I have put my MC18R5 back together and am experiencing a problem which I hope someone can help with.

If I run thru the gears up to approx 11000RPM and button off..... then wind the throttle back on I lose power briefly ...feels like 4 stroking both pistons. The longer I leave the the throttle shut the longer it takes to clear. Opening the throttle fully helps clear it or waiting longer on part throttle eventually clears it as well. Seems OK charging thru the gears or cruising.

The rear of the bike is semi splattered in black fluid from the cans (not sure where this is coming from, perhaps the rebuild, gearbox or simply too much fresh mixture finding its way into the pipes) .

I don't seem to be losing any gearbox oil although the test drives so far have only covered 40-80km. Idle is perfect after a carb rebuild. Bike has just had the crank rebuilt with new bearings and seals and I have stripped it once already to check I haven't crimped or damaged a seal after the first rebuild although I put the same seals back in and used plenty of Threebond 1104. Perhaps I damaged the seals the first time.

Have checked the TPS and solenoids against another NSR handy and they seem OK with a meter.

Am I right in assuming that if the right hand crank seal is gone only one cylinder would be affected?

Carbs are set up completely standard and I have the airbox mod with JHA cans otherwise standard.

Any Thoughts?

How have you mod'ed the air box?

The MC18 is very fussy with the size of hole in the lid.
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If I have to take the carbs off once more...

I put 4 x 20mm holes at the front of the airbox lid, but the problem predates the mod by a few days.....both plugs show dark brown.

it sound to me like your running a little rich my mc18 does it too.

Took the airbox off yesterday and went for a run....much better but still there, so will try rejetting the main and get adjustable needles in there as well.

The other plausible theory is flooding from the float valves at high revs due to vibration but not at idle. I'll be surprised if its just a jetting issue but we'll see.

Plug still reads dark with no airbox.

Check your carbs,chances are that they could use a bath

Kostas Dee I have rebuilt the carbs and thought I had been quite thorough but you never know I suppose. I have a spare set at home I rebuilt so will try these.

Stephen what do you recommend for the MC18 in terms of airbox lid cutout?

Swapped carb setups today along with the TPS and no change.

Have arranged some new float valve needles so will try these next week, assuming both sets of carbs have faulting float valves...... not impossible I suppose.

Will have to try to source another PGM2 to try.

Really feels like it is flooding on a closed throttle at high revs....very weird

I have picked up some float valves to install this morning and the seller had a plausible theory on what might be happening. He thought the emulsion tubes or 'needle jets' might be worn and letting fuel get past on a closed throttle causing the flooding at high engine speeds.

Happens a lot on the old 900 Kwaka's apparently.

So my problem now is parts availability. I have seen the NSR carb kits on line from cruzinimage

Admin: eBay link removed as per forum policy.

but have my doubts on quality. Can anybody point me in the right direction for a supplier?

or Keihin parts list for the TA21a?

I got one of those kits and as far as I can tell it's the same as the oe bits I replaced. Plus it was dirt cheap so I just used the bits I needed rather than sourcing all the parts individually.
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it wouldn't be fun if it was easy!

Thanks Dunkenb thats what I needed.

What was the problem you were trying to address?

My float valves needed replacing and they were silly money from Honda so thought I may as well replace the lot!
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it wouldn't be fun if it was easy!

These are the needle stacks from my Carbs. The theory is that this is where the fuel is getting past on a closed throttle which seems to be a complete explanation for what is happening on bike. I will get my float valve supplier to see if he can find a match for this lot next week. He said a lot of the Keihin stuff was shared.



I noticed on Yahoo Japan that the MC21 needles together with the piece that sits on top of the emulsion tube and the clip are available as a set.

Will these work on the TA21A carbs?

And after I pay OKShon fees and shipping its silly money ....is there an alternate supplier?


Check parts marked '3'

I have my doubts about your worn needle/atomizer theory.
Have you checked your float levels?

Yeh I've tried 2 sets of carbs that I supposedly checked the float level to 13mm on and it doesn't seem to leak fuel from a wonky float height. We thought this originally as well but its only flooding on a closed throttle from high revs ie not at standstill or charging thru the gears.