.049 runs good for 50% of the time then coughs and dies

Iceberg Mon Jun 08, 2020 11:00 am

I have two .049. One a black the other a golden.

Good compression, reed valve etc etc.

The start run normal for let's say 50% of their expected run time then sputter and cough. I have double triple checked the O-ring to make sure no leak. What the ** can cause this. I don't see any cracks or other holes. The pickup tube is clear and tight.

I tried switching needles too and will try later today. What might be a possible cause. I use the same technic for numerous other motors and they run just fine. Why these two little ** won't?

Thought?

Thanks
Ice

smooth_bill Mon Jun 08, 2020 2:13 pm

Ice,

You might try sealing your tank back. It sounds like it has an air leak that is covered by fuel until the tank level drops far enough to uncover. Some recommend a string pushed into the back plate slot before reinstalling the tank, but just smoothing the lip of the tank on very fine sandpaper should help.

Also check the fuel line inside the tank for splits that are very hard to see. The line is covered by fuel until the tank is run down far enough to uncover any air leaks in the pickup line.

Bill

NEW222 Mon Jun 08, 2020 5:33 pm

While this gets brought up frequently and I do know you are knowledgable, but I have to ask how the engines are mounted, upright or sideways, as well as where the fuel pick-up is located? In the bottom for standard flying, and to the 9'oclock position for control line. I have caught myself with the pickup being in the wrong orientation before....

Iceberg Mon Jun 08, 2020 5:35 pm

Hi The engines all mounted vertical.
I am using the aluminum tub bent as Gibeault describes. It is in the 8 pm position away from center of flying circle.

Thanks
Ice

Ken Cook Mon Jun 08, 2020 6:04 pm

Screw the needle valve down until it seats. Pressurize the tank with a large syringe and watch and listen for leaks. Put oil on the screw heads, tank connection, case to tank, needle valve body and needle. Double check the reed, I have seen brand new reeds fail. Flip them over and re try. If you put a 5 oz. syringe with tubing onto the venturi and your able to pull the plunger back even the slightest, the reed isn't sealing. I have even had the need to true up the reed seat in the lathe. I just took a faint pass on the center.

roddie Mon Jun 08, 2020 9:26 pm

Hi Darren, There's always the possibility that the tank screws are leaking where they seat. If so; it could be because of a couple different scenarios.
The "best case scenario" would be that your crankcase(s) weren't tapped deep enough for the screw's fillister-head to tighten against the backplate. This was not uncommon.. and can be checked by measuring the thread-depth using a tank-screw.. and then the depth of the bore. You may find that there's enough difference to cut a couple additional threads; using a 2-56 (American Standard Machine-Screw size) bottoming-type tap.
Another scenario would be that the backplate has issues where these tank-screw heads seat. If any of the screws were ever over-tightened.. they could have opened-up (enlarged) the seat-area of the soft/pot-metal. Look for leaks around all four screw-heads.. and be aware of how-well or "if" all four screws are seating/sealing. You "can" make seals.. if the backplate holes aren't damaged too badly. I've made some from kitchen-gloves (Playtex rubber-type) I used a paper hole-punch to make these..

.049 runs good for 50% of the time then coughs and dies Dsc04610

.049 runs good for 50% of the time then coughs and dies Dsc04611

.049 runs good for 50% of the time then coughs and dies Dsc04612

davidll1984 Mon Jun 08, 2020 10:31 pm

swap back plate bet u disasemble clean 2 engine at same time and change back plate golden bee us its own desing back plate wit its extra part inside ventury look for its golden look inside if some color remain

Iceberg Tue Jun 09, 2020 1:09 am

Thanks Roddie
Excellent suggestions. I'll put them into affect hopefully will fix the issues!

