I agree that heat is the obvious culprit, but it sounds like the problem isn't the engine-mounted fuel pump vapor-locking. If the electric pump has no effect, the problem probably isn't between the tank and fuel servo. Is the line from the servo to the distributor well insulated? I like to use the old-fashioned loose-fitting fire sleeve for this as it offers good insulation. The next thing is to make sure all components are as cool as possible. There should be a shroud around
the fuel pump with cool air ducted to it. The gascolator should be isolated from the engine compartment and cooled. Yes, there is a remote possibility of an air leak causing a problem. Sometimes air will leak in, but fuel won't leak out. And sometimes electric pumps are located higher than they could be or are in the engine compartment and therefore run hotter than they should. In order, I would:
1. Insulate all fuel lines with fire sleeve.
2. Duct cool air to the mechanical pump
3. Duct cool air to the gascolator.
4. Think about relocating the
electric pump
5. Look for an air leak
Gary Casey
Hello fellow Lacairians,
I've been dealing with a rough idle problem on a Lycoming IO-360-B1B in a
La=
ncair 360 for way too long. It only happens when the engine is hot, so I'm w=
ondering if anyone else has had this problem and what, if anything, can be d=
one about it. The engine runs very strong in flight, and the problem only o=
ccurs on the ground when hot and at low RPM. Turning on the boost pump has
n=
o effect. The previous owner said he had the same problem so this has been g=
oing on for a very long time.=20
After having 4 mechanics look into it and spending thousands of dollars, the=
problem remains. So far, we have put on a new fuel servo, new
injectors, ne=
w plugs, and checked the timing and ignition system and found no problems. I=
've also subscribed to Savvy Analysts and they can't find anything wrong in t=
he engine data. The next couple of things we are going to look at (again, bu=
t more thoroughly) are both fuel
pumps (mechanical and electrical), and the f=
uel flow divider. We are also thinking that there might be
an air leak somew=
here in the fuel system because the boost pump won't prime until the engine i=
s cranked on the first start of the day, but then it boosts just fine. We a=
re also thinking that we could have a vapor lock problem since it only happe=
ns when hot, and these are obviously tightly-cowled engines. I've heard from=
other Lancair 360 owners that many of these planes tend to idle rough when t=
hey're hot, so perhaps we've been chasing our tails this whole time and this=
is something we just need to live with?
One last anomaly that might be worth noting since it has now happened twice.=
During climb out on two hot days, fuel pressure began fluctuating (+/- 5 ps=
i), but then stabilized in level flight at higher airspeeds. Once again, tur=
ning on the boost pump had no effect. Perhaps another indicator of a possibl=
e vapor lock issue? =20
Any advice would be greatly appreciated!
Thanks,
Kevin