Mikuni RS leak.

Jota Rob

Jota Rob

Hero member
Location
England
Having cleaned and rebuilt my Mikuni RS, I was disappointed to see 2 of them leak fuel from the float overflow.

Stripped them carefully and despite minor wear on the float needle all were consistent, yet the leak was mostly confined to no.2 and to a lesser degree no.1 cylinder.

What I noticed immediately is the float needle body as slack as in all but noticeably no.2 carb. These hadn't been apart since new so I measured up the body, all the same.

What happened is the O ring has shrunk, flatted off and hardened. They all broke on removal. For now I've fitted new Flourine FKM O rings 11 x 8mm. It's easy to overlook the function of the O ring but it will give the same symptoms as dirty or damaged float valves.
 

Attachments

  • 20250727_173207.jpg
    20250727_173207.jpg
    75 KB · Views: 7
  • 20250727_170858.jpg
    20250727_170858.jpg
    88.9 KB · Views: 7
Happens all the time, Rob! Especially when left standing dormant for a length of time. Easy and cheap enough to fix though, I ordered the entire valve assemblies before noticing it was only the sealing rings.

piet
 
I guess that happens Piet. I just happened to wobble the brass body as I was about to remove it and thought " that ain't right".

I might have to eat my words if I still have an issue but I'm reasonably confident.
 
It's good information Rob, my Triumph 900 has been stood for ages and I have had persistent trouble with needle valves leaking. The carbs are a bastard to remove on those bikes as well but I'm going to have to do it once again.
 
Yes same bike, it's been sat in a container down in Portugal for ages, used to run like a train but the ethanol has caused havoc. It starts and runs but it will have to come apart and get new seals throughout the fuel system. I hate that job.
 
Shame they're a push-in design - prefer the Dell screw-in valve bodies. I'll have to have a squiz and see what the Keihin FCRs use. Good info to have in the recesses for future ref though, Rob.
 
And today going through boxes looking for carbi/brake bits I found a set of 3 o-rings for said float valve, Too bad I didn't find them a couple of weeks back when I had the carbs on my bench re-jetting etc.
 
I had same issue on trip to Club France rally couple of months ago, left hand carb over flowing when taps turned on, instantly stops when taps off as weight of fuel is cause of pushing past O ring (float needle working fine), rode 700 miles like this turning fuel off (forgot once and hydraulic lock) when engine off
Sprint Manufacturing in UK (used to make RGA Jota fairings) do Vitron seal kits (including the float needle tips) which I have fitted to all 3 carbs
 
  • Like
Reactions: pf1
You must log in or register to reply here.
Back
Top