Hi guys, I'm looking to get my 1978 ty250 ported as it's very flat at bottom end power,any recommendations where to get it ported/ rebored?

birkets maybe

Neil Dawson might be able to give you some info, think he has had his done. (His is a bit newer though)

Edited August 28, 201411 yr by b40rt

I would not bother. The standard TY 250s from 1975 on should have any amount of bottom end power if running correctly. It should be able to pull anywhere in second gear from the slowest tickover.

A clean exhaust, good timming and a rebore with a genuine piston ( at least a 2 ring piston ) to factory spec. is ok, for a little more punch you can play with he flywheel weight. That what I did to 2 ( an A and a B model ) and it work ok for me.

Guy

I have heard of 1 of our guys who has had his cylinder ported & the head modified by Bob Grinder of B&J racing in the states & everyone who has ridden it says it's an amazing motor, pulls great & will powerstand in 4th so it is possible to improve if you know what you're doing

With traction usually limited by rear tyre grip and rear suspension (only twin shock capability in this case) is more power really an improvement?

Just my opinion but I think the old Yam 250 motors were some of the sweetest running engines ever made and ideal for twin shock trials with adequate power in standard form, and I have always been a bit on the heavy side.

The problem in producing good power for trials in this engine is the exhaust port duration is far too advanced.

It needs the exhaust port lowering which is very difficult to do.

Thanks for the replies guys, maybe the rebore will give me oomph! I find it very flat at low revs but is fine mid to high revs. Crank seals have been replaced and electronic ignition fitted

Thanks for the replies guys, maybe the rebore will give me oomph! I find it very flat at low revs but is fine mid to high revs. Crank seals have been replaced and electronic ignition fitted

Might want to check the muffler. I've seen your situation remedied by replacing goo'd-up packing.

I would not bother. The standard TY 250s from 1975 on should have any amount of bottom end power if running correctly. It should be able to pull anywhere in second gear from the slowest tickover.

Exactly, mine pulls like a train at low revs,nobody who has ever ridden it has come back and said it was gutless.The last person who tried it at a practice day liked it so much he bought one of his own.