Clunk!

[Former Member]

[This posting has been removed]

[flight1]

The carb might have a weak pump action, what size pipe are you using as for a 50cc 2t large bore(3mm) tubing and tank fittings shout be used if not allready. got a picture of you installation? for all to check out.

[Gary Manuel]

Posted by flight1 on 02/04/2018 13:16:07:

The carb might have a weak pump action, what size pipe are you using as for a 50cc 2t large bore(3mm) tubing and tank fittings shout be used if not allready. got a picture of you installation? for all to check out.

I'll post a picture or two later.

[Ron Gray]

If it ‘twas me, theses are things I would do, in order:

1. Remove cowl and fly. If it makes no difference then the diaphragm air pipe is unlikely to help.

2. Tweak the low running (leaner) followed by the high.

3. Strip carb. I had a running issue with a Zenoah, stripped the carb, found no problems, reassembled and the engine ran fine!

I would also try and mount the filter so that it was vertical with it’s inlet lower than the tank outlets as this would help any trapped air to escape back through the tank.

[Martin McIntosh]

This hobby can be great fun can`t it. When I suggested a proper petrol filter I meant a type to install in a model, not the large car type which it seems to me that you could be using but without pics I don`t know.

It has been suggested that this could be an ignition problem which may be very likely. This may be obvious, but is the plug cap rammed firmly home? With an inverted motor it could be pulling away just enough to kill the spark under negative G. Have you tried renewing the ignition unit which may have an internal loose connection?

[Former Member]

[This posting has been removed]

[Petrol Pete]

Hi Gary, this is exactly the same as my dle 20 I mentioned earlier in the thread, mine was cured on the ground by richening up the idle mixture so I would say it's rich but idles ok about 1/2 a tire. Give it a try it only takes a moment! Pete

[Gary Manuel]

Posted by Percy Verance on 02/04/2018 13:10:52:

Possible ignition fault?

This thought went through my mind. I considered it unlikely but I'm not ruling anything out at this stage.

Posted by Martin McIntosh on 02/04/2018 14:33:12:

It has been suggested that this could be an ignition problem which may be very likely. This may be obvious, but is the plug cap rammed firmly home? With an inverted motor it could be pulling away just enough to kill the spark under negative G. Have you tried renewing the ignition unit which may have an internal loose connection?

As it happens, I have a spare one of those I can try. The only issue with this one is that the plug cap is larger than the other one and will probably need a hope cutting in the cowl to get it to fit.

Plug cap has been checked and is on properly.

Posted by flight1 on 02/04/2018 13:16:07:

The carb might have a weak pump action, what size pipe are you using as for a 50cc 2t large bore(3mm) tubing and tank fittings shout be used if not allready. got a picture of you installation? for all to check out.

All fuel pipe is wide bore. The engine also runs OK at full chat whilst climbing vertical or 1/2 throttle prop-hanging, so the pump and piping appear to be OK. I don't think that this is the problem.

Here's a few photos of the installation.

The offset leg of the T goes to the fuel dot.

Posted by Martin McIntosh on 02/04/2018 14:33:12:

This hobby can be great fun can`t it. When I suggested a proper petrol filter I meant a type to install in a model, not the large car type which it seems to me that you could be using but without pics I don`t know.

Here's the in-line filter. It is the car type, but I think the size is OK for a 50cc model. Note that it's still full of fuel even though the fuel tank has been emptied, so that appears to be doing its job.

Clunk pipe to T to filter to carb.

Fill pipe plugged with a fuel dot to prevent air being introduced here.

Simple plumbing and everything is still in place.

Clunk line is flexible enough.

Posted by Ron Gray on 02/04/2018 14:02:41:

If it ‘twas me, theses are things I would do, in order:

1. Remove cowl and fly. If it makes no difference then the diaphragm air pipe is unlikely to help.

2. Tweak the low running (leaner) followed by the high.

3. Strip carb. I had a running issue with a Zenoah, stripped the carb, found no problems, reassembled and the engine ran fine!

I would also try and mount the filter so that it was vertical with it’s inlet lower than the tank outlets as this would help any trapped air to escape back through the tank.

Posted by Petrol Pete on 02/04/2018 15:21:44:

Hi Gary, this is exactly the same as my dle 20 I mentioned earlier in the thread, mine was cured on the ground by richening up the idle mixture so I would say it's rich but idles ok about 1/2 a tire. Give it a try it only takes a moment! Pete

All good suggestions. I considered trying without the cowl fitted, but was concerned about CoG. I've now weighed the cowl which is 333g - roughly the same as the spare ignition unit plus an old 2200mAh 3s battery.

Here's what tests I think I'll do.

1. Leave the cowl off and strap the spare ignition unit plus battery (to maintain the CoG) to the engine box and see how it behaves.

2. Tweak the mixture a bit (I've already done a bit of tweaking but the engine should be more run in now.

3. Try swapping the ignition unit (with cowl off).

4. Add a pressure nipple, vented to the inside of the fuselage.

5. Strip the carb if all else fails - It's only when inverted, so I don't think it's this. This requires engine removal, hence my reluctance.

 

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[cymaz]

Are you absolutely sure that the clunk is free to move and doesn’t get caught in a corner of the tank?

[Gary Manuel]

Posted by cymaz on 02/04/2018 16:15:57:

Are you absolutely sure that the clunk is free to move and doesn’t get caught in a corner of the tank?

Absolutely certain. I can see the clunk about 1/2 inch from the bottom of the tank.

