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50 CC Gas... only runs fully choked

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Old 01-25-2018, 04:12 PM
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Richard39
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Default 50 CC Gas... only runs fully choked

I have a 50 CC Gas engine (not sure of make) that is no longer made and was sold to me by a USA hobby shop... I believe it was made in China and I have owned it for 5 years... I had problems when it was new and could not get it to run as I remember it... Last week I was cleaning up my shop and saw this engine in a box so I checked it out and it seemed fine... I took it to my flying field and got to it start running but it only runs if the choke is on full or almost full choke... I primed the carburetor and put gas down in the spark plug opening ...After a few attempts with a electric starter it started running... After 3 more primes it ran and kept running but only on full choke and a half throttle setting... What would be wrong with this engine and what should I do to get it running normal...? I am thinking air leak but have not taken the carburetor apart yet.... Thanks, Richard
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Old 01-25-2018, 05:01 PM
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The diaphragms in the carburetor have dried up from sitting. and possibly the float is sticking and there may be dirt in the screen ...all inside the carb .
I would get a rebuild kit for the carb , take it apart, clean it and replace all of the old parts inside.
Or, buy a brand new carb.
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Old 01-25-2018, 06:13 PM
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Thanks for the reply and good information.... that makes sense to me and I will get a carburetor rebuild kit soon.... I have started taking the carb apart and cleaning everything with carb cleaner. the float is working properly so everything should come together soon.. Thanks...
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Old 01-26-2018, 04:56 PM
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Do you have other gas engine that you operate just fine?
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Old 01-26-2018, 06:44 PM
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Originally Posted by kmeyers View Post
Do you have other gas engine that you operate just fine?

Yes I do.... several brands and sizes but mostly DLE, 30 and 55 size..... Usually no problems other that screen cleaning....
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Old 01-27-2018, 08:56 AM
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Originally Posted by Richard39 View Post
Yes I do.... several brands and sizes but mostly DLE, 30 and 55 size..... Usually no problems other that screen cleaning....

Sometimes those engines from China have knock off carbs even stamped Walbro. These like the spark plugs that come with these engines can be hit and miss. You mention you have a 55 size motor that runs just fine. I would see if I could put the carb off this motor on the one with the problems and try it. If it solves the problem I would pitch the original carb and order a new one.

Dennis
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Old 01-27-2018, 11:24 AM
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Richard39
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Good suggestion on the swap.... I will check that out... if it fits (interchangeable)
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Old 01-31-2018, 02:36 PM
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Originally Posted by flyinwalenda View Post
The diaphragms in the carburetor have dried up from sitting. and possibly the float is sticking and there may be dirt in the screen ...all inside the carb .
I would get a rebuild kit for the carb , take it apart, clean it and replace all of the old parts inside.
Or, buy a brand new carb.
I swapped out a DLE 55 from a good running engine to this engine .... No improvement... same situation on the choke... must be choked to run...
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Old 01-31-2018, 04:08 PM
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Well, if it's a rear-carb engine then the reed valve could be worn out and/or the pulse-port could be blocked.
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Old 02-02-2018, 03:55 AM
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Originally Posted by flyinwalenda View Post
Well, if it's a rear-carb engine then the reed valve could be worn out and/or the pulse-port could be blocked.
The pulse port is working, checked with fuel line to ear, and can hear the pulse and feel it... so I looked at the reed valve and it looks fine... it fact it looks brand new but I do not know what to look for so I will see if I can find one that will fit this 50 CC Gas... I bought it from Hobby king.....5 years ago....
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Old 02-02-2018, 04:15 AM
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Originally Posted by Richard39 View Post
. I bought it from Hobby king.....
That explains it !
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Old 02-02-2018, 07:11 AM
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Originally Posted by flyinwalenda View Post
That explains it !

Well one good thing out of all of this is I am learning more about Carbs and working on them.... I appreciate all of the suggestions and I believe that one day, some how, this engine will run and run good enough to put in an old airplane and fly.... Thanks... Richard
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Old 02-02-2018, 11:26 AM
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Sounds like you must have a vacuum leak somewhere. Check carb mounting adapter for cracks, the carb gaskets, the crankcase, cylinder base, and the front seal. You might try getting it running, and shooting ether, (starting fluid), on those areas, or thick oil.

AV8TOR
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Old 02-02-2018, 01:37 PM
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I have a pressure/vacuum setup I made to test two strokes. It is basically just two plates. One bolts onto the exhaust port with a rubber gasket and has a threaded hole to which I installed a 0 to 10 lb. pressure gauge. The other mounts to the intake manifold in place of the carburetor and has a metal automotive valve stem installed in it. I use a small hand held pump for basketballs and such to pump the engine up to 5 psi. (No more than that.) If the engine won't hold pressure, I use soapy water to find the leak.

It is also good to check them under vacuum as well. For this I use a hand operated vacuum pump. I remove the valve core from the valve stem fitting and connect that to the vacuum pump with rubber hose. Pump it down and see if it holds. If it holds pressure but not vacuum, suspect the crankshaft seal.

The pressure gauge can be sourced at a hardware store; they are used to pressure test home gas systems. The bolt in style metal valve stem can be found at the auto store. The hand operated vacuum pump can be found quite cheap at Harbor Freight, the little hand pump for basketballs I found in the sporting goods section of Walmart, and I make the block off plates out of 1/4" x 1 1/2 or 2" aluminum strap material. Doesn't take long to make nor cost much, and when you test your engine with it, you KNOW your engine is air tight, as it should be. (Must be!)

