Scooterotica

anyone using a vhst carb ? ,I need a few jetting details. set up is cast 175 with a very good tune, fresco under kick start exhaust, 28mm vhst. would like to know

slide
main
idle
needle/atomizer

currently has a 55 slide, 130 main, 36 idle and 60 choke, this is how I got the carb , float valve is 300 and I have drilled out the fuel inlet as this looked a bit small. cant read what's on the needle will have to fetch my magnifying glass home .

starts ok from cold and hot so choke is ok . but I am struggling to keep it ticking over so I guess I need to go up on the idle may be 38 or 40 as its not far off. on the road its perfect i.e. no bogging , pulls nice and clean from a lowish speed in top gear right up to full chat. but it seems to be running week . last week on the way back from Cleethorpes it nipped up , heard what I thought was my new weld on damper brackets that where in the tool box rattling then it nipped. back wheel locked but when I heard the rattle my hand was already covering the clutch leaver so no real drama. let clutch out when I nearly came to a stop and it started back up. when I got home I took the panel off to see if the carb was loose or the hose was split. but both where ok. I started the engine a watched the slide whilst working the throttle. the slide was going up and down but revs were staying high. I went for the kill switch and the engine carried on going , so I clicked it into first with the brakes on an stalled it. so I checked for air leaks, which there where none. fuel supply is good . any ideas welcome

The symptoms you describe are symptomatic of an air leak somewhere.

What's your plug colour like?

The 55 slide is the weakest. I have used 50 slide, not cheap. I have tried several times to set this carb and it still runs lean when shutting off the throttle. I never got it to tick over successfully. I like the size of the carb, small and does pull cleanly. However, I have finally given up with it. I hope you have more luck.

Simon

I tried a vhst when they first came out. I couldn't cure fuel starvation probs.
I drilled out all fuel passages, even tried a 350 float valve.
Maybe they're meant to run with fuel pumps?
It was a shame, probably the best carb i've tried, but I could only open it up for short periods.

defo no air leaks so i can only presume its the slide, might bite the bullet and get a 40 slide as its ok when flat out , but even i cant ride everywhere flat out . seems to be worse up to half throttle when warm. when flat out it would not matter what slide you have as its lifted up out of the way . will have a look at the needle/atomizer combo when i get home, oh and will take top end off to see how damage was done when heat seized.

ordered a 40 slide from dellorto should be here tomorow. hopefully this will cure it

update. after a bit more carb twiddling and then off to a local club meet which I did not make it to, lost compression about 8 miles into the run. when I got back home and strip down of top end I found the head gasket had cracked in two places and ring peg failure on the piston (high quality gomez ) with half of the lower ring missing . plug was a nice colour and no damage to the cylinder , no signs of excessive heat and piston crown and head nice and black . no bits of ring in crank , it must have fired it out of the fresco

atomizer is a 269
needle is a d41

Ive seen the pictures Simon

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