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yea the shocks are pretty garbage lol. alloy rims is something i want to do one day but that is $$. The pipe performs pretty well too, probably going to make another one after i get it ported. I originally wanted a bump seat but i just couldnt make it work with that tank

yea its 32:1 pre mix, if I go on a long enough ride i carry oil in my backpack
 

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That's a fuck of a lot of oil! make sure it doesn't gum up your rings and pollute your exhaust packing. I used to run Bellray MC1 @ 80:1 (full synthetic) in my TY's and never had a problem. Don't try and out run a cop, all he would need to do is follow the contrail.
 

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32:1 is about right for pre-mix. 38mm is pretty big for anything less than a full race motor and when it's ported, that might make it a lot less fun to ride at anything less than wide open.
 

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On a road engine you need the premix quite oily as suggested above. Remember you are only getting a fully oiled engine when the throttle is wide open so somewhere between 25 and 35:1 depending on the engine (iron or nikasil) and carb set up. Many race oils can be run very thin @race engine speed so go read the 1st sentence of this post again. 38mm is too big for a road engine only the very last of the tz350?s ran 38?s and they were power jets and we would run them over 10000rpm throttle wide everywhere breathing well and no siezures had a few pistons break up though and crawl out of the exhaust port. Also be careful as some some premix oils especially race types as they are blended for Race fuel mix like 50/50 pump with avgas and aren't ideal for a straight pump. Likewise good Race oils like Castrol xr77 don't mix well with Avgas. Avoid using modern blended castor oils they are nothing like original castor, modern castor oils are full of detergents a really don't mix well.
 

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Thanks for the tips. Im running yamalube 2R oil and im running 91oct pump gas mixed with some 108 race gas as I was having detonation issues with the high comp head
 

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Thanks for the tips. Im running yamalube 2R oil and im running 91oct pump gas mixed with some 108 race gas as I was having detonation issues with the high comp head
How much compression and what's head / piston clearance value? Port timing is fast road? Or race?

Strongly recommend running smaller carbs. 34's are ideal. TR2 / TR3 ran 34's and good enough to win world championships, Yamaha know a thing or two. You can bore these carbs out to 35.5mm if you need to (common mod in period, even works Yamaha did so).
 

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The stock enduro head had 6.8:1 compression and the GYT head is supposed to have around 8.2:1 compression ratio. Ignition timing is also set to 3.2mm BTDC. The port timing is stock which is why I would like to have the bike ported and and then I will fabricate a new pipe for it as well. Not dead set on the 38mm carby yet. still running the tm32 flatslide which is wayyy better than the stock tm28 roundslide
 

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The stock enduro head had 6.8:1 compression and the GYT head is supposed to have around 8.2:1 compression ratio. Ignition timing is also set to 3.2mm BTDC. The port timing is stock which is why I would like to have the bike ported and and then I will fabricate a new pipe for it as well. Not dead set on the 38mm carby yet. still running the tm32 flatslide which is wayyy better than the stock tm28 roundslide
38 will never work
like steve is alluding to you need to optimise the combustion.the squish band's depth.angle and it's % of area the width is not flash or fancy but unless you do that your wasting air
that cylinder simply does not have the transfer port capacity for bigger than 32
32-1 is a beautiful mix every race team in mx and supercross used 32-1 ,i used it to national enduro winning glory
and at 4oz to a gallon you dont need a degree in nigerian engineering like i have to suss that out
keep using the yamaha oil
mobil one 10-40 car engine oil is as good or better than anything as well
 

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alloy rims are a flash mod i would not do it unless you want a diff width rim
you wont gain any noticable perf increase
its only a very small weight savings ,less than a pound to just over a pond depending or rim width
but you have to fix the seat seat issue ,the tire hits it
you dont need fork brace on that and if not installed exactly right will be a downgrade
ive got some porting port timing and pipe specs if you like ill post em up here
a yz250 a or b jug and head would be tits but rare and high valued
 

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alloy rims are a flash mod i would not do it unless you want a diff width rim
you wont gain any noticable perf increase
its only a very small weight savings ,less than a pound to just over a pond depending or rim width
but you have to fix the seat seat issue ,the tire hits it
you dont need fork brace on that and if not installed exactly right will be a downgrade
ive got some porting port timing and pipe specs if you like ill post em up here
a yz250 a or b jug and head would be tits but rare and high valued
Yea if you have those port and pipe specs id be interested, pm me if that is easiest, thanks
 

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Is only my opinion but:
Powder coat paint and pin striping is a flash mod; reducing weight on part of your motorcycle that follows a generally uneven road surface, spins at speed and contributes significantly to inertia that the suspension, engine and brakes have to deal with sure sounds more like a performance mod to me. He's building a Street bike! Not something that is ever going to see closed course competition. The realities of riding a motorcycle on public streets is what motivated Yamaha to develop the autolube system. -> American Motorcyclist - Jun 1971 - Page 9 <- the link will take you to a handy little chart that was created to help explain and promote the Yamaha Autolube system as it applied to his actual motor and based on the now some 48 year old period fuel and lubricants, some logic will be required for him to determine where his intended application fits that model and how it relates to his modern fuel and pre-mix oil of choice. If he regularly experiences oil fire flare-ups inside the exhaust system and black goop pouring out of all the seams, there is probably more then the ideal oil concentration entering the engine.
 

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FYI, the 2018 YZ250 uses a 38mm flatslide, but it has huge inlet transfer and exhaust ports. I would stick with the 32mm for now unless/until you add more port time area and bigger reeds. Properly matched, you may be able to go up to a 34mm or maybe even 36 but start with ports and reeds and match that.