Thank you!

balogh Tue Jun 09, 2020 5:28 am

roddie wrote:Hi Darren, There's always the possibility that the tank screws are leaking where they seat. If so; it could be because of a couple different scenarios.
The "best case scenario" would be that your crankcase(s) weren't tapped deep enough for the screw's fillister-head to tighten against the backplate. This was not uncommon.. and can be checked by measuring the thread-depth using a tank-screw.. and then the depth of the bore. You may find that there's enough difference to cut a couple additional threads; using a 2-56 (American Standard Machine-Screw size) bottoming-type tap.
Another scenario would be that the backplate has issues where these tank-screw heads seat. If any of the screws were ever over-tightened.. they could have opened-up (enlarged) the seat-area of the soft/pot-metal. Look for leaks around all four screw-heads.. and be aware of how-well or "if" all four screws are seating/sealing. You "can" make seals.. if the backplate holes aren't damaged too badly. I've made some from kitchen-gloves (Playtex rubber-type) I used a paper hole-punch to make these..

Roddie,

I think the plastic washers put under the backplate screw heads will be good to prevent fuel losses there. Otherwise no matter if the screw head seats are air-tight or not, because the tank communicates with the outside atmosphere through the tank vents, anyway. Sorry if I misunderstood you message.

aspeed Tue Jun 09, 2020 11:46 am

Don't forget the most common ailment of the reedies, the crank to case seal. It does not take long for play to lose the seal. Pull the crank forward and try to rock the crank up and down using the prop. If you can see the piston moving up and down, that will be the culprit. Also check all the other normal leaks and the reed etc. A new case would be the fix for the case leak. Sometimes I make a bushing up, but that is too fiddly for most people, and the cases are quite cheap.

roddie Tue Jun 09, 2020 6:20 pm

Darren, I forgot to ask. After these cut-short flights; have you tried measuring the amount of fuel needed to refill the tank? If it requires an entire 7-8cc's re-fill.. then you're losing it all somewhere. aspeed (Alan) mentioned the "crank to case" fit.. and if worn; maybe there's what I'd call blow-by.. of raw-fuel out-through the front-end? You wouldn't notice this in the pit.. or maybe not-even during static testing.

EDIT: If the reed is sealing properly.. then on the down-stroke of the piston; the crankcase has positive-pressure which might blow some unburned/raw-fuel out of a worn crank-journal.

Just a bit more to think about bro.

Iceberg Tue Jun 09, 2020 7:03 pm

Hi Roddie
Only burns half tank so not all disappeared. I keep looking and little by little knocking out possibilities.
Thanks very much!
Darren

**944_Jim** Wed Jun 10, 2020 4:49 pm

roddie wrote:...somewhere. aspeed (Alan) mentioned the "crank to case" fit.. and if worn; maybe there's what I'd call blow-by.. of raw-fuel out-through the front-end? You wouldn't notice this in the pit.. or maybe not-even during static testing.

EDIT: If the reed is sealing properly.. then on the down-stroke of the piston; the crankcase has positive-pressure which might blow some unburned/raw-fuel out of a worn crank-journal.

Just a bit more to think about bro.

That's what took out my Golden Bee block...lots of hours over lots of years. I could see it pump raw fuel and bubbles on the test stand. I never did take the time to try other, newer cranks.

balogh Wed Jun 10, 2020 4:58 pm

I have a few anodized crankcases that are all slightly loose fit with the shaft and I always wonder if this loose fit is an advantage because of lower friction as Paul Gibault advises in his Mouse race paper, or disadvantage for weaker seal. True that their surface hardness better resists abrasion if the prop is unbalanced but somehow I still favour the oldschool old stock 049 crankcases with exact fit and no anodization. I make sure my props are always balanced though. The crankcases last a helluva long time then.

aspeed Wed Jun 10, 2020 7:37 pm

On my leaky cases I could see a wear spot on the bottom back of the crank hole, like when it would push the crank down when firing. I could see it and even measure to see something was oval. They are faster when loose, but at a certain point they leak, and rev up and down and generally make you mad. Of course it can be some other thing too. Maybe the nipple has a crack or some other tubing or gasket/O ring. I pressed in some bushings on the worst ones but never tested them since, as I got away from the reedies, and also I would have to press them apart to know which ones are which. Probably have a dozen, and two were rebushed IIRC.

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.049 runs good for 50% of the time then coughs and dies

.049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies

Re: .049 runs good for 50% of the time then coughs and dies