SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Aug 24, 2014, 07:00 PM
Registered User
rrothman's Avatar
United States, UT, Park City
Joined Nov 2011
31 Posts
Discussion
Evolution 50GX Fuel issues

Iíve been having a lot of fuel issues, I will prime the system by gassing from my fuel DOT till tank was 80% full. Then removed the spark plug on the plane, and with choke on spun the prop till there was no bubbles, and gas coming out the carb.

Put spark plug back in, activated the electrics and ignition, engine fired after 3-5 swings, and itíll run great for the first flight, but then Iíll have trouble starting it for the second flight. I noticed on closer inspection there would be a lot of air bubbles in the fuel line.

So I just recently purchased and installed a QuikFire filter and RotoFlow fuel tank from JLProducts, which was supposed to fix these problems.

With engine running I noticed air bubbles coming from the fuel tank, thru the QuikFire and into the carb, engine continued to run fine and had good throttle response. After a few minutes I cut the ignition.

Now I noticed there were bubbles flowing back from the carb thru the QuikFire and to the RotoFlow! I would not have thought it possible unless maybe the tank had built up a vacuum, but I have an overflow hookup, so no vacuum.

Anyone have any clue/advice as to why Iíd have gas/bubbles flowing back to the tank? Iím wondering if thereís a problem with the carb, but if that were the case how would I get it running the first time?
rrothman is offline Find More Posts by rrothman
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 24, 2014, 07:54 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,267 Posts
You might have better luck posting this in the engine forum. I'm not a gas guy so my help is limited.

Ken
kenh3497 is offline Find More Posts by kenh3497
Reply With Quote
Old Aug 25, 2014, 10:08 AM
Registered User
Jacksonville Fla.
Joined Mar 2007
2,222 Posts
I can't see my fuel lines as I am under cowling.
But I can tell you how I start my gassers. First off choke on. Throttle wide open. Flip the prop until the engine sputters and dies. Now reduce the throttle take the choke off and flip until it runs. Usually takes 4 flips choke on and 3 to 4 flips choke off.
Don't adjust a gasser like a glow engine when adjusting the needles small small adjustments 1/16 th at the most
jetmech05 is offline Find More Posts by jetmech05
Reply With Quote
Old Aug 25, 2014, 10:40 AM
Registered User
rrothman's Avatar
United States, UT, Park City
Joined Nov 2011
31 Posts
Thanks jetmech05, I'm not necessarily having trouble starting it, when there's no air in tubes it starts fine. the question is "why/how would gas/bubbles be returning from the carb to the tank" after it has run?

do you use cable ties? I'm starting to think this is my problem as the cable tie doesn't clamp down in a perfect circle...
rrothman is offline Find More Posts by rrothman
Reply With Quote
Old Aug 25, 2014, 11:49 AM
Registered User
Jacksonville Fla.
Joined Mar 2007
2,222 Posts
Yes I use tye wraps. It can't cause air bubbles though unless there's a hole in the line near one. Replace your tygon lines
jetmech05 is offline Find More Posts by jetmech05
Reply With Quote
Old Aug 26, 2014, 07:26 AM
Registered User
AA5BY's Avatar
East Texas
Joined Aug 2007
1,388 Posts
This is just a possibility based on an experience I had once. I could fill the tank without problem and the vent line spewed gas when the tank was full... but the vent line was crimping off enough that the lower pressure of fuel suction couldn't draw air into the tank. After five minutes, the motor would shut down for lack of being able to draw fuel.

It could be that the carb line is drawing some air because it is too difficult to draw fuel from the tank because of a one way vent line constriction.

