Posted Monday, January 11, 2010 @ 01:14 PM  

I would reinstall the Zenith carb. I would start with using the std size main jet. I am using a std main on my 1,400 cc engine full throttle climb I see 1,400F (760C) exhaust temps. If pull the thottle back 1/8" (3mm) the exhaust temps drops 100F (100C). If you need a float bowl gasket I can send one.

Collin

Posted Tuesday, January 12, 2010 @ 09:32 PM  

It is interesting that Collin says he is using a 'standard' size main jet on a 1400cc motor.
Between us, Matthew and I have four carburetors (one ofr each airplane and one spare).
We measured the actual diameters of the holes in what are supposed to bestandard 1.25mm jets and found a very wide variation, from an actual diameter of 1.25mm up to 1.32 mm.
We measured the diameters by buying a set of drill bits, 1.25mm, 1.26mm, 1.27mm and so on, up to 1.45mm.

By timing the aircraft's climbs and looking at the spark plugs, it seems that an actual jet hole diameter of 1.28mm or 1.29mm works best with a 1400cc motor. However, because I left my main jet in England I have had to make up one from a steel bolt. The only bolts I could get in Australia in that diameter and thread pitch were very hard, and I broke a number of bits drilling the holes, so I am currently flying HDO with a 1.32 jet. It seems to perform fairly well, but is does burn significantly more fuel than before.

Because of all this 'guesswork' I intend to buy an NGK AFX oxygen sensor, fit it to one of my exhaust pipes and ensure that the mixture is perfect with a 1.28 or 1.29 jet.

Unfortunately, having read the pdf manual, I have discovered that the 12-volt sensor actually measures voltage, and it has a heater incorporated, so presumably it will need a bigger battery to nesure a steady voltage for flight trials.

Is there anybody out there who has used an NGK AFX mixture sensor and can give me some advice?

Posted Wednesday, January 13, 2010 @ 12:54 PM  

I will send a gasket tomorrow.

Posted Monday, September 27, 2010 @ 03:36 PM  

I would try disconnecting the fuel line from the aerocarb and letting it drain out for a while and see if there isn't something else restricting fuel flow. If it is hot again, you might be able to see bubbles and confirm your theory.

A very important bit of information to know. I'm just a bit skeptical, that's all.

Posted Tuesday, September 28, 2010 @ 12:17 PM  

I think I already said that vapour-locking and other fuel flow interruptions are precisely the main problems with these bowl-less carbs.

Fuel line insulation only slows down the flow of heat into the fuel line; it does not stop it.

Worse, once the fuel and line are hot, that insulation also slows down its cooling.

And all this is ten times worse with mogas than avgas, for various reasons.

Somewhere else on this site you will see that I have flown several hours with a digital thermometer under the lower cowling, clipped to the air filter.

From memory, the inlet air temperature is generally 25-30 degrees C (50-60 degrees F) hotter than ambient, so that on a hot day it is VERY hot under those cowlings. This is good for preventing carb ice, but bad for performance, and very bad for vapour-locking.

If you fit a Zenith 28RXZ carb to a 1400 engine you will definitely need to open out that main jet to 1.28mm or 1.30mm or maybe even more, unless you always fly from a high-altitude airfield.

Several 1400 Fournier owners have bragged to me that they get 'much better fuel consumption' with their bigger-than-standard engine.
They have obviously not stopped to think why.

This is clearly because they are running with a lean/weak mixture because they have not openend out their main jet (or possibly their needle valve -- or both).

This is great for a few hours.
They will save quite a lot of money on fuel.
Although they will be a little down on posible performance.

Unfortunately after a couple of hundred hours they will need new cylinder heads.
Or, worse, they will loose the welded head off an exhaust valve due to overheating and have to make a forced-landing, with all the repairs, expense and risk that involves.

Sensible people think about what they are doing.
Silly people don't.

The information is all on this site.
All you have to do is find it, read it, and then do it.

Posted Tuesday, September 28, 2010 @ 05:24 PM  

If the problem doesn´t go away, dismantling the carb and wash/blow everything clean can be a cure and most often the culprit is never found. Keep us posted, I have a feeling that we will all be flying with progressively increasing alkohol content, so this might be a Fournier problem with increasing incidence.

Posted Friday, October 1, 2010 @ 11:58 AM  

It also deteriorates some kinds of fuel hoses causing particles to flow downstream into the carb.

I also tried the fuel pump and it aleviated the problem intially for a few seconds but then returned because my fuel pump is installed improperly and forms a short loop.

The return fuel line at the carb loops back to the gascolator instead of properly being returned back to the tank, so forming a loop about 24"
long and is nearly useless in that configuration as it simply recirculates the warm fuel and bubbles around in the hottest area under the cowl.

What I will do is tear down the fuel system under the cowl and inspect the hoses and clean out the carb to see if there were any issues with deteriorating fuels lines or other particles in the carb. I will also pressure test to see if there are any leaks.

I don't experience any problems when its cooler or I don't taxi long, but on that day, since I had just repaired the tank, I ground ran the engine for a good 5- 10 minutes, which I don't normally do, especially on such a hot day.

I am certain the tank repair is not a factor. I vacummed out the tank multiple times during the process and any particles that might have remained were sealed down under the epoxy. The epoxy itself is incredibly sticky and had the consistency of warm honey until it hardened. It is thixotropic which enables it to make an extremely good bond on imperfect surfaces without air bubles etc.

It dried to a hard but pliable texture....very interesting stuff.

I also had suggestions from the Aerovee forum as they are quite familiar with this problem and made suggestions such as thicker insulation (Pipe insulation covered in aluminum tape) and ducting of air specifically for the fuel lines.

I'll see what I can do in that regard, but heat on the fuel lines is never a good thing and anything can be done to minimize it is wise.