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  #1  
Old 09/04/2017, 07:17 PM
Mpb1p Mpb1p is offline
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Default Greeves hawkstone HELP

I have a hawkstone with a 250cc iron barrel, havn't ridden for a while but hope to get out this season, my problem is that ever since I replaced the piston the compression has been so that it is almost impossible to kickstart, I changed the cylinder head as an experiment and fitted a trials head with the facility for a decompression valve although this is plugged of , sure enough it made it much easier to kick over and it started 2nd kick, what I found then that it would 4 stroke when getting up in the higher rev range, it is fitted with an Amal 30mm concentric and I have always ran it on castrol R the main jet is 300'and the needle is on the richest setting, the reason for trying it on the rich side is I siezed the piston at ameys copse when I last raced it hence the new piston.
Can anyone give me any tips on any of these issues ?
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Old 09/04/2017, 10:29 PM
Brian Catt Brian Catt is offline
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The listing in the Carrick and Walker book shows a bigger main jet for the 1 3/8 389 carb on both the SAS and SCS bikes. Would the jets in the concentric need to be smaller? I note the 250 Griffon with a 930 carb uses a 280 main.
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  #3  
Old 10/04/2017, 05:43 PM
Kim275 Kim275 is offline
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Main Jet sizes for the concentrics completely different to the monobloc ... 300 is large cow a hawkstone but I run 320 .
I think first thing I would check is the squish clearance on the head ...... Can't believe any 250 head would have too much compressing unless the gap was too close?? .. If you have no less than 0.8 mm then on to ignition Timing ensure it is advance so it back cired before firing up 3 to 4 mm Btdc .... Then onto your jetting .... Keep your 300 and do a flat out plug chop ... Then I would go for pilot jet ( don't be afraid to go bigger if needed...// and then a plug chop on needle jet which should be a 106 again go with what the plug tells u
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  #4  
Old 13/04/2017, 01:33 PM
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ADickerson ADickerson is offline
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Hi Mpb1p, sorry to learn of problems with your Hawkstone. In case it's any help fourstroking just means it's running rich and it's a good place to start from as it's obviously getting ample lubrication. Just weaken(lower) the needle one position at a time until it doesn't. Might be worth checking the mixture screw is out one and a half turns from the closed position.
I concur with what Kim suggests although I'd be reluctant to go for a larger pilot jet.
It's difficult to advise specifically on jet sizes as varying exhaust systems have an impact here as well. I run my Hawkstone on a 389 monobloc so not able to advise further for comparison. However, my Square barrel MDS uses a 30 mm concentric with a main jet of 270!
Are you riding at Maylandsea this coming weekend?
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Old 14/04/2017, 05:16 PM
Mpb1p Mpb1p is offline
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Default Hawkstone

Hi Adrian
Thanks for the advice, I will try moving the needle to weaken the mixture, the other problem is with the compression being so high that it is almost impossible to kick it over, I took the head off and tried a head with the facility for a decompression valve which is plugged off and it started 2nd kick but I don't know if this head would be suitable, I have also heard that some folk place a shim between the head and barrel to lower the compression, easy enough to make but what thickness would be a good starting point?
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  #6  
Old 15/04/2017, 07:36 AM
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John Pattinson John Pattinson is offline
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Default Hawkstone Starting

The main trouble starting a Hawkstone is the foot rest stops you getting a full swing. To cure this I bought long cranked kickstart from Terry Weedy at Kempton Park. The other problem is if you fit aftermarket ignition then they sometimes have a very small flywheel which with the 12.1 head means again you do not get a full spin over when kicked. I added a small flywheel weight to the engine sprocket to help. This weight came from a Kart. Maybe this is the way to go!
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Old 19/04/2017, 01:18 AM
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ADickerson ADickerson is offline
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Quote:
Originally Posted by Mpb1p View Post
Hi Adrian
Thanks for the advice, I will try moving the needle to weaken the mixture, the other problem is with the compression being so high that it is almost impossible to kick it over, I took the head off and tried a head with the facility for a decompression valve which is plugged off and it started 2nd kick but I don't know if this head would be suitable, I have also heard that some folk place a shim between the head and barrel to lower the compression, easy enough to make but what thickness would be a good starting point?
I run my Hawkstone with a 10.5:1 comp ratio and it kicks over fine. I found 12:1 gave overheating and pre ignition problems that I wasn't able to cure. Certainly agree with John over high comp ratio and small flywheel scenario.
As Kim suggested the squish band needs to be sufficient. You can check this by pushing one end of a long piece of solder wire through the plug hole until it reaches a side wall, then turn the crank over top dead centre. Withdraw and measure across the resulting flat. 030"/0.75mm is good with .020"/0.5mm the absolute minimum. As mine has a central plug hole I use two pieces of solder against opposing walls at the same time and take the mean of the two. As for gasket thickness then one of .012"/0.3mm would approximately reduce the comp ratio from 12 to 10.5 if this is the way you choose to go. Good luck, let us know how you get on.
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Old 30/04/2017, 05:46 PM
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Rob Rob is offline
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Have you actually measured the compression ratio? I had all sorts of problems with my Anglian that I assembled from a basket case. In a trial, the throttle stuck so I whipped off the plug cap to find it carried on quite happily without it, ala glowplug engine!

I measured it and voila - 11.5:1!

I remachined the head until I got it down to 9.5:1 with a squish of 35 thou and what a difference!

Always worth checking, especially with today's dodgy fuels!
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  #9  
Old 13/06/2017, 09:01 PM
Mpb1p Mpb1p is offline
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Default Hawkstone compression

I have done a compression test on my hawkstone and on the gauge it was 12.1 bar, the squish is 1.05mm. With a different head which came of of a trials engine with facility for deco valve compression was 10.75, much easier to start but doesn't run well. Any advice please.
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Old 14/06/2017, 09:07 AM
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Colin Sparrow Colin Sparrow is offline
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Originally Posted by Mpb1p View Post
I have done a compression test on my hawkstone and on the gauge it was 12.1 bar, the squish is 1.05mm. With a different head which came of of a trials engine with facility for deco valve compression was 10.75, much easier to start but doesn't run well. Any advice please.
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