Rieju RS3 50 2012 non starter

[unfitforpurpo...]

Ok, got the new carb, a dellorto phbg.

It was going well same as before, great above 5_6000 rpm, and would idle but with idle screw (not pilot screw) almost right in.

I think I understand it's not the right way to do it, but the needle was on the top notch/clip so I've bring it down to 3 (from top/richer).

It has some pull now at the bottom end and great still up high but when it transitions it's crackling and will slowly die at idle. I haven't pulled the plug yet but it smells rich idling in the workshop and I'm pretty sure there is almost twice as much smoke as there should be from the exhaust.

Also the idle pilot screw makes little to no difference.

I'm after a bit of advice as I'm thinking to rip it all apart and put new gaskets and seals right through it, but guess I'll still have to tune the carb?

I know I'm capable and have the gist of what's going on but don't have the experience of petrols and 2 strokes to see the pointers intuitively

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Here lies the problem when people start pissing about with fuelling on 2 strokes. Jetting can be incredibly difficult to get right when you start modifying the airbox and carbs etc. Is the airbox exactly as standard, or modified/pod filter etc?

Can you not put fuelling and airbox all back to standard and just up the main and pilot jets to suit the bore kit, then start from there?
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[Feathers McGraw]

PHBG 21 should have W7 needle and 262AU atomiser.

Put needle clip on 4th notch down.

Start with 50 pilot jet, 110 main jet, and NGK B10ES plug.

Rich fueling prevents overheating.

It may sputter at full throttle. Reduce main jet size until it stops sputtering.

[Easy-X]

Maybe take another look at how carbs work?

There's a reason ppl say "throttle wide open" to start with. You have maximum fuel and air input with the minimum number of involved components.

Fuel (main jet size) + air (carb diameter) + restriction (airbox and exhaust)

So even in the simplest test there are plenty of variables!

After that the pin height determines the base amount of fuel the main jet can chuck out. Therefore if full throttle is good but mid-throttle is bad that's when you'd start looking at the pin.

The pilot jet dictates a base level of fuel added to the system regardless of slide/pin position. With the pilot jet you rarely need to worry about restrictions (air in, exhaust out) because when the slide is down only a little bit of air is allowed into the system - so small that the airbox is unimportant in the equation. By the time the slide comes up and airflow is important the proportion of fuel is trivial in relation to that coming from the main jet.

The mixture screw should effectively be a fine tune of the pilot jet but granted if you can't find the sweet spot for mixture you might consider a different pilot jet.

Finally the idle setting is the baseline throttle. Want 1200rpm? You'd turn the throttle. Release the throttle, what do you want it to go back to? (i.e. the base throttle setting) Just the minimum to keep the engine from stalling and then a touch more.

Now whether you start with getting the idling right or the full throttle is unimportant but you can't do anything about the mid range until those two are right.
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[unfitforpurpo...]

Thanks so much for the reply,

I do jobs that no-one else wants to do here happily, chasing down hidden break in a wire in a loom full if white wires on a 14metre coach and the like, mind numbing stuff that I love chasing down, but I just don't yet have the experience to know intuitively what to go for yet on a 2 stroke carb so this should really help.

Thanks for taking the time to reply with a full explanation. I'm short at work this week and family stuff so prob Friday night before I get another bash at it now. I'll see if I can find out what jet sizes it's currently got in the meantime.

Cheers

[redeem ouzzer]

[Easy-X]

[unfitforpurpo...]

You tried, I get you, ha

[unfitforpurpo...]

Ok, finally! Some positive noises.

I ordered a 50cc piston and barrel, and fitted it tonight, thought I could get away with doing it in the frame, but halfway through changed my mind. I know I was being proper lazy, but...

All done and tried bump starting it.....

Then I put fuel in.... and away we go. Hooked the jump pack up to the battery, and only takes 1 revolution and shes purring.

I literally have not touched the carb yet since starting it, I put the needle back to the top notch (lean) before I put the barrel back in but that's all I've done to that.

I will take it out for a ride tomorrow morning and see how it pulls, what adjustment etc it may need.

I guess the 70cc kit that had been fitted to it just didn't agree. I took the previous owner at his word that it was running fine and just started playing up (seemed like a decent bloke).
I'm happier with running it at 50cc anyway for my lad as it was quite pokey for what it was when you hit the right rev ranges.

Thanks very much to you all for your help, and I hope that your advice here will help someone else in the future.

Heres hoping tomorrow goes straightforward.

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