What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Carb floats

P

Pat Stewart

Well Known Member
I have been experiencing a fuel smell on climb out and a lingering smell once back in the hangar. Checked all the fuel tank and fuel line connections and all is dry. When I put my hand under the carb filters I get wet gas. My filters elements are starting to turn white from red.

I went back and looked at the Carb float SB and if reading correctly my engine and carbs are outside of the range. My engine serial no. Is 6779981, my l/h carb ser no is 116358 and the r/h is 120372.

When I start the engine cold with choke on the engine runs just a little rough so I immediately push the choke back in which drops the rpm and forces me to add a little throttle to keep rpm in the green. Other than that this thing runs great. Just don't like the possiblefuel issue.

For those that may have experienced this in the past I would appreciate your feedback.
 
Last edited:
Recently found the old floats (all of which were overweight) in an Aircam in which both engines/carbs were outside of the range of the SB. Obviously the SB doesn't cover all of the bad floats.
 
The old floats and the new floats are exactly the same composition. The difference is that the new floats have 3 acceptance test performed where the older floats only had two. The new additional test is a liquid pressure test. The new floats have two dimples on them to make them easier to identify. The old floats or floats not within the SB can still sink. Some floats last to TBO and sometimes one can get heavy. It has always been that way.-

If you have a sinking float the carb will flood and the engine runs rough at idle, you have fuel smell and can see fuel in the carb vent tubes or dripping into the drip tray. If you go up into the higher rpms like 5200+ then the engine smooths out as the throttle advances because you are now using that fuel and it isn't flooding the carb.
 
Rotax has had float problems, Lycoming has had float problems...of all the things to go wrong in an engine, you would think that making floats would be relatively simple. Why has this been such a problem over the years for aircraft engines?
 
Also as an FYI, I use the choke on my airplane the same way as you. It's not really a traditional choke as I understand it. As soon as it runs for about 15 seconds, I close the choke cable and open up the throttle to bring it to idle RPM to let it warm up. With the carbs balanced, it runs very smoothly there, not so with the choke out.
 
You can confirm the float issue by weighting your floats. The acceptable range was provided in a recent post. I have in my RV-12 one carb outside the range of "bad" floats and one within. Interestingly the one outside weights more than the one within although both are within acceptable weight range. This just confirms what Sink is saying as well as the need to monitor by weighting your floats during annual inspection. It is easy and fast to do.
 
This is a heads up for those who intend to order new floats from California Power Systems. I just received 4 floats I'd ordered that were shipped in a mylar pack!!!! There were 16 perforations in the outer package caused by the pins on the floats. Two of the floats were damaged by the pin(s) of other floats in the package. Incredible. If you place an order, make sure you make a note to have them shipped in a small cardboard box.

The capper is that CPS is filing a claim against UPS to have the floats replaced -- when it's their screw up. While I'll get new floats shipped directly from CPS it's really unfair to UPS.
 
After installing the new (2 dot) floats, we found fuel pouring out the right carb. air filter on one occassion. Upon carb. inspection, we noted significant wear on the bottom end of the needle valve. There was so much wear that the retaining clip was going to be lost. Also, the mating face of the float arm bracket tab had a .006? wear depression. The arms of the float arm bracket were obviously not parallel with the carb base as required by the Rotax manual. We put a new needle valve and float arm in the right carb. and got the float arms very nearly exactly parallel to the carb. base. Re-assembled the carb., remounted it, turned on the electric fuel pump to check for leaks and there was no leak from the right carb. But, there was fuel dripping out of the overflow tube on the left carb. We were going to clean and inspect the parts on the left carb. anyway, so we did the same for the left carb. and found exactly the same conditions for it as for the right carb. This engine had between 325 and 350 hrs. at the time. Even after this, we've noted some evidence of minor residue on the drip trays which tells me that fuel comes out of the overflow tubes on occassion.
 
