OOOoooowwwww, that's painful, but pretty much what you were expecting.

Barrel and piston are off and with My Motors in Redruth. He's seeing if I may get away with having the cylinder honed then I can go up a piston size. The piston itself just needs a rub over with some sandpaper and a polish, then it will make a perfectly good ornament.

InMotion will want £175ish for a new piston kit. Ouch, indeed......You live and learn, I hope....

On 08/04/2017 at 11:01 PM, bashplate said:

OOOoooowwwww, that's painful, but pretty much what you were expecting.

 

Edited April 11, 20179 yr by netley
spelling mistake

Barrel had be re-bored and is now ready for re-assembly today. Just checked main jet in carb, 130. Is that correct?

Neil

130 would be very close, though you might want to try a 140 as well. You don't want to be any more than two steps leaner than a rich stutter, which on my 350 with the same carb is between 140 - 150 so I run a 130. It'd be a good idea to check a few other things out while you're at it, just to help prevent the same thing happening again. Eg. the ignition timing with a timing light, check for adequate fuel flow through the tap and filter and that an appropriate heat range spark plug is fitted. These engines will definitely preignite with a 5 on a long uphill or with prolonged full throttle riding, especially on a hot day. I won't use anything hotter than a 6. Make sure the exhaust isn't partially choked up and check that everything is sealed up nicely and that there are no air leaks, and don't be too stingy with the 2 stroke oil. Properly set up these engines will go a very very long time between rebuilds.

Edited April 22, 20179 yr by oldjohn

I think a 130 would be ok for normal trials use where the bike only hits full throttle for short bursts, but by the sounds of it the bike was being ridden more like a road/trail bike where it would be on the main jet for quite some time so I would definitely go bigger if you intend doing this style of riding - 140 /150. If you go too big the engine wont rev cleanly and will splutter on full throttle.

Yes, as you say more road/trials. When pottering around a field or when actually on a trial it ran fine but i was being stingy with the oil I used but no more. I think I'll leave it at 130 then as I won't do any more prolonged full throttle runs.

 

Sounding much better now, thanks for all the help and advice. See you on the Montesa page in a few days

 

 

The carb needs setting sounds abit rough.

Edited April 22, 20179 yr by bondy

1 hour ago, bondy said:

The carb needs setting sounds abit rough.

In what way. It wasn't warmed up. Perhaps it would be be better to warm it properly and then film it.

Sounds lean.

 

Edit: I don't know if this is of any interest to the OP or anyone else, but here's a link to a fairly lengthy guide to jetting that I wrote on another forum: Rookies Guide to Jetting

If anyone thinks it's worthwhile I could post it up here.

Edited April 23, 20179 yr by oldjohn

Did you put New piston kit in it? Regardless of that it could be a number off things timing have you replaced the crank seals? The Mikuni carburettor can be some times hard to set up. I've just not long ago put the o k o on my 199A runs very well straight out the box. Another thing witch is over Looked has the Exhaust been repacked? This can make a big difference to the running. of the bike my A has had full Engine rebuild by me con rod kit piston kit job lot runs sweet a lot only skimp on rebuilds then wonder why they don't run properly not saying you have just pointing it out.

59 minutes ago, bondy said:

Did you put New piston kit in it? Regardless of that it could be a number off things timing have you replaced the crank seals? The Mikuni carburettor can be some times hard to set up. I've just not long ago put the o k o on my 199A runs very well straight out the box. Another thing witch is over Looked has the Exhaust been repacked? This can make a big difference to the running. of the bike my A has had full Engine rebuild by me con rod kit piston kit job lot runs sweet a lot only skimp on rebuilds then wonder why they don't run properly not saying you have just pointing it out.

The engine was re-built a couple of months ago, new mains, seals and crank. I also replaced the carb with a Mikuni from InMotion uk and added electronic ignition. It ran well, as far as my very limited experience could tell. I used the original piston and, I am now told, cr4p 2stroke oil, sigh....

Just had it re-bored and new piston, rings, pin and small end bearing fitted.

This was just tentatively started and only ran for a couple of minutes, if that.

 

Just ran the bike around the block to warm it up and set the idle screw. How does this sound, any different? I haven't touched the exhaust.

 

 

6 minutes ago, sherpa325 said:

 

Sounds much "crisper" than mine.