Nc30 poor run off idle, foul 1x plug

[Icemaestro]

So further on this - pulled off carbs that had supposedly been ultrasonicly cleaned balanced and services by a mate at the bike shop...left side pilot screws were completely turned in - will that effect the carb balance now that I have set them at 2 1/4? (Accounting for the half Yamamoto loud system).

Next q - jets were stock jap at 115f and 118r - shall I change to 118f and 120r while everything is out?


Next there was crap all through the carbs (if I don't need to get it re balanced as per above ill clean I think as then only me to blame


Lately I pulled the rear (brand new 300km done plugs) left slightly blackish but clean, right covered in red - petrol I assume and quite black - assume because it isn't firing at idle (had been idling just before pulling the plugs)...

[bikemonkey]

I'd clean them to get rid of all the crap.

And yeah you'll need to balance them

[Icemaestro]

So to bring this one up again..i haven't taken them off again for a second clean, but have confirmed that the no 3 is the problem at less than 5-6k rpm, but does fire intermittently above 2k. Above 7 is sweet. Vacuum hose to no 3 is fine (as fuel runs, and good auction from the end when I take it off the fuel tap and crank engine), I have oem rvf rubbers on the way.

The plug is definitely getting fuel, as when I pull the plug it has red fuel over it. I have a nice blue spark same as the left rear cylinder, so it's not coils. My question is - given the improvement with throttle, could this be related to compression? Ie check valve clearances (haven't been checked for 20k, but expensive)

Or is it definitely down to air leak (though wouldn't this get more lean as I open throttle) or blocked idle jet? And should I be looking to replace needles? (A guy on here has rick o road ones fs). I will also check floats when I get the new carb rubbers in, as I read they can affect the run off idle...

[Icemaestro]

They appear to be balanced just fine when all cylinders are going ... Forgot to mention - choke does absolutely nothing for it (? Due to the fact it's running on three regardless, again pointing to no 3 being rich at idle and boggy with throttle until 7k), and is a nightmare to get started from not-warm (due to it starting on 3 cylinders).

[Neosophist]

Do you know what carb balancing is?

The balance is only to get a smooth idle, it wont affect the carbs when the throttle is opened.

To get a smooth idle connect vaccum gauges and do a proper balance at approriate tempeture.

Without cleaning the carbs properly, checking the float heights and pilot screw settings your just wasting time.

If these are all set properly the bike will idle fine.

They need removing, good clean and check jets / needles / tubes / floats are correct.

Next you want to make sure they are seated right and your valve clearnces are not widley out of spec, then balance the carbs and it should run perfect.

There are many circuits on the carb, to control slow speed / mid rpm and what not.. you have dirt in them as they are very fine.

[Icemaestro]

The workshop guy who supposedly ultrasonically cleaned the carbs and replaced all the seals etc also balanced them on the bike, and didn't make a difference, which at that point is when I took them off again and found crap all through them. The tank has been cleaned so didn't come from there. I checked and set the pilot screw settings when I had them off, and I had cleaned out all the pilot jets (which the holes did look a little small). You talk about many circuits, am I missing anything that I can/need to clean?as want to get everything done this next time I have them off.

I wouldn't be comfortable doing valve clearances myself and don't have vacuum gauges to check balance yet again, but I guess if I have to fork out the cash I'll have to (bike ships here charge an arm and a leg for those two things on a vfr, 500$ or so I have been quoted 3x), hence why I want to make sure I get everything possible checked and done before doing that (esp in light of the fact they were already supposedly balanced). Hope that makes sense?

[Neosophist]

where are you located?

the jets screw into small passageways, you need to get high penetrating cleaner for carbs in there to disolve any varnish and blow them out with compressed air.

the number one failure of not being able to clean carbs is failure to unblock the passageways that the jets feed. You need a proper high penetrating carb cleaner to disolve blocked crud and compressed air to blow them clean.. many ordinary cleaners will struggle to clean well.

[Icemaestro]

Auckland, New Zealand. By passageways they feed, do you mean the emulsion tubes? Or a matter of taking the pilot jets out and cleaning where they sit? Last time I took the jets out, soaked in carb cleaner, sprayed through and used small wire to clean the holes, as well as clean crap out of the carbs , set the pilot screws and put them back

[Neosophist]

if you look the engine side of the carb butterfly you will see 3 small holes, these come from the pilot circuit.

where the pilot screw and slow-jet screw into the carb there are passageways drilled through the carb body.. if these are blocked up even a clean jet wont help.

some carb cleaner and compressed air will blow them out often.

[Icemaestro]

Thanks, will do that next time they're off