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Solving the mixture issue.

CopterJohn

Active Member
I am 36 hours into my 40 hour test period on my 0-360 with airflow performace injection package. Setup mixture initially last fall for 30 rpm increase at cutoff per Lycoming SB. Ran perfectly until a few days ago.

Now that it is hot out, the engine is barking and coughing at idle after a test flight and tries to keep running when the mixture is pulled.

We reset the mixture again today on a warm engine and it idled smoothly with the proper increase at fuel cutoff. Cowled it up, went flying, and came back to have the engine quit in the flare when the throttle was retarded to 890 rpm. Withe the Whirlwind, the prop stops dead.

Had to use the flooded start technique to get it going and taxi in. Quit again at the hangar when the throttle is pulled back with mixture in.

What now? Is this a heat or vapor lock issue we are chasing?
 
Sounds pretty normal to me... the AFP systems (as well as most Bendix) suffer from poor idle with the hot under cowl temps in the summer, low fuel flow thru the injector lines and FDM (spyder) will cause rough running at idle.

I would suggest you go back and set the mixture with the engine cold/warm (not hot) then leave it alone.

The AFP does not cut off fuel 100% like the bendix does, I take it you don't have the purge valve which is normally used for shutdown.
 
I've got similar issues with AFP and idling when hot. It is boiling fuel in the steel tubing going to the injectors, and I've messed around a bit with the lean idle mixture settings to no avail. I've found that as long as I keep the RPM's up around 950-1000, it runs fine when hot. Below 850-900 it starts to stumble. It idles fine when cooler at those lower RPM's. I've also got the composite lightweight prop, which doesn't help.
 
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It's going to come down to keeping the FWF fuel as cool as possible, insulate what you can with firesleeve and put a blast tube on the fuel pump.
 
This is not "vapor lock", vapor lock occurs on the inlet (low pressure) side of a pump at high temps due to fuel boiling, this condition is just the boiling of fuel in the fuel distribution manifold and FI lines to the nozzles (due to the low pressure in the FI lines at idle). That's why it clears up immediately at higher power settings.
 
fuel boiling?

Without knowing what model of fuel injection is on the engine or the installation you might want to give us a call to discuss your options.

We have two different regulator systems. One uses the purge valve for hot start fuel circulation and engine shut down. This is because this model regulator uses rotary idle and mixture control valves. Thus ICO is not zero leak on this model. The other model regular uses a different design fuel regulator. This model has a zero leak mixture control so most installations do not use the purge valve. This is standard on the FM-150, FM-150L and FM-250, but is also used on the FM-100A, FM-200A, and FM-300B.

You made a comment that the engine ran well for over 30 hours and just recently started having idle issues. So were the temperatures in those previous flights any hotter than the last few hours. If not then it?s possible that you have some other issue than boiling fuel in the nozzle lines.

At this point we need much more information about your installation and system than is described in the first post.


Don
 
And just for the record, I can idle all day when hot at 800 RPM with my FM-200A. That is the unit without the return line.

FM-200A_01.jpg
 
Rough Idle

Do you have a sniffle valve? I started with one. It got clogged (open) and caused all kinds of grief till I figured out the problem.
 
In my case, I have the dual muffler exhaust from Vetterman and that requires airflow into the muffler shrouds, which then creates plenty of hot air under the cowling where the fuel pump and lines are located. The cabin heat comes from just one muffler, and that produces lots of heat. At some point I will put the fuel pump cooling shroud on the engine pump with a blast tube.
 
Update on RV6A rough idle when hot

O-360 (40hrs tt) converted to fuel injection, RSA-5 just OH'd by Airflow Performance, All new teflon lines with firesleeve, blast tube and shroud on fuel pump. Electric pump in tunnel. .028 nozzle inserts. Steady fuel pressure. Replaced all intake gaskets as a precaution.

Smooth idle (set to 800 rpm with ww74 prop) when cold or when cowling is off.

After landing, she pops and sputters /- 100rpm and tries to quit. Boiling lines from flow divider to injectors is my guess. Must idle at 1100 or higher to prevent the engine from quitting. Above 1200 rpm smooths out pretty well.

In flight numbers are good. 184 degrees on oil, 350 +/- cht. Rock solid fuel pressure.

Fuel flow out from servo is exactly what Don at Airflow said it should be.

Should I try raising the injector lines and flow divider higher above the cylinders? Louvers or cowl flap in lower cowl? Been a nagging issue all summer and as others have noted, long taxi's are a pain trying to keep it running without burning up the brakes.
 
I just finished my 40 hrs Phase 1 about 5 hrs ago. I had boiling fuel and fuel psi fluctuations on my Bendix Injection in hot taxi. Not to the point of the engine dying but a lot of rumbling and sometimes backfiring. I originally mistook this for plug fowling but later realized it was only happening after landing and hot taxi. My red cube was mounted on the firewall with two 90* fittings.

11uku88.jpg


I sent two fuel lines back to Tom at TS Flightlines and had them shortened just a little. (No charge? Thanks Tom!:D) I received a tip from a VAF member and replaced the two 90* fittings in the red cube with straight fittings. Had to build a bracket and relocate the red cube to make this work and mounted it on the engine mount. Tom at FL had also suggested leveling out the fuel line arrangement and this accomplished that too.

2u9id11.jpg


I then wrapped the red cube with leftover fiberfax insulating material. Then finished it off with the sticky backed foil heat reflective covering.

28saib.jpg


My goal was to cure the fuel psi fluctuations and I have not had any since I've done this. (about 5 hrs flight time) The added benefit was it really improved the rough backfiring engine at low rpm during hot taxi.
 
RSA-5 eh?

You have a heating problem. How about some engine compartment photos?


POSTSCRIPT...just posted after Mike. He offers a very good example of why photos can allow somebody to help.


O-360 (40hrs tt) converted to fuel injection, RSA-5 just OH'd by Airflow Performance, All new teflon lines with firesleeve, blast tube and shroud on fuel pump. Electric pump in tunnel. .028 nozzle inserts. Steady fuel pressure.
 
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I have the RSA-5 too. On hot days with long taxi I occasionally have sputtering engine but turning on the boost pump seems to smooth it out. I also lean during taxi on hot days.
 
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