Monza carbs

Dear All,

I’ve got a Monza which is being recommissioned having not been on the road since 2006 and certainly not run for a couple of years before I got it. Valve clearances, compression test, new plugs, points, condensors, carbs cleaned all done etc.Â

What’s the best way of trying to balance the carbs as I’m having real problems trying to get it running at low speed and tickover on both cylinders. They’re both firing as you can take each plug cap off in turn. I’ve wound in the big screw and then back out 1 1/2 turns as per the manual but this often causes the engine to stay at a high rpm when you blip the throttle. What should be the standard set up for the smaller air bleed screw?

Any advice welcome.



ideally you need a pair of vacuum gauges connected to the inlet manifolds

but before you go too far check the choke cables and fee and not sicking

you can get 2 match sticks , one under each throttle slide stick out air inlet end of carb and carefully adjust the throttle cables so the both move togeather but its not ideal or accutate

set mine about 1.5 turns out as a base for the mixture

What part of the country are you in? I am in Staffs, and have a pair of gauges if you’re nearby.

Irregular idling sounds like an air leak. Idle screws could be leaking air down the sides, happens with age cos the threads get worn, but they can, and are supposed to anyway, have O-rings under the coil springs. HTH

A Gunson colourtune is a useful tool to assist this process.
All the above good advice also.

Where are you?
I have a pair of vacuum gaugesÂ
Used to have a colourtune, no idea what happened to it, maybe I will get another someday :bulb:


I am in Reading. One inlet manifold has a screw into which you could put a vacuem gauge but the other one unfortunately doesn’t so i don’t think I could go down that route unless someone has an inlet stub with one. I can’t remember of the top of my head which side it is but I’ll take a look.



Hello that’s odd ~ did you buy this as a “box of bits” ? Maybe your carbs don’t match either…

You should be able to get it close enough with fingers. Pull the carbs off so that you can get easily at both of them. Adjust the cables so that the slides clear the top at exactly the same time when the throttle is pulled wide open. Now let them drop and next wind out the throttle stops until they are clear. Next wind each in in turn until you see them twitch the slide.

Now with the carbs back on and the bike running wind them both in by the same amount until you have the tick over you need. Next turn the mixture screws back and forth until you get the best/fastest tick over. Then adjust the throttle stops again as required.
You can also pull a plug and do each side in turn whilst the other is dead.

If you’re struggling with this then there maybe something else is effecting the mix. Check for leaks around the manifolds, and check that the chokes (enrichers) aren’t being left on even a little. Over time the enricher plungers can get leaky on their rubber bases. New ones are not much money.