Hi All

Looking for some advise please...MY 1985 TY 250 Mono starts ok and would run ok, however, it keeps "hunting" and pinging once it gets hot...I have decoked the piston and exhaust, and even fitted a Mikuni carb to see if that makes any difference, but the same thing happens with the Mikuni as it does with the original Yam carb..

I've done all the other usual stuff like new plug and made sure both carbs are clean and using fresh fuel..

Does anyone have any ideas What I can try next?

I had similar problems back in 1990 when I had one,mine was cured very simply by using a larger main jet.Ran very well after that...

what is colour of plug if checked when ran up to problematic temperature ,, it does sound like it is running lean which will also cause hot running adding to the problem

I took the carb to pieces again and gave it another thorough clean with carb cleaner, but this time I used compressed air line to blow out every nook, and cranny of the carb and the jets..

Put it back on and it appears to be much better..I need to give it a good run first though befor I am happy that this is the cure...fingers crossed..

From experience, when the bike is just up to normal working temperature and it starts to 'hunt' and or 'pink' more than usual, this is symptomatic of the crankcase seals are beginning to fail. It is usually not the carb giving problems! This can happen without warning, quite suddenly in fact.

I thought I would update my post that I submitted sometime ago!.It may be of some use..not only to TY Mono owners but also to owners of "old" 2 strokes!!

 

Anyway...after doing the usual carb clean, new plug, new air filter the bike still would not run properly....So I had a chat with Mr Birkett and the first thing he advised was to decoke the entire exhaust system...I had previously tried caustic soda to try and clear it out, but he advised the only way to properly clean it is to cut open the exhaust...

 

Starting with the backbox ( cos I knew I could get an aftermarket replacement)Using a standard hacksaw I carefully cut off the lip that runs around it...As you do so you can see the two halves of the exhaust, and once you have removed the lip all the way round the backbox simply comes apart and in my case revealed 30 odd years of black oily carbon sludge! In fact It was so bad I 'm surprised it was running at all...and I ended up chucking it away and getting a Sammy Miller replacement.

 

Using the experience gained cutting the back box open, I used the same method to cut open the middle box and this too was completely cacked in black oily sludge..Inside the exhaust there is fibre packing too, so trying to decoke with caustic is NEVER going to work. It took me several hours to clean the crap out and one by one unblock the perforated holes in the baffle with a drill bit.

Once it was completely clean I repacked with fresh packing and took it to my local welder who welded it back up for me...

 

The bike now sounds crisper and runs so much better, I also replaced the standard Tekei carb with a Mikuni VM 26 from a Beta Rev3 and now it runs how it should....So in summary if you want to decoke your exhaust the bestway to do it IMO is to cut it open, you'll be surprised just how badly blocked they become...

 

 

 

 

 Nice read, but the best way to clean out a steel exhaust system is to burn it out. Granted you need a place with no neighbors close by. Once you get it started at one end, just feed it a small amount of oxygen. You can see it`s progress as it works it`s way through. Does not work with aluminum, though I have done it.