megaphonitis

Anything to do with motorcyles
Post Reply
125H
Posts: 56
Joined: 30 May 2018 18:36
Location: Loughborough UK

megaphonitis

Post by 125H »

When I bought my 125H the silencer was in poor condition, actually rotton inside with holes coming through.
Being over budjet on the restoration, I did not want to buy a pattern silencer at around 240 Euro so opted for a short megaphone instead, perhaps not my best decision, but it looks the part although there is nothing inside it. I am sure I read somewhere that a 125H would not run correctly without the right exhaust system fitted and although I appreciate Morini's are a little different to BSA, Triumph, Norton 'etc' would not have thought that the exhaust would make that much difference. Back in the day we were always changing exhausts and silencers without any undue problems.

So if anyone knows if there is any truth in the matter, please let me know, what system is everyone else running on a 125H?

Regards
Leonard.
Steve Brown
Posts: 1244
Joined: 12 Nov 2007 23:44
Location: Leicestershire

Re: megaphonitis

Post by Steve Brown »

I think you'll struggle to find many others with the same model let alone with a modified exhaust. Anyway in my experience an open mega won't help the running and will of course be a lot on the loud side. A little back pressure will help the running for sure. You could try making a pepperpot type muffler inside the mega by extending the down pipe inside it. For instance with a single and no other cylinder pulses to worry about, I would extend the down pipe about 80% of the length of the mega. Blank the end of the down pipe and then drill a number of small holes through the side of that extension. You won't actually need that many holes, I do a rough calculation to work out how many holes equals or slightly exceeds the same area of the (previously) open pipe. It will reduce the racket quite effectively and give a sensible amount of back pressure.
Reading some of your other posts I see you have a number of challenges with that bike! Hope you get it sorted as it would be nice to see a 125H on the road. :)
All donations to the rest home for old Camels, Leicestershire.
125H
Posts: 56
Joined: 30 May 2018 18:36
Location: Loughborough UK

Re: megaphonitis

Post by 125H »

Hi Steve,

thanks for the input, its worth considering if I cannot get a result as is, there is actually a plate which fits over the mega held on with a T piece and screw, sort of a gas diffuser, but it does not seem to make any real difference to the tickover . I will probably remove the exhaust or just the mega to see what happens with out it, if that works then it looks like I shall be doing the suggested mods or getting a pattern silencer from Italy (more expense).

I appreciate that 125H's are quite rare in the UK and from reading other posts others have had slow running problems and of course there are little or no resources that can come up with a definative answer. I did note that the exhaust and plug are sooty but the mixture screw does not seem to lean this out, I have ordered a number 43 pilot jet to try as this is also reccommended by some.

Its not safe to take it on the roads, behaves like an old Binks racing carb all or nothing!

It a shame really I am really pleased with my restoration - problem is it does note work!

Reagrds
Leonard.
Steve Brown
Posts: 1244
Joined: 12 Nov 2007 23:44
Location: Leicestershire

Re: megaphonitis

Post by Steve Brown »

OK, this may be something you've mentioned and tried before but I can't remember it all-and in so many places too! Ref the lack of effect of the idle mixture screw-the pilot jet is worth a try as you are doing, but also the 'progerssion' drilling needs to be checked and clear. It goes 45 degrees up and forward from the vertical idle drilling. Same as on Amals too. Then I recall you mentioned float height but have you checked fuel level? That wants to be something like 5 or 6mm below the float bowl joint face. I have found some where the float appeared correct height but the fuel level was out enough to mess things up. Lots of folk adjust things rich in the hope that too much fuel fixes a different problem. Lastly though, quite a few are now finding that a larger throttle slide cutaway helps with modern fuels in the same area that a smaller idle jet can cure problems with decent pick up. Also found that with Amals too! Sooty plugs you mentioned made me think of all these things. Air filter blocked by a mouse nest maybe? :D :wink:
All donations to the rest home for old Camels, Leicestershire.
Post Reply