Motocarb
telephone 0151 924 5383
10.00 - 17.30 Mon - Fri
or
email   sales@motocarb.co.uk
  • Home
  • New Carburettors
    • VM Carburettors >
      • VM22-133
      • VM26-8074
      • VM28-49
      • VM32-33 left
      • VM32-193 right
      • VM34-168 left
      • VM34-275 right
      • VM36-4
      • VM38-9 >
        • VM38-9 low fuel inlet
      • VM44-3
  • Parts
    • VM26 - VM44 Parts
    • TM Parts
    • TMX Parts 35mm & 38mm
  • Conversion Kits
  • Conversion Manifolds
  • Mikuni Main Jets
  • Mikuni Pilot & Air Jets
  • Mikuni Throttle Valves
  • Mikuni Jet Needles
  • Mikuni Needle Jets
  • Adapters & Connectors
  • Cables & Adjusters
  • Chokes / Starters
  • Yamaha TZ250 / TZ350 / 750
  • New Replacement Parts
  • UFO insert
  • Contact Us
  • Returns
  • Blog
  • engineering work

Boring carburettors

21/2/2019

0 Comments

 
Picture
Recently received a set of 4 x VM34 power jet carbs from a TZ750 for UFO fitment.
The customer told me they had been bored out to somewhere around 35mm.
At first inspection, it was obvious there were problems.
The boring job looked like it had been done concentric to the original factory bore.
Because of this, metal had been removed at the bottom of the bore which would otherwise provide the bottom edge seal on a closed throttle. You will see from the photo that with a closed throttle, the slide sits quite high. This would stop the carburettor from achieving a fully shut throttle and may leave it with an “idle”. 
Overboring if there is enough metal to do so, is normally done slightly high to retain the sealing edge at the bottom of the bore.
The point of us machining the body after fitting the UFO is to make sure the slide sits down properly on a closed throttle. It is not possible to do this if the metal has been machined away.
 
The second problem relating to the overbore is the amount of fresh air slipping down the sides of the slides as there isn’t a sealing surface there anymore. You can see this quite clearly by the light shining through at the sides of the slide.
The diameter of the slide in a VM34 is 35.5mm. The same slide is used in the VM30, VM32 and the VM34. You can see if you bore the 34mm version any bigger, it will cause problems which cannot be addressed.
Unfortunately, I couldn't fit these carbs with UFO’s for the reasons above. The carbs are probably not usable in the condition they’re in. The bodies are probably scrap.





​

0 Comments



Leave a Reply.

    Steve's Blog

    Occasional entries of interest, links, information and general ramblings.

    Archives

    November 2022
    May 2021
    April 2021
    June 2020
    February 2019
    November 2018
    March 2018

    Categories

    All

    RSS Feed

Copyright Motocarb 2014 | Website by RC