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Black Hawk 175cc


Vauxscott
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Hi, I'm new to paramotoring and have recently purchased a second hand Black Hawk motor.

It's a cors air engine, looks to be an M21Y.

I'm having problems starting it, it spits and pulls the pull start clean through my fingers, which hurts a bit!

It does run pretty well once it's started though. I've had the decompression valve out and cleaned it, but it's still hard to pull and spits a fair bit.

Anyone had experience with these engines?

Scott.

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Well I nearly made the mistake of trying to start it without the prop for my own safety but read the bit in the manual telling me this can cause" serious damage" so just left it as is.

Spigot, I'm not sure what the stator plate is? I took the pull start apart and greased anything that moves and made sure bits that don't move didn't.

Managed to get it started and warmed up, after it was warm it starts easily but is still a hard pull.

I'm not a small lad and I'm sure the effort required to pull this isn't normal so I'm still on the hunt.

I've got a few grades of plug coming in the post, both ngk and denso types to try, see if that helps with the backfiring/pulling the pull chord through my fingers issue...

Also, I see Con Air can supply a kit to convert to electric start, anyone got experience with this?

Thanks,

Scott

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Hi Scott,

My stupid! The pull start version don't have a stator plate it only has the side mounted coil.

While changing the plug, look at the plug cap/ HT lead (make sure it's properly screwed on) apart from that not much to go wrong except a failing coil.

Con air sports list a pullstart to electric conversion for the 25Y at £361.83 but double check what motor you have as I'm only going off your picture :-)

Colin

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Hi Colin,thanks for your reply. I've checked the ignition components and changed the plug.

I think I've got it Sussed now though, When I initially started it I noticed a chirping noise but didn't think much of it as I'm pretty new to 2 strokes and presumed it was normal, turns out the belt was slightly too slack and this is looks the be the cause of my starting issues. Apparently a belt even slightly loose wil make a motor a nightmare to start!

In my defence it wasn't all that slack and I probably put less than 1/8 turn on it but it has made it much easier. I found the figure of 20lbs torque slip for the belt tension and that seems to be right.

I've ordered the starter conversion kit from con air so I'll see how that goes, should make things even easier.

Thanks for everyone's help!

Scott

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The difficult starting with loose belt combined with the warning about running without prop would suggest that the prop is the majority of the engine's flywheel.

When starting, energy is stored in the flywheel and helps to get the engine over compression, smoothing the force on the pull cord.

Running without adequate flywheel means the crankshaft will accelerate hard during the power stroke and slow a lot during compression. This can cause excessive vibration not only of the engine as a whole, but within the crank assembly where it can cause the crankpin to move, resulting in a twisted crank. That is a bad thing.

I mis-spent too much of my youth fixing other people's 2 stroke bike engines (mainly RD's).

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Yep, that's pretty much it. Although I was surprised by the force produced if the belt isn't fully tight, would be very easy to injure yourself!

Reading back through the instructions, they do say the belt tension is critical, don't start without a prop ect, I have to admit to that information not sinking in first time...must be a man versus instructions thing.

I have the electric starter kit on order from Con Air so I'll put a thread up here on how it's fitted, as it doesn't come with any instructions. Should be fun.

Scott.

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