Mikuni RS36 flooding carb

Rob

Rob

Hero member
Location
Midlands, UK
I know Paul LeClair has experienced this issue and have re-read the many posts on this topic....!

Been working on my RGS.  Came to fire the bike up only to discover flooding centre RS36 carb.  Not had this problem before.  Bike has been parked with no fuel in carbs for last 3 months.

Tapped carb body in case sticking float to no avail.  Removed carbs and float bowls - all good and clean.  No contamination in fuel.  I operated floats and cut off air flow blown through the petrol pipe OK.  Float levels check out OK (17mm) Replaced carbs and still have overflowing problem on centre.

Any suggestions?
 
Is the little rubber tip on the float valve needle OK - not missing, damaged or contaminated with grit. Other possibility is a non-floating float. Perhaps you could try weighing the floats to see if the centre one is heavier. Also make sure there's nothing restricting the float movement.

Other than that, I'd suggest a bit of experimenting.

Sit the carb on the bench and feed fuel to it, try tilting to the angle that it sits on the bike and see what happens.

If you have a spare bottom plug for the float bowl, drill and tap it for a hose spigot, and fit a bit of clear hose so you can measure the actual fuel level. See whether they're the same on all carbs.
 
I suffered from this and the float needles were worn. They don't have rubber tips...

Keith replaced them for me on my recent visit with my other carb trouble. The trickiest bit was to remove the float pins. They are held quite firmly in the pillars, but these are apparently quite fragile if you have to drift them out be very careful!

--
Dick
 
VanguardontheLav said:
I suffered from this and the float needles were worn. They don't have rubber tips...

Keith replaced them for me on my recent visit with my other carb trouble. The trickiest bit was to remove the float pins. They are held quite firmly in the pillars, but these are apparently quite fragile if you have to drift them out be very careful!

--
Dick
Click to expand...
Yeah, put a socket behind it to support the mount,everyone knows that dickhead
I was the dickhead and I speak from personal breaking experience.....
 
Thanks Dick - have spoken to Allens Performance (www.allensperformance.co.uk UK Mikuni agent) to order new float valves (part no N149.040-2.8 ) and associated o-ring which comes separately.  Apparently not regarded as something needing replacement due to wear, but don't like sitting unused for long periods. Needle marks valve seat because its sat in one position.  Use it or lose it!  :D 

Found an alternative cheaper supply (www.nrp-carbs.co.uk) of a pattern part by Keyster but decided against it - repeated fighting with the airbox rubbers is losing its appeal!
 
Have similar issues with the Keihin FCR if you drain fuel before you store the bike for longer. From now on, I will leave the carbs with fuel in there, just drain it before I start the bike next time... also the paper gaskets dry out which can make the float bowel leak fuel...
 
Hi Rob, the Miks on Clyde have flooded a couple of times, in previous years.
The first time it happened, i stripped them down, found nothing significant to cause it to happen. Replaced nothing, re-installed and they behaved for another year until the 2014 rally down at Bello.  Uncle Ven fired up Clyde to depart for BrisVegas and the carbs, (or carb?), started flooding again.  Buggar!! 
So, i got on and fired Clyde back up again, still flooding, and leant it as far as i could to the left side and revved the crap out of it, and then leant it over to the right side and repeated to rev the crap out of it.  When i got Clyde vertical again the carbs had stopped flooding and have not flooded again after nearly two more years of use.
When i handed Clyde back again to Uncle Ven he said that's what he has also done to one of his bikes with Miks and it worked as well.  :D

I've become suspicious of turning the fuel on, while it's still leant over on the side-stand and without the engine running.  But have no further data, so it remains just a suspicion.
cheers,  Mark
 
Interesting - thanks Lothar & Mark.  Came to a similar conclusion as you Mark - went out to balance carbs 'just for the hell of it' whilst awaiting new float valves....and no drips from overflow pipe!  Going to go out and give the bike an airing to see  what's what.....
 
Rob said:
I know Paul LeClair has experienced this issue and have re-read the many posts on this topic....!

Been working on my RGS.  Came to fire the bike up only to discover flooding centre RS36 carb.  Not had this problem before.  Bike has been parked with no fuel in carbs for last 3 months.

Tapped carb body in case sticking float to no avail.  Removed carbs and float bowls - all good and clean.  No contamination in fuel.  I operated floats and cut off air flow blown through the petrol pipe OK.  Float levels check out OK (17mm) Replaced carbs and still have overflowing problem on centre.

Any suggestions?
Click to expand...

Hi Rob

yes, then in a ham fisted moment of "tapping" the center carb float bowl I put the brass punch right through the side of the float bowl and had a much bigger flow of fuel to deal with........  ::) ::) "fixed" with JB Weld  http://www.jbweld.com/  which has held up quite well for the past couple of years.

the Mikuni carbs still leak from time to time, in fact they are off the RGS again at the moment waiting on yet another set of float needles/seats and a new set of floats..... :o

be wary of fuel flowing into a cylinder and creating a possible hydraulic lock situation. Good luck on the repair.

Paul LeClair
 
I well remember that tale of woe, Paul.  Thanks too to Dave & Cosi for the reminder about fragile pivot posts.

Had a chat with a fellow Miki user and he advised tapping carb body is fraught with hazards - it's a delicate casting.  His suggestion was to let the slides drop under spring pressure from WOT as being an effective way of stopping dripping overflow.  Have just returned from a good blast that reminded me how good a decent RGS can be .... and guess what - no dripping overflow to be seen.  8)
 
and here is a photo of how to remove the float pin in question
do not try and punch that pin out without supporting the lower post

to install I just use a set of Multi-Grips at their widest setting and squeeze the pin into place



 
For what it's worth I had a lot of odd problems with the RS's on a GSXR1100 on alky in the 2 seasons we ran it here.
Due to the water collecting tendency of the alky, I was stripping the bank of carbs every meeting and flushing/cleaning with petrol. One thing I did which I'd do again on a set used on petrol was to drill into the ends of the main fuel feed gallery on the outer carbs. Tap 6mm and use a screw as a seal. After use, pull the screws and flush/blow across the gallery...You clean off the mesh dome fuel filters doing this.
Never had a problem with the float needles or floats.

I blame Cathcart for the throttle vacuum sticking problem which cropped up. Scrutineering for the NZGP meeting, I'm pushing the heavily modded GSXR, Cathcart had a Ducati in the line. He gets talking and asks if we'd had any sticking probs with the RS's...Up to then NONE....after that, yes, had to add some synth 2stroke oil to the mix. Bugger. Later in the meeting after Holden had won the GP and set a new lap record, I told Cathcart it was his fault as Robert hadn't been able to slow down...
 
Doesn't take much to stop them seating the tiniest bit of residue from when the fuel evaporates and their compromised. ( just look in the bottom of a set of float bowls that the fuel has evaporated out of )
So makes sense re Mark's suggestion. Even dropping the bowls out and "flushing" some fuel through may help.
Good side seeing Mark man handle Clyde from side to side lucky for him that Clyde didn't decide to bite him
Re-driving the float pins out yes definitely take heed of Red's advice and support the underside.
Good thing about  FCR's is they don't have that set up to remove the pin.
 
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