Carb or electrical problem? Hesitant between 7-9k

[revved-up]

Bought a NC29 last week that had been standing for 2 years.

We obviously drained the tank and flushed it as best we could. Then clean the crap and residue out of the float chambers and check and cleaned the jets (with an airline!!!) aswell as checking the slides and vacuum rubber boots.
Put it all back together and it runs lovely now... allmost!

If its standing it revs freely and sounds sweet.
But I took it out for a spin and it is smooth all the way up to 7k, then it'll splutter and misfire to about 9k then just literally just scream all the way to the redline perfectly!
I have noticed now though a slight hissing/sucking noise from the left of the carbs which Ive narrowed down to what looks like a circular brass bush pressed into the side of the carb, that pulses in and out and you can feel the vacuum - Should it be like this? It certainly sounds wrong.

I hope someone can help... Is the vacuum leak/ hissing noise coming from the carb related to the misfire/splutter, and if not, is the splutter definately carb related?

Thanks, Tony.

[revved-up]

Anyone got any ideas???

How do you balance the floats in the carb?

Thanks, Tony.

[Sanchezz]

I would say most likely carb related, it is hard to diagnose without having the bike infront of me, but a few things; there shouldn't be any sucking coming from anywhere outside of the air box. so i would cover that bush with blue-tak or something to see if that is causing it. from what you said it sounds like its over fueling but it mite be something completely different

[revved-up]

Well Im going to whip the carbs off now and have a look then...

Ill report back what I find...

Thanks.

[scarface]

My NC29 does that as well, more between 8-9krpm tho. I've just persumed it's cause the bike is overfueling, as I've got lots of carbon stuff on the exhaust. Never notice any sucking noise but then I've not really had a look.

I'll have a look tonight and see if I've got the same problem.

Stu

[little nick]

[quote="revved-up"]Bought a NC29 last week that had been standing for 2 years.
I have noticed now though a slight hissing/sucking noise from the left of the carbs which Ive narrowed down to what looks like a circular brass bush pressed into the side of the carb, that pulses in and out and you can feel the vacuum - ?
quote]

I think thats one of your balancing test ports (difficult to say without seeing it) - that has it's cover missing. If it is - it could cause the problem you are describing - running lean on one carb.

If it's not - as has been said before - the only place air should go in is into the airbox. Anything else is a leak - and would cause it to run lean.

If you posted a picture - it woud help

[revved-up]

Right... Ive noticed something now.

There are vacuum hoses that come out of each inlet and join up cyclinders 1+2 and 3+4. All four hoses where blocked off but cylinders 1+2 where split.

Are they meant to be joined together Ie 1+2 and 3+4, or is something to do with balancing the carbs, and each should be seperately blocked off at all times?

I have replaced the hoses and blocked them off for now, and Im about to put it back together...

Ill try and get a pic, but Ive found the pulsing and hissing comes from the circular end cap that closes off the end of the Butterfly(?) Ill try and describe it for now... The spindle that runs inside the length of the carbs that rotates and opens when you pull the throttle. Well this end cap is what covers it, if you get what i mean?

Ill try and get a pic. lol.

Anyone know about the vacuum hoses between cylinders quickly before i put it back together??

thanks again...

[Sanchezz]

Are you talking about the the little brass fittings that are on the engine block/manifold or on the carbs?

If you are talking about the ones on the engine block they should be blocked off seperatly, not put onto other cylinders.

[revved-up]

Sanchezz - I worked out they where meant to be blocked off individually, But I couldn't make them totally airtight. I renewed the vacuum hoses and plugged them with a bolt and also folded each of them in half with a tight ziptie.
How do you block them off??

Anyway, I put it all back together now, With the trumpets in the correct order this time according to the haynes, and Its not so bad now, but its still doing it.

Its starting to do my head in now!! It runs lovely up to 7kish then just splutters and struggles for a good few seconds before getting past it and then just literally flies to the redline.

Ive noticed though sometimes the rev counter goes a bit haywire when its doing it.
My battery is almost flat and I have been jump starting it, could this be a problem, although I doubt it.

[Sanchezz]

Mine still had the original caps on :) but i did loose one and made on by filling the end of a short peice of hose with sealant, the first time i done it i used sealant inside of the tube and got the hole plugged, next time i went to balance the carb the port was all clogged up and then i dropped the needle i was using to unblock it into the engine,. luckly the valve was closed though.

Im a bit stumped to be honest, have you got aftermarket exhaust? im no expert with carbs (why im looking to convert to FI ) Maybe get it on a dyno and see whats happening.