There is an easy check for a vent line issue. When first removing the fill line from the fuel dot... is fuel pressured back out of the fill line? If so, the tank is pressuring up because of a vent line restriction.
AA5BY is offline Find More Posts by AA5BY
RCG Plus Member
Old Aug 26, 2014, 04:19 PM
Registered User
rrothman's Avatar
United States, UT, Park City
Joined Nov 2011
31 Posts
tygon lines are new, the reason I suspect the tie wraps is that they don't form a perfect circle and possibly even pinching the line up right under the head. Donald from JL Products says no tie wraps are necessary, so I'm going to try without...
rrothman is offline Find More Posts by rrothman
Reply With Quote
Old Aug 26, 2014, 04:30 PM
Registered User
rrothman's Avatar
United States, UT, Park City
Joined Nov 2011
31 Posts
the miracle fuel dot I have seals when I remove the connector, but I did notice when I stopped cranking fuel returned/flowed to the external gas container, I just assumed it was sucked back by gravity or suction caused by temperature in the external gas canister.

I will do more testing with this in mind, thanks.
rrothman is offline Find More Posts by rrothman
Reply With Quote
Old Aug 26, 2014, 06:28 PM
Registered User
AA5BY's Avatar
East Texas
Joined Aug 2007
1,388 Posts
Quote:
Originally Posted by rrothman View Post
the miracle fuel dot I have seals when I remove the connector, but I did notice when I stopped cranking fuel returned/flowed to the external gas container, I just assumed it was sucked back by gravity or suction caused by temperature in the external gas canister.

I will do more testing with this in mind, thanks.
To test if the tank is pressuring up when filling, fix a jumper piece of tubing to the fill connector and disconnect at the jumper.
AA5BY is offline Find More Posts by AA5BY
RCG Plus Member
Old Aug 31, 2014, 10:40 PM
Registered User
rrothman's Avatar
United States, UT, Park City
Joined Nov 2011
31 Posts
I replaced all the tygon with a different batch/brand, simplified fuel system by removing filters that might leak, but still have problems with warm/hot starts and air bubbles flowing from carb back to tank after first run on cold start. if I wait long enough for the engine temp to return to +-80 degrees, it starts within 3-5 flips. also noticed that once engine has cooled I no longer have air bubbles coming from carb.

negative and positive pressure tests showed no other leaks in the system.

further research research indicates possible leak in fuel pump membrane and/or flapper valves.

next challenge is finding a kit for the 50GX carb!
rrothman is offline Find More Posts by rrothman
Reply With Quote
Old Aug 31, 2014, 11:10 PM
Registered User
AA5BY's Avatar
East Texas
Joined Aug 2007
1,388 Posts
Various pump membranes have been used, including the black, bluish and tan. The black is not as durable but works very well for a couple of seasons but seems to suffer a bit from modern fuel additives.

The bluish looks transparent and a lot like acetate. Durable but I'm not sure performance is all that good.

The tan is the latest and might be the best.
AA5BY is offline Find More Posts by AA5BY
RCG Plus Member
Old Sep 03, 2014, 10:12 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,267 Posts
The fuel is boiling in the carb send vapor bubbles back to the tank. How do I know this.... Well not exactly the same thing but I put an clear inline fuel filter on my ZRX (motorcycle). When ever I stopped after 15 to 20 seconds the fuel would start to bubble in the filter. Start the engine and they would go away after another 15/20 seconds. Never caused an issue though. Now this filter was in the wide open and though it was above the engine when you felt the temp of the filter it was "just warm". IMO not warm enough to boil the gas but it was boiling.

Is there an insulator block between your engine and the carb? If not you might give that a try. Where do you buy your fuel? Does the pump dispense several blends of fuel from the same hose? If it does the person before you may have pumped some ethanol blend fuel. The pump and hose can hold up to one gallon of fuel. Alcohol had a lower boiling point than gasoline. Pump a gallon or two in your car before filling your model fuel container.

Ken
kenh3497 is offline Find More Posts by kenh3497
Reply With Quote
Old Sep 03, 2014, 11:30 PM
Registered User
rrothman's Avatar
United States, UT, Park City
Joined Nov 2011
31 Posts
Quote:
Originally Posted by kenh3497 View Post
The fuel is boiling in the carb send vapor bubbles back to the tank. How do I know this.... Well not exactly the same thing but I put an clear inline fuel filter on my ZRX (motorcycle). When ever I stopped after 15 to 20 seconds the fuel would start to bubble in the filter. Start the engine and they would go away after another 15/20 seconds. Never caused an issue though. Now this filter was in the wide open and though it was above the engine when you felt the temp of the filter it was "just warm". IMO not warm enough to boil the gas but it was boiling.

