Derbi gpr seizing

mikej100 · L Plate Warrior Joined: 17 May 2014 Karma :

Chaps...
First posting so go easy on me.
My son has a Derbi GPR50 2005 that ran fine for most of the year he owned it then one day it seized with the piston detonating the head.

So i bought a cyclinder repair kit and rebuilt it ,again it ran fine but after only 2 days it seized again...gutted!!

So that was last November and after sitting in the shed for the winter i've finally got enough enthusiasm to tackle it again before selling it on.

I suspect the oil pump may not be working can anybody tell me how i can check it is working correctly?

Any other ideas/comments as to what may have caused this would be welcome as i'd really like to sell it on knowing it's going to behave itself.

Thanks
Mike.

PS anybody interested in a decent 2005 GPR50 MoT'd to Nov 14 new brakes ,chain ,sprockets,rear tyre less than 100 miles some where near 600 quid would do.

nathan k · Spanner Monkey Joined: 28 Mar 2012 Karma :

Premix tank, remove oil feed to the carb. When running oil should drip out the pipe slowly. It won't look like much but it goes a long way.

Being a 50cc...What modifications have been done to it?

A combination of tuning parts could cause an extremely lean running condition.

mikej100 · L Plate Warrior Joined: 17 May 2014 Karma :

Hi nathan...
No mods whatsoever,its compltely standard.

It has been suggestedto me that the cause may be down to it running lean but the underside of the orginal piston is sooted.

Thanks for the tip regarding the oil pump i'll try that once i get it back together and running.

It's been a while since i did any premixing any suggestion as to the best ration oil/fuel to use?

Mike.

_Iain_ · Banned Joined: 01 Feb 2012 Karma :

Inked · Two Stroke Sniffer Joined: 21 Mar 2014 Karma :

Did you check the crank for play when you had the bore off?

mikej100 · L Plate Warrior Joined: 17 May 2014 Karma :

Ok,latest is i've put everything back together and running on premix it starts and runs really good.

I've pulled the oil feed pipe from the oil pump and at 3000 rpm all i get is a very very small drip every few seconds but it's hardly noticable even if i hold the pump fully open by hand it doesn'tseem to push out much ,i can't believe that it is enough to pump up the pipe to feed the carb sufficiently.

Is this normal?What should i expect to see coming from the pump

I'm also going to purge the oil system and run it on fully synthetic,would this make any difference?

Thanks again chaps
Mike.

trisers · Scooby Slapper Joined: 29 Jul 2009 Karma :

If it's any help my old Honda H100 oil pump produced a drip of oil every two or three seconds at a fast idle say 1500 rpm?

bodger · Nova Slayer Joined: 18 Apr 2012 Karma :

Hi Mike
Its been a few years since I ran a two stroke, but the oil pump usually has a metering line scored on the quadrant wheel, the operating cable connects to..When the throttle is wide open the line should line up with one on the oil pump body.
To adjust the flow, simply adjust the actuating cable accordingly.
Hope this makes sense.
Good luck.