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Hot Rough Running

mike newall

mike newall

Well Known Member
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I'm noticing after a fuel stop, when I restart the engine it hesitates, surges and nearly quits. Runs like a bag of spanners - sorry, wrenches.....

Power check clears it and on take off, no problem.

I can't decide whether it is fuel vapour locking or a problem with hot P-Mags.

Any suggestions gratefully received
 
It would help if we knew what plane, engine, and fuel system you have, and what fuel you are burning. ;)
 
Sorry,

Used to be on my signature but I changed it.

RV7

Mattituck ECI motor, TMX IO-360, dual P-Mags, Silverhawk Fuel Injection.

Would never consider anything other than Avgas.......;)

The temperature spots on the P-Mags haven't gone black.
 
Try leaning your mixture after startup. Not sure your location but I'm at 5000' and have to lean every time I stop for fuel. I also have the Silver Hawk system.

Ron B
 
I have pretty much the same setup and mine does the same thing. Don't think it would ever stop running, but sure not the same smooth sound. Also does it after landing towards the end of a long taxi while really leaned out. I've just assumed its the slow moving fuel in the injector lines getting too hot and boiling.
 
RonB said:
Try leaning your mixture after startup. Not sure your location but I'm at 5000' and have to lean every time I stop for fuel. I also have the Silver Hawk system.

Ron B
Click to expand...

Highest spot in England is only 3200 ft. :)

And it's a nice hike up - Scafell Pike.
 
If it was actual "vapor lock" no fuel would be getting to the servo and the engine would quit (vapor lock occurs prior to the engine pump and blocks fuel flow).

I think the most likely cause is fuel boiling in the fuel injector lines and fuel distribution manifold. This is a common problem on most FI engines on a quick-turn (especially in hot climates). Not much you can do about it unless you want to add a purge valve (circulates cool fuel up the to the manifold), or as you have done, clearing with some extra power to purge the hot fuel.

Just my 2c
 
IMO Boiling fuel in the injector lines.
I have an IO-360. With dual P Mags. Runs well when cold but after flight and or a long taxi, engine runs with lots of missing and sounds terrible, to fix, apply power once the fuel starts flowing the missing seems to reduce BUT it won?t go away until full power for takeoff, that fixes it quickly.

FWIW Just after shut down the top of my cowl is nice and cool to touch but give it 5 minutes and you could fry eggs on it. The bottom cowl stays cool, inside, the exhaust is less than 1 inch away from the bottom cowl but you would never know it. I guess this just proves hot air rises and all this heat is boiling up those little fuel lines on top of the engine. I believe the fuel pressure in these lines is around 4psi and there is not much flow at idle so I think this is the reason for the rough running. I have got used to it now and don?t worry about it. I also open my oil door after shut down to let as much hot air out from behind the engine where my P mags are.
 
Agreed on the fuel boiling in the injector lines.

Question. Has anybody ever tried to insulate the lines? Just wondering.
 
As ever - great responses, thanks guys.

Mark and I discussed it yesterday and we tend to agree.

Not nice when you have a nervous first time flyer and you are trying to explain why it is running rough...:eek:
 
As pointed out, boiling rather than "locking" is more correct ;)

Extra effort between flights to leave aircraft exposed and pointing into wind, and open oil door may help to a small degree.
 
I experience the same thing with my IO-320B1A. I spoke with Bart From Aerosport engines and he sold me a slightly stronger spring to put in the fuel distribution manifold . It brought the pressure up a little in the supply line and reduced the amount of vapor being produced . That mod greatly improved running on the ground after a heat soak . Not perfect but much better . Sorry , I don't have a part number.

Marc
 
resurrecting old thread...

...to report that I have added cowl flaps and leaving them open while parked on a short turn around appears to help reduce the rough idle problem.
 
Cfrisella said:
I have pretty much the same setup and mine does the same thing. Don't think it would ever stop running, but sure not the same smooth sound. Also does it after landing towards the end of a long taxi while really leaned out. I've just assumed its the slow moving fuel in the injector lines getting too hot and boiling.
Click to expand...

Put me down as well... Similar setup, runs awful after a hot start. Running the fuel pump helps a lot.

I have an Airflow Performance purge setup, which helps immensely with hot starts. However the heat soaks back into the fuel after purge and start, and it starts coughing again at idle.
 
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