Yamaha SR250 - A clean standard build

I like your tail light choice.

zap2504 said:

You should drill the wire hole a little larger and use a rubber grommet to keep the wire wrap from chafing away.

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Good call! Thanks for reminding me of that

Welded the holes up and had a go at tapping out the dint - didn't go so well but I think it'll buff out

I'm going to blast it and powder coat it black so I'll get away with using a tiny amount of metal filler anyway.

You want that metal stripped and super clean. It makes a huge difference in the weld. Sometimes with a dent like that, you can hit it with a torch to get it to pop out instead of planishing. Regardless, it's a lot of soft tap tap taps.

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+1 on the clean. Get some good hand files.

deviant said:

You want that metal stripped and super clean. It makes a huge difference in the weld. Sometimes with a dent like that, you can hit it with a torch to get it to pop out instead of planishing. Regardless, it's a lot of soft tap tap taps.

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Very true. I would usually sand/grind back to bare metal and especially remove the rust. But you know some of those afternoons you just cant be arsed and just wanna get it done in 15? Welding with gas is also a bit more forgiving in that sense too - more so than TIG where it likes to be cleaner. It was popping a bit though!

Good tip with the torch on the dent though - forgot about that one. Might have saved me some tap tap taps!

I got the first off-tool sample of the seat foam from my supplier a couple weeks ago and although it was good quality and looked great, it was a little too hard and a little undersized - when I referenced all the dimensions with my drawings. They hadn't accounted for enough shrinkage in the mould (I think they calculated for 2-3% and it ended up being 5-6%). So a couple weeks later, they had made a new tool (at their cost) and sent a new sample with a slightly softer compound as well. Now its perfect!

Now just waiting on the tooling to be completed for the plastic base and the metal fastening parts production order to be completed

Looking good! I'll be moving back home soon and would be so happy to see it live some time.


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Seat looks great!

Spent some time in CAD the last few days 'cos I got inspired from getting these foam samples. I thought I could possibly design another more 'cafe' style seat for the SR while still using the same base construction. This would mean only one new tool, rather than 2 new tools to get a new design completely. I think its workable. The idea is that the classic cafe 'hump' is foam and makes up an even portion of the whole seat so it can be used as a pillion seat - like a lot of the wrenchmonkees seats. Just because for me personally, as much as I love riding solo, the joy of taking your mrs on a ride is too awesome to not include a space for her on the back

Thoughts?

Thought I would post up the way I was intending the intake bellmouth to work with an existing K&N filter. There is just enough flex in the lip of the filter to be able to push in the bellmouth and then position it in place with your finger while you tighten the clamp. Once the clamp is tightened, you push the whole assembly over the opening of the carb and screw it in place with two set screws. Now just waiting for quotes to make it in aluminium from my suppliers.

I just put together the filters and air box velocity stacks for a CB750 K to do essentially the same mod, also I fond a set of UNI filters with the bellmouth built in.

Dirty carbs don't make sense, must be a third party reseller.

Tune-A-Fish said:

also I fond a set of UNI filters with the bellmouth built in.

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Do you have a link for that? They sound sweet. Or are these the ones in the pics? Are the red things just adapters for different carbs?

I found them on eBay searching for UNI's for CB750

why not run a velocity stack inside the filter ? does that make too much sense ?
but yeah that big beautiful k&n she's got some belly on 'er, a pot (pulp fiction ref)swallering a stack ,no issue,.thats all

xb33bsa said:

why not run a velocity stack inside the filter ? does that make too much sense ?
but yeah that big beautiful k&n she's got some belly on 'er, a pot (pulp fiction ref)swallering a stack ,no issue,.thats all

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I bought these to do just that mang!

A little dirty but you get where I'm going

Tune-A-Fish said:

I bought these to do just that mang!

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Looks awesome!

I'm on holiday in Australia, hence the lack of workshop activity. It has however left me with dangerous pondering time...

What if I designed a bracket that allowed the re-positioning of the ignition timing pick up unit - which is fixed from the factory. Might sound stupid, but I have read and heard that if your old engine is down on compression - say up to 20psi, you can add advance to get the power back up and not run the risk of detonation (because of the lower dynamic compression). Then I read a whole lot of hot rodding stuff and many guys run about 14-15 degrees of initial advance (then you have the curve on top of that). See the attached table (ignore the dyno graph) of different pulls with the different ignition settings.

I looked up the SR timing and it is fixed at 10 degrees BTDC with a 2 degree either side tolerance. I calculated in CAD that by moving the pick up 6mm along its mounting arc, the advance could be increased or reduced by roughly 5 degrees. Because of the CDI controlled ignition it would have an effect on the entire rpm range based on the pre-programmed (un-controlable) advance curve.

Anyway, it will be a fun exercise to see if there is any noticeable difference in power or throttle response. Then it could be cool to be able to retard ignition slightly if ever there were to be a boosted application ;D