250 rebuild from bits

[Parker3865]

A newbie so apologies if issues have been covered before. I have bought an unregistered 250 v in bits and am slowly piecing it together. I have got it to the point where I have the engine in the frame, battery and ignition connected. I have purchased a Horse Power Ignition set for it.
So question 1; has anyone experience of this equipment, was it plug and play as the instructions imply?

I am at the point where I am trying to start it. When it does start (brake cleaner in the carbs helps to boot start it) it does not want to run at low revs and small throttle openings. I suspect the carbs (it might be ignition, see que 1). [Thanks to a previous thread where I read about the link pipe needed on the vacuum take off pipes]. Standard jetting apart from a 260K atomiser, but not running an aircleaner yet. I have had the carbs apart and cleaned them, but only carb cleaner and blowing through
Question 2; Would they benefit from ultrasonic cleaning AND any suggestions for why it might not want to run a low revs/small throttle openings?

Finally I keep a record of what I have done on youtube, it may amuse: https://www.youtube.com/@richardparker679/videos

[72degrees]

Have you checked the idle jets for crud and correct size? Ultrasonic cleaning won't hurt though the VHB carbs don't have as many nooks and crannies as some. Check the idle mixture screw as an o ring and washer. Running without air cleaners won't help. Have you tried winding the pilot fuel screw out a bit?

Bad low speed running could be ignition related. I have no experience of the Horse Power ignition. On standard setup the ignition winding is the first thing to check.

[Parker3865]

Thanks for the suggestions. I have o rings and washers in place, about 1 1/2 to 2 turns out on the idle adjuster; have gone as far as 4 turns out.
Ignition runs direct from the battery (12v conversion) so should be fine. Am waiting for a new strobe so I can check when it is firing.

[72degrees]

Does it need one 'choke' (starter jet open), two or none to start? If none then it could even be over rich. Not possible to do a plug chop, but do the plugs look white or sooty?

Ignition timing being out would not help, but so would a 'weak' spark. Then that might make starting at all very difficult.

There has to be a logical explanation - presumably it has good compression?

[mbmm350s]

Hi Robert,

Nice to see a 250 being saved!

These bikes should have VHBZ 22 HS carbs sometimes these come with different idle mixture screws - long tip and short tip.
I have 6 of these carbs 2 with short and 4 with long.

As 72 degrees says the long tip type will need to be further out, if the idle mixture screw has no effect then for sure clean out the idle circuit.
After cleaning bath, I use carb cleaner and squirt through the passages to make sure they are really clear.
There is a tiny hole engine side of the slide make sure cleaner squirts out of there.

whilst this won't affect the idle 260K atomisers aren't going to work for the 250 2C, which uses the unobtainable 260 BR
so this 260K needs to be modified (open out the holes) to have larger holes lower down.

Not sure i would try too hard on set up until I have air filters, do you have the airbox?
The air filter is the same as a 500 and a reasonable reproduction is available from Mdina Italia

Cant help with the horse power ignition I am afraid, was original igntion system lost/broken?
With the original ignition 250s are not usually difficult to start, and idle very smoothly,
and are not sensitive to ignition timing for starting.

I say clean out the idle circuits and fit an airbox as next steps.
good luck

cheers
Mark

[Parker3865]

Thanks for the ideas.
I have some 260BR on order. Not sure which idle screws I have, can they be measured or is it obvious? (found the dimensions on Eurocarb, will have a measure).

I have the airbox, many hours designing and 3D printing out the airbox to carb connectors in TPU. Will get an airfilter and try that.

Have compression tested it and had good figures on both cylinders.

The bike came minus any ignition system, so needed something complete. Mdina's system was too expensive for me and the horse power ignition system seemed to fit the bill, but am wondering now!

As I said bike came in boxes, all the important parts there, but nothing to put it together. Missing lots of fixtures and fittings so trying to attack it in stages...
Its Richard, by the way!

[mbmm350s]

Sorry Richard, no idea why I put Robert?
I watched your videos very good well done.

The engine running video seems very familiar
I had 250 that was difficult to start and wouldn't idle below 3000 rpm it was cutting out on one cylinder, turned out to be ignition related. But that was another non standard ignition system.
Also the choke fuel passage up and beyond the choke jet was totally blocked made starting hard.
You should be able to modulate the revs with the choke levers as the so called choke is actually an auxiliary or bypass carburettor with slide and main jet.