Forget a YZ250A. They were not exactly common. You could look for an MX250 top end of the same year, but probably better to have someone like Scott Clough take a look and he can advise on what porting to do and head shape to work with it. There are others here, apart from myself who could also do that and design a pipe to match, but Scott or Chuck Quenzler in FL or Mick Abbey in the UK are all in the business to modifying two strokes. Scott raced a DT1 I think in AHRMA and while you don't need his race tune, he has done the research and knows what's possible and what works.

Or, work out the numbers yourself and see what's possible. Try exhaust opens at 90 ATDC, transfers at 120 and see if there's enough metal to take them there. Buy a spare barrel and carve away and see what works. There's one on ebay now

https://www.ebay.com/itm/72-73-YAMAHA-DT250-DT2-DT3-250-OEM-CYLINDER-JUG-BARREL-TOP-END-70MM/202069103708?_trkparms=aid=222007&algo=SIM.MBE&ao=1&asc=20160908110712&meid=d87fb98cbab9412b9544739b805eaa7c&pid=100677&rk=8&rkt=13&sd=201510058631&_trksid=p2385738.c100677.m4598

https://www.ebay.com/i/201510058631?chn=ps&dispctrl=1

I believe that the stud spacing changed so make sure you get a barrel that fits.

Cheap trick: buy the base gasket for the barrel you want to fit and see if it works on your bike. Even cheaper trick, look up the part numbers of your base gasket and the MX or YZ and see if they are the same number. Or check on one of teh online sites to see what bikes they fit and sometimes that can be illuminating - as in light bulb moments.
 

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Last word on this from me: Find out what the ignition advance figure is for your engine in degrees and set the ignition with degree disc. IF you decide to tune the engine, don't go mad, optimising the combustion chamber is essential if you want to run a bigger carb and burn all that extra fuel. Piston to head clearance, in the squish area, not less than .8 not more than 1.0mm. I would tuned for torque rather than HP a bit like race sidecar guys would do in period so a little more width in the ports with a little more height, I wouldn't touch the transfers just leave them rough and 34mm carb would be as big as I would go, lengthening the inlet tract can help the engine to pull better lower down but you need to balance this with everything else.

The thing with strokers is that even a fire breathing TZ750 will ride like a commuter bike until you give them a handful of gas higher up the rev range.

WARNING tuning your engine will seriously shorten its life.
 

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;) you know they did make that nearly identical motorcycle in a 360cc version called the RT1

... there comes a point where chasing down RT1 power in your DT1 just doesn't make sense unless you are required to displace no more then 250cc's,
and DOT looks only at the frame VIN, they usually don't give a crap about the engine serial number matching anything.
 

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A little bit of 80's café racer and its not a Honda!

Just finished this and delivered it today - Harris Magnum with Z1000J engine. Started with a the Magnum frame (for GPZ750) then modified for the 1000J (rubber mounted) and then found everything else to build a period spec bike.

image5A.jpeg
image9a.jpeg
 

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A little bit of 80's café racer and its not a Honda!

Just finished this and delivered it today - Harris Magnum with Z1000J engine. Started with a the Magnum frame (for GPZ750) then modified for the 1000J (rubber mounted) and then found everything else to build a period spec bike.
Steve, you never disappoint!
 

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and it looks like you paid more then $500 for the bike, also exceeded the $20 parts budget too? no cheap Chinese parts ? kidding aside it looks beautiful.
Well I started with a frame and collected or made everything else. Nothing quite like cutting 10mm Dural plate with a hacksaw!

"exceeded the budget" well just a bit! When i started the build the deal was to complete for a fixed price, then they said they wanted a "period" bike and as a Harris would have built around the late 70's / early 80's. So Dymag wheels, Marzocchi M1R 38mm, Lockheed callipers, Magnum / F1 bodywork etc. Strangely he expected me to hold a fixed price....yeah right!

Full Spec as follows;-
- Harris Magnum 2 frame for GPZ750 converted by Harris for the Z1000J engine. Harris Magnum arm for Suzuki GSX (wider than GPZ750).
- Kawasaki Z1000J engine c1982 - Stock tune.
- Mikuni RS33 carbs
- Boyer Micro Power ignition and coils
- Bespoke exhaust
- Earls oil cooler and fittings
- Suspension: Marzocchi 38mm M1R forks (New old stock from Hesketh), rear shock is a rebuilt rebuilt WP (KTec)
- Harris Magnum Yokes 38mm offset
- Dymag Wheels stripped, crack tested, chromated and painted,18 x 2.50 front and 18 x 4 rear. Avon AM26 tyres
- Harris rearsets, milled and modified now 1/2 the weight they were.
- Scitsu Revcounter and electronic speedo (Daytona).
- Brakes; AP variable ratio master cylinder pushing 2x 2 pot callipers biting 300mm floating discs up front. AP 2 pot calliper biting 260mm Brembo disc pushed by Brembo master cylinder. All Goodridge Lines and switches.
- Magnum 1 alloy tank and Shaw aerofiller cap.
- Bodywork: Harris F1 seat, Harris Magnum 2 Fairing, RG500 front guard
- Bimota clip-ons (SB1).
- Bespoke items - Rear sets, fairing brackets, rear splash guard in stainless, front calliper hangers, rear calliper hanger, rear torque arm, steering damper brackets / clamps, oil cooler mounts and engine oil take off.
- All fasteners lightened.

A few more pics, I think it turned out OK considering 90% of the bike is almost 40 years old!

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final image 5 enh.jpeg
final image1 enh.jpeg
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