OzVMX Forum
Marque Remarks => Yamaha => Topic started by: Gerard De Ruyter (Twistandshout) on June 11, 2014, 12:21:36 pm
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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!
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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.
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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.
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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.
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Thanks for info, PM sent, Thanks Col.
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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 :(