Hi, I have recently become custodian of Silk 76/78. I am still learning its foibles but I must admit to being slightly disappointed with its performance. The bike is fitted with a 38mm carb and seems to carburate reasonably well. I have a letter from the factory dated 9 August 1978 that says:
"I will also uprate your engine and do the following work. Re-paint your barrel, new transfer cover, new 38mm carburettor, but this will incur a cost of £45."
I read elsewhere on the forum about "Peter Green Porting" but I there doesn't seem to be much detail on what is involved. Is there work on both barrel and pistons? How would I identify if the porting work has been done?
The bike has the usual recommendations (recently repacked exhaust, ramair filter, correct chain tension). It has the original lumenition ignition. I have had a couple of instances of running backward so I need to check the timing but I am not sure of the correct settings without know about the porting.
Welcome aboard, I agree much to learn for what is a pretty simple bike.
There are loads of threads here to help- but Peter Green Porting is new to me.
This forum has been a great help to me as I use mine most weeks April to October.
Both with a Classic Club and had 2 runs with the Scott owners club.
Most of my problems have been due to lack of use or poor set up, or both they don't like to sit in the garage and this new fuel!!!
I would be interested on how you packed your exhaust and what with?
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Peter Green porting was used on later bikes. If you use the search function you will find reference to it but not details of what it entails. I believe it is position and sizing of the ports in the barrel. The pistons didn't change. Regarding performance with the 38mm carb, check the slide is opening fully when the twist grip is wide open. I found my mine wasn't opening fully - again you will find a topic on it in using the search function. Another owner and I found that if you time the Lumenition system statically and then check it with a strobe it is 2-3 degrees retarded. Probably due to wear in the advance/retard mechanism. Setting the ignition to correct for this made a big difference to performance. My handbook says 0.2" or 5mm static advance.
My Silk is pretty docile up to 4000rpm and then takes off from there - not quite what the literature of the time says about low speed torque!
I think I have the original Peter Green data I can upload it when I get time and have pictures of a tuned barrel.
To be fair as Hendred says timing is the most important thing and best set with a strobe and correct marks on the rotor and stator or using a disc.
Also remember depending on the model or early or late MKII the timing could be full advance at 27° or 34° my late MKII definitely is more perky at 34° full advance off the top of my head 0.2" and 0.3" BTDC.