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Help !! Compression issue


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Hi Guys

i reported some time back that I was having some issue with a friends HE 120 paramotor

I was having the same issue as Clive with there being way too much compression. I have reported the issue to HE paramotor in Spain and they have being great but I am in Australia there are in Spain so its all emails to and from.

So way too much compression to the stage it is near impossible to pull start.

Remove spark plug all good.

So far I have followed the step from the link in the second post in this link:

viewtopic.php?f=4&t=6214

I recevied a new gasket which was meant to resolve the compression issue (which it has not) and some new O ring for the cylinder head.

I have cleaned the Piston and the cylinder following the guide by Alex Varv

http://www.aerocorsair.com/id107.htm

I have now put it all back together and I still have the same issue, there is no decompression hole I have looked everywhere!!

I am at a loss now, I am now thinking its a carbie issue as it there is no fuel reaching the shiny piston head not a even a hint of fuel. Anyone out there have any ideas of where the possible issue is, Its driving me nuts plenty of head scratching. If I remove the carbie will there be a whole world of pain trying to get it back in good running order.

Any ideas would be greatly appreciated.

Dara

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Based on what you have said I would be surprised if it was a carb issue.

I cannot think how a carb problem would increase the compression, unless it is filling the chamber with fuel.

My gut feel is it is more likely to be blocked exhaust. But it does sound like a bit of a strange one.

Is it possible to remove the silencer etc easily?

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LOL

That just reminded me of my days giving the 2 stroke screamers a de coke....

Exhaust off, balanced so that the PETROL that you poor in cant get out, and set fire to it. :-)

Let it all bur off and then tap it with a hammer,,, out comes the coke.

I AM NOT SUGGESTING THAT YOU DO THIS TO YOUR PARAMOTOR EXHAUSTS !!! OR EVEN BIKE ONES FOR THAT MATTER.

I am sure there must be some dodgy chemical you can poor in in this day and age...

SW :D

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Based on what you have said I would be surprised if it was a carb issue.

I cannot think how a carb problem would increase the compression, unless it is filling the chamber with fuel.

My gut feel is it is more likely to be blocked exhaust. But it does sound like a bit of a strange one.

Is it possible to remove the silencer etc easily?

Hey Guys

We have already removed the silencer, I did that when I removed the cylinder head.

Its not an oversized spark plug as it the same one we being using for the last couple of months.

There is a blockage somewhere no fuel is making it too the piston.

Back to the whatever I can find on the net!!

Many thanks all.

Dara

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I have now put it all back together and I still have the same issue, there is no decompression hole I have looked everywhere!!

This has got to be the crux of your issue. Either H&E forgot to put it in, or it is so well blocked, it's hard to see.

The PA125 (similar to H&E) has a 2mm diameter hole in the cylinder that leads from the exhaust to the head.

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I have now put it all back together and I still have the same issue, there is no decompression hole I have looked everywhere!!

This has got to be the crux of your issue. Either H&E forgot to put it in, or it is so well blocked, it's hard to see.

The PA125 (similar to H&E) has a 2mm diameter hole in the cylinder that leads from the exhaust to the head.

I really dont think this is the issue as I have looked over the cylinder with great detail and no decompresson hole to be found. I was ask HE paramotors the question if there is a decompression hole. I will take a picture tonight and put it on this post.

Darragh

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Where are you based Darragh, then someone else may be able to have a looksee for you.

Sometimes, another set of eyes can find something you might have missed, or give some other ideas?

Relocated to the land down under!! Australia to be exact.

If I was back in the UK I be giving Paul D or Pete a call!!

No luck finding a go kart mechanic who will work on it as there will not be held responsible if I crash on first flight etc.. Rubbish I know but that what I have got so far.

I have taken off the carb and giving it a good clean with carbie cleaner. Its doing my head in and I am only doing this as a favour for a mate!! I doing the round with some friends to see if any knows a good go cart mechanic..

Also don't think its any to do with timing.. If it was how is that adjusted..

Time for some research

http://en.wikipedia.org/wiki/Two-stroke_engine

Many Thanks Guys

D

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I have now put it all back together and I still have the same issue, there is no decompression hole I have looked everywhere!!

