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FM-150 issues

SuperCubDriver

Well Known Member
I had rough idle from the very beginning. Low power settings like 50 percent above 10000ft causes the engine to run rough. Only some higher than necessary fuel flow let the engine run acceptable, which is in fact not acceptable! I believe the fuel servo could be the problem and is not regulating correctly. Idle fuel flow is above 2 GPH, more like 3 GPH.

Right now while idling I got high EGT on Cyl. 4 and I can even hear some popping exhaust sound, probably from the lean cylinder.

I checked several times for intake leaks and the fuel line plumbing - no findings.

Now I intend to open and clean the fuel divider to get at least rid of this leaner cylinder. Of course I have the AFP manual but I thought I ask for your input and experience.

I know it would be best to send the whole thing back and have it checked but doing so from Germany is not what I like. The airplane is flyable, it?s just not perfect on very low power settings and idle.

It is a IO-375 with AFP 150 fuel injection, two Pmags. Total time 250 hours
 
You need to provide more data:
- With the engine at idle, does RPM increase before shutdown as you lean to cut out?
- Will all four cylinder EGTs go up when you lean at power?
- What is the GAMI spread?
- Disparity between CHTs?
- Are you really sure you timed the pMags correctly (as in the crank at TDC or 5 degrees after TDC depending on parallel valve or angle valve heads).

Have you sent an email to Don at Air Flow Performace on your issues?

Carl
 
I will answer the questions one by one:

- There is no noticable RPM increase while leaning at idle power, engine does not really idle at a stable RPM. Having hard time to adjust idle mixture.
- At cruise power everything is almost normal. Cyl 3 & 4 EGT is lower 50 - 100F.
- Gami spread is very small having different injector nozzles. All Cyl. peak at the same time, just 3 & 4 with lower EGTs.
- CHTs are very close together, no difference to worry about.
- Yes I would say the Pmags are timed correctly. On my -7 I have the same setup ecxept ECI fuel injection with no problems at all.

- One more point: At all power settings the mixture lever is almost unresponsive during the first half travel. During cruise flight it is around 80 percent of it?s travel pulled.

And yes I did sent (several) e-mails to Don and followed his comments like intake leak, fuel leak. Of course he is referring to the manual, however for opening up the fuel divider I would be happy to get any further advice and tips.
 
Not sure what size nozzles you have but I think Don is recommending the .024 now instead of the original .028". The larger nozzles will tend to cause the symtoms you are experiencing. The idle mixture setting is difficult to get dialed in, doing it when the engine is cold and making very small adjustments to the arm has worked well for me.
 
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I had similar issue with high fuel flow at idle. It should be about 1 gph not 3. Somedays engine would quit after landing due to rich fuel flow.

After much local messing with it, sent it to AFP.

When it was returned, problem was gone. Never did find out what the issue was, they found nothing wrong testing it.

Seems like disassembling and reassembling it fixed it, may have been foreign object in system and got washed out.

It is a bullet proof system when it is working right.

dd
 
I never thought cam timing off. How can I check proper timing?

Installing smaller nozzles will tend to move the mixture lever more forward during cruise flight. My T/O fuel flow is about 15 GPH and on the low end I believe. Smaller nozzles will decrease T/O FF.

My next action should be cleaning the fuel divider to get rid of the high EGT on Cyl 4 while at idle power. Any inputs for doing this are welcome.
 
Installing smaller nozzles will tend to move the mixture lever more forward during cruise flight. My T/O fuel flow is about 15 GPH and on the low end I believe. Smaller nozzles will decrease T/O FF.

My next action should be cleaning the fuel divider to get rid of the high EGT on Cyl 4 while at idle power. Any inputs for doing this are welcome.

Not so on FF, perhaps you should call Don so you can hear it from him.
Divider assy is covered in the AFP manual.
 
Now I disassembled and cleaned the fuel divider. There was a small bug in there and I can´t believe it was there all the time because it was not dissolved.
Anyhow the issue with high EGT #4 is gone. Testflew and installed the next smaller injector nozzle.
 
Here is an interesting update:
Being out of ideas I sent the fuel servo back to AFP. After installing it again on the engine did a testrun with cowl of, shutdown and inspected for leaks. I saw fuel dripping out of the hole on the flow divider on the engine case. Luckily I ordered all extra gaskets and a divider overhaul kit so could exchange the diaphragm. The next day I thought the spring is not correctly installed. Opened the thing again and in fact the spring was on the wrong side. Now - I?m finally able to adjust the idle mixture, the engine is running smoother and the belly is clean now!
I had a small leak a long time already because the cowl above the divider had fuel stains, also the lower engine case disturbed by the airflow. Everything is clean now.
The problem with low fuel flow at higher altitudes is still there however the critical fuel flow is about 1 GPH lower than before. And T/O fuel flow is still low and kind of disappointing.
Going with smaller injectors will be next.
 
Now - I did two things at the same time. I installed the next larger main jet and 0.022 nozzles - well, on two cylinders and guessed the other two a little larger after previous nozzle tuning.
T/O fuel flow is now close to 17 GPH at sea level which looks good to me.
I got the plane up to 14500 ft (DA above 15000 ft) and leaned down to 6 GPH. There is still the problem with continuous low steady fuel flow at high altitude but now it is much better and acceptable for me. The mixture lever is still almost all the way out when leaned and still almost unresponsive during the first half travel. Cylinders are peaking all within 0.2 GPH so for the time being I leave it alone. However I might try a stronger spring in the fuel divider sometime in the future.
 
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