It lives!

[Itsme]

Hi All

Well I have had the MM running on petrol. But not with any great consistency, sometimes it will start and sometimes not. Either way whenever it did start there was no tickover. I have tried everything that you have suggested and everything I know but the result is that I am no nearer a solution than I was months ago.

I have the Inazuma which I am happy with so rather than spend any more time or cash on the MM just now it is going under a cover until inspiration or enthusiasm strike me again.

Thanks for all the help but time to move on.

Ian

[Moto63]

Today.... is a sad day
Today... the MM has been put under a cover in the corner of a dark n gloomy garage (when Ian turns the lights off anyway) possibly never to see a stretch of tarmacadam again 🤷
At least you gave it your best shot Ian!! Who knows you may just come to enjoy the inazuma given a bit of time and hopefully some sunny ride outs in the not to distant future 🤞🤞
Cheers, Michael

[Itsme]

Thanks everyone. Michael you have a talent for sympathising and yet inspiring me to keep looking for possibilities. The MM is currently 'resting' but fear not I already know that I just can't totally abandon the little brute. I shall take a break and enjoy Newzuki the Inazuma for a while but I will re-visit the MM soon.

Ian

[Itsme]

Hello all

J thought a quick update and a question were in order so here is the latest on the Mighty Midget.

After, using fresh fuel and fitting a Chinese carb specified for a GN250 I can now more-or-less get a consistent start, even though there is some 'chugging' to get a start if I have left it for a few days. If I get the motor warm  it will happily tick over and stay running for as long as I want. BUT there is a huge flat-spot just off idle that will bog the motor down and cut it out and although once properly warm it is possible with a little throttle juggling to get the engine past the flat-spot so that it revs high with no problem. I have checked the float height and it is fine.

To me this would seem to indicate that the needle is too rich, but what do you think?

I'd be grateful of thoughts as I just don't want to leave the MM when I am so close to getting it back to full health. At the moment i am taking a wee break from the bike as a) I have the Inazuma and b) it is my wife's birthday on Friday and I have a small metal work project to finish for her as a present.

Grateful for any advice as ever chaps.

Ian

[iansoady]

If it's just off idle then it's usually the cutaway at fault (too weak ie higher number) as the needle - in theory - doesn't start to take effect till the throttle is opened further. I tried a Chinese carb on my Tri-Greeves and it worked quite well but had to bodge it around a bit.

It might be worth trying a richer idle jet. I have a small selection (for Mikuni VM22) as well as some main jets if they would help - no further use for them.

[Itsme]

Hi Ian

Thanks for the info and the offer of jets (another thoroughly nice TC chap is Ian). I am having a break from the MM, but when I get back to it I will let you know if I need anything.

Thanks

Ian

[Itsme]

Hello All

After exhausting my tiny brain with possible faults I finally got round to buying a compression tester and I think I really have found the problem now. The tester read a high of 75psi which as far as I know is way too low. So it will be an engine out job when I have time and a look for a stuck valve, debris under a valve or even the demise of my cheap Chinese piston rings which have done about 3000 miles.

Anyway it is a job I will get round to eventually, but at least I have a definite idea now of what I'm looking for.

Ian

[Itsme]

Right this time I really have found the problem! After finding the compression to be so low I decided to strip the top end of the Mighty Midget's motor and have found that one of the exhaust valves (four valve head) has a piece missing! A small piece has broken off from the edge of the valve, there is evidence of some minor dimpling on the front of the combustion chamber where the piece must have hammered around a bit before exiting out of the port. I haven't stripped the valves out yet, but I expect the seat is damaged as well.

When I rebuilt the top end last year I noticed that the valves were looking a bit tired so don't think anything too nasty has happened, I think they were just worn out after 30 years and 51,000 miles. The rocker arm contact pads are very worn as well though the cam is still in excellent condition as it runs in an oil bath.

I know a small, local engineering place run by a chap who is into his older bikes so I will pop in to have a word with him about the cost of a head re-build. It might cost a bit, but as I said to my wife it will be cheaper than buying a new bike and I really do love the MM so it would be worth it.

Ian

[iansoady]

Sounds good Ian. If one exhaust valve has failed it may be a good idea to change both?

[Itsme]

Thanks Ian, I still haven't decided what to do with the MM, but I have found a complete set of second-hand valves on ebay for about £25 so if the valve seat on the broken valve has survived I might just buy them and renew all of the valves. Obviously it will depend on me being able to lap the new valves in if the seats are ok.

This would be one way of getting the MM back on the road as cheaply as possible, but it might not be the right course of action in the long run. There are lots of little niggles that really need addressing and now, whilst the bike is apart seems to be an opportune time to do them. There will be a cost implication, but as I said in my previous post any outlay will be far less than if I were to buy a new bike to replace the wee beastie. Besides which I am really getting into the Inazuma, it is quick enough, handles well now I have it sorted and is very reliable and easy to run. No it doesn't have the 'character' of the MM or bikes like it, but maybe just for once I could be tempted by a summer of trouble-free getting to places and enjoying riding. Long-term it will have to go as it still upsets my knackered shoulder, but hey ho why not make hay whilst the sun shines!

Ian

[Itsme]

Just a quick update. I looked again at the valves on ebay and they're not worth buying. The exhaust valves have been ground flat on the faces and three of them seem to have two collet grooves rather than the correct one.

The search goes on.

Ian