Exhaust popping

[scotjell]

I have just put my NC30 back together hoping and thinking I have cured all my problems. Well at the moment its not overheating as its sat on tickover at the mo. The problem I have now discovered that around every 5-7 seconds the exhaust will pop not very loudly but its like some backpressure has built up in the exhaust and it lets off a little love puff. Any advice apperciated please note that this is completely standard and have just rebuilt the engine.

[DoktorMandrake]

I would imagine there's a leak somewhere. Probably in the exhaust itself, although when I failed to blank off the carb vacuum ports on my CBR after balancing it popped then too like a fuckin' drag bike which sounded awesome only it wouldn't idle at all - just stalled without the choke as it was running way too lean. So I guess it's possible it could be something like the inlet rubbers that are perished/not on properly. My bike currently has a massive leak where the front pipes join the rear section and pops a lot. Not usually on tickover though. I only hear it when rolling off the throttle but that could be cus she's too damn loud when I wind her up so I don't notice it.

[scotjell]

Coming close to putting other engine in as its starting to get to me with all the other probs i've had after rebuilding this one!!!

[DoktorMandrake]

If it's popping in the exhaust odds on it's a simple fix. It could be sumat more serious but I doubt it. Stick with it, matey. You can check ya exhaust by blocking the end and running the bike up and seeing if/where it leaks or being careful and just running ya hand round underneath it (obv being careful not to burn yaself) and someone on here suggested blocking the pipe and spraying it with washing up liquid, starting the bike and watching for bubbles. As for the carb intakes, someone on here also suggested spraying the 'easy start' around the carb intake rubbers when the bikes running and if the revs rise then you have not got a perfect seal. It's just a process of elimination. Stick with it though. If you have the engine all rebuilt you've done the difficult bit.

[The Hamster]

TBH, it sounds ot me more like a Carb Balancing problem if its popping on Idle, or you have got it set to tick over slightly too high, like just under 2000rpm for instance when it should be at about 1300-1500rpm. I sometimes screw my Idle adjuster in a bit depending on the weather as it can make a big difference to how the bike runs!

Check the carbs for dirt and corroded seals etc etc, then just make sure all your carbs are balanced and synchronized with each other correctly as this will give the same problem. Also, check that your choke plungers on the carbs themselves are rreturning and operating nicely. If you have one slightly out, then you could be over fuelling that cylinder which would give the popping as the excess fuel burns off and leaves the exhaust.

Its certainly not a new engine job mate, thats a bit extreme.


Where are you based?

I had problems after rebuilding my motorbike and Kev at Projex-UK in Cradley Heath, near Birmingham was able to find the fault and help me fix it within 15 minutes of taking the bike to him. Then he gave me loads of advice and let me use his workshop and tools to fully balance and synchronize my Carbs and get them set up to the level of tune I wanted at the time..


http://www.projex-uk.co.uk" onclick="window.open(this.href);return false;

[alexwitham]

little love puff

Im sorry, but did anybody else smile when reading that?

[Neosophist]

Most Likely:

Exhaust Leak
Carbs off balance
Carbs running too rich
Dirty / Clogged Carbs.

If it's popping it's burning fuel in the downpipes. Check the above :)

[scotjell]

At which bit was you smiling, unfortunately I'm not, but am inside!!! popping popping

Carbs have been stripped and cleaned jets checked all of the above idle was at 1300rpm thats why I'm stumped came across the plunger before on my other NC so checked all that too. What I did notice whilst stripping the other cylinder head that my spring compressor is pants whilst using it managed to bend a valve so along with the valve thats now in the bin. Have ordered a decent one now, but thinking if that happend removing a valve when i replaced the ones on the engine in the bike as that engine had a rebuild too maybe some of them are stiff. What do you guys think?

Hang on we are talking about stiff now!!

So a slow engine rebuild this time for the spare. Another little question is the pistons in the carbs could they cause this if not returning smoothly. Please note priced one up today at £100.

So all advice taken in good faith.

[scotjell]

Right getting into the thick of it now. Carbs removed off my running bike and exactly the same so not a carb problem, rubbers are good and sealing. So any further ideas????? Could it be a sticky valve as like i say in another post whilst removing the collets the compressor was crap.

[Neosophist]

Right getting into the thick of it now. Carbs removed off my running bike and exactly the same so not a carb problem, rubbers are good and sealing. So any further ideas????? Could it be a sticky valve as like i say in another post whilst removing the collets the compressor was crap.

Checked the exhaust system for leaks?

Spray all joints and where the headers join the mainfold with soapy water and start the bike up with a rag in the end-can.

Did you regrind the valves after you removed?