Scooterotica

Scoot always start first kick from cold. goes well while riding.
But, if I stop for say 5 minutes, turn engine off, fuel tap off. Then it will only start and idle at full open throttle.
after say approx 3-4 minutes it clears up and revs upp.

Had this issue when I used a dellorto phbh28. changed to PWK28 but the issue is still exactly the same.

Engine is a mbgm RT195 with a mbgm clubman, piston ported, i.e. no reed. BGM stator DC. Both carbs tried with filter. Filter used is a foam type, Ramair.

Any takes?

Prepare for it to be a stuck piston ring; typical symptoms.
Hopefully it's something less dramatic like CDI or LT coil.
Try a different spark plug first.

Always thought it was flooding but when both carbs showed this symptom I started to suspect some other problem might cause all of this.
Are stuck rings possible here? Do they actually get unstuck after a while since the behavior here is that my scoot clears up after, say may 3 minuter of wot on the stand. (It chugs and chugs until it clears and revs pick up).

Thought that stuck rings meant fatal breakdown.

When you say you turn the petrol off, do you turn it off before you turn the engine off? Your symptoms do sound an awful lot like spit back which is very common on tuned non-reed motors. The fuel needs to be turned of maybe 10 or 20 seconds before you stop the engine and not turned on until the engine is re-started and always keep the throttle closed when kicking it over.

Rings stick due to piston seizure which is not really likely with a ceramic bore, you would notice a loss of compression and cold starting would be difficult too.

My RT200 sometimes does the same and it's definitely spit back. As I've got the jetting closer this doesn't happen so often now. Butt if I brake heavily and stall it will. If I stop for petrol say, I'll turn the fuel off and burn a bit off before shutting down the engine. It will then usually kick first time before turning the fuel back on.

I had the same issue on my scoot a few years ago running a PWK, and it was indeed a flooding issue. It wouldn't start at first and then with WOT it would just start and catch and sit there chugging very slowly for a while and then suddenly rev up as the flooding in the carb cleared. Whenever I stop now, I blip the throttle and turn off petrol and then switch off ignition.

I'd also add that I gave up on the remote filter as well and now run a Ramair filter through the side panel. This is not always an option I know but it definitely helps...

Well, I probably shut the scoot off before I turn the fuel tap to off possitoin.

What amazed me was that
- from cold it start directly, good compression chocke out a short wile only
- If i shut the ignition off and on directly It kicks with no problem
- It's only when it stays of for between 30 sec and approx max 10 minutes that this happens
- On my Dellorto this happened with the remote Ramair
- on my pwk I use a marchald foam filter attached directly on the carb, no remote rubber hose
- I do run it with 4% as Im on my first 100km
- I do use a BR8ES plug

Ill try to use a cooler plug and remember to shut fuel of 30 seconds before scoot ignition.

Anyone remember if the pwk air screw is IN to richen and if it should be 2 turns out max or 3/4 of a turn max?

Cant help with yout problem but I never turn my fuel tap off, except when i fill up, but i use it everyday.
Rt225 with small mb filter, phbh28 and denso 27 plug

I am using same carb; 225 in high state of tune and sometimes I forget to turn the petrol off when we stop or when I park up I'm the garage and I NEVER have an issue.
Having to turn the petrol off is indicative of another underlying issue such as poor float closure. Turning fuel tap off before you stop is just masking that failure.
Did I understand correctly; are you using choke?
I still stand by my "rings" as a possible cause but I do really hope it is simpler than that. Good luck.