1980 Z500 carb emulsion tube "O" Ring replacement etc.

[linuxrob]

About 20 odd years ago at around 69000 miles I fitted a spare set of carbs, which had done around 20000 miles to the Z. I was having an issue where the bike would stumble a bit just off idle and slow speed running. This I found to be the emulsion tubes getting oval due to the needles. The needles were fine but had worn the brass of the emulsion tubes to a point were the hole was slightly oval shaped and causing a rich mixture as the slides started to open.

 

You can see the ovaling more on the 3rd from left which is the worst one.

 

Apparently MK1 1200 Bandits do this too and a repair kit is readily available. The MK2 1200 Bandit I have has done over 61000 miles now and does not seam to have this problem (Yet) They have different carbs to the MK1.

These Z500 spare carbs with unworn emulsion tubes have done approximately 11000 miles since then and until last year have worked faultless. I removed the plugs at the end of the riding year 2021 to pop some oil down the bores for winter storage and noticed No3 plug was a lot blacker than the rest, No3 must be either running rich or flooding a bit. The float heights were checked using the clear tubing method and were perfectly in spec, so, investigation was required. My MPG was down to 60 - 65 to the gallon and I put that down to the age of engine parts and the modern E5 fuel.

Before the start of the 2022 riding season I removed the carbs and gave them a good inspection. All looked well until I noticed the “O”rings round the base of the emulsion tubes were a bit hard. I ordered some 5mm I.D. X 2mm cross section area Vitron "O" rings from a UK supplier and when fitting them No 3’s tube “O” ring was very hard and snapped on removal. Possibly a combination of ethanol in the fuel and the fact that I drain the carbs and tank fully at the end of the years riding, this draining may not be a good idea as the seals may have dried out too much even though I pop some GT85 in after draining.

 

 

 

The other “O” rings of concern are the air screw adjuster’s these are 3mm I.D. X 1.5mm Cross section. They are still very pliable as they are not subject to any fuel.

 

These are the spark plugs after 300miles running with the new “O” rings.

 

 

The fuel used has been exclusively Shell V-Power E5 and speeds of around 55 – 60 mph on A roads.
Air screws are still set to STD. 1 and 1/8th from fully in and ignition timing also STD. The bike is now averaging approx 75 MPG which is only 5 MPG lower than it did 35 years ago with std Unleaded fuel and a lot less miles on the clock. Engine response is excellent and smooth.

 

Next time the Bandit carbs are off I will fit new emulsion tube "O" rings and see what happens.