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Carb issue.. maybe?

irishfield

Registered User
Penetanguishene, Ontario Canada
Case history:

Last winter, unless very well preheated, my O-320-C2A (B2A derated to 150hp) wouldn't start at all if below freezing. It then almost left me stranded twice after ice fishing ... and thankfully started just as the battery was about to go dead. New Odyssey 980 so I'd cranked it for a long long time. Was starting to think the speed it cranks with the new battery vs the old Gill didn't let the impulse coupling do it's job and once the battery started to get low it would fire.

This summer, it fired up like a champ every time. Always within a turn and never an issue.

I flew home in September, took the airplane off amphibs and returned it back to my wheel skis and it's sat in the hangar ever since with the fuel shut off. Other than a movement around the yard here where I noticed I had mag differential at 1700 rpm... 70 drop or so on left.. 120 on right.

Finally got around to setting my mags the other day... left was firing at 27 BTDC and right was at 21. They are both set damn near on 25 now.

Without preheat, after setting the mags, I gave it two shots of prime and she fired RIGHT up. Then died... I gave it two shots of prime, it fired right back up and died... then I realized I still had the fuel shut off. Opened the fuel valve, fired her up again and she ran like a dream.

With Jen getting a green light for now, I thought I'd treat myself to some ski flying. Went to go flying yesterday... crank.. crank.. crank.. crank.. and fuel pouring on the floor out of the air box after the failed start attempt. Farted around with it for a bit with more floor washing. Took the carb off... popped the bowl off, cleaned every orifice, made sure the float sits level... needle seats okay and put it all back together.

Tried to start it this morning... same deal today, with no start and fuel pouring out. I should have tried starting with the mixture pulled lean I guess. Waiting for it to dry out and heat up right now.

I disabled the primer line, to be certain the fuel wasn't being sucked through it.

Carb does not leak when sitting with fuel on, so I know the needle / seat is working. It only pours fuel out after cranking for start.

Questions:

Could it be the high speed cranking of the Odyssey battery keeping my impulse coupling from working?

Could the high speed cranking be sucking fuel out into the carb throat and then when no start it just pours back down and out?

Is it possible my fuel level is too high in the bowl and that is why it gets sucked out??

Can I put a 10-5135 that I have here in O/H condition on in place of my 10-3678-32 without issue? I'm fairly certain it was a Cessna 172 carb for 150 HP.

THANKS!
Wayne
 
Wayne, try taking your finger off the start button after 2 blades and see if it starts as it slows.

Glenn
 
So how does it idle once it's running? If you say it idles properly and isn't loading up, I'd say it's not your carb. You are just getting guel accumulating in the manifold, then running back out when you stop cranking.

If you're comfortable doing so, try priming it up and hand propping at idle with left mag only. If your impulse is working correctly at low speed and your left mag is in decent shape, it should fire right off. Overall, this sounds to me like an issue with the left mag. Possibly E-gap is off causing a weak spark.

-Cub Builder
 
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I've had previous "excursions" of cranking on cold days and never had fuel pour out on the floor after a no start.. never in 19 years. I gave more thought to it after I posted and am giving consideration to when on amphibs it sits carb slightly nose down... and as a tail dragger it sits with carb nose up, and wonder if that little bit extra fuel to raise the float (and seat the needle) has the fuel JUST high enough that with the rear mounted mixture and tube (that puts the fuel in the throat) there's enough suction to draw fuel. If I lower the fuel level it might stop the overflow.

THAT SAID... in the bit of time I was in the house posting the original message, the bit of preheat it managed to get with a moving blanket thrown over the engine.. no lower cowling on... I went out.. mixture cut, hit the key and it fired right up with no prime. Pushed in the mixture and it ran and idled as smooth as it ever has.

With the mags so far off before timing... YES I believe I may have an E gap issue and time for mag overhaul, but concerned about the fuel pouring out. As noted I'd never had this happen before, but again I was never able to crank at the speed I do now with the old Gill battery.

