LCGB Forums

Hello all. I’ve changed the air filter and exhaust on my Mugello 185. The old girl will now not tick over. I’ve looked at a few You tube videos and read some stuff but I still don’t actually understand jetting and what it does. Is it a jet that governs my tickover? Would someone be kind enough to explain ( in very basic terms) what each jet does, pilot, atomiser , main, the needle etc etc. What each does so I can understand what I’m looking at please??

Tickover on basic carbs is usually governed by the gap between the bottom of the Venturi (the round hole where the air enters) and the bottom of the slide. This gap is adjusted by the screw on the side of the carb. It simply pushes the slide higher (or lower), depending on whether the screw Is screwed in or out.

Yes, there are other things which change running at this engine speed, but as you have relatively minor changes to your engine, it can propbanly be corrected by screwing in the throttle screw a bit. You don’t say which carb you are using, but if you are using the SH carbs, the adjuster is on the top of the carb (RHS) by the cable.

If you want to learn more about how carbs work, find the Dell’orto manual on-line. It appears a bit high-brow, but actually it is a very simple explanation of how carbs work. What you need to realise is that carburettors cannot be simple AND deliver the correct ratio of fuel and air for ALL the different progressions through the rev-range. In order to do this, the carb has several routes to deliver the correct ratios. The Dell’orto book explains how their carbs can be fine tuned to deliver the correct ratio at the chosen throttle (side) opening.

I hope this helps a bit

Hi Knowledge. Thank you. I suppose I should have mentioned the carb! It’s a 28 phbh. I’ll try that screw. I’ve looked at the parts diagrams trying to understand what is what but they’re in Italian and don’t translate directly. I’ll try the manual. Thanks again

There used to be a very good site here:- https://bristollambretta.webs.com/30mmphbhjets.htm , well it's still there but it appears they need to put a shilling in the meter to make it work. Any of of you Bristol lot able to get this site back up and visible please.

Rich'