Thanks for the suggestions fellas - I'm still open to further ones.

Edited By Gary Manuel on 02/04/2018 16:20:43

[cymaz]

Working from the clunk

• All the pipe work and fittings ok
• All the connections to the fuel filter ok
• From the fuel filter to the carb ok
• Has the carb been cleaned, stripped and checked
• Has the motor had a different cdi pack...to be done

Have you tried flying the plane without your car fuel filter? If, at any point fuel can slosh from the filter to the tank then you would have fuel starvation. Saying that do you have a filter like that in another plane ?

Thought about putting a small key fob camera in the fuselage to try and capture what might be happening in the fuel system

Edited By cymaz on 02/04/2018 16:27:25

[Denis Watkins]

Apologies with your certainty over the clunk length Gary

But that clunk tube is way too long

Keep this up though as this is the best reading on the site

[Gary Manuel]

Posted by Denis Watkins on 02/04/2018 16:34:56:

Apologies with your certainty over the clunk length Gary

But that clunk tube is way too long

Keep this up though as this is the best reading on the site

It's not as long as it looks in the photo Denis.

It does not reach the rear of the tank with the stopper fully in, even though it may look it in the photo.

[Ron Gray]

As Gary hs pointed out, flying inverted isn't an issue so I think that kinda rules out a clunk problem doesn't it? The problem is when neg G is introduced into the mix. Some DLE's have a similar problem which can be caused by incorrect engine timing, running too rich or oil fouling the plug. The first is cured by retiming the ignition, second by leaning the low end and the last by fitting a Bowman ring.

@Gary, have you checked the colour of the plug? and what make of plug is it?

Edited By Ron Gray on 02/04/2018 16:50:39

[Gary Manuel]

Posted by cymaz on 02/04/2018 16:25:46:

Working from the clunk

• All the pipe work and fittings ok
• All the connections to the fuel filter ok
• From the fuel filter to the carb ok
• Has the carb been cleaned, stripped and checked
• Has the motor had a different cdi pack...to be done

Have you tried flying the plane without your car fuel filter? If, at any point fuel can slosh from the filter to the tank then you would have fuel starvation. Saying that do you have a filter like that in another plane ?

Thought about putting a small key fob camera in the fuselage to try and capture what might be happening in the fuel system

Edited By cymaz on 02/04/2018 16:27:25

Cymaz - The filter was added in an attempt to address the initial problem described at the beginning of the thread. I've never used them before, but I'm pretty sure it is doing no harm - only doing good.

Key fob camera sounds like a good idea. I don't have one, but I might have to get one (or borrow one) if I can't cure the fault.

[Gary Manuel]

Plug looks OK Ron (Pale straw). It's an NGK CM6 - I never use the supplied ones.

It was a bit wet with un-burnt petrol though.

Edited By Gary Manuel on 02/04/2018 16:54:57

[Ron Gray]

Another thing you have that is different from my gassers, I run the vent pipe to a loop above the tank/fuel, you have yours alongside it, not sure if this could be a problem (vent line full of fuel?) Where does the vent exit the fuselage?

[Ron Gray]

Plug sounds fine.

[cymaz]

Posted by Gary Manuel on 02/04/2018 16:53:38:

Plug looks OK Ron (Pale straw). It's an NGK CM6 - I never use the supplied ones.

It was a bit wet with un-burnt petrol though.

Edited By Gary Manuel on 02/04/2018 16:54:57

Correct gap?

[cymaz]

Posted by Gary Manuel on 02/04/2018 16:46:59

Key fob camera sounds like a good idea. I don't have one, but I might have to get one (or borrow one) if I can't cure the fault.

Borrow mine. Cable, camera, card and instructions. Not used it in ages so no idea the status of the battery.

Edited By cymaz on 02/04/2018 17:12:05

[Gary Manuel]

Posted by Ron Gray on 02/04/2018 17:03:26:

Another thing you have that is different from my gassers, I run the vent pipe to a loop above the tank/fuel, you have yours alongside it, not sure if this could be a problem (vent line full of fuel?) Where does the vent exit the fuselage?

The vent exits the bottom of the fuselage just in front of the undercarriage (about 4 inches in front of the tank).

I'm willing to consider anything, so I'll move the loop to the top of the tank rather than the side. It might help it to drain better if nothing else.

[Gary Manuel]

I couldn't find the specs for setting the plug gap for the AGM55 when I installed the plug, so I set it to 0.018" as specified for the very similar DLE55. I've just checked it and it's still 0.018".

[Ron Gray]

On little trick you could also try if all of the above fail, if you have room for it, bring the vent into the fuse and attach a small (inflated) balloon to the vent with a cable tie just before flying. This will pressurise the tank and will rule out, or otherwise, fuel feed problems. Make sure that the balloon won't get punctured whilst in the fus and it's only a temporary thing!!!!!!!

[Martin McIntosh]

My money is still on the cdi or maybe even the battery pack or switch supplying it. I would think that replacing everything in that area would be a good idea. I am sure that we are all awaiting the solution. I would say that I have had more problems with petrols than glows over the years no matter how reliable they are supposed to be.

[Paul C.]

Hi Gary, no expert on these engines but noted that you said the condition of the plug was 'a bit wet with unburnt petrol' . would this suggest that you have fuel being delivered but for some reason you are not getting the spark to ignite it.

enjoying following this thread I am sure you will get it sorted soon

Paul.