Oh.. and BTW.. I've never hand swung this thing since day one.. always had a warp drive or the now Prince prop on it figuring it wasn't heavy enough to flywheel (swing my J3 and many others all the time FROM BEHIND!) After I started it the second time this afternoon... I got out with it on Left and flipped the prince a blade and it fired right up
 
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Are you pumping the throttle as you are trying to start. That will cause fuel to run out. I had a small leak in my float that caused similar problem float was 1/2 full of fuel ran fine at 2400 but would bog down and had hard time starting. If you have slick mags I would say that is the issue.
DENNY
 
Bendix mags... floats are metal and empty. NO I did not touch throttle and make the accelerator pump shoot fuel. Simply cranking, mixture full.. throttle idle.
 
FWIW, my other plane (O-200 engine) did a similar thing last weekend. Has P-mags on it. With no preheat, it dragged down the battery enough that the P-mags wouldn't fire while cranking the engine on the battery. Sure enough, it was drooling fuel out the bottom of the cowl from the non-start.

Pulled it through 10 blades backwards with the ignition off to clear the engine, set the switches and throttle and it lit off on the first blade when I propped it. BTW, it also has a Prince prop.

I really think you're battling a tired mag that could use a proper tune up or overhaul. Since you don't seem to mind pulling the carb, it's not a big deal to check the float level while you've got it off, but I would be surprised if you find anything wrong with it.

-Cub Builder
 
Okay.. THANKS! Before I set the mag timing I'd talked with some lads about going Electronic on at least one mag. Figured I had a left mag impulse issue and why the hard start last winter, but if I have to pay to overhaul I might very well put a Pmag on instead. I don't have a real hard "click" on mine, so thought it might be stuck.. but while timing the mags it seemed to be working fine as I had to go past it and then back for the buzz box as the impulse was delaying the point opening.
 
yup your points fowler is worn and its changed the internal timing of mag...

anytime a mag move 3 or 4? degrees(overall since install, assuming you timed them) you might suspect it's time to have them looked at/adjusted...

it shows up as hard starting... A "Slick Start" booster will "Mask" this issue also....
 
My Left mag was at about 27 BTDC.. and it's the impulse starting mag. So it hadn't moved much assuming it was 25 to start with. The Right being at 21 or so had me worried, but it's not the starting mag and now that I set them both at 25BTDC I have no mag differential from left to right.. they are identical with minimal drop from running on both.

I'm probably going to be pulling both Bendix and having them O/Hauled or going one or both Pmags if that's the issue.

.... is it normal with a multi crank no start to suck fuel out of the carb and have it pour on the floor?
 
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When I first got my -18 I found it had primer nozzles with holes bigger than... No atomization at all, just pissing fuel. Installed AN4022-1 nipples, no issues.
 
Yah, mines not far off that... but it does this without hitting the primer. With the primer line disconnected as matter of fact and why I isolated it to make sure.
 
.... is it normal with a multi crank no start to suck fuel out of the carb and have it pour on the floor?

Yup. It happens. You're drawing fuel up into the manifold with a lot of it condensing along the manifold tubes. When you stop cranking, it runs back down the manifold and out the carb.

-Cub Builder
 
....Finally got around to setting my mags the other day... left was firing at 27 BTDC and right was at 21. They are both set damn near on 25 now.

Questions:

Could it be the high speed cranking of the Odyssey battery keeping my impulse coupling from working?

yup your points follower is worn and its changed the internal timing of mag...

anytime a mag move 3 or 4? degrees(overall since install, assuming you timed them) you might suspect it's time to have them looked at/adjusted...

it shows up as hard starting... A "Slick Start" booster will "Mask" this issue also....

Mike is correct. The internal timing of the mags needs to be set correctly. Also do you have a new style light weight high speed starter? Some times these starters can turn the engine too fast for the impulse to give the retarded spark for starting. If you have the old direct drive started, it bogs down in cold weather and will not turn the engine fast enough.

