Like a rev limiter?

Hi. My British Track Star GY200 has started playing up. A few weeks ago I stripped it down for a bit of TLC after being use for 250 miles a week commutes over the winter. The damping rod on the rear shock had snapped, the front sprocket lock tab had worn away and kick-start level had got AWOL but it was still running. I fixed all the broken bits and re-gapped the valves to 0.07mm. When I took it out for a spin I found it had developed a problem. It starts fine, pulls well at low & mid revs, but at high revs it just stutters like there's a rev limiter fitted? I've swapped out the CDI in case it was the ignition not advancing, but it was the same?
The only thing I can think of is that I might have set the valve gap at TDC on the the top of the exhaust stroke instead of the top of the compression stroke. Would this have make a difference? Is the cam profile differenct depending on which TDC stroke the engine is on?

Fuel line somewhere blocked after re-installing the tank?
Sounds to me like a lack of fuel.

Thanks for the reply. The fuel pipe has been changed for a piece of proper fuel hose to replace the iffy looking rubber one. I've checked the routing and it all looks ok. The stutter is like a rev limiter. The bike will pull up to 50 mph in top gear and then if you open the throttle a tiny bit more it just gets louder & slower?

How does the ignition advance work on a GY? I thought it was a single pick-up system and the advance was done by the CDI? Are there two pick-ups, one for low speed & one for high?

I'll try to stick a strobe on it if I get home from work early enough this week and see if the it actually is advancing.

I have no idea, as I don't even know what your bike model is (lack of interest in Chinese bikes on my side, not your fault).
But I strongly believe that most of mishaps after wrenching, are caused by that same wrenching.
What I mean is, an ecu is not all of a sudden broken, just because you set the valves (unless you created a short, but that is an other story)....

So therefore I think you should review your actions, and go over it one by one.
Try to think what could have gone wrong at each step, related to the problem you face now.

I don't think you could have messed up on the valve setting.
However you can check. Normally there is a notch at the end of the crankshaft, indicating the top.
Check again, the operation of the valves is: open-nothing-nothing-closed -open-nothing-nothing-closed-open -->

It however still sounds fuel related to me.
You removed the tank, is there dirt inside?
You might have moved it big time, and that same dirt might now be clocking your filter.
Check that first before anything else.

I hear what you're saying. I'll take the fuel tap off and make sure it's not blocked. I still think it's a timing issue though. On the bright side with the GY off the road I have to ride my RD350LC to work which gets me there 25 minutes faster.:lol8:

Quote:

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Originally Posted by Griff

I hear what you're saying. I'll take the fuel tap off and make sure it's not blocked. I still think it's a timing issue though. On the bright side with the GY off the road I have to ride my RD350LC to work which gets me there 25 minutes faster.:lol8:

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Look, NOW you are talking bikes .... RD350LC, what a name, what a bike!
I bet with you for the RD, it is not the ignition:lol8:.

http://i1043.photobucket.com/albums/...2b7028bc_z.jpg

Yeah, you can crate it and ship it after you loose the bet :icon10:
Very nice bike!

Looks like we were both wrong. The rocker arm on the inlet valve was in two pieces. :0 There was enough metal left to open the inlet valve to let the engine run (suprising well considering). But the broken piece meant the valve wasn't opening wide enough or long enough.

http://i1043.photobucket.com/albums/...Y/IMG_0047.jpg

Well, it saves you the RD, but still not good news.
I hope the remaining part of the rockerarm did not destroy your cam lob surface in the meantime.

But now; why did this happen?
If this is indeed the result of a wrong valve clearance setting, then it might have damaged other parts as well, such as the valves.
You better pull the head, now you are there already.

Good luck!

Had a better look today. The cam on the inlet valve side is ok, but the valve seat has broken up due to the hammering caused by the valve slamming shut. The aluminium under the valve spring also looks like the hammering has started to wear it away. The lobe on the exhaust side of the cam-shaft looks pretty worn due to a poor surface finish or low oil in the past maybe?
I had a spare rocker arm from another engine so I lashed the engine back together and it actually ran! I think I'll just run it until it dies again and then look at swapping the engine over, or getting something less delicate.

Ouch…the valve clearance is set at TDC on the compression stroke, .07 on the inlet is correct but the exhaust should be at 0.10-0.12 they are different.