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Looks terrific! I'd keep the Spec2 pipes, they look like new after the refurb. Massive thumbs up for M in SC's front brake upgrade if you go that way - it's a very cheap, bolt on conversion, and you end up with modern race-bike quality brakes.

Cheers gents. Still a hint of detonation at 23cc, so off with the heads again and up to 24cc this weekend. I went up to 270 on the main, which was getting too rich...not quite enough to choke it but enough to slow it down.

I might just order the jets to do the Dave F mod now I have a bit more time and start again. It would be nice to eliminate a little fluff before it gets on the pipe.

Haha - cheers....they're only the second set I've made so are a bit rough! I'd like to say I'm getting better but at one set a year, it's going to take a while.... ;) They're quite fun to make, although it takes me bloody ages.

They work a treat - full props to Mick Abbey. I'd done a design that he looked at and said, 'not bad, but this will be better.' It was interesting to see the tweaks he made, nothing in overall length, but all the sections, diffuser, dwell and baffle cones were a bit different. His tunes, with a similar set up are doing low 50s hp @ 8500, with a load of grunt. Feels like I'm in that ballpark.

Thanks gents. I should have left it in the project section! First proper jetting pass last night on 260 mains and the fuel ring looked decent but there were some signs of detonation, so I had to whip the heads off and pop them back on the  lathe....now 23cc, will see how I go today.

It absolutely rips now though - will be great if I can keep if from melting down....

Very cool, I love it.

Oh wow, that must be a handful. Is it a RM125 or 250 engine?

Here's my little RD. Bought it last year, it was an abandoned movie prop and had a load of bits missing. I rebuilt it, ported the 250 barrels and made some pipes for it but it was a bit all or nothing. This year, I wanted to lose some weight and give it a bit more grunt. I've made a box section swingarm that I've not fitted yet, which is RD400 length and half the weight of the original. It's also lost a bundle of rotating mass thanks to M in SC's front brake conversion, which along with stiffer springs and emulators is a terrific bang for the buck. I know it's not the shiniest, but it really does go well!

Just got to fine tune the jetting, then I'm off for a good 3 day thrash around northern cal. Next year, I fancy  making it into a 4mm stroker, with some cylinder mods to facilitate more advanced porting ideas. I might make some billet triples too as the stock ones weigh a ton.

Cheers.

Set up now:

- Chinese Cylinders, ported by me, raised / widened exhaust, raised transfers and redirected a bit, widened and raised boost and redirected. Decked and pegged on centre for RD400 gaskets. Pro-x pistons, set around 2.5"thou clearance.
- 250 heads recut by me, 45% squish, bath tub shape dome, 22cc total volume, 0.95mm squish. Seems to run 91 pump gas fine, at 145(ish) psi.
- Pipes made by me from a Mick Abbey (thank you Mick!) design for around 8.5K peak. Made in 22ga steel, weigh 3.5lb each, inc silencers.
- Banshee cross over intakes with the stuffers removed, 6mm reed spacers to lower crankcase compression a bit
- stock cages, opened out with trimmed yz85 reeds.
- HPI ignition, set 1.8mm btdc.
- Racetech straight rate springs, with cheapo xs650 emulators and 7.5wt oil.
- 520 Chain conversion.
- M in SC, FZR600 disc / r6 caliper conversion from dxf files - cut on a waterjet at Send Cut Send.

Yay - gave it a couple of good rips in 2nd and third this evening and it didn't blow up! Wheelies nicely in 2nd now on 15/40 gearing. Feels a bit rich everywhere, bit sputtery on the pilots, better on the needles and takes full gas on the mains, without bogging or sputtering. No sign of detonation, which was a bit of a concern as I'm up near 150psi. Hopefully that means my heads are working well!

I'll do a few more miles tomorrow and give it a proper plug chop. So far so good....

That's a cracking deal. Nice one!

Cheers chap. Got it running and heat cycled today, so will have a crack with jetting after work during the week. Sounds happy.

Apologies if this has been done to death. Is there a difference in main jet sizes running the Dave F mod vs stock?

I'm just about to start up my little home grown 350 - it has stock high tops, stock needles, y-boot with UNI filter, ported cylinders (exh raised a little and widened to 68% of bore. Transfers and boost raised and widened.) I recut the 250 heads for about 45% squish and a total volume of 22cc, squish is 0.95mm. Pipes are home made by me for about 8500 peak from a Mick Abbey design.

I've got a 32.5 pilot / 230 main in it at the moment, fine for some heat cycles and pootling but reading here, seems like the main might want to be bigger?

I'll probably try the Dave F mod at some point but don't have time to order the jets before a ride next weekend.

Cheers!

You need to adjust the ports for the extra stroke. RZs already have pretty racey port timing as stock, so I guess it would just involve lowering the floor of the exhaust and transfers. Doing that would still give something like 192/122 on a 4mm. If the exh port has been raised in the past, you're going to end up with a LOT of exhaust timing, which might not be ideal.

I didn't even need to touch the roll pin on my 250 forks, at least at the setting I was happy with. It's an excellent budget mod, particularly in conjunction with stiffer, straight rate, springs. Cheers!

That's good to know. I'm nearly finished a similar set up, with home made pipes and port / headwork and was going to start with a 230main / 35pilot combo. Sounds like that will be safe.

Many thanks for this M in SC. Cool part! I was planning on making one but as I'm a bit short on time, I just sent off the dxf to Sendcutsend. Technology is a wonder! Cheers.