A new set of points and a condenser should fix the mags. No need for an expensive overhaul.

You do not have a carburetor problem.
 
Okay.. THANKS everyone, was just concerned with the excessive fuel puddle on the floor. That was a new one...

As noted I was suspect of the mags before now and they have about 400 hours on them. I just got home from a 6 hour drive and will be heading for the hangar to pull them off as it's 32F / 0C right now. Going down to -20C tonight and will be no fun working on that tomorrow!
 
Took me a GOOD 20 minutes to remove them after setting 25bdtc.. seeing the indicators in the window and pulling everything apart. Anyone else ever pulled their mags in the winter and found such ice? Maybe my impulse is freezing without preheat? Anyhow, points and condensers ordered (and of course Back Ordered just to add to the misery!) and will update when I have the new parts in, set and installed. The old points look darn good, with very minimal pitting and I still seem to have about 20thou gap.

Really pissed to see that when I got my fresh engine, that Leavens didn't even replace the condensers in the mags... they are dated '87 and '89 !
 

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Make sure your vent tube is clear and has the slot cut in it in case of freezing and plugging up...run the engine to 180 on the oil temp and keep it there for awhile to get the moisture out of the engine....
 
As noted in a previous thread.. I like to keep my oil temp above 215 F.. so would have thought moisture wouldn't be a problem...so that proved me wrong! lol No signs of rust spots anywhere in the gear case though!
 
If you got up to temp and your case vent is open, the moisture would not be sitting in there like that...how are you preheating?
 
I haven't this year.. other than yesterday just to see it start. Hard to believe temperature swing and humidity in the hangar could do this, but it sure shows what is possible for others to be aware of. Not very often someone pulls a mag in such environment to see this. If I had of pulled it in a heated hangar, you'd never see this!

When I do preheat in the winter, the cowling is totally covered by a heavy quilt or moving blanket and heated with a 900 W electric heater. You can barely hold your hands on the cylinders after the heater has been running for over 3 hours.
 
Preheating and running for a short time without bringing the oil temp above 180....would produce that amount of moisture. Also heating the oil and not running the engine could produce excess moisture....
 
Took me a GOOD 20 minutes to remove them after setting 25bdtc.. seeing the indicators in the window and pulling everything apart. Anyone else ever pulled their mags in the winter and found such ice? Maybe my impulse is freezing without preheat? Anyhow, points and condensers ordered (and of course Back Ordered just to add to the misery!) and will update when I have the new parts in, set and installed. The old points look darn good, with very minimal pitting and I still seem to have about 20thou gap.

Really pissed to see that when I got my fresh engine, that Leavens didn't even replace the condensers in the mags... they are dated '87 and '89 !
Those condensers weren't necessarily bad just because of the date. Maybe Leavens has had a case of them in stock for a long time? They do do a lot of engines.
... Hard to believe temperature swing and humidity in the hangar could do this, but it sure shows what is possible for others to be aware of.

If the ice was preventing the impulse from operating, you should not be able to hear it clicking when you pull the prop through. If it is clicking it should be working. Although it could be slow.

If the points are smooth, the condensers should be good. A slight pitting is a sign of them starting to go bad. The 20 thou gap is not what you should be looking for. You want the points to just be just opening at the point of peak flux in the magnet while you are turning it by hand in the direction of rotation. (You don't want the impulse snapping while you do this set up.) You will be able to feel the magnetic strength vary with your hand. Use a piece of paper between the points, pulling it with your fingers. When it starts to move and the flux is at it's max strength, the points are set right. This is a fussy operation which you will be certain of when you are finished. Accept whatever gap that provides. Test the mag by turning it by hand on the bench with a screw driver placed from the case to the center rotor pin. You should get a nice big, fat, long (1/4"+) dark blue spark. Once the mag is timed to the engine, any change in the timing will be because of the wear in the cam follower and/or the points. This means that when during the annual inspection you find that the timing has changed, you need to remove the mag and reset the points. Sure you can just rotate the mag for a small adjustment, but it will not be putting out it's optimum spark.

