Frustrating carburetor issues.

[CamTom12]

I took my airplane apart for the condition inspection last year and saw some blue stains around the float bowl to carb body gasket area so I sent it off for overhaul. It was probably due anyway, I had no idea what internal components it had at the time.

Shortly after I started a new position at work and got super busy. Poor airplane sat. The carb arrived back with a fresh overhaul pretty quick, but sat in a box in my garage for a few months.

I finally got some free time to put it all back together, did some ground runs, set the idle mixture, and was ready for flight. Then I came back to the hangar and found this (see pictures below). It had fuel in it for ~2 weeks.

I’m very frustrated.

The carb rebuilder wants me to put the tail up and clean the residue to help diagnose the issue before I send it back. So now I get to make some time to go do that.

 

[PA-16]

Who rebuilt it? I am going to get an exchange or rebiilt carb soon, mine doesnt leak though.. thats strange, the gaskets usually seal tight, wonder if the carb is not mating up right

 

[CamTom12]

Who rebuilt it? I am going to get an exchange or rebiilt carb soon, mine doesnt leak though.. thats strange, the gaskets usually seal tight, wonder if the carb is not mating up right

D&G. The guy I’ve talked to seems super knowledgeable and they appear to have a strong reputation in the industry, too. Sometimes stuff just happens, I guess.

 

[PACERGUY]

It is not uncommon for a fuel leak at the top of the fuel bowl from gasket drying out or bolts getting loose. It is usually a simple fix with just a new gasket. I would expect a bench rebuild with a experienced shop to have no problems. If you look close at the bottom picture the gasket looks like it is compressed more at the bolt holes then in the center. Is this a condition from bad gasket material or from a uneven mating surface? I think it is the carb bowl gasket and with that much blue it should show up quickly if you shake the plane also look very close at that 90 degree fitting going into the carb. Had a friend that went through 2 cab rebuilds only to find the leak was in the fuel line fitting. Clean it well and then use colored paper edge to touch around the fitting fuel will show up quickly. I have seen cast items like the oil screen housing warp, that is a easy fix with flat surface and sandpaper. Not sure about a carb bowl. DENNY

 

[Smokey]

The carb rebuilder wants me to put the tail up and clean the residue to help diagnose the issue before I send it back. So now I get to make some time to go do that.

More than likely to make sure that the float is shutting off the bowl needle at the correct fuel level. He must have set it to shut off at the required 10/32" below the top of the float bowl, not knowing that it was going on a modified taildragger.

It appears that your main float drain is under some sort of modified plenum. Normally you can make a clear tube that attaches with an elbow to the float drain. You can the see the float level in the clear tube, that is tail up against tail down. My guess is that may not be possible for you to do. It appears that your float level is to high for your application which is flooding the bowl and leaking out the gasket.

 

[PA-16]

The gaskets job is to seal, if the float is not stopping the fuel from entering the carb the gas will be a lot more than that blue stain, its going to be real good stream of gas, been there done that LOL

 

[Steve Pierce]

The float sticking on a new carburetor is something I have seen several times and the result is the stain in your picture. D&G does know their stuff. Those bowl gaskets have to be torqued, let sit and then torqued again before bending the lock tabs or safety wiring. Have had to do several. Common on Super Cubs for the float bowl to get loose and we guess it is because of the long rod to retain the air filter to the airbox. I would do as he says and see what happens. They do know their stuff and it is nice to deal with skilled people and not just some salesman on the phone with new working knowledge. I know your frustration but if it were easy everyone would do it.

 

[PA-16]

I never heard of a float setting being different for nosewheel vs tailwheels, is that true? The issue I had was a float not working at all and gas steadily flowing out the carb, had that fixed and no leaks at all since, but my carb did not have those pushdown tabs for locking, had the safety wire.

What did you do to fix a sticking float on a new carb?

 

[Smokey]

I never heard of a float setting being different for nosewheel vs tailwheels, is that true? The issue I had was a float not working at all and gas steadily flowing out the carb, had that fixed and no leaks at all since, but my carb did not have those pushdown tabs for locking, had the safety wire.

