Author Topic: TT250 time  (Read 3163 times)

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TT250 time
« on: June 11, 2014, 12:21:36 pm »
Its the unsung smaller brother of you know what, and time to give it a bit of attention.  I picked up a H for $700 a couple of years ago, purportedly 'going', with the idea of just racing a four stroke dunger in the heaven 250 4T class.  The 'going' bit proved to be a euphemism really - unless you define going as the ability to roll on wheels, which it did.

Top end clapped out, rear shock no good, running gear - marginal. 

Eighteen months later and its got a rebored cylinder, a YFM350 cam and (1mm oversize) valves, and a flow ported head.  Tossed the oem carbie away and put in a TTR250 carb.  Works Performance monoshock and IT175 forks.

Two years later and I've finally got the jetting sorted, and she runs a beaut.  Vuury nice mid and top end, and crisp jetting all the way thru.  New suspension all good too - pretty raceable unit methinks!  Sad thing is, not sure I'll be the one racing it - putting a lot of time into racing dirt track these days, and don't do heaven events any more.  She's good for a few things, but dirt track wouldn't be one of them.  (doing up a '69 TS/TM250 for that).

I can vouch for there being some nice extra horses in these things if you go hunting for them - she pulls like a train!

Offline oldcol

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Re: TT250 time
« Reply #1 on: June 12, 2014, 01:09:59 pm »
Hi Twistandshout, I have one of these motors in a 79 KX125 frame that I am slowly building up. I am interested in what year YFM350 cam and valves you used and who ported the head? Just looking for a bit more power than standard. Thanks Col.

Re: TT250 time
« Reply #2 on: June 16, 2014, 08:41:12 am »
Not really sure what year YFM, but I don't think they changed much over a decade or longer.  I think it would have been a nineties model.  They sold stacks of them in the states so plenty of yfm stuff on ebay.  The yfm valves are 1mm bigger than tt250.  I had a local guy (who knows what he's doing) flow port the head and fit the larger valves.  YFM cam fits straight in (even with tt valves).  You can get stage 1 and 2 hot cams for yfm's too.  i have a new stage 2 cam if you'd be interested in it.  and the bigger ttr250 carb suits the bigger/better head very nicely (plus the bassani pipe).  All up she goes very well.  There's a guy in new zealand who sells aftermarket cdi's for these with a better ignition curve - he sells on ebay from time to time, but can't remember the name - search for tt500 or 250 cdi's.

Offline OverTheHill

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Re: TT250 time
« Reply #3 on: June 16, 2014, 10:34:49 am »
Talking ignition curves etc reminds me--my [should be scrapped] tt250, had a 'totaly' worn off inlet lobe, which is how i got it [given to me], had the same running symptoms as when they stuff the cdi box & stay full retarded [seen lots at work with that problem over the years]. Anyway--thinking cdi, i advanced the ignition to prove a point by leaving the flywheel key out & gave it a 'key' width advance--did go better but of course kicked back. Eventually found the cam problem [didn't rattle as expected] & replaced, plus inlet rocker, but left it 'half a key' over advanced & definitely livened it up. That was a year or two back. Might put it back to std just to experiment again if i can find the key. 'Did' do it up super tight with a 'solid' holding tool against the footrest & a half inch breaker bar but not a recommended practice [no key that is]. Cheers.

Offline oldcol

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Re: TT250 time
« Reply #4 on: June 16, 2014, 08:17:42 pm »
Thanks for info, PM sent, Thanks Col.

Offline Ekka

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Re: TT250 time
« Reply #5 on: July 01, 2014, 07:19:36 pm »
No the tt not sorted well it was but I wouldn't recommen that local guy for the head work or anything for that matter , 9 laps at the first vinduro and the thing was blown weed , so not happy  :(