2 Stroke info

[kerabo]

Hello all this is my first post on here.

I have an old 1963 classic 2 stroke motorcycle. This is a villiers 9E engine but it has a sports conversion 250cc head piston and barrel made by Marcelle fitted that is supposed to give this engine a fair amount of power. The thing is it runs out of steam too easy. It seems to have about the correct torque that I would expect and the gearing feels about correct but once it gets to about 45 mph it just seems to struggle. The exhaust is clear and the plug is the correct colour after a long hard run and a plug check. There is just a possibility that the porting is not for road use but as I have only just put this on the road I am just searching for answers.

Any ideas?

Regards Ken

[rev-erend]

A compression test sounds like the way to start the diagnostics
but I have no idea what a good value is for a two stroke.

[Boosted LS1]

If the porting was changed then it would be to make it go faster I'd compression test it but also take a look at the carb. Maybe it's not opening far enough to be truly operating on the main jet. Also, have a close look at the spark plug tip to make sire there isn't evidence of pinking or detonation and finally, check the ignition timing's correct.

[kerabo]

Thanks for the reply

I havent had a compression tester on the engine but it feels to have good compression for a 2 stroke and also you can feel the crankcase compression on the kickstart. carb new and the same bore as the inlet port and open fully. The porting worries me but will have to seek advice from someone that is very good on 2 strokes.
What i need is some info on this Marcelle conversion but its not easy to find

Thanks all for the help

[AtticusFinch]

kerabo said:

The exhaust is clear
Regards Ken

Try posting on one of the bike forums you may find more people that understand 2 strokes. I may be way off but exhausts back pressure is very important on a 2 stroke.

[tr7v8]

AtticusFinch said:

kerabo said:

The exhaust is clear
Regards Ken

Try posting on one of the bike forums you may find more people that understand 2 strokes. I may be way off but exhausts back pressure is very important on a 2 stroke.

Nope clear as in not carboned up.

A lot of older 2 strokes can withstand a reasonable increase in compression ratio. How high will depend on the porting & whether you wish to run on higher octane fuel. Also is it still running the 9e original carb? It may need an increase in carb size after the 25% capacity increase. Another possibility is trying an increase in ignition advance.

[Mr2Mike]

Check the ignition timing. Older two strokes tend to run fixed timing advance, and setting this accurately is very important for both performance and for avoiding holes in pistons.

Has the carburettor jetting been changed appropriately for the larger displacement?

[blitzracing]

AtticusFinch said:

Try posting on one of the bike forums you may find more people that understand 2 strokes. I may be way off but exhausts back pressure is very important on a 2 stroke.

You want to get the exhaust gas out as easily as possible, but not the air fuel mix that's being pushed up from below the piston. There was a big power step forward when racing two stokes where fitted with expansion pipes that basically filled up with exhaust gas, but then once full, became restrictive due to the small outlet. This reduced the flow through the exhaust port at the point most of the exhaust is displaced so the good inlet charge did not follow it. This point is both RPM and throttle opening dependent and can be tuned for specific use, and is a lot better than a straight through pipe, just look at any modern scooter engine exhaust.

[m8rky]

I think for an early 60,s small capacity two-stroke that may be somewhere near its full performance.

[Pumaracing]

kerabo said:

Thanks for the reply

I havent had a compression tester on the engine but it feels to have good compression for a 2 stroke and also you can feel the crankcase compression on the kickstart. carb new and the same bore as the inlet port and open fully. The porting worries me but will have to seek advice from someone that is very good on 2 strokes.
What i need is some info on this Marcelle conversion but its not easy to find

Thanks all for the help

If the carb is new does that mean it is a standard carb with standard jetting because that's almost certainly not going to be right for the larger engine conversion. If you still have the old carb I'd check the jet sizes. A quick Google for the power output of this engine reveals it should do 60 to 70 mph with average motorbike aerodynamics. At only 45 mph top speed I doubt you are getting 5 bhp when it should be triple that with the 250cc conversion.

[Stan.]

These engines are still used to this day in Kart Racing - how does over 30bhp at 9000rpm sound?

There's a healthy following and you can get all manner of engine parts that have been re manufactured using modern materials.

A certain Nigel Mansell used to race in this class back in the day. Here's some links for you........

http://villiers210.tripod.com/id1.html

http://www.users.globalnet.co.uk/~pattle/nacc/arc0...

http://www.lortim.demon.co.uk/vsih/intro.htm

Hope this helps.