drove me nuts for a year, and after doing things like having the mags overhauled, valve wobble test, and a few other things I kinda just gave up, as it didnt seem to cause any harm. Plus I had a friend with a -6 that did the same thing. Stumbled across those symptoms in the Sky Ranch Engine Manual, and it reccommended switching to the pepperbox jet. I did so and its worked perfectly ever since! So if you do start to get those symptoms, just be aware it may be the un-drilled jet being the issue.

 

[YellowJacket RV9]

Out of curiosity, do you happen to mean 10-3678-32? I can't find a 10-3278-32. I recently installed the former, and have overall better operation and finally enough fuel flow for adequate climb cooling, however I have 3 cylinders that are very closely aligned in EGT, and one big outlier, suggesting some mixture distribution issue. I like the simplicity of the carb, but there does seem to be some black magic involved...

Chris

 

[petehowell]

Out of curiosity, do you happen to mean 10-3678-32? I can't find a 10-3278-32. I recently installed the former, and have overall better operation and finally enough fuel flow for adequate climb cooling, however I have 3 cylinders that are very closely aligned in EGT, and one big outlier, suggesting some mixture distribution issue. I like the simplicity of the carb, but there does seem to be some black magic involved...

Chris

Hi Chris - yes - 10-3678-32 it was a late night typo - thanks for catching that!

 

[AlexPeterson]

5217 Nozzle- Pepperboxed

Pete - is that the jet we drilled out ~15 years ago?

 

[71459]

I've had the original carb on my O-320 for 3040+ hours now.

Wow you are fortunate! 1400 hours and I think I'm on my 4th carb (I've lost count). I find them delicate and finicky almost to the point of being dangerous. They can fail at a moment's notice, completely randomly, placing the pilot in immediate danger. Easily the most disliked piece of gear on my airplane.

 

[Mel]

Wow you are fortunate! 1400 hours and I think I'm on my 4th carb (I've lost count). I find them delicate and finicky almost to the point of being dangerous. They can fail at a moment's notice, completely randomly, placing the pilot in immediate danger. Easily the most disliked piece of gear on my airplane.

Well.....Something is wrong somewhere. I flew my -6 with the same carb for over 25 years (and no telling how long it flew before I bought it). The only time the carb was apart was to do the "one piece Venturi" AD.

 

[petehowell]

Pete - is that the jet we drilled out ~15 years ago?

It is!!

 

[MNN]

I have a 10-3678-32 on my 0-320. I'm looking for a little better distribution. I can't find the pepperbox for sale anymore. Can someone give me some guidance on how to make one correctly?

 

[petehowell]

I have a 10-3678-32 on my 0-320. I'm looking for a little better distribution. I can't find the pepperbox for sale anymore. Can someone give me some guidance on how to make one correctly?

Some info here - Pepperbox

 

[BH1166]

I have a 10-3678-32 on my 0-320. I'm looking for a little better distribution. I can't find the pepperbox for sale anymore. Can someone give me some guidance on how to make one correctly?

Just because this post mentioned distribution, I’m not finding the carb and jet having a noticeable impact on my O320 distribution. I had my 10-5217 rejetted to flow 14gph (D&G Supply Niles MI FAA repair shop). Pepper box style was removed and I still get nearly exact same distribution running LOP ( using EGT) as before the new jet and flowed from 11.2 to 14 gph. I understand the thought jet change would make better….just a very documented NO Change for me. More to distribution I’m guessing than just jet.

 

[petehowell]

Just because this post mentioned distribution, I’m not finding the carb and jet having a noticeable impact on my O320 distribution. I had my 10-5217 rejetted to flow 14gph (D&G Supply Niles MI FAA repair shop). Pepper box style was removed and I still get nearly exact same distribution running LOP ( using EGT) as before the new jet and flowed from 11.2 to 14 gph. I understand the thought jet change would make better….just a very documented NO Change for me. More to distribution I’m guessing than just jet.

Interesting Butch -

Big difference for me - the new carb significantly changed my distribution. I went from a 5217 pepper box to a 3678-32 non-pepper box, and it brought my EGT peaks from ~.9GPH to .1 GPH apart. My #3 used to be much leaner, running 70-85degF cooler when running LOP and always peaked much earlier than the other 3 - now it is right in line. There does seem to be some airflow voodoo that govern how these engines breath. The carb could also be offsetting some other issue in the system.

