Rough Idle/Whirlwind 200RV

flickroll · #1 05-12-2009, 08:05 PM

The idle on my engine (O-360-A1A) is rough/erratic. If I try to idle at 650, it will run 630 to 680. I have a brand new Avstar carb, 10-3878, and have installed new rubber induction tube connections. One thought that I have is the Whirlwind 200RV prop has lower inertia than either a fixed pitch metal prop or a Hartzell CS prop. Could this be a reason? The carb I THINK is set up properly. The mixture screw is 1 1/2 turns out from full in, and while it is hard to tell because of the erratic idle, it looks like about a 50 RPM rise when I pull the mixture. The timing (Slicks) was just set at 25 deg, and the plugs were just cleaned and gapped. Any ideas? One other clue is when I am shooting touch and goes I smell a little gas when landing and then giving full power for take off. Maybe still too rich? Thanks

RV7Guy · #2 05-12-2009, 10:55 PM

My engine idles at about 760-800. Maybe you are too low. The lighter weight prop should make this better. It isn't a prop issue.

roee · #3 05-13-2009, 02:53 AM

Quote:

Originally Posted by RV7Guy

My engine idles at about 760-800. Maybe you are too low. The lighter weight prop should make this better. It isn't a prop issue.

Darwin, just curious, but why would a lighter weight prop make this better? Like Jim, my intuition says that a heavier prop would be advantageous for a smooth low-RPM idle because of the greater flywheel effect to keep the engine turning between power strokes. No? What am I missing? Again, just curious to understand the issue. I have no idea if Jim's problem (if it's a problem at all) is prop related, I would guess not.

flickroll · #4 05-13-2009, 05:42 AM

Quote:

Originally Posted by roee

I have no idea if Jim's problem (if it's a problem at all) is prop related, I would guess not.

Let me try a little faster idle to see if that smooths it out. Duh...shoulda already done that...however I didn't try it because I thought I would get a smooth idle at 650...

Webb · #5 05-13-2009, 06:23 AM

Check your mixture. Different prop but mine was too rich.

Lean the mixture at idle and see if you get much of an RPM rise. If you get a bunch (>100), it's set too rich for idle.

flickroll · #6 05-13-2009, 08:57 AM

Best I can tell is it's about a 50 RPM rise. I say best I can tell cuz the RPM bounces around and it's hard to pin down the exact rise.

rich · #7 05-13-2009, 10:25 AM

My 0360-A1A/Hartzell CS/ Slick mags runs rough below 700 rpm.
700 -800 rpm runs smooth.
Rich Rudolph
RV6A 900 + HRS.
Fort Worth,Tx.

SteinAir · #8 05-13-2009, 02:34 PM

Pretty common - extremely light props on big bore aircraft engines do not like slow idles without either a balance ring or flywheel of some sort. Heavy metal props rarely exhibit that issue, but it's common with wood.

It's a well known fact that wood/composite props that are really light will make extremely low idle speed pretty difficult....so that's probably just the penalty you'll have to pay with little to no weight on the front of the crankshaft.

That being said, a well tuned up Lyco with a Hartzell or other metal prop on it should easily and smoothly idle down in the 600's pretty easily. If you have to keep the engine at 800rpm and you have a FP prop, you'll never land!

My 2 cents as usual.

Cheers,
Stein

flickroll · #9 05-13-2009, 05:49 PM

Stein, thanks for your response. I had a hunch the low moment of inertia on the Whirlwind 200RV could be the culprit. Looks like you've confirmed it. Thanks again

breister · #10 05-14-2009, 08:44 AM

It is even worse with high-compression engines. I have 10:1 pistons and idle below 900rpm is annoyingly rough even when leaned on the ground.