DT 125 Running Problems

[Carl-H]

Hi, my brother has a DT125 which my dad has been using recently because my brother is at uni in Cardiff. The bike will start and run great. It will tick over for ever. When you ride the bike around the block it seems fine so you decide to go abit further and as you shut off to slow down the bike cuts out and it always seems to be at the worst possible place for it to happen. You get to the edge of the road and sometimes it will start and other times it takes ages. When you do try to start it it backfires sometimes. It sometimes will cut out waiting at the lights as well even when blipping the throttle. He changed the plug recently and the same happens with a different one in. He also recently changed the oil pump because the old one was leaking but it seemed to do the same then but not as often. I don't have any idea what it is to be honest and was hoping someone from here could help.
Thanks in advance, Carl

[BliarOut]

Easiest checks first... Run it for a while and then crack the petrol cap open. Can you hear a hiss of air. If you can it indicates a blocked breather causing a vacuum in the tank.


It sounds like a fuelling issue of some sort to me. If it's not a blocked breather and you're up to it I would suggest stripping down the carb, blowing out the jets and checking the float height.
ETA:
Check the fuel filter(s) aren't clogged too.

Edited by BliarOut on Sunday 18th March 12:26

[Carl-H]

Thanks, he will try it later if it stops hailing. He fitted the new oil pump last week which he got second hand off eBay. When he checked the minimum stroke, it was less than that on the original pump. If he adds a shim to make the clearance bigger, does anyone know if this will increase the oil flow or decrease it.

[Carl-H]

My dad has just been trying the bike. Usually it will start up and run well but this time it took more kicks than usual to start and when it did if the revs dropped below 3 it would cut out. It would only run for a few seconds and then cut out and backfired as it died. It was smoking alot more than usual. We tried it with and without the choke but it kept cutting out. He took the plug out and it was really oily. He cleaned the plug and put it back in and the same happened again. We removed the fuel cap first so it hadn't had chance to build up a vacuum as it only ran a few seconds. Then we drained the carb and the float bowl was full of clean, clear fuel.
Thanks, Carl

Edited by Carl-H on Sunday 18th March 15:27

[BliarOut]

Sounds like it's oil fouling now.... Get the oil pump within specifications first and then see how it is.

[ssray]

Refit the orig oil pump,that would not give fuel starvation problems.
run around the block with the cap off or just about on(dont smoke while riding at this point) this will tell you if its the breather(mcn had one on test a year or so ago that did the same)
what colour is the plug?
as you have had the float bowl off and found no crap in there,try the fuel tap remove it as it has a filter built into it.
Ray
P.S. report back

[biker's nemesis]

What was it like before you changed the pump?

[Carl-H]

The bike would still cut out 'every now and then' with the original oil pump on but I think that is just because its 2-stroke and not to do with the oil pump. We changed the pump because it was leaking from the top even when the bike was standing. We fitted the new oil pump and the bike seemed to run OK for the first 10 - 20 mile but these were not covered in one go. The bike now cuts out and the plug looks oily. We cant start it and keep it running anymore. It splutters and backfires and the plug is covered in oil.
Thanks, Carl

[BliarOut]

BliarOut said:

Sounds like it's oil fouling now.... Get the oil pump within specifications first and then see how it is.

[biker's nemesis]

BliarOut said:

BliarOut said:

Sounds like it's oil fouling now.... Get the oil pump within specifications first and then see how it is.