Truckracer

My Feedback: (19)

delete .... wrong thread

JoeMamma

Been flying my Great Planes Big Stik for a few months with the GT33.

Have had a backfiring problem with it since day one that seems to be getting progressively worse. The engine starts very easy, transition both up and down is great, and she idles down nice.

On my first flight of the day she runs great with no backfiring. On the second flight she may backfire once or twice. On the third flight she is backfiring about every 20-30 seconds. On the fourth flight she is embarrassing me ! Not just a little backfire but a big KA-BOOM, KA-POW !

The backfiring seems to get worse as the engine (or ignition module) gets warmer on each flight.

I have tried numerous spark plugs with different gaps, still backfires. I know it’s not the carb or carb adjustment because she runs too great. I took the carb apart anyway......no dirt, no sludge, looked like brand new. More wasted money on a carb kit as the exact same backfiring condition exists.

It’s as if the battery voltage is being momentarily cut off. As it warms up it gets much worse ????

I don’t have anyway of checking the ignition module or the crankshaft sensor so first I replaced the engine kill switch (an MPI/MAX unit). I also replaced the jumper harness between the ign. module and the kill switch. A new replacement 6-volt, 5-cell 2500mah ignition battery was installed as I was thinking maybe the battery may have an intermittent open circuit. The exact same backfiring condition still exists.

Ordered a new RCEXL module and crankshaft sensor and installed them. Was a waste of money as the exact same condition exists. Again, first flight OK but then..........

I was complaining to my fellow flyers about this long-term problem and mentioned I may just pitch this engine into a bonfire ! Then one of my fellow flyers mentions the RCEXL module does not like any more than 4.8 volts. I said: But they are recommending 4.8 up to 7.4 volts ? He then tells me he has cured the backfiring in the past by simply changing to a 4.8 volt pack. I was a little skeptical, but down to the local hobby shop I go and picked up a new 4.8 volt NiMh 2000mah ignition battery.

Just amazing........after all of the time spent with this engine, absolutely no more backfiring !! All I can think of is my ignition module is mounted inside the fuselage and not in any airstream. This would explain why the problem got worse with each flight as the module was warming up more than usual due to the higher battery voltage ?? I never took any before and after temps. of the module so I’ll probably never know for sure.

Your comments please ?

Joe M.

BarryReade

My Feedback: (1)

JoeMamma, Thanks for sharing your experience with the 33GT. I have one and it is my first gasser. It is good to know what you have gone through if the backfiring starts happening to me.

MTK

JoeMama,

My OS CDI module is mounted inside the fuse too, away from an airstream. I run a regulated voltage supply to my CDI at 5.4 volts.

Mine has never backfired.

I have also run the 33 on an RCExcl CDI, a Syssa30cc CDI and a DLE55cc CDI. They all worked fine.

The only issue I've had with the original OS CDI is that it is hard to hand start first run of the day. Probably due to the internal programming for minimum rpm. I use a Dynatron starter...problem solved

JoeMamma

Hi Matt,

5.4 volts ?

I never thought of using a regulator. This is because it isn't mentioned in the O.S. owners manual. You would think if it required a voltage regulator they would have mentioned it ??[] Installing a regulated voltage supply would have saved me a lot of grief, time and money.

Of course Hobby Services (the O.S. repair facility) says it will run OK on my 6.0 volt ignition battery.[:@][:@]

Joe M.

bells33

My Feedback: (19)

Running my GT33 in my 26% Pilot RC yak 54. One fromeco 2600ma running both ignition and receiver with a Sahara regulator.
About 20 flights so far... Loving it!!

Flew the other day for a solid 60 minutes. Used about 1500ma. I think it's a great setup for a plane this size.

MTK

Joe,

Actually, my set-up is as follows: I use a 2 cell Lion/LiPo with a nominal voltage of 7.4 volts (8.4 on full charge) and 2000 ma capacity in my airborne system. This voltage is regulated to 6.3 for the radio.

Then I have an IBEC (Tech Aero) installed in the retract channel (the IBEC is just another "servo" connected to the radio) that connects the airborne radio system battery to the CDI. The input voltage to the IBEC is the same as for the radio, 6.3 volts. The IBEC drops the voltage down to 5.4 to the CDI through its built in Vreg. So in essence there is double voltage regulation going on

This way I use one battery for everything and save the extra weight of a second battery, switch, etc. It is such a convenient set-up too because I arm/disarm the CDI from the retract switch of the TX. I get 75 minutes of flying on this set-up comfortably, driving both theradio and CDI from the same V source

CDI's are dumb systems in regard to input voltage. As long as the appropriate amount of voltage is present and capable of supplying enough current (they use so little current that its nonissue in reality) they don't care where the supply is coming from.

