Blackhawk Paramotor blows a piston

[helimed01]

Hi Tyrhone.

Sounds to me like your instructor set your carb too lean from outset when you had trouble starting the engine which is why he blamed the sand.

The instructions are a bit vague and refer to rev settings instead of mixture settings. Just to be clear. You have two mixture settings on a Walbro carb, high and low. Screwing in / clockwise makes the mixture leaner. Too lean and the engine will fail.

The high setting provides the fuel at high revs the low at idle and lower settings. You need to recognise which screw is which. There may be a third screw on your carb that adjusts the tickover revs. This one is obvious as it mechanically adjusts the stop point of the throttle cable lever. Often the high screw is a T shape screw but not always. There may be a H and an L on the carb body indicating which is which.

To set the carb correctly start with them both open a bit further from the advised settings (anti clockwise). Have your engine secured to a post or something / someone that can hold it at full revs so you can use both hands. Make sure the area around you is clear and no loose bits anywhere.

Start with the low rev screw and try and achieve a smooth transition from tick over to full revs when accelerating very quickly. If it is lumpy and difficult to quickly rev from low to fast very slightly close the low screw and try again. If it cuts out, open the screw slightly. Do this until the transition from idle to full revs when grabbing a hand full of throttle is smooth.

Then for the high screw setting get to full revs (having a rev counter attached is useful for this) and slightly close the screw (clockwise) until you find the max rev point then open 1/4 to 1/5 turn open (anticlockwise) from the max rev point and leave at that. Try not to keep the engine at full revs for more than a few seconds as its new. When at full revs and closing the screw you will hear the revs climb then suddenly drop, this is the "too lean" point and will damage your engine very quickly so be quick in doing this. If unsure open the screw and start again. Just remember open is ok close can be damaging.

When you have done the high screw check and adjust the low again. Both high and low work together in transition from idle to full revs and any large adjustment on one may alter the other. Always start with low then high. Then check again.

Starting problems are often technique with initial priming. If fails to fire after a few pulls, take the spark plug out, dry it and put back and try again.

Head bolts need to be checked after the first few hours. You will need to find the torque settings and get a torque wrench and probably deep socket. When they settle put a spot of bright nail varnish on the nut so you can check if they have moved at a glance. I had one paramotor that the head nuts worked loose each flight for the first 20 hours!!!

As for fuel mixtures. If using a good quality synthetic 2 stroke oil these engines can take a range of mixes. I tend to use 2.5% on new ( running in) or high revving engines like the small H&E R120. And 2% on Simonini and the like.

3% is 30ml of oil per litre fuel 33 to 1 mix

2.5% is 25ml of oil per litre fuel 40 to 1 mix

2% is 20ml of oil per litre fuel 50 to 1 mix

Have different coloured fuel cans for mixed and un mixed fuel and never never lose discipline on using them correctly.

Review:

Get starting procedure sorted.

Keep carb setup correct. check every 20 hours or so.

Choose fuel mix, quality oil. Maintain mixture discipline.

All the nuts bolts exhaust brackets and the exhaust itself will spend their lives trying to work loose or break and throw themselves through your prop and it's your job to stop them from doing so.

Hope this helps.

Whitters.

Thanks Simon and ptwizz, very helpful.

Well I am going to make sure that when the engine is repaired I will use maximum 2% Motul oil, and I will set the carburettor to 1.5 turns instead of 3 (as it sounds like the mixture was too lean), and the rev screw to whatever is required, I guess about 1 turn.

I have this from the engine manufacturer (it is an HE engine):

You can set the carburetion at the desired revs. By the long black downward screw C. By turning it anticlockwise you rich the mixture, while the opposite you lean it. The basic setting is between 1,5 and 1,7 turns from the shut position. The C screw must be turned very gently, always verifying the cleanness of the "passage" (the point where the nozzle of the idle enters the nozzle of the full, at about half revs.) in revving up. If the engine pops, you tighten it; if it abates you loosen it.

The D screw sets the revs at idle, by opening the butterfly valve (for additional information please contact your local distributor). If the idle is high, turn the screw in an anti clockwise direction. If the idle is low, turn the screw in a clockwise direction.

ptwizz, how would I go about changing an over or retarded ignition? I have seen many a post about it around Google so won't complain too much as I know the reasons, but it does still amaze me how unreliable these things seem to be. In the future maybe I will try and go for a 4 stroke, the only viable option of which seems to be the bailey.

But for now I just have to learn how to read these engines better. Any where you guys could point me for basic 2 stroke or even paramotor maintenance courses would be great.

As for a motorbike shop mechanic, well my trainer is a mechanic and has been flying and working on paramotors for a decade, of course more opinions is always better in my mind, but I am in Guatemala and wouldn't know where to even begin looking for a second opinion. So if it is OK, you guys are kinda taking that place

[Tyrhone]

Wow dude that helps a lot, thanks man. My parts have arrived in Guatemala and hopefully the instructor should get them tomorrow and we can repair the engine. I am a little nervous about it blowing again after he works on it, but my choices are basically limited to him and me, so going in armed with your advice means I can at least keep things in the "safe" zone so it doesn't blow again.

The hard start and too lean setting, plus probably loose headbolts seem to be the culprit here. I can sort all 3 to some degree, I just gotta try and find a torque wrench in guatemala.

Thanks for the advice, hopefully I'll be in the air again in the next couple days, and staying there for more than 20 minutes!

Hi Tyrhone.

Sounds to me like your instructor set your carb too lean from outset when you had trouble starting the engine which is why he blamed the sand.

The instructions are a bit vague and refer to rev settings instead of mixture settings. Just to be clear. You have two mixture settings on a Walbro carb, high and low. Screwing in / clockwise makes the mixture leaner. Too lean and the engine will fail.

