I want to go above 70mph

[ukpco]

Over the last couple of years I've tried everything I can, short of rebuilding the engine, but my 700S runs out of steam at about 70mph. I've finally admitted to myself I'm not going to fix it myself. Can anyone recommend who might be able to sort it out for me - I don't want to entrust it to a garage without experience of Silks. thanks

[Smokey_Paul]

I have three booked in still but happy to go thru it if you are willing to wait until my next slot.
Is it a Mk1 or MK2?
Obvious quick question have you checked your ignition timing and advance mech?
Paul

[Fredvincent]

Also, have you decoked the exhaust, particularly the removable baffle perforated tube?
By clearing all the holes and replacing the insulation material you will re-introduce a bit of back pressure which will help. It will also be a bit quieter.
Removing coke from the main exhaust is not so easy. A bit of gentle bashing helps release the worst.
Good luck.

[ukpco]

Hi Paul
I didn't realise you repaired Silks. I'd be happy to have you look at it, there's no rush as winter is coming.
It's a mk 2.
Just for info, I've:
Done a compression check (good).
Checked ignition timing and moved it a bit advanced and retarded of standard and checked mechanical A/R.
Swapped (unsuccessfully) to Boyer, now back with Lumenition.
Rebuilt carb with new jets.
Tried a larger 36mm carb.
Cleaned and repacked exhaust.
Put in new crankshaft oil seals.
Checked for inlet air leaks.
Had bike on dyno (31bhp and running very slightly rich). I would have expected this to be enough to go faster, even though well short of the claimed bhp.
Checked chain tensions and brakes for dragging.
Checked speedo reading against gps on my phone (getting desperate but speedo was surprisingly accurate).

[Smokey_Paul]

I have just finished one for a forum member Bill he said he is cruising at 70 and to be honest I had his timing set on the safe side.

You should be quicker than you are it maybe worth just swapping lumenition units or sending me yours and the optical pick up to test.

I now have lumenition test set up and test boxes.

Sent from my Samsung Galaxy smartphone.

-------- Original message --------

From: "ukpco [via Silk Motorcycles]" <[hidden email]>

Date: 10/10/2020 21:53 (GMT+00:00)

To: Smokey_Paul <[hidden email]>

Subject: Re: I want to go above 70mph

Hi Paul
I didn't realise you repaired Silks. I'd be happy to have you look at it, there's no rush as winter is coming.
It's a mk 2.
Just for info, I've:
Done a compression check (good).
Checked ignition timing and moved it a bit advanced and retarded of standard and checked mechanical A/R.
Swapped (unsuccessfully) to Boyer, now back with Lumenition.
Rebuilt carb with new jets.
Tried a larger 36mm carb.
Cleaned and repacked exhaust.
Put in new crankshaft oil seals.
Checked for inlet air leaks.
Had bike on dyno (31bhp and running very slightly rich). I would have expected this to be enough to go faster, even though well short of the claimed bhp.
Checked chain tensions and brakes for dragging.
Checked speedo reading against gps on my phone (getting desperate but speedo was surprisingly accurate).

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[ukpco]

Thanks Paul, I will remove the ignition in the next few days and send it to you.
I've been cruising happily at 60-65, it's just when I open up to overtake there's nothing there, whether I change down or not.

[Smokey_Paul]

Actually what air filter have you got fitted as I noticed a massive difference in performance from a pod type filter when changing to a RAM Air foam type like the Silk Original filters.
I have a 36mm carb on mine which seems right to me and doesnt 4 stroke too much at lower revs.

[ukpco]

Time to finish the story.
I rode the bike to Smokey Paul's, very sedately. When I rode it back home again it was much more lively!

Paul found that a previous owner had modified the porting, presumably trying to match the Peter Green porting, but hadn't done a great job. Paul improved the porting, fitted a matching 38mm carb and Ram Air filter, sorted a few electrical gremlins and a lot of blockages to the waterways to give me back what felt like a different bike. I'm now enjoying riding it again. Thanks Paul.

[hendred]

That's good news.  Hope you enjoy riding your Silk now. Well done Paul.

[Smokey_Paul]

Two more coming 😁

[Smokey_Paul]

Found another real original spring for you

[ukpco]

Great, I look forward to receiving it.

[Smokey_Paul]

On its way this week