93 Super Rat idling issues

[edo1400]

Hi All
So I finally finished putting my 1970 93 Super Rat back together and started it for the first time today. It started after the 4th kick with the choke on and run, albeit with some throttle. However once warm I turned the choke off and it just would not run or restart without choke, it did start again instantly with choke. I adjusted the mixture screw to one and a quarter turns out and tried again but it wouldn't start without choke despite being warm. I did get it to idle nicely with the choke on however as soon as you turn the choke off the bike revs up and stops?
I have fitted a brand new NGK 10HS plug as per the Super Rat specs, however I realise this is the coldest plug and the motor did have a near new NGK 8HS fitted when I bought the bike so not sure if the cold plug is causing any issues? I am running premix 25/1 with Penrite semi synthetic motorcycle two stroke oil.
Any suggestions gratefully accepted!
Cheers
Edo

[thrownchain]

I’d clean the carb out and check for proper jetting.

[ossa95d]

You are describing classic lean symptoms. Hopefully it's just a clogged pilot jet, but it could be anything that introduces more air or less fuel.

[Bullfrog]

Here are my recommendations.

1. Disassemble carb. Re-clean the pilot jet AND pilot jet PASSAGE/TUNNEL , , , AND pilot air PASSAGE/TUNNEL. It sounds like your pilot circuit is not working. This is a common situation. The pilot circuit has the smallest jets and passages in the carb. Be SURE that you prove that carb cleaner squirted in "here", comes out over "there" (the other end of the passage).

2. Has your engine been pressure/vacuum tested? ALL two-stroke engines MUST be airtight. If they are not airtight, they will draw in extra air thru the leak. This will make them run lean - engine damage WILL result.

3. Install an inline fuel filter. Steel fuel tanks which are half a century old are notorious grunge sources.

[edo1400]

Hi Guys
Thanks for your replies I will definitely pull the carb and check all jets. Absolutely run an inline filter even though my tank is clean it's cheap insurance! Thanks for the prompt reply and advice I will let you know how I get on.
Cheers
Edo

[edo1400]

Hi Guys
So I stripped the carb and found blocked primary jet also found an air leak at the inlet manifold as the o-ring was hard and needed replacing. The bike now starts second kick needs virtually no choke and idles perfectly with excellent throttle response it is also smoking a lot less as it is running without the choke on!
Thanks for the help very much appreciated!
Cheers
Edo