weird coloured plugs

[facthunter]

Just adding to my post #9 , the effect will increase the faster you go as the pressure drop across the cowl area increases. Check Vent OUTLET location. Not being blocked is not enough. Ring Floods and check what they say. It's mentioned bu Rotax somewhere. It leans out the motor quite significantly...Nev

 

 

[bones]

Just adding to my post #9 , the effect will increase the faster you go as the pressure drop across the cowl area increases. Check Vent OUTLET location. Not being blocked is not enough. Ring Floods and check what they say. It's mentioned bu Rotax somewhere. It leans out the motor quite significantly...Nev

This is true Nev but if nothing has changed since he parked it up, i cant see why it should be the problem, providing it wasnt doing it before..

 

 

[facthunter]

The instance I was involved with the tubes were just left to dangle in the cowl which was probably a high pressure area. Not a thing you would worry about unless you realised it's significance. You get a lot of this effect on gas installations on cars where the equaliser tube at the back of the regulator? (The bit with the diaphragm in it) is not connected to a place that has equal pressure to the air intake. Nev

 

 

[jetboy]

One issue I will re-state is that the float needle valve rubber tip deteriorates with time. It will often fail during extended park-up and the fault is not even visible looking at it.

 

On engines with fuel pump this causes serious over-rich running.

 

On gravity feed installations like mine it shows up as minor fuel seepage out of the carb if fuel is not turned off in the hangar. I found this out when my plane would only cold start without "choke" actually it was starting better than ever in this condition. Float level did not change, and EGT are normal.

 

Ralph

 

 

[turboplanner]

What's your location tiketyboo? so we can get an idea of climate and altitude.

 

 

[Guest Maj Millard]

tikityboo, In your first post you state that only the #3 plug and cylinder has the problem. The majority of the solutions offered would affect at least two cylinders, on the same side.

 

Because the engine sat in storage, I wouldn't rule out that you may have a sticky valve on #3 or some ign problem relating to that cylinder. ould also be you have a gummed up hyd lifter on that cylinder, or one that hasn't pumped up correctly with oil. You say you have put in new plugs, which ruled out my initial thought..bad plug.

 

Any carb or manifold problem will effect both cylinders on that side, not just one.

 

The small clear plastic'equalization tubes out of the fuel bowls are very important, and supply ambient pressure to the carb bowls. Any alteration of these, especially T-ing into one can, and will effect carb operation. They are often mistaken simply for fuel overflow drain lines, which is their secondary purpose.

 

The standard set up with those is about 5 inches long, and tucked under the bowl retaining spring on the side that the exit the carb.

 

Please do not go changing settings in the carbs, they are ment to be set and left alone, you will only be chasing your tail here.

 

A 912 will not start to give you a reliable colour on the plugs until well after 50 hrs TT anyway, and often it will take 100 hrs for things to be reliable, and readable colour wise.

 

The nikasil bores take a while to seat the rings, and until this occurs you will be burning some oil which will give you a blackish rich reading on the plugs........................................................cheers...........................Maj...

 

 

[Kev]

The correct position for the vent tubes is either tucked inside the carburettor bowl spring, or routed to a connection on the air filter box.

 

Sorry, but can't find the Rotax reference right now.

 

Safe Flying

 

Kev

 

 

[tiketyboo]

well gang, thanks a million for all the ideas and thoughts, the bird is running much better, routed the vent tubes, replaced the gaskets and needle jets, cleaned the carb and finally replaced the bloody fuel lines forward of the filter, now is running even better than before. thanks again.

 

 

[Guest Maj Millard]

tiketyboo, thanks for listening. Good to hear things are fine again...................................Maj...

 

 

[RickH]

Rotax recommends that the vents on the sides of the carbs be joined by a length of tube as mentioned above with the hole located at mid point as the standard setup as this insures balanced pressure across the carb. Have a look at their operators manuals.

 

 

[tiketyboo]

it is a funny thing, but rotax came out about a month ago with an urgent update, replace the high pressure fuel line from the fuel pump, guess what we did months ago to solve the problem, replaced the fuel lines... i plan on checking the plugs as one member said at 25 hours to see if there is a difference

 

thanks gang been flying around nice and smooth now