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Decompression valve fitted, now doesn't start!


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Thanks Kiwi, for some reason the post isn't showing but I saw it on the email.

 

And thanks Tom, I recall reading something about removing the grub screw and clean the hole, doesn't make sense but I'll have a go.  Did it work for you? Though I know you fitted a decompression valve.  I'l, try the cleaning out the hole before trying to tap a 10 mill thread!

 

Ah, reading the article about cleaning I get it!  The hole is connected to the exhaust port. ie, when the engine is not running as in when starting, there is no pressure into the cylinder from the exhaust but there is a small loss of compression. Once the engine fires it the back pressure from the exhaust compensates for the hole and any loss of compression. (I think!) 

Edited by Bob Moore
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So do you think by closing the internal decompression port and using the decompression valve instead I could get a few more horsepower eh? Now that does sound worthwhile...

Seemed to work for mine, it starts easily now so long as I don't use the decompressor valve that I unnecessarily fitted!

 

It still won't reach full power though. I've ordered a new primer bulb as there are a lot of bubbles in the fuel line and that's the only part I haven't yet replaced. In the meantime I'm flying a Radne Raket motor that I have borrowed from a local pilot. Early morning flight tomorrow...

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1 hour ago, tomarnold said:

Seemed to work for mine, it starts easily now so long as I don't use the decompressor valve that I unnecessarily fitted!

 

It still won't reach full power though. I've ordered a new primer bulb as there are a lot of bubbles in the fuel line and that's the only part I haven't yet replaced. In the meantime I'm flying a Radne Raket motor that I have borrowed from a local pilot. Early morning flight tomorrow...

Good call on primer bulb as they go hard on the ends and allow air in, and could well be your bubble cause,and as for full power must be down to carb settings but be careful if it's that far out you could cause irreparable piston or engine damage.

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Annoyingly I'm pretty sure it isn't the carb settings as I have tried every setting (spent a very long time over it and turned each screw just 1/8 of a turn at a time) with no difference - it just gets to mid-throttle and then dies. Still, I'll see if the primer bulb makes a difference when it arrives...

 

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2 hours ago, tomarnold said:

Seemed to work for mine, it starts easily now so long as I don't use the decompressor valve that I unnecessarily fitted!

 

It still won't reach full power though. I've ordered a new primer bulb as there are a lot of bubbles in the fuel line and that's the only part I haven't yet replaced. In the meantime I'm flying a Radne Raket motor that I have borrowed from a local pilot. Early morning flight tomorrow...

Interesting.  I'm going to remove the head again from the second motor and check out the small port. You also answered my next question which was going to be why did you fit a decompressor! The one I ordered was less than a fiver so if clearing hole does work in reducing compression to a manageable level I won't have lost a lot!

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Oh well, removed the head on motor two, removed grub screw but the passage was clear right down to the exhaust port.

Did discovered that the carb that was on it is the WB 37 which is thought to be better than the WB32 so refitted that. I had put on the new WB 32 that I bought.

All I'm waiting for is some fuel pipe and a priming bulb then I can see if this is a runner though it still is hard to hand start pull.  Might need that decompressor?.  

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 it just gets to mid-throttle and then dies.

Sounds like fuel starvation? But I guess someone has said that. Is the crankcase driven pump working hard enough.  New membrane in it? Dirt in the small built in filter in the pump side of the carb? I'd have thought that air locks in the line would stop it all the time and not just mid throttle?

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