Hey guys,
First post

So essentially, I've been pulling my hair out over this issue I have wherein my BN 125 just does not want to start from cold at all really. When it's cold, you'll have a faff on gettin it started in the first place (with the choke on), but when (or if) you do, when the time comes to take the choke off, you have to keep the revs up, else it'll cut out. Keeping the revs up is no easy feat in itself because most of the time if you open the throttle more than practically 1mm, the revs completely die, you might get one little pop of backfire (at least it sounds like backfire) and then in all probability, it cuts out. If you're very gentle with it and manage to move off, the power is almost non-existant, and often, it'll cut out, which to me is pretty dangerous when you're pulling out onto a main road. The normal level of power will usually kick in somewhere if and when it eventually feels like accelerating. Same with the shift up to second where you have to close/open the throttle - after shifting there'll be next to no power whatsoever, until again, it feels like it.

I have exhausted my own train of thought as to what in the hell is wrong with it. My step Dad is a motorbike mechanic (which is very handy) and even he is at ends to suggest what could be causing, though he did suggest that it could be the CDI, but given that they're cheap, it's a bit risky. What he also said was that if I really, really wanted, he'd strip it over the course of a weekend and see if could find the cause.

It does seem to run pretty well when it's warm however...

Really, I just wanted to ask on here to see what thoughts people had before I go ahead and waste his weekend - he's not too keen on doing it anyway because I want to sell it ASAP, it's just I don't want to sell it and have the guy I sold to come back and say 'you sold me a heap of crap' if you get my drift, and I like to think I'm a very sincere man

Any suggestions are appreciated, but before you do - here is a list of things that have been fitted/done in order to try and sort this bugger of a problem out:

• Brand new carb
• Brand new ignition coil
• Valve clearances adjusted
• A few new spark plugs
• Oil & filter just changed

Cheers

 

Welcome to KF

I do not have a manual on the 06. I think that the mikuni BS28 is the same as on all of the BN 125's.

A brand new carb? (that sounds extreme), Float height adjusted? Pilot jet adjustment? Air Jet size correct? Throttle valve size? (you did say it ran good in warm weather assuming you used the same adjustments)

How is the air cleaner?

How old is the gas? You would be surprised how that will affect cold starting on the smaller Kawi's.

I know, no answers just tossing out questions.

Good luck

 

Thanks for the suggestions pal.

Just a few things - this problem has been going on since I bought bike in the Summer of this year, which I think just about rules out it being bad petrol. Also, I meant the bike runs well when it has been warmed up, I should've made that a bit clearer, hehe.

Anywhow, I bought the brand new carb because the air mixture screw on the original one was cross threaded and after sending it around loads of different people and engineers to see if they could drill the air screw out, let's just say it didn't end well, hence the new carburettor - which has all the correct sized jets, and the air screw turned out the correct number of turns. Indeed though, it is a BS28 carb. After fitting it though, things were exactly the same - as far as I know theres no problem with any of the vacuum hoses or anything either - cant see any kinks/tears etc. Perhaps if anything, the carburettor was indeed a geunine Mikuni BS28, but it was advertised to fit a Qinqi somethingorother. Though on inspection, the only difference was the shape of the choke lever. I swapped all of the jets from the original carb over and they fit snugly, so, in my eyes, caburation may not be causing the issue.

The air filter was cleaned and moistened with oil (as it said in the manual) and there is nothing obstructing the flow of air.

Cheers for the response though, not to rule any of them out completely.

 

There is a good ignition troubleshooting chart in the BN manual. If you have already replaced the coil, how did the crankshaft sensor test out? (with alternator lead disconnected, BN-A3 = 190-290 ohms.) There is also a good CDI test procedure and chart in the manual as well to help eliminate that possible issue. pg 15-50 and 15-51

I need to see if there is a manual listed in the General Discussions thread for this ride.

 

This sounds similar to what was happening to my EL 250 Eliminator when I first got it. It had sat for a season and it was hard to keep running when cold. It had no off throttle response and would often die with a slight roll of the throttle even with full choke. When riding at a steady pace I didn't have a problem, unless I tried to accelerate, even down shifting 1 or 2 gears didn't help. My shop thought I needed a carb rebuild at first, but upon his inspection he found the fuel in the float bowls was way too high. As he put it "breath on the throttle and flood the engine". After that and a syncing the carbs to near perfection, my bike runs great. Although I did have him raise the levels a back up a bit, because the bike seems to run stronger and with a wider RPM band than at the recommended levels, even if I have a slight off throttle stumble.

 

I took the tank off just the other day to find that the carb's pilot air screw was about 1/2 turn premature, so I corrected that. It runs a tiny (really tiny) bit better, but now the backfire seems more prominent - and louder when cold. I'll put a new sparkplug in just in case (if I recall, I think I may have mixed it up with one of the sparkplugs from my CB500 ). I'll hand her off to my Step Dad at the weekend and tell him about the float height (He knows an infinite amount more than me). Thanks for the suggestion! Again, I'll let you know!