RB25 (250) - Pictures & Spec....

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drunkmunkey6969
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Here we go again!!!! :lol: :lol:

This post won't be nearly as 'in depth' as the RB20 (200) post i made earlier, as the RB25 (250) is obviousley very similar in many ways, but with a few distinct differences that we can easily cover. If you wish to see a bit more detail about the RB kit in general, refer to the RB20 post first: http://scooterotica.org/forum/viewtopic.php?f=7&t=296

OK, so....the RB250 kit:
Image

Here next to the RB20, both externally similar, using same size reeds, manifold and exhaust:
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Inlet ports on both RB20 & RB25:
Image

Rather interestingly, the entry to the transfers on the RB20 are practically the same size as the RB25....which means in percentage terms they are bigger than the RB25:
RB25:
Image

RB20:
Image

The transfers also seem to be meatier on the RB20:
RB25:
Image

RB20:
Image

So what about the inside, lets take a look at the port layout:
Image

You can see that, like the RB20, we have a triple boost port again (3rd port being more of a transfer due to its angle of entry) but unlike the RB20 there is an exhaust port with two auxilaries. The main exhaust port is smaller than the RB20, but the auxillaries make up for that. Something to note is, that the RB20 is therefore easier to widen and work on, and the RB25 will require welding up first if you wish to re-work the exhaust port to any great extent.

The inlet, from this external shot, can be seen to be very similar to the RB20:
Image

The internal shot below shows the boost port and transfers....note that although the boost port looks offset, it is actually inline in terms of the two main boosts seated between the transfers, and the 3rd port/transfer is the only 'offset' port.
Image

Below is a shot of the boost port from the underside:
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And a close up, you can see the angle of entry as the boosts face upwards, and the 3rd port is flatter, like the main transfers, you can also see the direction of the ports from the side:
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The feeders that wrap round the studs, come through to the transfers......flow!
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Last, but not least, we have the exhaust port with auxillary side ports:
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A closer shot:
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And from the outside, the bridged auxillaries can be seen joining the main port:
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So that's your lot, not so much text here....because i dont want to just repeat whats already been said in the RB20 post. The port map below, will give you a rough idea of how the ports are measured out on the RB25, and at least one thing worth noting is that the port sizes an the RB25 are not proportionally bigger than the RB20. In my mind this will result in the RB20 being branded as more of a screamer, and the RB25 as more of a thumper....both performance based motors in their own right....and both tunable with slants bewteen touring and racing.....but as the inlet port and the transfers on the RB20 is almost physically identical to the RB25, this means as a proportion/percentage of the bore the RB20 comes in a more extreme state of tune as standard.......which is what i like.....and the exhaust port is easier to alter that the RB25 too. However, the RB has the wider exhaust by way of the auxillaries as standard.....and it's 40-60cc extra will give it some real umph!! Two cracking kits, both from the same range, both looking similar....but with subtle differences that will give each its own character.......and power delivery. In terms of progress, the RB range is undeniably a huge leap forward in tuning terms, and takes Lambretta's to yet another level............i just want to get one on the track now! :D :D :D

Take a peek at the port map, and see what you think:
Image

RB20 map for comparison:
Image
Note: The port maps are rough guides...not super-accurate, just for illustration purposes.

I hope you enjoyed that, and dont forget to draw reference from the RB20 post: http://scooterotica.org/forum/viewtopic.php?f=7&t=296

Cheers

Dan 8-)
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truls221
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Brilliant Dan!

A lot of useful information and a nice comparison!

cheers

Truls
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Another excellent write-up Dan, and some of the photos are the best I have seen taken in such a restricted space.

Well done
Martin
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damdam
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Great job mate ! :D
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Dimitrios_231
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The good thing with this kit,seems to be that inside city riding,
won't need gear changes :mrgreen:
RBG
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Are we going to get the threesome with the RB22 :?:
We all know you can do it! :D
stockcar
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an idea of rough RRP costs might help peeps.......certainly will the likes of me trying to get some bits together on a budget!! ;)

as for head/crank/etc what sort of specs will be needed??
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lambro63
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great info yet again dan, the format is brill....you should create a manual it would be a winner who needs cad cam systems to design any thing when your around...... with your pencil....... well done great photos
regards
big pete lambro63 (spiderman)
muttonjeff
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yes,yes, all well and good. may i ask for the kit back asap, also remind me,your not welcome in my shed with a camera. kits, for cutdownkevs wildcat,
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drunkmunkey6969
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muttonjeff wrote:...... also remind me,your not welcome in my shed with a camera......
I shall sneak in disguised as a 64mm crank, with a hidden webcam and leak the FOXHAT engine building secrets to the world! :lol: :lol: :lol: :lol:
See our YouTube scooter channel for Tech-help: https://www.youtube.com/c/TheScooterFactory/videos
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