What did you do to fix a sticking float on a new carb?

It has to be setup after overhaul. level that is. Once installed aircraft parked mixture control in ICO fuel selector shut off the fuel level remaining in the carb leaks out at the parting surface due to the angle of a tail dragger.

Normally if the float or needle sticks, gentle rapping can cause the float or needle valve to unstick. of course unless the float has sunk or the needle valve seat or taper pin is worn.

 

[CamTom12]

The float sticking on a new carburetor is something I have seen several times and the result is the stain in your picture. D&G does know their stuff. Those bowl gaskets have to be torqued, let sit and then torqued again before bending the lock tabs or safety wiring. Have had to do several. Common on Super Cubs for the float bowl to get loose and we guess it is because of the long rod to retain the air filter to the airbox. I would do as he says and see what happens. They do know their stuff and it is nice to deal with skilled people and not just some salesman on the phone with new working knowledge. I know your frustration but if it were easy everyone would do it.

Thanks, Steve. I’ve got the tail up and fuel valve set to both again. I’ll go back tomorrow morning to see if I get more blue stains.

Does a soaked gasket mean another rebuild? Or just that it stuck open once and once unstuck the carb is good to go?

 

[Gilbert Pierce]

I have had Bobby at Aircraft carburetor and injection services of Texas just do a repair when an overhaul or rebuild was not necessary.
(940) 648-2277

 

[PACERGUY]

It is a very simple task to replace the gasket. Does not need a "rebuild or overhaul" Denny

 

[CamTom12]

I guess to restate my question differently: do I have to replace my current gasket? Or will it be fine once it’s dry?

 

[Pacerfgoe]

Why not just tighten the bowl screws.....the gaskets usually compress slightly at first and can be snugged up again quite easily after a heat cycle or two....

 

[PACERGUY]

If it is just some kind of stuck float/needle valve issue you might get by with that gasket. My issue was loose screws and tightening them worked but if your screws are tight I suspect a new gasket will be needed. Fuel is sloshing all over that carb once the engine starts /runs and they don't leak That is why I think this is a carb body issue. If I am wrong and it does need to be replaced it is not hard just pull the carb and do the gasket on a bench. Hard part is getting the mixture shaft into the hole, helps to have someone with a light and hold your lower jaw to the right. You will know if it is not right because you won't be able to kill engine with mixture. Give it a try before you bolt on carb box and cowling. Been there and done dat!! You can reuse the little bolt clamp things a few times or just get new. DENNY

 

[59pacer]

After a carb overhaul on our Pacer, I saw a similar stain. After cleaning off the stain, I used some white paper towel to try to locate the leak. Turned out it was at the copper washer at the steel inlet fitting. The fuel was tracking down, caught by the bowl gasket and tracking around the back of the carb as it evaporated, leaving that type of stain.
I softened the old one (very carefully, as it’s quite thin), reinstalled, no leak.

 

[PACERGUY]

I never heard of a float setting being different for nosewheel vs tailwheels, is that true? The issue I had was a float not working at all and gas steadily flowing out the carb, had that fixed and no leaks at all since, but my carb did not have those pushdown tabs for locking, had the safety wire.

I agree, never heard of adjusting carb after going from small tires to bushwheels. If the float was that sensitive you should have issues with steep climb also. Steve, any instruction you know of to change the float setting for Tripacer vs Pacer?
DENNY

 

[CamTom12]

To close the loop, it looks like the float was stuck. No blue stains parked with the tail up overnight, and none the next with the tail down all day.

I had a local A&P/IA friend look at it and he thinks it’s fine but to keep an eye on it. He’s heard of freshly rebuilt carbs hanging floats too.

 

[tnowak]

Don't forget to insert the cotter/split pin through the bolt that the throttle cable attaches to!
TonyN

 

[PACERGUY]

Thanks for the follow-up.
DENNY

 

[CamTom12]

Don't forget to insert the cotter/split pin through the bolt that the throttle cable attaches to!
TonyN

Done, but thanks for double-checking!

