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Mar 28, 2016, 12:19 PM
KV4PL, FAA 107 Certified
FloridaFlyBob's Avatar
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Help with a OS GT33 that won't run


I have a Waco Biplane that has a OS gt33 motor on it. The plane has sat for around a year and a half. I tried to get it started without luck. I'm not a gas engine expert by any means so any ideas would be appreciated. Where should I start first? Should I take the carb apart and clean it with some carb cleaner?
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Mar 28, 2016, 02:19 PM
Oh...that's gonna leave a mark
capt kurt's Avatar
How did it run before you parked it? First, I would check that I'm getting spark and secondly and probably most likely, the diaphrams inside the pump have dried out.
Kurt.
Mar 28, 2016, 02:25 PM
Registered User
Cleaning the carb would be a good start.

Likely reasons for the engine not starting would include (i) ignition, (ii) fuel supply and (iii) compression.

For (i) ignition, do a spark check. Remove the spark plug and rotate the engine whilst keeping the spark plug ground on the engine block. You should see the plug sparking. This is done with the ignition switched on.

For (ii), fuel supply. With the spark plug removed, either turn over the engine with a starter for a few seconds and check that the engine is drawing fuel. You should be able to smell raw fuel. Or, turn over the engine by hand with the choke on, or your thumb on the carb intake. As you rotate the engine, you should see fuel being drawn in the fuel line.

For (iii), compression, turn over the engine and you should feel compression towards the top of the stroke.

Once you've carried out the above 3 checks, the likely cause can be narrowed down.
Mar 28, 2016, 04:27 PM
I kill throttle servos
3d-Chris's Avatar
Its dry. Squirt some fuel in the carb to get it to draw fuel again. You should be good to go after that .
Mar 28, 2016, 06:34 PM
KV4PL, FAA 107 Certified
FloridaFlyBob's Avatar
Thanks guys, I checked the spark with the plug out, I could see a spark, I'm not sure how strong it's suppose to be. It has good compression and ran good until I put up. I'll check if I can smell gas from the spark plug hole after a few flips this weekend. I have a Hobbico starter that will turn over a DLE 20 I have on a Hellcat but the starter isn't strong enough for the GT33 so it's hand starting.
Mar 28, 2016, 06:38 PM
I kill throttle servos
3d-Chris's Avatar
Never EVER turn the prop over with the plug out! You could do some serious damage. Like I said, it is dry. You need to squirt some fuel in the carb to get it wet so it will pull fuel again. Watch the line to see if its getting fuel.
Mar 29, 2016, 01:49 AM
The great Brutufier
Quote:
Originally Posted by FloridaFlyBob
I have a Hobbico starter that will turn over a DLE 20 I have on a Hellcat but the starter isn't strong enough for the GT33 so it's hand starting.
Wasn't there something with the OS ignition systems that they more or less required electric start?

I seem to remember something like that...
Mar 29, 2016, 09:24 AM
Registered User
jhaywood's Avatar
He said it ran fine until he put it up.
99% chance that the carb is stopped up inside. The gas evaporates and sometimes leaves oil on a tiny little screen. Also, the diaphragms get sitff from sitting with gas in them. Get a carb kit, and carefully disassemble the carb. Clean the junk out with carb cleaner and compressed air. Make sure you flush with gas before reassembly so that any residual carb cleaner will not harm new rubber parts.
When you disassemble, the diaphragms should be rubber like, sort of supple. If they move stiff, or you can hear them crinkle as you flex them, they are bad.
Make note of which side the gaskets go in relation to the diaphragms and flapper valves.
Mar 29, 2016, 09:40 AM
Registered User
los36's Avatar
Quote:
Originally Posted by 3dFlyingMaster
Never EVER turn the prop over with the plug out! You could do some serious damage.
Explain.
Mar 29, 2016, 10:07 AM
KV4PL, FAA 107 Certified
FloridaFlyBob's Avatar
I hand started the motor for 1 season. Except for the tendency to start in reverse without enough throttle it started after 3-4 try's . The DLE 20 I have I'd try and hand start that, but probably drop dead before it would start without an elec starter. I'll search youtube for any videos on OS carb bebuilding. Are they Walbro carbs? The motor has hardly any time. It was just barley broke in. the plane takes a good 30 - 45 min's to put together and take apart.
Mar 29, 2016, 01:03 PM
Oh...that's gonna leave a mark
capt kurt's Avatar
Quote:
Originally Posted by Brutus1967
Wasn't there something with the OS ignition systems that they more or less required electric start?

I seem to remember something like that...
Ya, the manual says you can't start them by hand cuz you need at least 400 rpm....... that is in my 15cc manual......not sure about my 22. I've been starting them by hand however AFTER the first start of the day,
Kurt.
Mar 29, 2016, 02:02 PM
Registered User
los36's Avatar
The OS will start by hand. The OP has done it as have I. Yes, the ignition has an RPM threshold, but a swift flick of the prop overcomes it. However, the 33 does have a tendency to start backward if it started at too low of a throttle setting.
Mar 29, 2016, 02:30 PM
I kill throttle servos
3d-Chris's Avatar
He said his DLE 20 wont hand start. The dle 20 hand starts fine, I think your setup or tuning is wrong.

But as I said, squirt some fuel in the carb and you will be fine. Everyone is complicating it.
Mar 29, 2016, 02:33 PM
Registered User
los36's Avatar
Quote:
Originally Posted by 3dFlyingMaster
Never EVER turn the prop over with the plug out! You could do some serious damage.
Still curious about this one. Explain.
Mar 29, 2016, 03:10 PM
KV4PL, FAA 107 Certified
FloridaFlyBob's Avatar
Quote:
Originally Posted by 3dFlyingMaster
He said his DLE 20 wont hand start. The dle 20 hand starts fine, I think your setup or tuning is wrong.

But as I said, squirt some fuel in the carb and you will be fine. Everyone is complicating it.
That's the easiest and the first thing I'll try is to squirt some gas in the carb before I take it apart


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