Rough Idle

Brambo · #1 06-04-2009, 04:16 PM

I just went over 10 hrs in my fly-off, so decided to do my first "cross-country" today. Flew to Kingman, AZ and shut down for about 15 min (looking for a diet coke) and the hopped in to return home. I have a Lyc IO-360 and have heard all the stories about hot starts but had no trouble starting mine. It did however seem to be running very rough at or near idle. The run-up and mag check was normal (ran smooth at 1700 rpm). Although a little nervous about the takeoff, all went well and I returned home safely. Once on the ground again the engine idled normally. I assume the roughness had something to do with the engine already being warm/hot. Can anyone tell me if this is normal and what the cause might be?

Guy Prevost · #2 06-04-2009, 04:53 PM

Loping, rough idle is really common with fuel injected RV's when they're hot. The consensus is that the fuel is vaporizing in the injector lines. Mine does it, and there are a few threads on this forum on the subject. I have better luck if I lean aggressively during taxi and use higher than normal taxi RPM. Since I don't like to ride the brakes, this leads to somewhat faster than normal taxi.

Let us know if you figure out a surefire cure!

Guy

Russ McCutcheon · #3 06-04-2009, 04:59 PM

This is normal for mine, Bendix injection. It lopes and carries on a bit idling after hot starts but never misses a beat on run up or takeoff and flight. If mine is any indication then your doing fine. Maybe caused from fuel boiling off in the system (vapor lock) don?t know. I have also noted others doing the same thing as they taxi buy after starting hot.

gear1 · #4 06-04-2009, 07:51 PM

I first experienced this when I was going through transition training in my RV8 with Dave Austin. Dave is a great instructor, hailing from Denton, TX. Right after start, the engine (IO-360-B1B) began to run rough. Dave had me start the boost pump and the problem immediately ceased! Dave explained that the higher pressure of the electric boost pump collapses the vaper lock in the injector lines. Seems reasonable to me!

Craig

PS: I would recommend Dave for RV transition. I have rudder, throttle and prop controls in the back seat, which Dave required for training in my own aircraft. What a treat to train in the aircraft that I will be flying!

CT

Webb · #5 06-04-2009, 08:17 PM

Call Don at Airlfow Performance. He mentioned somthing about smaller restrictors helping this.

cguarino · #6 06-04-2009, 09:57 PM

Quote:

Originally Posted by Brambo

I just went over 10 hrs in my fly-off, so decided to do my first "cross-country" today. Flew to Kingman, AZ and shut down for about 15 min (looking for a diet coke) and the hopped in to return home. I have a Lyc IO-360 and have heard all the stories about hot starts but had no trouble starting mine. It did however seem to be running very rough at or near idle. The run-up and mag check was normal (ran smooth at 1700 rpm). Although a little nervous about the takeoff, all went well and I returned home safely. Once on the ground again the engine idled normally. I assume the roughness had something to do with the engine already being warm/hot. Can anyone tell me if this is normal and what the cause might be?

My RV-4 ran absolutely awful on the ground in Kingman AZ. It actually quit while I was taxing in. Maybe there is some kind of magnetic distrubance there that interfers with the gasoline atoms and ...I hope you aren't buying this. Funny though mine did run very rough there.

nucleus · #7 06-04-2009, 10:29 PM

It has to be pretty hot for mine to do it, like 88 F. Boost pump made no difference in my case.

Hans

smithhb · #8 06-05-2009, 07:09 AM

Quote:

Originally Posted by Brambo

I just went over 10 hrs in my fly-off, so decided to do my first "cross-country" today.

Bill, I am at the 25hr point in my Phase 1 and I have an IO-360 as well. I also see the loping after the engine is warm and have been told by a couple of different A&P's that adjusting the idle mixture will help. The also advised that this is normal for a new-run engine and the idle mixture will help at lower fuel flow.

They also advised, as others have already mentioned, to lean somewhat at idle until you sense the engine run more smoothly.

HTH

Brambo · #9 06-05-2009, 08:08 AM

Thanks for all the replies. I'm glad to hear this is semi-normal and not some engine malfunction.

osxuser · #10 06-05-2009, 06:07 PM

Pretty normal and standard... Going into Chandler AZ on a 110+ degree day... I actually had those symptoms on the Carb'd O-360. Boost pump fixed it, but i threw me for a loop.