Hope this helps everyone wondering if there is a better more convenient way to do things. It's a small amount of set-up up front to add the IBEC but the convenience and certain knowledge of when the CDI is armed and when not, also, no reaching behind a spinning prop to turn ignition off, etc., makes this approach more worthwhile than other alternatives.

TimBle

I am running one Mintor on a Tech Aero IBEC set to 5.5V. No problem.s
The other is running off a Hyperion 1700mAhr 6.6 LiFe. no problems

neither engine back fire, pops in flight makes anyother strange noise.
Neither Ignition has been fried to heel and gone as has been suggested would happen
All my engines run a NGK CM-6 gapped to 0.6mm (0.024")

Nickolas

Hi all,

I have done 3 flying sessions so far with my EF Extra 78'' and OS GT 33, still a bit reluctant due to the break in . I run it with Bel Ray H1R and Mejzlik 19x8.

The EF Extra with this engine is an excellent combo. Flies better than 100cc aircraft.

Here is a sample from the latest flying session, please here that sound with opean muffler and mid range response.

BR,
Nikos
[link]http://www.youtube.com/watch?v=zQ3HgbnR1D8[/link]

MTK

Yia Niko,

My OS33 is piped turning an apc 20x10.5. Now that cooler weather is here the power from this engine is amazing. My 11# pattern plane could be driven out of sight vertically, at half throttle.

Compression is very good, the best of any engine in this class that I have played with. After 10 gallons through it the bearings have finally fully loosened and any internal tightness is gone. I also use Bel Ray racing oil, MC1, at 50:1, from the start

coronabob

My Feedback: (10)

Very nice flying, Nikos.

gibatta

My Feedback: (1)

Hello MattK, so what is the pipe brand and model you are using?

Please advise

MTK

ES Composites 40G carbon pipe. But ESC 30G also works the same as the 40G. The 30G is 1" shorter than the 40G. The original 30G was basically a 40G with a shorter muffler section, built to my specs. Ed Skorepa liked it so he offered it as another option.

I use the Hatori header with a small extension added to bring the exhaust length to 27" from the exhaust flange to the reflection baffle in the pipe. Pipe length doesn't appear to be terribly critical; I've used lengths as long as 30" to the baffle and the results were the same. But I wouldn't go lower than 27"

I have also used the Mintor 38cc pipe which is all aluminum. It is also very lightweight at 5 ounces (the carbon is about 3 1/2 ounces). Same exhaust length as above.

Jeff Worsham

My Feedback: (28)

Hi All,
Pretty new to gas engines and am setting up a 33 in an Aeroworks Edge 540. Seems like the throttle return spring wouldn't be a good thing for my throttle servo- do you guys remove the springs from your engines? Thanks

MTK

Jeff,

Most don't bother removing it. The servos have plenty of torque to overcome spring tension.

I compromise by relocating the spring loop to the large hole in the plate. It reduces the amount of tension but still assists in bringing throttle to idle. Or you can remove it outright; as long as you have a reliable servo set-up, it won't matter whether there's a spring or not

Jeff Worsham

My Feedback: (28)

Matt,
Thank you for the reply. I like the idea of relocating the spring to reduce tension while leaving it in place in case I might decide to put it back at some point. BTW- enjoyed reading your experience with the pattern plane setup- great job!

MTK

Thank you!

For pattern, if this was available 8 or 9 years ago, it would have replaced most of the YS, OS, Webra, Mintor glow set-ups overnight. But it probably would have cost $700 for the "Pattern Version". Electrics would have still taken over, but it would have taken much longer....this 33cc set-up is that reliable!

FSFLYER

My Feedback: (12)

I have the ES Composites 40G pipe. Do you recall the distance from the pipe inlet to the baffle?

MTK

It's easy to determine by yourself...take a dowel and insert it into the pipe, along the wall. Easy does it until you feel the baffle inside

john josey

I have a bit of running time on my 33 now and have noticed it runs a bit leaner when inverted or knife-edge ! anyone else have this issue ?

I'll post some pictures of my install, a fresh pair of eye's can often help.

                                 cheers
                                        john

TimBle

quite a few of the gassers do that when new. It clears itself up with running,

john josey

john josey

Ah, i do apologise, i posted the pictures without refreshing the page to see if anyone had replied.

Thats the best answer i could of hoped for. All my other petrol engines are zenoah and i've never noticed the same lean running with them.

Thanks for the reply
john

dobro

My Feedback: (3)

Howdy , could you share the spinner nut item number that works with the GT-33? I'm searching for one myself . I'm converting my OS 1.60 tru turn spinner to the 33. Need to come up with the spinner nut. Thanks Much. Bob.

MTK

I think the OS160FX has an oddball sized crankshaft close to10mm. At least my FX160 does. The 33 has an 8mm shaft. The prop nut is the same as that used on the OS140RX. Tru Turn makes what you need....you might call them and also ask about a spacer for the spinner hole to accommodate the smaller shaft diameter