Is this a horribly obvious statement?

[Gazdaman]

My 10 year old eastern block 2 stroke doens't like being ridden flat out in top.

*cue laughter*

the bike rides nicely, but if I take it on a flat straight bit of road, flat out, it'll get to about 65, and it'll stay there for a minute or so, then it'll start acting up.

it'll suddenly slow like you've eased off the throttle or touched the brake.

obviously my first thought is that it's an early warning sign my engine is about to seize.

it happened today, and the engine did in fact cut out, why I'm not quite sure, everything happened quite quickly, and I was playing with gears trying to remedy the situation, but I did roll to the side of the road, where I kicked her over, and she was fine again.

It's quite happy doing 50mph, which I tried. No problems at all.

Is this obvious? Should I not push this kind of bike to these kinds of limits?

Gaz

[stinkwheel]

First off, what bike?

Assuming it is a generic 125.

You will find that the world goes by at 55mph. They will do this all day long. However they shouldn't be doing what you describe, if it is a 125, 60 shouldn't be outwith the realms of possibility, a sustained 65mph on some of them will mean it is going to get hot though.

What you describe sounds like the engine tightening up, as you say, ready to seize (hey, at least they give you plenty of warning).

Couple of questions:

Does it have a fairing? some models were fitted with full fairings that only have a small hole in to let air get to the engine. These cause them to seize up on-piece.

What 2-stroke mix are you using? Most (mz, jawa, cz, various soviet) are designed to run at 40:1, later models will state 50:1 or even 60:1 as they failed european emissions tests otherwise. Oil pumps on these bikes can be very hit or miss (some jawa oilmasters have been known to put out down to 70:1 when the marks are aligned), try richening up the mix a bit, the worst that can happen is it will need a de-coke sooner.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Wave2k]

they say with 2 strok u shouldnt redline rag em.
lets say RS50 that does 55mph
treat it as a bike that does 45mph and occasionally does 55mph
this will extend its life greatly
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Ducati 1299 Panigale
2009 Corvette C6 z51
RS125->CBR400->RXS100->GSXR750K2->Ducati749S->CBR600RR5->TL1000R->DRz400->RSVR1000->Honda VTR SP1->CBR400->GSXR1000K6->Honda H100->CBR600RR3->Ducati1299

[Frost]

cruising speed = 3/4 of top speed
My 125 does 75mph, however on long journeys it wont last long at that speed, and may die. 60+ it normally get s little too warm.

Blast it up to high speed for short periods, but dont leave it there. it should be happy at half-3/4 throttle in top.

[Mr C]

[Robin]

Looks like you've hit top speed mate

If it is starting to complain it obviously aint happy. Might need some general maintenance on the engine, try whipping the head off and checking the piston, and bore, also look for carbon build up.

My MZ250 went for about 400 miles slowly losing a bit of power until it siezed solid on the A1. The small end bearings had worked their way up the side of the piston and were bouncing about in the chamber.

Other wise just accept that this is top speed for that bike.

[Gazdaman]

it's an MZ 125 ETZ.

I realise this is the top speed, but the tightening up can never be good.

I guess it's possible it's just getting hot and the piston is just expanding causing it to tighten. Another possibility is the 2 stroke oil pump being nakered. Although it does smoke when cold, so at least some is getting through.

Gaz

[Kickstart]

Hi

Also check that the fuel tank breather is clear. As the speed increases you need more fuel, and if the breather is marginal then the fuel cannot get from the tank to the carb quickly enough.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Gazdaman]

good call, it has been standing for a while, and the bike has never really been loved.

it goes down on the to-do list.

Gaz

[Gazdaman]

Just an update:

I've been riding (read, thrashing) the bike for a couple of weeks now. And it'll hold top speed quite happily now. I think the bike had just been stood for a while, and appreciates a bit of a lube.

Gaz

[Lone-Wolf]