Carb service/inspection at 200h

jrich said:
After installing the new (2 dot) floats, we found fuel pouring out the right carb. air filter on one occassion. Upon carb. inspection, we noted significant wear on the bottom end of the needle valve. There was so much wear that the retaining clip was going to be lost. Also, the mating face of the float arm bracket tab had a .006? wear depression. The arms of the float arm bracket were obviously not parallel with the carb base as required by the Rotax manual. We put a new needle valve and float arm in the right carb. and got the float arms very nearly exactly parallel to the carb. base. Re-assembled the carb., remounted it, turned on the electric fuel pump to check for leaks and there was no leak from the right carb. But, there was fuel dripping out of the overflow tube on the left carb. We were going to clean and inspect the parts on the left carb. anyway, so we did the same for the left carb. and found exactly the same conditions for it as for the right carb. This engine had between 325 and 350 hrs. at the time. Even after this, we've noted some evidence of minor residue on the drip trays which tells me that fuel comes out of the overflow tubes on occassion.
Click to expand...

Curious if these carbs were disassembled and inspected at 200 h per the Rotax maintenance recommendation, or was that skipped?
 
I did not own the plane until after 200 hours. and the engine log book does not indicate the extent of the inspection.
 
Pat Stewart said:
I have been experiencing a fuel smell on climb out and a lingering smell once back in the hangar. Checked all the fuel tank and fuel line connections and all is dry. When I put my hand under the carb filters I get wet gas. My filters elements are starting to turn white from red.

I went back and looked at the Carb float SB and if reading correctly my engine and carbs are outside of the range. My engine serial no. Is 6779981, my l/h carb ser no is 116358 and the r/h is 120372.

When I start the engine cold with choke on the engine runs just a little rough so I immediately push the choke back in which drops the rpm and forces me to add a little throttle to keep rpm in the green. Other than that this thing runs great. Just don't like the possiblefuel issue.

For those that may have experienced this in the past I would appreciate your feedback.
Click to expand...
Take the floats out an weigh them, thats the only way to really know if they are a problem. If they are sinking (heavy) call a Service Centre with your engine informaiton. Even if its outside the range they will get a warranty for you.
You need a small scale, like they use for measuring gems or jewelry. You can get a cheap one from Harbor Freight for about 20 bucks. If the 2 floats as a set in one carb are more than 7 grams they are no good. The floats come in a set so change them both if necessary.

They changed the check at the inspection to include a weight check now for the floats.
 
Fuel Odor on Takeoff

I am currently doing my first condition inspection of my RV12. There has been a faint odor of fuel on takeoff so I removed the carb bowls and weighed the floats. The left carb floats each weighed 3.0 grams but the right carb floats weighed 3.6 and 3.4 grams. I spoke with the Lockwood technician today and he said to replace both of the floats from the right carburetor.

This is becoming a real annoyance. A couple months ago I replaced one of the floats in the left carburetor which was provided under warranty due to the service bulletin. I did receive a warranty rebate on that float as well.

Now to see if they reimburse for the two that I just ordered.

Mitch Garner
N2ET flying
 
Hi Mitch,

Fill out a Rotax CSIR and make a copy of your logbook entry of the float replacement. Those should go to your service center where you purchased your floats. You will need to have the invoice or have them pull up your order. Service centers do not automatically track these things or refund money unless the paperwork is filed.
Out of curiosity were the floats that just went bad on the recall list?


p.s.
You should always replace floats as a pair which should be the way they are shipped.

p.s.s.
For those that don't know weighing the carb floats is now in the manuals for the annual condition/100 hr. inspections.
 
Last edited:
Might have changed

Latest manual I've read says "200h or annual check" which is closer to 100h for most of us.
 
Sorry I was trying to think and write. Sometimes it comes out jumbled and my typing isn't always spot on.
The carb inspection and bowl check is indeed 200 hrs.
 
Last edited:
Well Mine was at 20 hours and started with that same smell of fuel especially during take off climb. I don't understand the paperwork warranty concern. Until they develop an acceptable replacement they should replace them all as many times as it takes regardless of time on the engine. This is a design defect not a limited warranty issue.

My 2 cents
 
You must log in or register to reply here.
Back
Top