125-200cc I seized her again...

The fuel is about the only thing you listed that would make it do it.

did that rod get there already?!

Yep the rod arrived yesterday and was setup within 10 minutes Seems much better, thanks again for that!

Clutch side bearing seal changed yesterday and intake area all re-sealed, ill see how it goes when I take her out today...

Scratch that, the rod's worse and I'm done.

Think I'm just gonna toss it to the back of the garage at this point and move on. I'm getting nowhere, the bikes only getting worse the more I change and I'm starting to get frustrated enough to do damage.

Both main bearing seals were done and I bought some RTV gasket maker and done the intake - no difference noticed really.

The MS3 rod isn't so great... It certainly hasn't solved any problems and now the bike is just too rich all over the place, four-stroking no matter what I do really - I simply cannot get it to rev out clean! The top end is like some rumble jumble affair, the mid is just constant four-stroke. The only thing I can get right is the idle. Been at all ends of the PJ from 1 turn to 3.

I don't feel like I had these issues with the 3-2M. I think if anything I'll just put that rod back in and ignore the detonation, or maybe even my old carb.

Before you say "leak-down test" or "replace x" I'll have you note that I'm SERIOUSLY reluctant to spend any more money on the bike at this point let alone a £100+ leak tester. I'm on the lookout for a crutch boot, PVC cap and tyre valve and I might do it then!

So there you go. If any of you are ever over this way you are welcome to take a look at it!

Shit thats not good, yup throw it in your shed an forget about it till the winter then start over with new vigor.
Sorry we havent managed to sort the issue out between us all.
Fair play to you for trying everything suggested.
Im going to be in the isle of man over x-mass if youve got mates near or any ones going similar time i will gladly have a look at it.

If it's detonation from crap fuel a couple gallons of AV gas or race fuel will tell you and then you can either buy better fuel or possibly get the cyl head re-cut for the crap fuel that you are using. There is a lot to squish band on a 2 stroke, I think Walt hinted that direction. You have tried most of the least expensive suggestions except fuel. You will have to tune it a bit with the good fuel to know if it solved your problem but at least you would know. Detonation is more likely in a lean situation but it can still happen with a rich condition and retarded timing if the compression is greater then the fuel can handle. This situation (high compression with crap fuel) killed about every 1960s muscle car engine that tried running on the crap fuel in the mid to late 1990s in the USA.

what settings did you try the rod at?

This is indeed something I have been considering, I'm looking into where I could get better fuel though. I was thinking about trying 98 octane but I'm almost sure all you can get around here is 95. Avgas could be a possibility, theres an Airport quite local to me but I'd need to make some calls and figure out if I can just grab 5 litres in a can..

I was really thinking this was just an air leak lol.

As for the fuel, would an "octane booster" such as Silkolene Pro Boost be of any benefit?

The thing thats blowing my mind right now:
Yes the seal looked sketchy, yes I had some hand-cut gaskets on the intake side but even after everything I've done, the detonation hasn't changed. Surely changing the squish clearance would have made a change to the detonation?
On the other hand, I could be just plain dumb and missing something else!

Well, correct me if I should do it otherwise but I set it up like this:

• Engine already warm
• Idle set at 1.5 turns out
• PJ at 2 turns out
• Rod installed at 49.5mm
• Start the bike, it started no-choke and sat around 3400rpm
• Higher idle than desired so I adjusted the rod richer (two quarter turns) to get idle at 2300rpm
• Throttle response seemed acceptable/normal

I messed around with the PJ quite a bit when I found it to be four-stroking real bad and all round misbehaving... I think I maybe went as low as 1 turn out and as high as 3 turns out. Approaching and up into the powerband it just wouldn't rev out cleanly, lots of breaking up/stuttering etc. Richening the PJ seemed to help up until a point but didn't really fix it and going leaner didn't help any.
Obviously I was highly frustrated at the whole affair and probably wasn't thinking so much but I've calmed down considerably since earlier so I'll probably mess around more tomorrow

Harley with the MS3 you can close the pj right down to a 1/4 to 1/2 turn so dont be affaid to go leaner .
Is that lectron fitted with the short pj tube ? as the long one is not really suited to ms3 as it starts to come into use way to early.

PS If al else fails pop the carb into the post to me and I will set it up on a 125 and post the thing back to you.

Take johnyboy up on his offer!

Solid advice, I went out today and screwed the PJ in to 1/2 turn out and it was immediately better by miles! Gave me a little lift for sure anyway so thanks for that.

Thanks for your offer but I think im close enough now to be happy. Next think on the list is to try some better fuel.

I have heard of the squish band shape causing problems in cases where piston dome shape is changed or if someone has modified the head for max power with race fuel and then they switch back to pump gas. The width and shape of the squish band makes a big difference. Older GasGas bikes have a stepped head with a domed piston and some people use the GasGas piston to up the performance by putting it in an engine that a flat top piston used to go... or the opposite and replace the dome with a flat top but either way usually requires machining the squish band. I only mention this because when you buy a used bike you really have no idea what has been done by previous owners.

Just another take on the situation.

is the sound you hear really the sound of detonation?

if you have leeway on you piston bearing or play in the piston pin in the piston you might have similar noises

Did you check if there is play in the con rod, piston pin to the con rod, and the piston pin to the piston?

Robert-Jan

All checked in the last rebuild (when it seized at the beginning of this thread). Piston, rings, pin and bearing done.
Con rod and lower end had no play and still didn't when I added the other base gasket.

Only other thing it could be is the chain hitting the swingarm but im pretty confident thats not happening..

Just a thought how good is your exhaust sealed and are the springs fresh? I ask as i noticed a distinct banging sound as im flic flacking from side to side and im 73% sure its my exhaust moving in the cylinder outlet.

Springs and o-ring are good and the exhaust is mounted well, but thanks for the suggestion!

Dag nabbit!

Sorry, i must have skipped - what was the reason of detonation their?

This was a while ago now, Im still certain I diddnt hear any detonation sound but if I remember correctly I did find that the crank seal on the stator side was leaking air. Replaced both seals, retuned as detailed above and have been using pistons from HTM Racing. The Makita pistons I was using were junk! Full top end on there now from HTM although I have a new bike now and so this bike doesnt get tortured as much now.