Running lean at low RPM OK ?

[Stanley]

After running too rich for months put new points and swapped the SM's for modded N-27's. I balanced the mix and set it lean, then set it 1/16 of a turn richer every few days. Now it goes lean when first leaving a stop sign, burbling a little except on very hot days, but runs well otherwise. I could easily richen it up but I love the gas mileage around town. I can drive for an hour and the gauge doesn't move. I've read that these engines like a rich mix but I seem to have more power when it's a little lean, especially on hot days. The N-27's are polished down at the mid-range, cruising, and top end stations so there's no lean miss or burbling when I get on it. No overheating at all.

I do have to pull the choke now to start it. I plan to richen it slightly to the point where there's no burbling, but no richer.

Does the danger to the engine from running lean still apply if it's lean at low RPM only and engine temp is normal or less ? Also, the plugs are showing leanness. Will a little light gray stuff on the plugs hurt performance ?

[Mark Maras]

 Curious. What wt. oil are you using in the carbs? Neither too rich or too lean is good for the engine. Keep going richer with the screws until you get the light tan color on the plugs. I doubt that a little light gray stuff on the plugs will hurt anything although new are always best. When starting out from a stop sign, are you sure the mixture is lean? You can check to be sure by adding a little choke during acceleration. If it is lean, you'll feel the additional power as you add a little choke.

[Captain Obvious]

If it's lean only when you first hit the gas pulling away from a stop, methinks you need thicker oil in your dampers, or there is something wrong with your jiggly bits.

That or you just need a set of flat tops!!!  

[Mark Maras]

35 minutes ago, Captain Obvious said:

If it's lean only when you first hit the gas pulling away from a stop, methinks you need thicker oil in your dampers, or there is something wrong with your jiggly bits.

That or you just need a set of flat tops!!!  

NOOOOOOOOOOOOOOOOoooooooooo

[Stanley]

Yes it's lean at idle, intentionally. Just wondered if it would hurt the engine. If I pull the choke a little the burbling instantly goes away. In fact, I've been driving with a hand on the choke when there's a lot of stop and go, until it warms up. It doesn't do it once I'm going 5 or 10 mph so I push the choke back in. Using straight 30 wt. in the carbs per book and red springs that are stiffer than stock. I could easily tune it out by dropping the nozzles a little more but it accelerates great at all other conditions and the gas mileage is incredible. The needle profile is richer than stock in the cruise and top end zones so there's no miss when I stomp on the gas like with the stock N27's (and no fouling the plugs at low end like the SM's).

Plugs look too lean though, so it's bye bye 35 mpg I guess.

[Captain Obvious]

Well here's a theory then... If you hadn't messed with perfectly good needles in the first place and made them richer everywhere with the exception of at idle, then maybe you would be able to drop the nozzles a little and end up with the mixture where you want it... Even at idle.      Haha!!! Sorry. Just had to!

I agree that 35 mpg would be hard to walk away from.

So if you pull the lid off the air cleaner and lift up on the pistons:
Are the pistons hard to lift? (Are the dampers damping?)
Are the two dampers the same?

[Stanley]

Yes, the dampers were the same and hard to lift two weeks ago when I balanced the carbs. I had to put a few drops less oil in the front (IIRC) one to get them the same.

[Captain Obvious]

As long as the dampers stay fully submerged even at full height, then the amount of oil shouldn't matter. If you're able to tune the amount of resistance to lift by adjusting the oil volume, then you don't have enough oil in there. They should be to the full mark, and at the full mark, they should both feel the same.

[Stanley]

Thought I had them both full to start with but not sure. Maybe one jiggly bits functions different than the other. Next time I'll try swapping the plungers with oil levels topped off and see pressure required to lift the pistons changes.

[Captain Obvious]

I've seen that. One stalk damped a lot more than the other. The check valve on the one that didn't damp wasn't working properly.

IIRC, the center shaft was cocked off to the side a little and because of that misalignment, the check valve didn't work right.

[Stanley]

I gotta look at my book. Didn't know there was a check valve. If I take those plungers apart, wonder if I'm more likely to learn something, or mess something up, or both ?

[Stanley]

Seems like the difference could also be caused by one damping too much due to a blockage. I gave it a good blast of carb cleaner, though. Didn't do anything.