Trials Australia Forums

I have just purchased a TY250D that I plan to ride in twin shock trials. It has been suggested that I should remove the oil pump. Is this a good idea? Can somene please explain what is involved in removal of the pump and what throttle cable would be used. Also what oil/fuel ratio ?

Whether it is a good idea depends on how you perceive the risks apply to you

Possible causes for catastrophic engine damage with standard oil injection:
Pump stops working (cable failure, pump problem, hose problem).
Rider forgets to add oil to oil tank.

Possible causes for catastrophic engine damage with premix:
Rider forgets to add oil to petrol.

My personal experience in 35 years is to know of 3 Yamaha off-road motors seized by failure of the oil injection pump amongst my riding buddies. I don't know of any destroyed by forgetting to add oil to the petrol. Both are pretty rare occurrences but using premix does mean you have more control over whether or not it happens to your own bike. Oil pump failure is undetectable and mostly unpreventable.

Removal of the oil pump requires taking the clutch cover off as the drive gear won't fit through the drive hole and can only be taken off from the inside. A blank is needed to seal off the drive hole. I usually use 3mm thick aluminium sheet for this. Some people leave the pump in place but it will eventually be damaged without oil going through it. The oil injection port needs to be plugged. Its a good idea to use a new single throttle cable instead of the one-into-two cable to avoid any problems with the one-into-two cable operating without the pump return spring keeping things sweet inside the joiner. The action of the throttle is nicer without the oil pump.

You can get a cable made at your local bike shop ($20) or you can buy one from a specialty twinshock trials supplier ($30) or you can modify (shorten the inner) of a cable from a Yamaha of the same era that didn't have oil injection (ie MX125/YZ125 etc) and shared a similar twistgrip with the Ty250D ($35) or you can make your own cable from individual components available from bike shops ($10)(this is what I usually do).

You should not need to change any jetting to suit running on premix.

You will get a range of recommended oil:petrol ratios from different people. Just remember that modern motors are liquid cooled so operate at a much lower peak temperature than a TY250D. This means that you should use an oil ratio that is recommended for air-cooled motors and you should also consider how you ride and how hot the conditions are where you ride. I live in a hot place and am not known for being gentle on the throttle when riding up mountains and use a 3% oil rate in my air cooled motors.
If you live somewhere cool and ride like a granny, you might get away with using less oil in the petrol.

Thanks for your reply David. It definitely sounds like removing the oil pump and running premix is a good idea and will give me piece of mind so I will be doing this modification.
regards,
Paul

Hi, we used to just unhook the cable at the oil pump snip it off if it looks like it will foul something and start running pre mix. you get a lighter throtle and you dont load up on long downhill sections. the premix ratio is open to debate, i use 40 to1 but there are guys out there using 100 to 1 because it sounds impressive and they like to buy expensive oil ( my bike is still going but )

Hi husky005
Ross is right about the throttle cable. Cut it about 50 mm below the join. Saves buying a new cable . Dont forget to cover the hole in the side of the carby. Simplest method is to heat the end of the plastic tube with a lighter and squeeze together with pliers till cool.Then cut short piece and push onto carby.
Good to see another great Champion from the seventies rise from the ashes. Ross Grimsey was the first Canberra rider to push himself to the top of the sport.
Cheers
Peter

all the guys are right! get rid of the pump alltogether! i run my ty,s on full syn motul at 40/1 , if you go to your local bicycle shop you can buy a universel brake cable kit with several inner and outer cables, these make great throtle cables,simple to make and dont jam like some of the cut standard cables do

Gents,
You can ride yourself completely of the pump, but you must blank of the hole in the crank cases. Yamaha used to have a bike back in the mid 70's called a MX175. They had no oil pump but the same cases as DT /TY 175s. They had a flash little blank over the hole.
By completely removing the pump you will get a bit more horse power as the crank isn't driving a dry pump.