Backfire and burble trouble.

I am having real trouble with my IO-360 engine burbling and making all sorts of testosterone exhaust type noise as I throttle back. I have to make this verrrrry slowly to keep it from making all kinds of noise. What should I be looking for and how do I fix it?

I have been advised that this could be air in the exhaust, so I borrowed a smoke generating exhaust leak detection tool. There is quite a bit if leakage between the short stack and the main crossover pipes. How do I stop this? Should I have the pipes welded or can I tape them up somehow, at least for a test. Welds seem to be a bad idea but may be the answer. Opinions? Thoughts? Help!!!

Are there other places I should also be looking for the source of the problem?

I am having a hard time sneaking the plane in and out of the airport without people calling the fire and police about the airplane that is inevitably gonna crash with engine failure.

Are you talking about something more than the normal exhaust popping noise when the throttle is almost or fully closed?

This has been covered before.Try this link and see if this is what your talking about. If not you have a problem.
Rich
http://www.vansairforce.com/communi...highlight=exhaust+popping+noise+throttle+back

Hum....

Aerosport O-360-B1B, Lightspeed Ignition, Airflow Performance FI, Vetterman Crossover 4-into-2 exhaust.

I never cut to idle quickly. I start several miles out before pattern and just nudge it out or the popcorn machine will kick in. It will pop just on a taxi also unless I give it some throttle to quite it down.

Thanks for the replys. I had bought into the just live with it until my neighbor with the same engine claimed no noise from his plane. Could he be pulling my leg?

I will look into what he is using for an exaust system. I think this popping is excessive for my plane. I can look into mixture at idle also. Could changing the exaust system to another style fix the problem?

TOAD said:

It will pop just on a taxi also unless I give it some throttle to quite it down.

Click to expand...

This is certainly not the norm for RVs. I have never seen one pop while taxiing and mine doesn't do it (although it does in flight if cutting the throttle quickly). Sounds like you've got something else going on.

TOAD,

I replaced the seals around the intake tubes into the sump and mine stopped popping. I checked everything under the sun to no avail. When I replaced the intake tube seals, it became a different engine. Good luck.

Excessive lean mixture at idle can cause popping on the ground. To check for proper mixture slowly lean the mixture at idle and you should get a 50 to 75 RPM rise just before idle cut off. If you don't I suspect you are running lean and need to enrichen the idle setting. Is this Carb or injected?

Gary Specketer

This is a fuel injected engine

This is an injected engine. I am wondering if the AirFlow performance induction system is different from other injection systems or plays into the issue in some way.

Now that I am searching my memory I am convinced that the engine used to run much better and that things are getting worse. I will head out to the hangar as soon as I get home tonight to look into mixture and look for a leak on the induction side. I suspect the exhaust is as tight as it was on day one. All my efforts were directed to exhaust and I will switch to other areas because I do not see anything that looks significant there.

It sounds like you have already checked for leaks around the exhaust, but anywhere it can suck in air (exhaust to cylinder head, exhaust probe, a pin hole in a weld etc) will cause it to pop in the exhaust pipe.

loose bolts

Toad,
You might want to check the exhaust and intake bolts where they attach to the cylinders heads. The first couple hundred hours everything loosens up.
I had a blue streak(gas) leaking from the top of #3 intake. The gaskets were shot after 500 hrs.I check mine at annual and some need to be re-torqued.
Hope this helps.
Rich

Gary 40274 said:

Excessive lean mixture at idle can cause popping on the ground. To check for proper mixture slowly lean the mixture at idle and you should get a 50 to 75 RPM rise just before idle cut off. If you don't I suspect you are running lean and need to enrichen the idle setting. Is this Carb or injected?

Gary Specketer

Click to expand...

I agree that it probably can be minimized (but will still do it on rapid closing of the throttle) by messing with idle mixture. The AFP can be a bit finicky on idle mixture, and may even need to be changed winter to summer.

When I do simulated engine out landings, I go full rpm, mixture pulled all the way. I keep my hand on the mixture, and periodically during the glide run it in and clear the engine. If I just pull the throttle to idle, it will after fire a lot on the glide. When at 100', I push mixture in and move to the throttle.

Setting Idle Mixture

TOAD:

Try this for setting idle mixture. 50-75 RPM rise is too much, but I have had a lot of customers come in here with the mixture set way too lean, plus then they lean the mixture on the ground with the mixture control. If you have a manifold pressure gauge we use this for setting the idle mixture. First run the engine up on the ground to get the oil temp up to operating temperature, then throttle back to idle. At 750 RPM, slowly pull the mixture control and watch the MAP gauge. If it starts to go up while leaning the mixture the mixture is too lean. If the MAP goes down while leaning the mixture is too rich. Usually we set the idle mixture so that the MAP only goes down none at all or maybe only 0.1? or 0.2?. In any case you good throttle response off idle (no hesitation on the acell). If you get the mixture set to the lowest MAP and there?s a little hesitation on a brisk throttle advance, richen the mixture 1 flat. Then you set. On most 4 cylinder Lycoming?s in good health the MAP at 750 RPM is around 9.5? to 10? Hg and the idle flow is around 1.2 to 1.5 GPH.

Obviously make sure you don?t have a manifold leak (intake pipe connections, manifold drain sticking, etc.). Always run the engine up (1800 to 2000) for a bit to clear out the engine between mixture adjustments. We always set the mixture with the engine running, but DON?T DO THIS UNLESS YOU KNOW WHAT YOUR DOING AROUND SPINNING PROPELLERS.

If you still have issues with the idle performance call us directly. We can walk you through the procedure again. Or bring the plane here and we?ll set it for you.

Don

Still loooking.

Well, Thanks Don I am very grateful for the instructions on Airflow performance setting the idle mixture. I always fool with this stuff when I have instructions
The invitation to fly from Seattle to Florida to have you set the mixture for me is most appealing .

I trust. Your response was a little unexpected and GREATLY appreciated. I am thinking that the only thing I may need would be a gasket seal if I get that far, or there looks to be an induction problem. As I say I had been focusing on the exhaust and still think that there is too much leakage around the slip joints but I am broadening my search.

I need to get some pictures posted here soon. I have the plane painted up and my son is doing some nose art for me. The plane is looking awesome.

Rich mixture helping... stop the pop

Saturday I set the mixture a little richer (about a flat and a half). This did help a lot. It is now set so that I get zero increase in RPMs as I lean it out. I will try it just a little richer tonight. I am still popping but it is not near as bad as it had been. I had an explanation comparing the lean idle setting... to the pop you get as you turn the gas off on a torch. I get it now. I think I truly understand the mixture setting for the first time. I am excited to think that I can finally mitigate this popping to a reasonable level for me. Wish me luck, and the kid is painting the nose art as I write this....