AV8TOR

Last edited by av8tor1977; 02-02-2018 at 01:56 PM.
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Old 02-02-2018, 02:27 PM
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All the DLE and similar engines use (2) double sealed bearings on the crank. It is very unusual to have all 4 seals fail. I have torn into some engines (not DLE) where a seal had failed on the rear bearing but that is all. Some engine companies remove the farthest rear seal next to the crank web as they thought the bearing would be better lubed with oil from the fuel than the grease packed in the sealed bearing. But the point is, it is very unusual to have an air leak through the crank bearings in current engines. Most of the time, I see leaks from loose cylinder hold down bolts or a damaged / warped / cracked reed block or carb spacer.

I'm thinking the problem with the engine in this thread is just a bad carb or pulse port that is somehow restricted.
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Old 02-02-2018, 07:40 PM
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Richard send your engine to me . If I can't repair it I promise to send back all the broken parts .
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Old 02-02-2018, 08:13 PM
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Now that sounds like a good honest deal!
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Old 02-03-2018, 10:48 AM
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Originally Posted by Truckracer View Post
All the DLE and similar engines use (2) double sealed bearings on the crank. It is very unusual to have all 4 seals fail. I have torn into some engines (not DLE) where a seal had failed on the rear bearing but that is all. Some engine companies remove the farthest rear seal next to the crank web as they thought the bearing would be better lubed with oil from the fuel than the grease packed in the sealed bearing. But the point is, it is very unusual to have an air leak through the crank bearings in current engines. Most of the time, I see leaks from loose cylinder hold down bolts or a damaged / warped / cracked reed block or carb spacer.

I'm thinking the problem with the engine in this thread is just a bad carb or pulse port that is somehow restricted.
I totally agree that nowadays leaking crank seals are very rare, though it can happen, and if it does will cause you a tuning nightmare if you don't know to look for it. It had been a long time since I encountered one, but I did run across one in a Zenoah last year. Many people don't understand that unlike wet sump four stroke engines, total crankcase sealing of a two stroke engine is imperative. Many years ago, many people changed the crank seals on two stroke race motorcycles after every race, but modern seals and oils are now much better. Nowadays a crank related leak on a new Chinese engine would more likely be the result of a factory defect; seal damaged on assembly, poor machining of the seal bore, etc., especially on the non-RCGF, non-DLE alphabet engines.

The OP stated that he substituted a known good carb on the engine with no change in behavior, and that he verified the pulse operation. That's why I am thinking possible vacuum leak. Using my pressure tester will find any leak, including the most common;: which is the cylinder base gasket or carb spacer as you stated. I recommend trying the ether or thick oil test first, as it is easier and quicker on a mounted and running engine. You do have to be careful with the ether so that the engine doesn't suck the ether into the carb throat and give you a false positive for a leak.

AV8TOR





Last edited by av8tor1977; 02-03-2018 at 11:10 AM.
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Old 02-03-2018, 11:37 AM
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AV8TOR, yes, I agree completely with you. Was just adding some info to the thread.

Considering this engine has never run properly since new, this complicates the issue. Perhaps this engine has a design or manufacturing flaw that prevents it from running. Any number of problems could cause this and could be common among some of the early Chinese engines. Some were noted to never run as expected. My bet is that with engine in hand, an experienced engine person could analyze the problem in short order then decide whether the engine was worth keeping or just time to move on.
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Old 02-03-2018, 12:39 PM
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My offer still stands , Honestly
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Old 02-03-2018, 12:44 PM
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I agree with the thoughts on pressure testing it is truely the best way to find case defects and shaft seal leaks . I have also pressure tested with smoke to locate leaks which is also a great way to check leak locations . I had access to an automotive evaporative emissions leak tester befire retiring and it was an incredible time saver .
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Old 02-03-2018, 01:14 PM
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With the dam shipping costs so high now, it makes things difficult to offer service.

AV8TOR
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Old 02-03-2018, 03:44 PM
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20.00 to 30.00 bucks shipping each way sure does cut down on the non local business .
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Old 02-05-2018, 04:40 PM
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Thanks to all and your suggestions.... I have the engine running now... Took a few days off from worrying over the engine... Came back yesterday and cleaned the carb one more time... changed everything out that I could..... There seem to be a leak around the gasket...replaced gasket... Engine drew gas from the tank and ran ( but not well).... Adjusted the needles and engine became smoother and running on the high end well... Choke open during running... I had already returned the 55 DLE Carb to the engine it was on and ran that engine several days ago... seems fine to me....

Thanks again... with out your help and suggestions I would have given up.... It is times like this that I would love to have a good r/c gas engine tech available to me in Birmingham....... would have saved me a lot of grief but I have learned a lot and am more comfortable working on the r/c carbs.... Richard
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Old 02-05-2018, 04:58 PM
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Great !
Yeah, sometimes you have to walk away for a bit. I remember one time I had a Walbro that wouldn't pump. I tore it apart and rebuilt it and it still wouldn't pump. Stayed on it and couldn't figure out the issue. Left it alone for a few weeks , came back and figured it out.
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