I purposely left it off until I was sure I wouldn’t have to pull the carb again

 

[rocket]

Don't forget to insert the cotter/split pin through the bolt that the throttle cable attaches to!TonyN

Good catch. Once apon a time early in my bush mechanic carrier I had a processe for draining the sumps on a round motor that involved screwing them back in a thread so they cold drain the upper case without dripping on my walkboard or in the river. Yep, came back to bite me, there were other factors primarily fatigue, but in the end I made a rule: if it required a safty of some kind it never went in without said safty fully installed. Also made a rule with the DO, our mechanics, means me, would work a 12 hour duty day max. It's never one thing is it, pilot or mechanic or whatever, studies say it takes three things catch us or kill us. Rocket

 

[rocket]

One more handy trick. Any gasket associated with intake and or fuel I massage some fuel lube into the fibers before installing leaving just enough, but not enough one could scrape any into a fingernail. I have removed gaskets 20 years later from intake systems still supple after said treatment. I don't touch aircraft carbs as a rule but I have done the same with the parting gaskets with success. The carb to sump and card to carb heat box gaskets, any raw fuel stays contained rather then dripping down the outside where it's more likely to become an issue, say during a flooded miss start back or after fire.Rocket

 

[59pacer]

To close the loop, it looks like the float was stuck. No blue stains parked with the tail up overnight, and none the next with the tail down all day.

I had a local A&P/IA friend look at it and he thinks it’s fine but to keep an eye on it. He’s heard of freshly rebuilt carbs hanging floats too.

My experience with stuck floats (3) was that the fuel ran out the throat of the carb, through the air box, and dripped onto the floor.
I guess it depends on how far open that the float has stuck.
Learn something every day!

 

[CamTom12]

The way it was explained to me is that since I have a tail dragger the fuel wouldn’t make it to the jet in ICO with the tail down? I think I said that right. I’ve never taken an aviation carb apart, so they’re still magic to me.

 

[Gilbert Pierce]

I have never had a carb issue on either one of my taildraggers. They don’t leak, seep, or sport blue stains. Not had an issue other than old auto fuel in the other five tail​draggers I maintain.

 

[N2709P]

The little Stromberg’s on the small Continentals’s had a nose wheel/tail wheel issue. The carb was originally installed on the Ercoupe which had a nose wheel configuration. As the aircraft that the Strombergs were on became more plentiful, the Ercoupe carbs were sometimes installed on a tail wheel aircraft. The tail wheel carb’s had the fuel bowl vent in a different location. The Ercoupe carb would leak from the vent if installed on a tail wheel aircraft. I do not know if the MS carbs have this issue but it could be something to check.

 

[Pacerfgoe]

Thanks for the update.

I love to take carb's apart massage them and put them back together....I've done a number of them. The only one that gave me troubles was the one I bought off Mark Moyle....O-290 carb, I set the float wrong and it stumbled after going to WOT after 1500 RPM. Fixed that and ran strong afterwards.....it's sitting in the cupboard now.

 

[planenut]

i was thinking the same thing!!!

Don't forget to insert the cotter/split pin through the bolt that the throttle cable attaches to!
TonyN

 

[Steve Pierce]

The little Stromberg’s on the small Continentals’s had a nose wheel/tail wheel issue. The carb was originally installed on the Ercoupe which had a nose wheel configuration. As the aircraft that the Strombergs were on became more plentiful, the Ercoupe carbs were sometimes installed on a tail wheel aircraft. The tail wheel carb’s had the fuel bowl vent in a different location. The Ercoupe carb would leak from the vent if installed on a tail wheel aircraft. I do not know if the MS carbs have this issue but it could be something to check.

Same here, have read that exert in the manual but never experienced it.

 

[59pacer]

I have never had a carb issue on either one of my taildraggers. They don’t leak, seep, or sport blue stains. Not had an issue other than old auto fuel in the other five tail​draggers I maintain.

On every occasion (3 different MA4SPAs) it was after the bowl had been emptied during annual, or after overhaul. My engineer suggested a tap with a soft mallet, or starting the engine. Both methods worked.