Ypvs head

[bozzwoldo]

Morning,

New to the forum.
I'm after some advice. I may be interested in a ypvs which reportedly has a Bob Farnham rebuilt engine in a state of tune. The seller cannot confirm this.
Running Swarbick pipes
Bike looks tidy but I am told the head has no thermostat housing?
Is a 1WT motor and I thought it should have one?
Am I right and if so any idea why this motor wouldn't?

[rich]

Nah all the YPVS engines should have stat fitted so you are indeed correct

[midlifecrisisrd]

Most likely it doesn't have a stat to make it run cooler but the housing will still be there as it is mostly part of the head

The standard stat is 71 degrees so that's the coolest the bike will run but that will be for emmisions

Performance is best between 50 and 60 degrees hence why the stat would be removed

Luckily now you can get a 55 degree stat from a Yam snow mobile that fits with the original rubber seal

Steve

[3tj6]

So would it be ok to run a engine without a thermostat in then ?

[hoist1]

Give it longer to warm.

[hoist1]

Or use cardboard and string.

[midlifecrisisrd]

As long as you let it warm first and don't go out on cold days it would be ok but for the sake of £30...

Steve

[veg]

Being cynical I’d take any reports of a bike having this build or that tune with a pinch of salt. No receipts no evidence, no evidence therefore means whatever the seller states amounts to nothing.
We’ve recently had a few new members who have bought bikes with rebuilt engines that have popped not long after they’ve bought them. Upon investigation they’ve have either not been rebuilt or done badly.
The other consideration is, say it has had a tune, what state is it in? Is it useable on the road or is it all top end? So many things to consider, I would tread carefully.

[Tobyjugs]

Mar 27, 2021 13:12:32 GMT 1 3tj6 said:

So would it be ok to run a engine without a thermostat in then ?

Yes

[steve63]

My 31K had a full Stan Stephens production tune. By full I mean the whole engine was done, crank cases matched to cylinders, holes in the pistons opened up. That bike had more power everywhere than a standard 31K and was very quick. my point being that a YPVS unlike a 4L0 can be as flexible after tuning as a standard bike.

[steve63]

It was fitted with the standard thermostat.

[dougw]

Around 1985 I rode Terry Shepherds production race 31K that he did all his devoplment work on.
Best two stroke road engine I have ever experienced, fueled perfectly, sounds same as Stans full 31K tune, totally civilised just more power everywhere.

Mar 27, 2021 23:00:35 GMT 1 steve63 said:

My 31K had a full Stan Stephens production tune. By full I mean the whole engine was done, crank cases matched to cylinders, holes in the pistons opened up. That bike had more power everywhere than a standard 31K and was very quick. my point being that a YPVS unlike a 4L0 can be as flexible after tuning as a standard bike.

[steve63]

Mar 28, 2021 18:42:40 GMT 1 dougw said:

Around 1985 I rode Terry Shepherds production race 31K that he did all his devoplment work on.
Best two stroke road engine I have ever experienced, fueled perfectly, sounds same as Stans full 31K tune, totally civilised just more power everywhere.

Mar 27, 2021 23:00:35 GMT 1 steve63 said:

My 31K had a full Stan Stephens production tune. By full I mean the whole engine was done, crank cases matched to cylinders, holes in the pistons opened up. That bike had more power everywhere than a standard 31K and was very quick. my point being that a YPVS unlike a 4L0 can be as flexible after tuning as a standard bike.

I bought mine off a guy in Bradford. He bought it new in '83 and had it delivered straight to Stephens. It must have been one of the first Stan had done. My mate had one tuned in 1985. Stans new 1985 tune. We went to a pre-season test session (a local quiet road) and mine sailed past his on the straight without even needing to slip stream. The guy was very upset and kept asking me what I had done to mine. He was straight on the phone to Stan. His bike had, shall we say an airbox 'mod' which he was caught for early in to the season and mine was legal. He went on to win the championship. He'd actually started the season on a 500LC but said it was a pile of crap when the 350s were all beating him. He sold the 500 for more than he paid for it though. Me and the now Mrs went to Spain on that same YPVS in 1986 complete with production tuned engine and then I used it as a commuter bike for a while after that.