Fuel screw, anyone know a fix?

[warren3200gt]

Got a set of Vm24ss fuel screw only carbs which have zero low revs fuel/air mixture control. Above 1500 rpm it'll run fine but low that its grossly rich. Standard 15 pilot jets. It had Tourmax fuel needles in when I got them (right in picture) , I swopped out for genuine mikuni (left in picture) and even have tried ebay shiters and regardless which are in them with the needles fully seated (closed) they still colourtune very rich.

So I've come to the concludes the bodies have been mullered previously.

Any sneaky fixes anyone knows.

[zed1015]

The "genuine" one on the left has been messed with and shortened with the tip incorrectly ground and the taper having bowed/rounded sides and not straight like the one on the right as it should be.
Most likely to fix a broken tip and you can see where the threads have been cut back and shortened when it's been done which was probably performed with a file while spinning the screw in a drill chuck.

Quality replacements of the correct profile can be found on ebay from seller bbrbri
https://www.ebay.co.uk/itm/123104873696

[warren3200gt]

Thanks Rob, bit I'm not understanding is the Tourmax ones will screw in and have a about 3 mm showing in the throat so closing the port off entirely yet they still show very rich on colourtune.

Also, are all vm fuel screws the same profile regardless of carb size?

[zed1015]

Spraying carb cleaner or similar up the pilot jet with the fuel screws fully closed will show if they are seating fully.
I presume the choke plunger seals have been renewed or at least also checked that they are sealing ?

[warren3200gt]

Choke seals you did and I sealed the choke pickup hole in the bowl to ensure no fuel was available for the enricher circuit.
I'll try some carb cleaner up the pilot with both screw types tomorrow.

[warren3200gt]

OK, float bowl choke pick up port blocked, fuel needle screw closed, (both needle screws tried), so in theory there should be no fuel being delivered, fired it up and still rich.
Carbs off, fuel needle screwed shut (again both needles tried), carb cleaner sprayed up the pilot jet and fuel sprays in the throat.
However, as the fuel needles clearly are not shutting got me pondering. The owner stated that a bike shop put Tourmax rebuild kits in them and as generic kits they contain all the parts for fuel screw and airscrew carbs. After digging out the "remaining" unfitted parts it suddenly struck me what the issue was.
The bigger airscrew springs had been fitted on the fuel screws and as a spring diameter increases as its compressed the spring was locking up on the carb body fuel screw recess bore prior to the fuel needle fully seating but giving the impression of it being fully seated.

Lesson to learn never take for granted the work carried out by previous, even reputable, agents.

[zapo]

Lesson to learn never take for granted the work carried out by previous, even reputable, agents.

+1 story of my life