LSA running rough on take off

[kfowler]

hi my lsa has a problem i went for a fly today as most take off it runs rough at about 300 feet agl the only way to get it to run smooth is to pull the carby heat on back the throttle back till the engine tacho just starts to drop the engine has 400hrs the plugs replaced and tappetts adjusted 10 hours ago the spark plug leads where also replaced it has a economy kit with a 2.85 mm jet fitted 340 hrs ago the problem only started when i moved up to the N.T. the temp today was 31.5 degress with they humity above 50% any ideas thank keith

 

 

[Ultralights]

could be Mixture related, or carby ice, jabirus Love carby ice. but if bringing the throttle position back till RPM just begins to drop, it sounds more a Mixture issue. closing the throttle valve is reducing the air in the air/fuel mix, and bringing it back to a more normal/correct mixture.

 

 

[Modest Pilot]

Maybe an obstruction in the fuel system. If you have a fuel flow meter should be around 31lt/hr at your OAT. You could also check by disconnecting the fuel line at the carb and measuring a minute of flow on the boost pump.(be careful fire risk!) If flow is low check the fuel filter and for kinks in the fuel lines. One other thing, check the fuel bowl somehow a white compound had built up after 50 hours in my aircraft. Looked like fuel slosh, how it got through the filter beats me, it was extremely difficult to remove.

 

 

[Tomo]

Is it Hydraulic or solid lifters?

 

Have you checked the propeller by any chance also?

 

 

[Guest Nelson Smith]

Running Rough

 

Hi Keith

 

If it isn't an ice problem,then the fact that pulling carby heat on and reducing revs improves the running, it would suggest that the carbureter is not geting enough air via the naca duct.Pulling heat on gives the carby an alternate source of air.

 

Lets know what you find

 

Nelson

 

 

[Yenn]

Sounds like a too rich mixture. There have been a few cases of sticking slides in the US. A bit of corrosion on the slide causes it to stick in the full throttle position, meaning that the needle valve is giving a too rich mixture.

 

 

[facthunter]

Slide stuck OPEN.

 

Slide stuck open does not give a too rich mixture. The mixture will go lean of the slide jams open. That conclusion is incorrect. You can't always believe what you read. Usually applying carb heat will enrichen the mixture . The carb may have a build-up Of white powdery material in it. Clean it out and if you have the lean needle replace it with the later one. Nev.

 

 

[cherk]

G'day Keith,

 

could check the hose from the carby fuel bowl to the air box(from memory),

 

something to do with pressure equalisation... pulling carb heat tends to iron it out smoother!

 

 

[Kiwi]

As "cherk" just stated, We had a jab with the same symptoms as yours and all that was wrong was the equalizer tube between the carb and the air box had been knocked off.

 

Kiwi

 

 

[kfowler]

hi solid lifter

 

 

[Tomo]

hi solid lifter

Ok, thanks.

 

I know of a 3300 that had very similar problems. They thought it was everything else, but once they changed the hyd lifters to high flow the problem stopped.

 

Hope you get it sorted asap.

 

 

[kfowler]

hi all thank you for your input the balance tube is not blocked this week end i went to emkaytee. on take of this time i did not use W.O.T. and the engine ran fine, on take the same coming back.it looks like to rich with W.O.T. at cruise 2800 rpm the fuel burn is 13.63 lts / hour thanks keith

 

 

[jetjr]

If carb heat helps your running too lean

 

When putting in new needles did you adjust float levels as required as this will do this and can lead to lean running right through rpm range, Can have serious consequenses

 

Often ONLY seen as EGT problem or "running out of fuel" feeling after 20 sec or so of WOT

 

 

[kfowler]

thanks jetr i am going to bundaberg this week and i will pick up a new set of needles and jets thanks keith