We are going to mod a 3678 jet to pepperbox. I'll report back on that one when we run it. I'm less incented to move fast on it since this one is working well, tho.

I'll keep testing - good excuse to fly!

 

[Walt]

I flew my -6 with the same carb for over 25 years (and no telling how long it flew before I bought it). The only time the carb was apart was to do the "one piece Venturi" AD.

Sorry Mel but I'm not so sure admitting that is a good thing .... someone may get the impression that you're somehow endorsing that carbs don't need to be overhauled periodically as recommended.

 

[scsmith]

Sorry Mel but I'm not so sure admitting that is a good thing .... someone may get the impression that you're somehow endorsing that carbs don't need to be overhauled periodically as recommended.

Condition-based maintenance. If it ain't broke, don't fix it. (I'm half kidding, half serious).

Wow you are fortunate! 1400 hours and I think I'm on my 4th carb (I've lost count). I find them delicate and finicky almost to the point of being dangerous. They can fail at a moment's notice, completely randomly, placing the pilot in immediate danger. Easily the most disliked piece of gear on my airplane.

I'm wondering what is 'finicky? The only adjustments on the whole thing are the idle mixture screw and the idle throttle stop. The carb seems pretty bullet proof in terms of basic function. Mixture and distribution may be tricky to get just right, but once you got it, its not going to suddenly change.

What can go wrong at a moment's notice?
The only event I'm aware of turned out to be a glob or orange RTV that somehow found its way in and plugged up the carb.

A float could spring a leak I suppose - that seems to be a common failure. Poor seating of the float needle valve? I wonder if that would even cause an issue at cruise power? probably just over-rich idle and fuel dripping out.

 

[Walt]

Condition-based maintenance. If it ain't broke, don't fix it. (I'm half kidding, half serious).

I'm wondering what is 'finicky? The only adjustments on the whole thing are the idle mixture screw and the idle throttle stop. The carb seems pretty bullet proof in terms of basic function. Mixture and distribution may be tricky to get just right, but once you got it, its not going to suddenly change.

What can go wrong at a moment's notice?
The only event I'm aware of turned out to be a glob or orange RTV that somehow found its way in and plugged up the carb.

A float could spring a leak I suppose - that seems to be a common failure. Poor seating of the float needle valve? I wonder if that would even cause an issue at cruise power? probably just over-rich idle and fuel dripping out.

I think the question should be, if you choose to disregard recommended scheduled maintenance and the engine quits, now what happens?
Do I really need to repost the accident chart on how many mishaps are due to mechanical problems (most are the engine quit)?

I think 'we', as in EAB owners/operators and 'ambassadors' of this hobby, should be doing a better job of encouraging good maintenance practices, instead of undermining them with statements like "if ain't broke don't fix it", even if said in jest.

 

[YellowJacket RV9]

I think the question should be, if you choose to disregard recommended scheduled maintenance and the engine quits, now what happens?
Do I really need to repost the accident chart on how many mishaps are due to mechanical problems (most are the engine quit)?

I think 'we', as in EAB owners/operators and 'ambassadors' of this hobby, should be doing a better job of encouraging good maintenance practices, instead of undermining them with statements like "if ain't broke don't fix it", even if said in jest.

What percentage of those accidents due to mechanical problems occurred after recent maintenance or other changes? Without that data, it’s a bit presumptuous to assume that they were due to LACK of maintenance. Should we all overhaul our engines no matter what at 2000 hours or 10 years, also? I'd be willing to bet if we all did that, the failure rate would go UP, as shortly after overhaul is the most common time to have a failure.

I get that there is a line somewhere, but there are some very smart people here who are perfectly able to make informed maintenance decisions. The best time (theoretically) to overhaul a part is right before it fails. The hard part is knowing when that would be.

 

[Dugaru]

The best time (theoretically) to overhaul a part is right before it fails. The hard part is knowing when that would be.

Yup. My theory: magnetos get attention every 500 hours without fail. Everything else - there’s a lot of variables. Time limits declared by manufacturers are scrutinized… carefully.