912 Carb leak when running

[Avidfox]

I just got my carbs back on the plane and the right carb has fuel coming out of it when it is running. The fuel is coming out of the tube that is at the top/side of the intake end of the carb. I switched float and needle assemblies from the other carb and it still does the same thing (not a float or needle issue) Any ideas?
Thanks,
Dave

[sturdee]

How full is the bowl when you remove it?
With the bowl removed does the fuel stop when you raise the float manually?
I suspect the floats are incorrectly set! Causing flooding,
You say you swopped the needle and floats across but did you swop the metal adjustable part as well,?
Do you have an electric fuel pump? If you do Ensure that it isn't over pressurising the system! This is a low pressure system try with pump off!
Has the carbs been balanced ? There shouldn't be any shaking at idle, 1200
Is the choke returning to fully off?
Do you have the throttle springs ?

Good luck

[Av8r3400]

(Idle to 1800, 1200 is too low)

Sounds like floats are too high, or not closing needle to prevent over filling float bowls.

What color vitan tips are on the needles you have? This is critical. There are two available. I don't remember what color is the preferred one, though. A quick call to LEAF, extension 154, Brett Laughton, will get you the answers you need.

[Avidfox]

HI,
I swapped the metal bracket as well. It is something other than the floats, float needles or float bracket. I did notice that the idle needle valve was set at 1/2 turn before I tore the carbs down last spring. the other one (LH) was set at 1 1/4 turns. I set them both at 1 1/2 when I put them back on the engine. I turned the R/H one down to 1/2 but the result was rough running and fuel still comming from the inlet side tube.
Also No electric pump. Chokes are full off. I have them disconnected (choke cable removed)and springs to hold them off.

[kitfox5v]

I would check the seat the needle goes into. May be something in the seat not letting the needle seal. Oh yeah, be careful around that prop.:eek:
Eddie

[68niou1]

You need to check fuel pressure off of your fuel pump. If it is over 2.5 pounds to the Bings it is too much- you will need a fuel regulator. The float needle color should be black, the old ones are pink- and air fuel mixture will vary from plane to plane, Rotax always says to set at 1 and 1/2 but mine runs much better at 1/2. Lot of variables, and unfortunately tuning is a science:rolleyes:

[Wheels]

Do you have fuel coming out of the tube after you leave idle and get out of the idle circuit? 3000+ Rpm? When I had that problem I replaced the very old and brittle rubber mounts in the vibration dampening part of the engine mount. That helped, then I put in a fuel return line (with the restrictor) problem solved. So how old are the rubber mounts?

[sturdee]

Avid flyer, ok here's what I would do,
Close the throttle completely with engine stopped!
Now back of both throttle stop screws off the stop, check the stop bracket isn't bent by excessive pulling on the throttle this is your idle setting screw so if both look the same screw the stop screw in until it just touches the stop bracket, now when both the same screw in both screws EVEN AMOUNT ie one and a half turns. This may not give you the correct idle speed however the can be adjusted later too achieve rpm for idle, but must both be turned even amounts start with half then quarter to set idle!
If you have a balancing kit great if not purchase a (twin max) electronic carburettor balancer, they are quite cheep run off a nine volt battery and will indicate accurately which carb is out of sync .
1 disconnect the balance pipe of the carbs ,I remove one end,
2 attatch the small pipes from the balance kit I use a cut down bullet shell which pushes nicely into pipe connector
Now ensure prop clear set the balancer too zero and low sensortivity, watch the indicator when the engine starts and see which side is lagging stop the engine now Slacken the throttle cable and adjust forward or aft accordingly NOT THE SCREWS YOU SET EARLIER,!
When you have the needle remaining centred increase the sensortivity, and check the balance through the range there may be a slight difference so when happy, remove the kit ,re attatch the balance pipe,
3 start the engine ,check the idle, too low screw. The stop screws even amounts until your happy the idle is correct!
4 Please do not be tempted too adjust the carbs with the engine running the prop is too close always shut down and restart from inside the cockpit,
Hope that helps good luck these engines I think should be balanced more often,
Cheers

[Avidfox]

I took both carbs off and checked everything out. I am getting closer. I found that one of the float brackets was twisted a little. At Idle (1400ish) it gets rough and now the L/H side has fuel coming out of the over flow (The right side is good now. Fuel stops at above 27-3000RPM. From two to 3500 the Carbs are in sync. I am getting ready to head out to the airfield and play with the idle screw settings and going to check the float fuel level again. I am starting to wonder If I need new Motor Mounts. Are they Specific made for KF or are they something I can Buy from A/C Spruce? I figure the engine Has been hanging on the for the past 10ish years so they are probably due for replacement!

Do all Model fours have a little cup (funnel) attached to the motor mount just under the intake side of the carbs. The overflow tubes just sit inside of the funnels. Seems sort of hokey set up but there must be a reason.

[Wheels]

I could use a pic but I think you are looking at a "drip pan" that would keep a small amount of fuel from dripping onto a hot component. Not sure though.
The motor mount rubber is also called a vibration dampener. Hmm, I got rid of the fuel leaking at idle when I changed them. the engine is under quite a vibration at low rpm, when you get out of the idle circuit everything smooths out. and the fuel is being consumed from the bowls at a rate that doesn't allow them to overflow while the agitation of low idle lets them shake rattle and roll. That shaking allows the floats to drop to a position that in turn opens the flood gates for more fuel. Fuel that gets ported out of your overflow tubes. "Savvy?"
Ask Rob Seaton or Roger Lee, I think they have the vibration explanation down pat. I just fought it for so long that now I swear by engine mounts and return lines.

[Avidfox]

Well I finished up for the day tinkering. I put the cross tube back on and discovered that she now idles at 1800 without ****ing any fuel.
I ended up sacrificing some carb sync at the higher end so that I can get her to idle at the lower end.

[Wheels]

I cant live with that. We fly at wide open throttle and the engine has to be smooth at our operating rpms. I need Idle for taxi, midrange for slow decent and WOT for take off and cruise. Better chase that gremlin down.
there will always be an rpm range that makes a rougher vibe or a less than ideal feel, but we have to be smooth at the ranges we operate.
I'm voting for new rubber mounts, but it could be other stuff, I just know what I had to deal with on an 80 horse 912 in a model IV. 450 hours of ops in two years and then almost two years of maintenance. Long story, maybe a happy ending this week with the new engine mount.

[sturdee]

Hang on my engine mounts are ten plus years old and my engine doesn't shake!
The vibration and shaking is down too carb balance! Get them even and you will have no issue if set correctly! It is only possible with a vacuum balance tool ,trying too guess won't work and you will end up waisting a day scratching your head! The rotax web sight maintenance video explains what is going on! And it's free, It takes me less than half an hour from start too balance the carbs, with the right kit easy !
If the carbs are in sync, check your prop, that can shake your teeth out if not set correctly! Good luck

[Avidfox]

I am fallowing the Rotax Maint book and I am using a electronic carb sync (Carbmate) Not guessing! Don't worry I am not giving up on this. I want to make sure she is safe to fly. I am going to look into the Prop too.

[Avidfox]

She is dialed in at 3500 and not leaking and smooth at 1800. With any luck (weather looks bad for the next week). Soon I will be checking out our Hunting grounds (Tanis Mesa) Already reserved the cabin! Thanks for the Input!