Is there an insulator block between your engine and the carb? If not you might give that a try. Where do you buy your fuel? Does the pump dispense several blends of fuel from the same hose? If it does the person before you may have pumped some ethanol blend fuel. The pump and hose can hold up to one gallon of fuel. Alcohol had a lower boiling point than gasoline. Pump a gallon or two in your car before filling your model fuel container.

Ken
Thanks Ken.

I bought the 50GX (with a wrap around muffler) as a Kit with a 27% Hangar 9 Extra 260, this plane got destroyed in a crash and was replaced with an Aero-Works 260 of the same wing size but happens to classified as a 35-45cc plane. To make it fit I had to put a hole in the firewall (with Aero-Works blessing) for the carb with the engine bolting directly to the firewall. So the muffler is right under the firewall box.

The carb does feel warm after a run, would it help to put aluminum foil around the firewall box to deflect the heat?

I've had some trouble recently with my weed whacker and blower, and was told it's the ethanol in the fuel that's causing the problems, would ethanol-free fuel help or stop this boiling?

We don't have any ethanol free pumps in town, thought I had put in a fuel stabilizer and ethanol treatment (Rislone Gas Fuel System Treatment), but

Richard
rrothman is offline Find More Posts by rrothman
Reply With Quote
Old Sep 05, 2014, 11:05 AM
Registered User
rrothman's Avatar
United States, UT, Park City
Joined Nov 2011
31 Posts
I put one of my telemetry temperature probes on the top of the carb, got the engine up to temp around 180, and the carb temp went up from 75 to 114 within minutes of shutting down the engine.

Then used some reflectix tape between the muffler, the engine and the firewall to try deflect some heat.

Also went and got some TruFuel, repeated the temp tests. Carb temp still went up to 114, and although I didn't see the same bubbles/boiling from the carb, it was a little harder to start than when cold but at least it started if I set the throttle at idle rather than 30-40% as I do when cold!

Conclusion: use high octane ETHANOL FREE gas no matter what the stabilizer/additive says, or use premixed TruFuel available at Home Depot or Lowes etc.!
rrothman is offline Find More Posts by rrothman
Last edited by rrothman; Sep 05, 2014 at 11:10 AM.
Reply With Quote
Old Sep 05, 2014, 06:18 PM
Registered User
AA5BY's Avatar
East Texas
Joined Aug 2007
1,388 Posts
A flying friend got one of the OS gas four stroke engines. He had starting problems beginning about the 3rd outing. They got worse but if once getting it running, it ran fine. It finally got to the point that it was very difficult to get the engine started. After trying everything imaginable with the fuel system, he tried an RcXel ignition and the beast now starts easily.

It was my first time to see a gas engine with ignition problems that made starting difficult but then run fine. Usually it is the other way around, an engine will start easily but not spool up or will miss at higher rpm when an ignition is balky.
AA5BY is offline Find More Posts by AA5BY
RCG Plus Member
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
For Sale Nice! Bisson Custom Muffler For Evolution 45GX & 50GX rcidaho Aircraft - Fuel - Engines and Accessories (FS/W) 0 Jan 28, 2014 06:52 PM
Sold Evolution 50GX binujoe Aircraft - Fuel - Engines and Accessories (FS/W) 1 Nov 07, 2011 10:51 PM
Sold Evolution 50GX Gasoline 50-cc Engine / Muffler Dynomike Aircraft - Fuel - Engines and Accessories (FS/W) 3 Oct 18, 2009 09:47 PM
Discussion Evolution 50gx jschauer Giant Scale Airplanes 0 Jun 14, 2009 10:31 AM
Discussion Evolution 50gx jschauer Engines 0 Jun 08, 2009 07:35 PM