New member of the 'Sinker Club' (carb floats)

[dinowal]

Just replaced third set of floats. Only have 35 hours on the Hobbs, which has taken me 2 years ... (Other distractions have kept me on the ground too much!) With new floats & all new plugs installed engine is still running rough on both ignitions & plugs black with carbon after taxiing.My latest idea is that I have faulty fuel, have always used BP ultimate unleaded, which is 98 Octane, I believe. Can the Aussie 12 drivers please let me know what you are using, & any comments? Thanks. DEAN....

[NinerBikes]

Originally Posted by dinowal

Just replaced third set of floats. Only have 35 hours on the Hobbs, which has taken me 2 years ... (Other distractions have kept me on the ground too much!) With new floats & all new plugs installed engine is still running rough on both ignitions & plugs black with carbon after taxiing.My latest idea is that I have faulty fuel, have always used BP ultimate unleaded, which is 98 Octane, I believe. Can the Aussie 12 drivers please let me know what you are using, & any comments? Thanks. DEAN....

Is your Mogas straight gas, or with Ethanol added up to E-10 ? Trying to see if there's a trend with ethanol in the Mogas causing the floats turning into sinkers as being causal.

[AJSWA]

Originally Posted by dinowal

Just replaced third set of floats. Only have 35 hours on the Hobbs, which has taken me 2 years ... (Other distractions have kept me on the ground too much!) With new floats & all new plugs installed engine is still running rough on both ignitions & plugs black with carbon after taxiing.My latest idea is that I have faulty fuel, have always used BP ultimate unleaded, which is 98 Octane, I believe. Can the Aussie 12 drivers please let me know what you are using, & any comments? Thanks. DEAN....

Dean,

From the home work i did a year ago BP ultimate 98 fuel seemed to be the pick of the Australian fuels for consistency. (Meeting the Australian stds particularly in the eastern states)

I use shell 95 here in WA, not by choice, (unless flying or not flying is the choice), it's all we have available at my location.

How long has the fuel been sitting unused in your aircraft fuel tank? How often do you fly?

I have no idea and would doubt if BP or any of the other suppliers blend ethanol or other different components with their fuel without declaring the change. Although unfortunately where additional profits for products are involved these days it does leave you wondering.
Like why are so many floats failing these days? Is it a float manufacture / material change? or is it a result of a more sinister change of fuel chemistry ingredients? What else is there that could bring about such a sudden change of float durability?
or has the problem been there all along and just being talked about more openly these days?

[crashley]

I fly out of latrobe valley victoria 500 hours on out rv12
I use either BP 98 or caltex 98 when flying here and avgas when on trips if I cant get mogas
no problems and still on original floats

Plugs are black after taxiing but that is normal according to bert floods
They state that the plugs especially the rear 2 ( I think ) will run very rich at idle

[AndrewR]

Originally Posted by dinowal

With new floats & all new plugs installed engine is still running rough on both ignitions & plugs black with carbon after taxiing.My latest idea is that I have faulty fuel, have always used BP ultimate unleaded, which is 98 Octane, I believe. Can the Aussie 12 drivers please let me know what you are using, & any comments? Thanks. DEAN....

I fly behind a 912S (but not a RV... one day hopefully!) My engine does not seem to like the 98 octane fuels.

I recall 20ish years ago when these fuels were introduced there was a lot of debate about using them in motorcycles. They tended to run rich in carb engines.

I suspect the same problem still exists. The fuels are denser than e.g. Avgas. The data sheets I can find list a density around 0.75 kg/l whereas Avgas is 0.71-0.72 kg/l. I think Mogas is assumed to be the same density as Avgas.

The additional density gives better fuel economy if the mixture is adjusted to suit, which modern cars with EFI and O2 sensors do automatically. A regular carb does not, so I think it ends up about 5% richer - maybe too rich in some circumstances.

My engine runs much better on 95 octane from the local Apco than the BP/Shell 98 octane. On the 98 it feels harsh, on the 95 it is much smoother. I asked Wal from Bert Flood's about it, his reply was to run it on the 95, that's all it needs. So I guess I just have to put up with paying 10-20c a litre less

I have no idea whether the 98 octane fuels affect the floats - it is possible they have something in them that is more aggressive to the material. I haven't had any float problems to date, although my engine predates the major float issues.

Caveat: I think these carbs run leaner with more prop pitch (less rpm = less airflow = transition to cruise settings on the needle at higher manifold pressure). I know the RV12 typically has quite a lot of pitch, so maybe a richer mixture has benefits (as does additional octane).

[blythet]

485 hours in 6 years here in eastern NC. Floats are original. They are weighed each year with no noticeable weight change. As with most other owners, I use Mogas, mostly with 10% ethanol. Only AV gas used is on my treks down to Sun N Fun and back. Plane is used almost exclusively for cross country flights. The RV12's Fun Factor far exceeds that of my old Skyhawk, plus its faster!!

[Handclutch]

Floats seem to be a lottery. I have 330 hours on mine with original floats in LH carb while the RH hand have been changed twice. At the annual in January last year RH were heavy and replaced. About 6 months later I started to get strange fuel flow indications. Floats were found slightly heavy again although I think the main problem was fuel level too high. New floats, level corrected, and all good again. At the annual this week all floats ok, thankfully.

For quite some time I was refuelling from the local flying club mogas tank - BP 95. They?ve been running their Tecnams on 95 for several thousand hours with no problems. That supply is no longer available, so now mainly using 95 from Apco, like Andrew - much cheaper. Hadn?t heard the Flood?s recommendation for 95 but fits in with local experience here.

(For our US friends - almost certain we use a different octane rating scale in Australia.)

Jack

[AndrewR]

Originally Posted by Handclutch

Hadn?t heard the Flood?s recommendation for 95 but fits in with local experience here.

It wasn't a specific recommendation, more along the lines of
Q: "My engine feels harsh running on BP/Shell 98 octane. It feels much smoother if I use the cheaper 95 octane. What should I do?"
A: "Use the 95 octane"

I do suspect my engine runs rich in the mid range but have been reluctant to mess with the needle clips.

[Jeff Vaughan]

I am doing my first inspection on my 12. All of the carb floats are over weight.
Have not been able to locate any replacements. All Rotax dealers tell me they are back ordered currently 30 days or indefinitely.

I only have 74 hours on the carbs.

Now that sucks.

[Piper J3]

Originally Posted by Jeff Vaughan

I only have 74 hours on the carbs.

Now that sucks.

Yes, it does...