Odd running on a closed throttle

[Swarfcut]

 A cheap inline filter will catch the bits and a short term swap to ye olde  transparent PVC pipe and you can see what's going on.

 Swarfy.


 Additional. Played with a non starting Stihl Chainsaw last week. The fuel line in the tank was happily softening in the fuel mix and closing up under suction. Looks as if our higher alcohol content  in the fuel is playing havoc with everything it touches. On my 2 stroke garden stuff I always drain the tank and run the carb dry before storage.....this guy hadn't.

[BSA500]

I replaced the pipes ages ago. The pilot jet was black and the wrong size(20 instead of 25) but it's been like that for years. It's just odd how it is always mucking about

[BSA500]

Not consistant

[BSA500]

Ok this is driving me mental. Forget everything I've said so far lets start again....

Bike starts fine and ticks over. Won't rev out very well a bit bogged down. Try to pull away tries to die/does die. Settings are pilot 25,needle jet 1065, main not an issue we don't get that far(270). i CLEANED IT OUT BEST i COULD UNTIL i GET SOME ULTRASONIC CLEANER SOLUTION,OH NEEDLE CLIP MIDDLE POSITION. Sorry caps lock. I haven't touched the mag valves only a small adjustment. Just I don't know I will order some new plugs as well. Help

[berger]

i think if it's dying under load i would be checking the spark generation side of things now

[BSA500]

Well I am going to replace the plugs first and see if that helps(cheapest option first). I had a quick look at the mag to see if there was excessive arcing,point spring touching bearing play etc but all good. Checked HT leads/plug caps/carbon brushes. Before I started the carb strip down etc she was running really well. Found a bent needle and eventually after a few dead ends found the pilot jet partially blocked with,what looked like,rubber deposits from the destroyed fuel line.

[berger]

well it sounds like you have a gremlin that needs finding by trial and error, i don't like gremlins when they get into the bike they take some finding and kicking out!!

[BSA500]

One step at a time

[BSA500]

OK no idea how it happened, we'll it was me. Set the needle on clip 2 not 3 duh. Now it runs what a twat

[Greybeard]

Yay! 😁

[Slymo]

What do the plugs look like? If they are rich perhaps you have the wrong cut away on the slide go from 3 to 3 1/2 perhaps or perhaps you need to lower the needle a notch. Lowering the needle jet will mimic raising the slide cut away but will result in an overall leaner mixture. The plugs are the windows to the combustion chamber (poetic  ). You say that the main jet is no problem and I accept that but can you rev the bike past the flat spot? if you can then it isn't likely to be the plugs or the spark if you can't then you need to look there too. I had a bike that had a similar issue and I only found out that the plug caps were leaking when I started it in the dark and saw the lightning from the plug cap to the tank. That was more of a miss than a flat spot though.

[BSA500]

Well since I put the needle clip into the right notch its alot better . Still needs fine tuning and the exhaust pipes are leaking and an odd vibration has appeared on the clutch side, so plenty to do

[BSA500]

Vibration turned nasty looks the the crank shims have given up, again