Mark

[Parker3865]

More jets ordered from Eurocarb; will see if these have an effect? Mine had very long mixture screw, so I'll see if a 'standard' one works.
Again many thanks for all of the suggestions.

22 Dec 2022;
All jets back to standard, fuel gets into engine. So I am guessing it is now an ignition problem. Have had to ordered a new strobe light, so will see what the timing is when this arrives.

[Parker3865]

So latest update; Carburettor back to standard jets. Waiting for cleaner fluid so I can properly clean them in the new ultrasonic tank I have bought.

In the meantime the front cylinder developed a squeak, like it was very dry, and the engine was a little difficult to turn over. So I thought I would have the head and cylinder off to investigate. Apart from being obviously used, they don't look in too bad condition. The barrel will need a hone to clean of the rust that has built up from the engine sitting about for so many years unused. HOWEVER I pulled on the piston and am getting a nasty clonking from the big end. So it looks like I am going to have to take the engine apart to find out what the damage is. I have taken the rear cylinder and barrel off, they appear to be NOS, and the big end is fine.

Anyone got suggestions for sourcing the big end bearings and are there any hints/tips that will make my life easier?

[72degrees]

Oh!

Big end. The good news:
'Half bearings'
350 - 25.03.07
250 - 25.03.07

Undersize (after crank regrind)
25.03.08

https://www.mdinaitalia.co.uk/M250307.html

The bad news.

When I rebuilt my 350 the conrod eyes were oval. I had the last set of new rods from NLM (back in 2016) - though they had 'good used ones'.
12.04.02 (early 350 and also 250 as far as I can tell)

Fingers crossed.

https://www.mdinaitalia.co.uk/M120402.html

I've never parted the cases on a 250 so no specific tips I can give.

[Parker3865]

Again, most helpful, thanks.

I think the main difference between the 350 and 250 is the 250 has a wet clutch. Otherwise looks much the same to strip (although not mentioned in the 'blue book'). The 250 2c handbook looks to have lots of details about rebuilding it as well.

[mbmm350s]

Hi,
Doesn't sound good, couldn't you hear the big end knocking when the engine was running?
I think that you should check the oil pump and pressure relief valve, because there could have been or still is a problem with oil starvation.
The crank oil ways and sludge traps must be cleaned out.
You can refer to the 125/250T for primary drive noting different number of plates. Clutch springs are blue painted.
Make sure to use the user manuals torque settings because they are not all the same as other models.

Take care of all parts removed specific 250 parts are very difficult to obtain new.

Head gaskets 59mm aluminium are presently unobtainable, you will need to reuse after annealing, dont use composite gaskets.
Other gaskets are common to 350s even primary drive gasket.

Mark

[72degrees]

Hi,
Doesn't sound good, couldn't you hear the big end knocking when the engine was running?

One youtube video does mention a noise Richard hopes is just tappets.

I have a nasty feeling my 375 engine is suffering big end issues. The vibration levels last time I rode it are certainly worse than I remember (perhaps just relative to the Husky 401 ). Then I confess it is long overdue for an oil change. May have to swap the rebuilt 350 unit back in and perhaps exchange the top ends while I am at it. Can't face parting the cases on both to swap in the L5 cam.

On the 250 that became the last Forgotten Error, I did investigate the clutch and primary drive side before I sold the engine,as the kickstart was not returning properly. You guessed it - the spring hadn't been 'wound up' properly last time it was assembled. Evguru video to the rescue.

[Parker3865]

Yes I did hear the knocking, but chose to ignore it and got side tracked on other things. Live and learn! Thanks for more useful info.

[mbmm350s]

I feel your pain,

I watched your youtube video, given the incorrect head gasket* and missing circlip,
I would not rate the previous engine rebuilder with any confidence.
So double check everything - especially the orientation of the 2nd gear!

circlips should not be re-used. These are same as 350s.

I suspect the green seal (or black tube replacement) on the oil pump has been lost/dislodged

*Moto Morini reused the part number in transition from composite gaskets to Aluminium gaskets,
see ATG381 for more information.

Mark