NC29 pilot screw setting/fuelling problem

[Bonzo]

Hi all, I need a little advice with regards to the pilot screw setting on my NC29, after a thorough carb strip and clean.

Everything is standard on the bike (can, air filter, jet sizes). I have set the pilot screws as per the Haynes manual, 2 and a quarter turns out and now when on part throttle, the bike feels like it's running out of fuel, like when you go onto reserve! It starts, ticks over and picks up much better than before I stripped and cleaned the carbs, nice and crisp. It's just when pootling along at 40-50 mph on part throttle, it's horrible! Feels like its not getting enough fuel?

Anybody got any ideas? Does anyone else use a different setting with the same setup? Or could I have an air leak somewhere?

[Bonzo]

Anyone?

[gullarm]

The pilot screws only work up to certain level of revs.

Pootling about, doesn't mean anything.

You will find all carb bikes have a point were they swap from the idle screws to the main jets and it can be lumpy on some bikes and ok-ish on others - mine is ok. I read somewhere up to 4000 revs for the idle jets and after that the main jets - but I could be talking rubbish.


Sounds to me like an air leak running the bike lean from the change of idle to the main jets. Spray some wd40 round the carbs and see if the revs change on tick over, I did this to mine and I thought my carbs were seated correctly and the bike was running fine on tick over, but there was a leak rubber bent in maybe, removed and re-seated and it was fine after that.

[Bonzo]

Cheers for the reply, I'll check that the carbs are seated properly and see how it goes from there.

On a plus side - it passed its MOT this morning so I fully expect the weather to turn crappy now and winter to be here tomorrow!

[Bonzo]

I tried spraying carb cleaner on the rubbers while it was running, but the revs didn't rise or fall. I've removed the carbs and put them back on, making sure they are seated properly, but the problem is still there.

Bike tries to stall when setting off, almost like how fitting a race can upsets the fuelling. You have to rev it to get it moving now. It doesn't matter what revs the engine is doing, it only happens when the throttle is very slightly open. Like I say, it is most noticeable when setting off or when travelling at 50 - 70 ish in top gear.

Anyone got a spare set of carb rubbers I could try? I've heard the ones from China on eBay are not good, so if that is the problem, I'd buy some genuine Honda ones. I don't really want to throw money at it without knowing what the problem is though! Is there a way of checking the rubbers for cracks/splits, apart from spraying stuff on them when the engine is running? They're not the easiest things to get to!

[gullarm]

Check the sliders in the carbs are sliding up when you rev the bike and that all the butterfly's are opening together.

I'm assuming you have balanced the carbs.

Did you replace the pilot screw rubber seals, these can corrode and let air leak through. You can also squash them as well.

Is your choke cable on slightly, the slider on top of the carb should be all the way back and seal off the holes.

Failing that I would get it on a dyno. It may be over fuelling at low revs.

[Bonzo]

Cheers for the reply.

I've checked and lubed the choke cable, slackened it off, lubed the rail sliders/plungers. Also tried spraying the rubbers again, but with no success - it's still the same.

Sliders are sliding, butterflies are opening together. Next thing I'll have a look at is the 'o' rings on the pilot screws. I didn't change them when I put the screws in. Anyone know what size they are by any chance? I think they only come in the complete gasket set from what I can see on the fiche. I'm hoping I can find out what size they are and just buy what I need.

[gullarm]

Don't know the size, mine were fine.

Expected them to be corroded are misshapen but they were ok.

Get them out and have a look at them.

Did you strip the carbs completely and spray carb cleaner thru all the galleries etc. And are they balanced.

[dunkenb]

You can get the O rings from Graeme France