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Chickened of on the rebuild. I am packing it of to Benjy Straw so it can be sorted by a man who knows his stuff.

Front calipers rebuilt. Seals and pistons from Gemini Karts (https://www.geminikarts.co.uk/product/g ... r-pistons/) . Pistons needing turning down from 18mm to 16 mm. New pads from EBC. Any suggestions for re-furbing the brake disc? Chrome has pitting and rust on it. Remember from my 3 1/2 days (1980s) that the disc worked much better once the chrome had worn off.

That´s my expierience too. The brakes get better with the chrome off. They don´t look that nice after having been parked in the rain. But after three times braking they are better the less chrome they have (my expierience).

I would try to pass steel wool with WD40 or stuff like that and then clean it with brake cleander spray. Give it a try. Normaly the discs will be ok after a very short time if they are not realy damaged.

Just an update: Life has got in the way so little progress in the intervening time!
Engine rebuilt by Benjy Straw.
FYI; Tried a 500 airfilter and it does not fit for me!
Have been trying to start the engine and the same as before the rebuild.
Have tried the HPI system and managed to get hold of original pickup and trying it with cheap Vespa type transducers. With I seem to get a good spark, and using a strobe it seems to happen at the right time.
However I don't seem to be getting wet plugs either, which suggests to me the idle/choke circuit are not working properly. Both cylinders though, seems unlikely both carbs would be faulty?

Does it need the airbox and filter installed to draw properly? I have had other bikes and they start without either, even if they do not run properly.

I’ve no experience of the 250 but certainly with the 350 It’ll start with/without an airbox even if it doesn’t run great without. A spray of coldstart down the carb mouth is a good way to rule out carb or ignition issues.

If you’re not even getting a pop then:

Are you absolutely certain that the pickup isn’t 180 degrees out?

Has the flywheel been remagentised?

Have you got a decent resistance reading on the green wire from the stator?

Pretty sure I have the pick up timed correctly
Do not know about the flywheel, is there a way of testing it? Iron things stick to it!
Resistance at the green wire just below 200Ohms.
Thanks

Hi

Hopefully it will be a runner soon.
Probably you already considered these points, but in case there was something missed.

Tried a 500 airfilter and it does not fit for me!

It, if its a genuine 500 filter, will need to be filed a little to clear the posts or it wont sit properly, but it will fit.

Certainly engine will run without airbox.
250s are no different to 350s
If the engine is really dry and its brand new some oil squirted down the plug holes may help to get the compression.

Definately need to check that rotor is not fitted 180 degrees out, check with TDC on front cylinder compression stroke and rotor magnet cut out faces to the rear which is the pickup for front cylinder (standard pickup)

Generator 200 ohms is low end of what is considered acceptable. Flywheel will hold something like a 22mm spanner

Scooter coils will need ignition retarding because scooter full advance is only 18-25 degrees rather than 34 degrees, try retarding the ignition. Yes I mean retarding!

Plugs should be wet, you can emulate the old ticklers by giving the carbs a good shake.

Hope this helps

Mark

If you have a good spark, then as Tom and Mark say, it might be in the wrong place. You could try quickly swapping the pickup connections round. The problem with a 250 is that the unequal HT lead lengths make that less easy. You should get some kind of reaction on just one cylinder that you can swap though.

I suppose both carb idle circuits could be gummed up after a long time unused. Well worth giving the carbs a good clean. A drop of juice down a plug hole might be informative, or a squirt of Easy start.

Hi, Just was reading and think you are trying to use a 500 air filter housing. I might have a 250 one and I need a 500 box. Maybe we could help each other out. I will look at my parts and check if i have another 250 one if you want. Good to see another 250 done.

Thanks for all of the advice very much apreciated.
A little oil in the cylinders seems to have helped suction/compression.
I have an airfilter and transducers coming from Ian Lucas and will try again when I have these. Getting so frustrated I am likely to break something if I carry on! So have walked away and will come back to it next week.
Bedfordowner: I have a proper 250 2c airfilter housing, sorry I have mullered the 500 filter to see if I could get it to fit.

Sadly Ian's transducers seems DOA. BUT oil in the cylinders has definitely worked. Got it started today using the blue transducers. Woo bloody hoo!
Mark: can you explain why the ignition needs retarding if the transducers don't give enough advance at 6000? I would have thought to advance them. Thanks.

Hi,

Glad to hear it runs.
Brand new bore and/or rings will take some time to bed in and give good compression.

Mark: can you explain why the ignition needs retarding if the transducers don't give enough advance at 6000? I would have thought to advance them.

Scooters advance earlier - the controlling resistor inside the transducer is larger (480 ohms) than standard for 250/350 (68 ohms) ergo the scooter reaches its full advance much earlier at a lower rpm, the scooters full advance setting would be typically between 18 and 25 degrees, so scooter ignition advances earlier and reaches maximum earlier. Its not that the transducer doesn't give enough total advance, in fact the scooter transducer has less advance range.
The uncorrected advance is too much for the Moto Morini engine at idle and would be something like 48 degrees at 6000 rpm if you set the pickup to the same static position as you would have with the standard transducer setting. Therefore you need to RETARD the ignition by moving the pick up. Some people have found that the static setting is too high even to enable the engine to start, but typically if uncorrected the revs will hang up on the throttle opening and there will be a deal of overheating. Trust me, if the ignition setting hasn't been changed then just retard the ignition by about 5mm on the pick up by rotating the pickup in the same direction as the rotor travels. Then check the full advance dynamic setting for 6000 rpm ANT1 (though probably best to wait a few hundred miles )
I am assuming of course that during the engine rebuild the arrow of the pickup was realigned with a mark made on the casing this is the default position.
We have been using Scooter type transducers since 1990s with no issue whatsoever.

For further checking of suspect transducers you can checkout the Youtube videos of Paul Compton. On there he demonstrates a simple circuit that anyone can make that shows whether the thyristor inside is able to switch. You can measure the secondary coil resistance it should be something like 7.5K ohms

hope that all makes sense
Mark

Mark, very clear. Thanks for the explanation. Some re-timing to do on the ignition then!

So finally almost all together. It runs and I have had a naughty ride in our cul-de-sac just into second gear. Temp seat while I decide if I am going to have a go at re-foaming and covering the seat myself or pay for someone else to do it. I am collecting the mudguards next week from my friend who has been doing the tinwork paint. A few more little jobs to finish, things to refurbish, all the things that take far more time than you realise. Now to start trying to get it registered.

Looking good, soon be out there!