Cold Weather Starting Difficulty

[rv7adriver12]

I have a RV-7A equipped with the TMX-O-360, a MA4-5 carb and Slick mags with impulse coupling on the left one. When it gets down to 40-50 degrees, I have considerable difficulty getting the engine to start. I have tried leaving the primer pump on for 5 seconds and also 8-10 seconds. With about 10 seconds, it will cough, sputter and then die. When I do get it running, even up to regular idle speed, it dies about 3-4 seconds later. It seems to be running just on prime and is then starving for fuel. After a dozen attempts, it will finally stagger to life, and then idle just fine if I can keep it running at least 5-10 seconds. But I once ran a battery down in the process. Since the engine doesn't seem to want to stay running once it does start on the first few attempts, it makes me wonder if idle mixture is set too lean or if float level is low. Maybe it wants more than 10 seconds prime at lower temps? In warmer weather, the engine starts immediately. Any thoughts/comments appreciated.

[krw5927]

Sounds like a lot of priming. My O-340 takes 2-3 seconds prime and that's enough. (My primer goes into cylinders 1&2 only.)

Is there a chance you're making it too rich by over-priming?

[crabandy]

Could be bad advice, please read rest of thread later.I don't have a primer on my O-360 MA4-5, I found 2 shots of throttle and pulling the throttle all the way closed to the stop works best for mine. I was in the habit of only pumping the throttle if the prop was spinning, on the RV it didn't work as well. I believe close the throttle all the way helps richen my mixture, after it starts I bring the idle up to a normal 600-800 RPM.

[Ironflight]

Originally Posted by crabandy

I don't have a primer on my O-360 MA4-5, I found 2 shots of throttle and pulling the throttle all the way closed to the stop works best for mine. I was in the habit of only pumping the throttle if the prop was spinning, on the RV it didn't work as well. I believe close the throttle all the way helps richen my mixture, after it starts I bring the idle up to a normal 600-800 RPM.

I just want to point out that pumping the throttle with the engine NOT cranking is a significant fire hazard - you end up with a pool of gas in the FAB, and a backfire is likely to set your pride and joy on fire. Yes, you can get away with it a long time, but if it happens - you can't get an RV cowling off fast enough.

If it won't start without doing that - I'd find out why. Pumping with the engine cranking works really well for most everyone that does it, and if not, you might have an accelerator pump problem.

[jdiehl]

Get a couple light bulbs and hang inside the cowling via the oil door. That provides about 60 F of heat for a quick start on the coldest morning. Of course, use caution so they're not touching the cowling or other heat sensitive areas. As Paul noted, never pump the throttle without cranking.

Jim Diehl 7A
Lycoming 0-360
Lock Haven, Pa.

[F1R]

All lycomings start easier with warm air in the bottom end and intake tubes. The easiest way to do this is a 110V oil pan heater strip siliconed onto the bottom of the sump. 100W is plenty of heat. There is no need to leave it plugged in all the time, only for 1-2 hours before start up. With cowl plugs in the cooling intakes or a blanket over the cowl, you can even be outside in the wind and get good pre heating.

A hot air pre heater like "The Hornet Heater" from aircraft spruce is also an excellent, safe and easy way to make life much easier on the Lycoming. They have proper temp limits and won't blister your cowl or paint.

If the oil is cold and stiff, the impulse mechanism on the LH mag might not always function as intended, only adding to longer than needed cranking.

Warm oil on start up also extends the life of any engine.

[Vlad]

Preheat when cold as mentioned by Jim and F1R. Any method is good as soon as oil is warm and battery preconditioned. I am parked outside and don't have a luxury of an electric outlet so I use a propane heater loaned by a fellow RV builder. Works like a charm at ANY low temps.

[crabandy]

Originally Posted by Ironflight

I just want to point out that pumping the throttle with the engine NOT cranking is a significant fire hazard - you end up with a pool of gas in the FAB, and a backfire is likely to set your pride and joy on fire. Yes, you can get away with it a long time, but if it happens - you can't get an RV cowling off fast enough.

If it won't start without doing that - I'd find out why. Pumping with the engine cranking works really well for most everyone that does it, and if not, you might have an accelerator pump problem.

I should've been much more discretionary on my reply. I once caught a C150 airbox on fire using someone else's over priming procedure. I couldn't get out of the airplane fast enough much less continue cranking the engine with the mixture in idle cut-off or de-cowl the airplane.

My RV7 O-360 has dual EFII electronic ignition, everything seemed to run very well except the start. On the first start of the day I watched the prop spin for 7-10 seconds (pre-heated to 50 degrees or 80 degrees OAT) as I pumped the throttle 3-5 times as the starter spun the blades for a normal start. Initially I thought the ignition may be browning out during start. Long story short I found that 2 pumps of the throttle followed by a quick start button push (1 one thousand count for 2 pumps and starter hit) with the throttle at the idle stop fires the engine within a couple blades. Emphasis on the quick pumping of the throttle and spinning the engine to minimize any fuel pooling in the airbox.

I suspected the carb was a little lean for my RV because my idle mixture screw was 4 turns out instead of the initial 1 1/4 turns out. 4 turns out gave me about 10-15 rpm rise at idle cut off, Further turns out didn't seem to enrichen the idle circuit any more and very little residual resistance to hold the screw in place. At full power My leanest EGT at cold temps was only 80-100 degrees ROP, warmer temps yielded about 150 -180 degrees from full rich to peak EGT.

I'm currently in process of my first condition inspection, since my carb (MA4-5 3858) was still within the warranty period the fine folks at Marvel Schebler were willing to check it out. My carb flowed to within factory spec's, some throttle positions were closer than others. Marvel Schebler did en-rich both the idle circuit and main jet of my carb, based on my EGT and idle observations. I'm hoping to find out more specifics later. I hope to have some more real flying numbers soon.

[N941WR]

You said your left mag has an impulse coupling, are you starting on just the left mag or on both?

[LettersFromFlyoverCountry]

One trick that works well for me. After you try starting a few times (with a normal start routine and normal priming), just wait.... sit tight for about a minute... then try again.

I can't explain why this works (for me), but it works (for me)