lycoming 0320 narrow deck hard starting

the super cub has gotten miserable to cold start in the past few years, and just can't quite figure it out. This cub used to start with ease down to 10F and now she wont go if it gets much under 40F. In the past year, I have replaced plugs, wires, and carburetor, with only limited improvement on the situation.

the last annual showed good compression, and primers were cleaned and serviced.


Maybe I should ask all of you about your procedure for starting your 0320's? What is your exact procedure for starting - particularly on cold mornings?

I've never had success using primer, so its just a "pump throttle and grind" method here. Maybe you can enlighten me as to why primer pumps will never start my plane?


tia,

When is the last time you did a 500 hr inspection on your mags?

Does you primer system work? Have you verified that it pumps enough fuel on each stroke? How many cylinders have primers? Are they in good condition?

Web

If you have slick mags that is the first place I would look for a problem!!
DENNY

yup, mags need serviced

If you have a primer system installed, take somebody out to the plane with you that uses them a lot and have them start the plane. There are primers that hold their prime and others that have to be refilled before every prime, presumably due to some small leak somewhere. Somebody that uses primers can help you figure out if yours works right, and if so how to make sure you have a good plan for priming.

If you are already a primer start expert, then disregard...

But as to why it is harder to start than it was before...mags.

500 hours adjust the e-gap.

https://www.supercub.org/forum/showthread.php?t=46009

If the plugs test good, under 5000 ohms, I'd look hard at the mags.
A 500 hour inspection (at about 1200 hours time-in-service) for my two Bendix mags a couple years ago cost me close to $1200.
As Cliff at Aircraft Magneto Service explained, the "500 hour inspection" is basically an overhaul but without replacing all the parts as required for an "overhaul" per the mag service manual unless they really need replacing.

I think replacing points & condenser and re-setting the e-gap would be reasonably inexpensive (relatively speaking)
and would likely solve your problem. A regular A&P can do this if he's familiar with magnetos.

Mag shops (and some mechanics) have a mag-testing bench where you chuck the mag up and spin it at a specific rpm to check for proper spark at a specific gap on test electrodes. This is the only way to accurately check for proper operation IMHO.

If you technique was successful for a longtime and now it's not then obviously something physical has changed, such as the above.

Without a primmer, I could never get my aircraft to start without the throttle being on or almost at the closed position. I would pump it a few times as the prop started turning, but then I would have the throttle closed. After looking at the picture of the carburettor found in the member resources section of this site, I figured it must have needed to have the butterfly valve near closed to creat a suction off a fuel jet.

I passed my thoughts onto a friend with a Cub and no priming system and he said it's improved his starting no end.

10F that's minus 12 degrees C. Too bloody cold for flying???

I had a similar problem years ago with the O300 in my old C170.
I was CERTAIN it was the mags.
Pulled them off and had them bench tested.
Nope, spark was within spec & plenty good.
I didn't believe the mechanic when he told me it was my 500-ish hours old plugs,
but he talked me into buying 6 of them.
Bingo!
Bought 6 more and away I went.

Since then I discovered Aircraft Magneto Service's trouble-shooting guide.

http://www.aircraftmagnetoservice.net/magneto-troubleshooting-guide

Does your magneto have an impulse? With both mags off, pull the prop through several blades (CAREFULLY AVOIDING GETTING IN THE WAY OF THE PROP). At some point you should hear a clicking noise, which is the impulse coupling on a mag. If you dont hear that, have a mechanic check the mags.

MTV

I see the opening poster has only one post.....not sure if we will get a reply, but did you resolve this starting problem?

He might be a one-hit wonder.