This has got to be the crux of your issue. Either H&E forgot to put it in, or it is so well blocked, it's hard to see.

The PA125 (similar to H&E) has a 2mm diameter hole in the cylinder that leads from the exhaust to the head.

I am inclined to agree about the decompression hole (my H&E definitely had one).

Does it turn over any easier with the spark plug fitted but no plug lead on the top?

Does it turn over much easier without the exhaust fitted?

No fuel in the combustion chamber is likely a carb problem, but it is not going to be the cause of the high compression problem

Stuart.

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Hey Stuart

I have been dealing with Pierre from HE paramotors who has being very with his technical support.

I am not to worried about the fuel issue as I think its all related. I hope to god they haven forgot to drill a hole for decompression hole :shock:

Now that would be crazy. The paramotor has being running fine for the last 15 hours its still a newish engine (15 hours)

To confirm the paramotor in question is the R120

http://www.he-paramotores.com/index.php ... s&mod=r120

Does it turn over any easier with the spark plug fitted but no plug lead on the top? Yes turns no problems!!!

Does it turn over much easier without the exhaust fitted? its being stripped so the the exhaust is off at the moment I will have a good with plug in have the exhaust off.

The cylinder body is made by polini i think (sure I saw there stamp on it) cant imagine it would have being forgotten about.

Mate i could ask a massive favor, if you have the same motor would please take a picture of where the decompression hole is position on your paramotor.

Many thanks.

D

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I am slightly lost:

In the original post it was the case that you could not pull start it because the compression was too high. But it would turn over ok with the plug removed.

In the last post I am unclear.

I thought that what had been asked was to test 2 things.

i.e.

1. With the exhaust on and everything connected normally - disconned the spark plug lead. Does it turn over normally now?

2. With the spark plug in and the exhaust disconnected does it turn over now.

As for the fuel getting in, if it is a pump type carb, it is quite possible that if it is not turning over properly that the pulse is not being sent from the crank case to the carb.

Can I just check that you have tested the above, as I was a little unsure with your reply.

Might just be me though :)

On rereading the thread, the original problem was the compression. (Is that now ok) and the problem you are having is getting it to start. Or is it still the case that the compression is very high.

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Hey Stuart

Does it turn over any easier with the spark plug fitted but no plug lead on the top?

Yes turns no problems!!!

Does it turn over much easier without the exhaust fitted? its being stripped so the the exhaust is off at the moment I will have a good with plug in have the exhaust off.

Mate i could ask a massive favor, if you have the same motor would please take a picture of where the decompression hole is position on your paramotor.

Many thanks.

D

OK, so just to confirm; The compression is fine and the motor turns over nicely when the plug is properly screwed in but there is no plug lead on the top and when you put the plug lead on the compression is so high you can no longer pull against the compression?

If that is the case, it is most definitely a (spark) timing issue and the flywheel has rotated slightly on the crankshaft. Actually a reasonably(?) easy issue to resolve, but you will need a timing diagram (I used to have one on pdf somewhere) and ideally a dwell gauge to measure where Top Dead Centre is (when the piston reaches the top of its journey up the barrel) which isn't very expensive, (it's possible to do the job without one if you are lucky). You are also supposed to use a puller to get the flywheel off, but i used a couple of large screwdrivers and some heat.

If the above is correct, there's really no need to check the compression without the exhaust.

Unfortunately i no longer have the motor so I can't take a pic of the decompression hole. From memory it's a 3mm hole drilled in the bore at 45deg about 20mm above the centre of the exhaust port, with the corresponding exit hole about 20mm away from the piston the inside the top of the exhaust port. You should easily be able to see one or other of the holes. If i'ts not there, I would wonder why? but then again if you have had no problem up until now, perhaps you really don't need it?

Stuart.

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Thats what I said ????Check the timing... :?

the reason I say this is because I had a ros engine that used to do this exact thing It snatches back and nearly takes your hand off when you tried to start it

the flywheel moved around the crankshaft because there is no woodruffffffff key to stop this happening only the crankshaft nut tightness and friction stops it from moving....

once adjusted there was no problem starting it mine also did not have a decompression button/hole.....but once the timing was sorted it didnt need one...

ps ( I bet you a marsbar ) timing is your problem :shock:

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Hey Stuart

Does it turn over any easier with the spark plug fitted but no plug lead on the top? Yes turns no problems!!!