IF
the mag is not putting out a good spark on a cold day, it will not ignite a pool of gasoline which will then run back down the intake risers and out of the bottom of the carburetor.

One way to reduce or eliminate moisture from the inside of the engine is to stuff oily rags into the exhaust stack and breather pipe immediately after engine shut down. When the engine cools down it draws in moisture through these openings. The oil in the rags stops the moisture.
 
Thanks for all that skywagon!! Good point on the condensors.... although I found the "build" sheet for my engine and while they put points in they did not do condensers. OH well... I ordered two new ones to go with the point assemblies that are unfortunately back ordered.
 
I forgot to say that it is important to double check the points opening after tightening the two screws. Just tightening the screws can move the points enough to throw the timing off. Have them only loose enough to be able to move the points with a screw driver in the adjustment slots, with a little drag. Any looser and you will be pulling your hair out.
 
Yes.. thanks. Have done many points and distributors in my 5 decades. Mags are the only thing I've ever kept my distance of for some dumb reason. If I can't figure it out or zap myself too many times, I have an 82 year old AME (our kind.. not yours.. lol) just down the road from me.

Points look really good.. still smooth, so I guess I could just reset them... but taking Mike's advise on worn follow tabs I may as well wait for the new assemblies to get here... compare.. and install the new ones regardless. I'm sure I can find lots of other things to work on here instead of playing in the sky for now!
 
Thanks for the encouragement to go forward with this guys. It seems my main issue is just an inconsistent impulse coupling. I was playing with it yesterday.. turning and turning with it in a vice in similar engine mount attitude and it often missed "hooking in" to snap.

Gave it a good cleaning.. oiled... checked for the #35 drill bit clearance bendix specs out and while I am close I can't get one in there. Checked the cam to post "X + .014" maximum allowance for pivot wear and I'm only about 6 thou. Reset the points using my buzz box and a grade school protractor to mark 10* on the case for the Egap... and I now have a spark that shoots out of the distributor spring up and to the case. That should start it!!

Think I'll still wait for my new points and condenser before I reinstall. Lots of other shop work to get out of the way.. so shouldn't be out playing anyhow I guess. ;-)
 
You don't want to be shooting out from the spring on just one. The other three will shoot sparks inside the mag. Not good for the mag. Use an insulated screw driver from the case to the center distributor rotor pivot. Each spark will jump to the screw driver. It will not zap you.

By your description you are good to go. Put your new points and condenser on the shelf for a rainy day when they arrive. They do normally last for a long time.
 
Yes.. I was doing that with the screw driver... jumps a good 5/8". Only about twice I've turned it and seen it shoot from the spring. Guess I'll go over it again... make sure I have the setting just right (as I was just playing waiting for the new contact assembly) and then do the right mag next, as it was the one that was 4 degrees off on timing. The Left impulse was only about 2* early. THANKS Skywagon!
 
Mags back in.. both set at 25BTC with buzz box lights coming on simultaneously. Great spark at harness plug end. Put the #1 plug back in and cranked.. and cranked and fuel on the floor again.

Am I expecting too much for it to start without preheat at -12C / 10 F ???

Thought I'd give it a whirl, even though it's always been a bitch to start without preheat. It's just never put fuel on the floor when it wouldn't go, so I'm still suspect of a fuel issue somewhere.

Tomorrow I'm going to pull all the plugs, clean, gap and pressure spark test them all.

Video of my right mag spark.. rolling the gear with a gloved hand. Let me know if it works.. I may have to change the viewing settings. My left (starting) mag had a heavier spark thanks to the impulse coupling.

 
Hmmmm? Did you connect the plugs to the harness and set them on the outside of the cylinders so that you could see all of the sparks while pulling it through? Did not even get any firing at all? Do you have a four cylinder primer? Sometimes priming just a single cylinder gives the symptoms which you have.

This is your video:
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