The high setting provides the fuel at high revs the low at idle and lower settings. You need to recognise which screw is which. There may be a third screw on your carb that adjusts the tickover revs. This one is obvious as it mechanically adjusts the stop point of the throttle cable lever. Often the high screw is a T shape screw but not always. There may be a H and an L on the carb body indicating which is which.

To set the carb correctly start with them both open a bit further from the advised settings (anti clockwise). Have your engine secured to a post or something / someone that can hold it at full revs so you can use both hands. Make sure the area around you is clear and no loose bits anywhere.

Start with the low rev screw and try and achieve a smooth transition from tick over to full revs when accelerating very quickly. If it is lumpy and difficult to quickly rev from low to fast very slightly close the low screw and try again. If it cuts out, open the screw slightly. Do this until the transition from idle to full revs when grabbing a hand full of throttle is smooth.

Then for the high screw setting get to full revs (having a rev counter attached is useful for this) and slightly close the screw (clockwise) until you find the max rev point then open 1/4 to 1/5 turn open (anticlockwise) from the max rev point and leave at that. Try not to keep the engine at full revs for more than a few seconds as its new. When at full revs and closing the screw you will hear the revs climb then suddenly drop, this is the "too lean" point and will damage your engine very quickly so be quick in doing this. If unsure open the screw and start again. Just remember open is ok close can be damaging.

When you have done the high screw check and adjust the low again. Both high and low work together in transition from idle to full revs and any large adjustment on one may alter the other. Always start with low then high. Then check again.

Starting problems are often technique with initial priming. If fails to fire after a few pulls, take the spark plug out, dry it and put back and try again.

Head bolts need to be checked after the first few hours. You will need to find the torque settings and get a torque wrench and probably deep socket. When they settle put a spot of bright nail varnish on the nut so you can check if they have moved at a glance. I had one paramotor that the head nuts worked loose each flight for the first 20 hours!!!

As for fuel mixtures. If using a good quality synthetic 2 stroke oil these engines can take a range of mixes. I tend to use 2.5% on new ( running in) or high revving engines like the small H&E R120. And 2% on Simonini and the like.

3% is 30ml of oil per litre fuel 33 to 1 mix

2.5% is 25ml of oil per litre fuel 40 to 1 mix

2% is 20ml of oil per litre fuel 50 to 1 mix

Have different coloured fuel cans for mixed and un mixed fuel and never never lose discipline on using them correctly.

Review:

Get starting procedure sorted.

Keep carb setup correct. check every 20 hours or so.

Choose fuel mix, quality oil. Maintain mixture discipline.

All the nuts bolts exhaust brackets and the exhaust itself will spend their lives trying to work loose or break and throw themselves through your prop and it's your job to stop them from doing so.

Hope this helps.

Whitters.

Thanks Simon and ptwizz, very helpful.

Well I am going to make sure that when the engine is repaired I will use maximum 2% Motul oil, and I will set the carburettor to 1.5 turns instead of 3 (as it sounds like the mixture was too lean), and the rev screw to whatever is required, I guess about 1 turn.

I have this from the engine manufacturer (it is an HE engine):

You can set the carburetion at the desired revs. By the long black downward screw C. By turning it anticlockwise you rich the mixture, while the opposite you lean it. The basic setting is between 1,5 and 1,7 turns from the shut position. The C screw must be turned very gently, always verifying the cleanness of the "passage" (the point where the nozzle of the idle enters the nozzle of the full, at about half revs.) in revving up. If the engine pops, you tighten it; if it abates you loosen it.

The D screw sets the revs at idle, by opening the butterfly valve (for additional information please contact your local distributor). If the idle is high, turn the screw in an anti clockwise direction. If the idle is low, turn the screw in a clockwise direction.

ptwizz, how would I go about changing an over or retarded ignition? I have seen many a post about it around Google so won't complain too much as I know the reasons, but it does still amaze me how unreliable these things seem to be. In the future maybe I will try and go for a 4 stroke, the only viable option of which seems to be the bailey.

But for now I just have to learn how to read these engines better. Any where you guys could point me for basic 2 stroke or even paramotor maintenance courses would be great.

As for a motorbike shop mechanic, well my trainer is a mechanic and has been flying and working on paramotors for a decade, of course more opinions is always better in my mind, but I am in Guatemala and wouldn't know where to even begin looking for a second opinion. So if it is OK, you guys are kinda taking that place

[notch]

Just a tip - put locktite on your head bolts to make sure they don't come loose. They screw down onto a soft aluminium head, as well as a soft base gasket, so will come loose after a few hours.

So, make sure you re- torque them after ~3 hours running. However, don't over tighten them as this will cause the base gasket to break apart (been there done that).

Then, as part of your post flight checks, check for oil around the base gasket - if there is any, it probably means you need a new gasket, or the head bolts need re-torquing.

I also use gasket sealant on my bask gasket to improve its sealing ability, after finding air leaks there with just the standard gasket.

[Tyrhone]

Thanks Notch,

The new piston has arrived and hopefully I can put it together tomorrow. I will try and keep all these bits in mind and make sure I have more control over what he does this time.

So 1.5 turns more or less, locktite and make sure bolts are tight on head gasket, and take it easy at first.

Just a tip - put locktite on your head bolts to make sure they don't come loose. They screw down onto a soft aluminium head, as well as a soft base gasket, so will come loose after a few hours.

So, make sure you re- torque them after ~3 hours running. However, don't over tighten them as this will cause the base gasket to break apart (been there done that).

Then, as part of your post flight checks, check for oil around the base gasket - if there is any, it probably means you need a new gasket, or the head bolts need re-torquing.

I also use gasket sealant on my bask gasket to improve its sealing ability, after finding air leaks there with just the standard gasket.