D

So sorry guys got this wrong (the shame), I replied to this late last night hence my error.

To confirm super hard compression near to the point it impossible to pull start with spark plug in and exhaust off (Same with exhaust on)

When I remove spark plug its easy to pull start again. I dont think its a timing issue but I could be wrong.

To date I have removed cylinder head cleaned piston and the cylinder, new gasket which was meant to help with compression from HE paramotors and has not helped at all, new o ring. I have also taken the carburetor off and cleaned it.

I know it got to something simple as you guys said I need another set of eyes to assist, I will put the feeders out to the Australian Paramotoring community today and see if I can find any one who can assist .

I am sure I am not the only one to have even have this issue on there machine. Its driving me crazy as I can see no fault anywhere..

Once again SORRY for the above statement. :oops:

Dara

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Hey Stuart

Does it turn over any easier with the spark plug fitted but no plug lead on the top? Yes turns no problems!!!

D

So sorry guys got this wrong (the shame), I replied to this late last night hence my error.

To confirm super hard compression near to the point it impossible to pull start with spark plug in and exhaust off (Same with exhaust on)

When I remove spark plug its easy to pull start again. I dont think its a timing issue but I could be wrong.

To date I have removed cylinder head cleaned piston and the cylinder, new gasket which was meant to help with compression from HE paramotors and has not helped at all, new o ring. I have also taken the carburetor off and cleaned it.

I know it got to something simple as you guys said I need another set of eyes to assist, I will put the feeders out to the Australian Paramotoring community today and see if I can find any one who can assist .

I am sure I am not the only one to have even have this issue on there machine. Its driving me crazy as I can see no fault anywhere..

Once again SORRY for the above statement. :oops:

Dara

Based on this comment "To confirm super hard compression near to the point it impossible to pull start with spark plug in and exhaust off (Same with exhaust on) " we can rule out any thing to do with the exhaust in any capacity.

Based on this comment "When I remove spark plug its easy to pull start again" We can tell that there is no physical issue. i.e that the piston is too tight for the bore etc. (With the exception of the piston hitting the plug)

So to check if the problem is with the ignition timing. You need to do one of the tests mentioned earlier.

1. Check that with the spark plug in but with the HT Lead disconnected does it turn over normally? If the answer to this is yes it turns over normally and you then connect the HT lead and the compression increases then the problem is the ignition timing.

If this is the case I will explain what is happening. IMHO

Without the HT lead connected and you turn it over you will be getting the compression of the piston and the fuel in the chamber but with no spark so all the fuel mixture is sent down the exhaust.

With the HT lead connected (Assuming that the timing is too advanced ) As you begin the compression stroke you will draw in fuel and air wich will continue to compress as it approaches Top Dead Centre but the spark will be fired too early (i.e. Before it is at the top) and will effectivly be trying to push the piston back down the cylinder (hence the feeling of increased compression). The compression has not changed, just that it is firing too early.

The timing only needs to be slightly out for it to make a big difference.

I hope this helps and is clear enough to understand.

Edited by Guest
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Hey Stuart

Does it turn over any easier with the spark plug fitted but no plug lead on the top? Yes turns no problems!!!

D

So sorry guys got this wrong (the shame), I replied to this late last night hence my error.

To confirm super hard compression near to the point it impossible to pull start with spark plug in and exhaust off (Same with exhaust on)

When I remove spark plug its easy to pull start again. I dont think its a timing issue but I could be wrong.

To date I have removed cylinder head cleaned piston and the cylinder, new gasket which was meant to help with compression from HE paramotors and has not helped at all, new o ring. I have also taken the carburetor off and cleaned it.

I know it got to something simple as you guys said I need another set of eyes to assist, I will put the feeders out to the Australian Paramotoring community today and see if I can find any one who can assist .

I am sure I am not the only one to have even have this issue on there machine. Its driving me crazy as I can see no fault anywhere..

Once again SORRY for the above statement. :oops:

Dara

Based on this comment "To confirm super hard compression near to the point it impossible to pull start with spark plug in and exhaust off (Same with exhaust on) " we can rule out any thing to do with the exhaust in any capacity.

Based on this comment "When I remove spark plug its easy to pull start again" We can tell that there is no physical issue. i.e that the piston is too tight for the bore etc. (With the exception of the piston hitting the plug)

So to check if the problem is with the ignition timing. You need to do one of the tests mentioned earlier.

1. Check that with the spark plug in but with the HT Lead disconnected does it turn over normally? If the answer to this is yes it turns over normally and you then connect the HT lead and the compression increases then the problem is the ignition timing.

If this is the case I will explain what is happening. IMHO

Without the HT lead connected and you turn it over you will be getting the compression of the piston and the fuel in the chamber but with no spark so all the fuel mixture is sent down the exhaust.

With the HT lead connected (Assuming that the timing is too retarded) As you begin the compression stroke you will draw in fuel and air wich will continue to compress as as it approaches Top Dead Centre but the spark will be fired too early (i.e. Before it is aat the top) and will effectivly be trying to push the piston back down the cylinder (hence the feeling of increased compression). The compression has not changed, just the it is firing too early.

Theis only needs to be slightly out for it to make a big difference.

I hope this helps and is clear enough to understand.

Should read timing to far ADVANCED not retarded (firing to early)

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Based on this comment "To confirm super hard compression near to the point it impossible to pull start with spark plug in and exhaust off (Same with exhaust on) " we can rule out any thing to do with the exhaust in any capacity.

Based on this comment "When I remove spark plug its easy to pull start again" We can tell that there is no physical issue. i.e that the piston is too tight for the bore etc. (With the exception of the piston hitting the plug)

So to check if the problem is with the ignition timing. You need to do one of the tests mentioned earlier.

1. Check that with the spark plug in but with the HT Lead disconnected does it turn over normally? If the answer to this is yes it turns over normally and you then connect the HT lead and the compression increases then the problem is the ignition timing.

If this is the case I will explain what is happening. IMHO

Without the HT lead connected and you turn it over you will be getting the compression of the piston and the fuel in the chamber but with no spark so all the fuel mixture is sent down the exhaust.

With the HT lead connected (Assuming that the timing is too advanced ) As you begin the compression stroke you will draw in fuel and air wich will continue to compress as it approaches Top Dead Centre but the spark will be fired too early (i.e. Before it is at the top) and will effectivly be trying to push the piston back down the cylinder (hence the feeling of increased compression). The compression has not changed, just that it is firing too early.

The timing only needs to be slightly out for it to make a big difference.

I hope this helps and is clear enough to understand.

Good, clear well thought out post :acro:

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I have been thinking about this a little more.

If the timing is out and it is to advanced, then you will be losing all the power from the power stroke and there may be insufficient pumping action in the crank to cause the pulse to the Carb. This MIGHT explain the lack of fuel from the carb as well.

This is just a theory though. I have never seen it happen. And I am not sure how far out it would have to be to get no fuel at all.

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I have been thinking about this a little more.

If the timing is out and it is to advanced, then you will be losing all the power from the power stroke and there may be insufficient pumping action in the crank to cause the pulse to the Carb. This MIGHT explain the lack of fuel from the carb as well.

This is just a theory though. I have never seen it happen. And I am not sure how far out it would have to be to get no fuel at all.

If it is primed right you will have fuel at the carb, the pumping action does not really work until started.

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Hi Guys

Many thanks for the details response, I am learning something new about the mechanics of two stroke which will come in handy for diagnosing any future issues.

Right to Answer you question:

1. Check that with the spark plug in but with the HT Lead disconnected does it turn over normally?

A: I have tested the unit and I can confirm that it doesn't matter if I have the HT lead on or off the spark plug, as long as the plug is in it becomes near impossible to pull!! If I take the plug out it easy to pull again.

I have now noticed that the pull start mechanism is now looking a little worse for ware from all the excessive pull due to the hard compression.

I understand its going to be very hard to diagnose without actually seeing the motor, I am going to take a short clip tomorrow and post it on this post. I have spoken to a local pilot who has said he will assist, it will be good to get the extra set of eyes.

Also one last question with regards the rings on the piston, what position should they be on the piston. I placed them where there was a little nipple on the groove on the piston for both rings.

Once again thanks for your help.

Dara

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