out of ideas need help nsr125

[fully677]

So my nsr has been playing up for ages, randomly dies while riding, every now and then back fires and doesn't start unless it feels like it and back fires trying to start it.

At first seemed to die when going above power valve. Got a new ecu and power valve unit.

Didn't fix it, previously my top end went so I have now bought a new top end, and a really good condition bottom. So have changed the whole engine.

Tried 3 different set of reeds. And the only thing that hasn't really been changed what I can think is the carb.

Can anyone suggest anything plz

[Efes123]

Backfiring is an indication of too rich a mix. I'd have gone for carbs in the first instance.
____________________
Honda Goldwing GL 1000 Current love
Honda VT500 ED - SOLD
Projects Suzuki GS125 Done, then stolen - Kawasaki GPX750R SOLD - Honda VF750S SOLD

[fully677]

Well before it wasn't backfiring as such just losing power but now with the new engine is backfiring.

So I been adjusting the mixture via the carb and had no joy.

[fully677]

Standard jets but conical air filter. Had been running on this the past 6 years so didn't think the jets were a big issue. Though I have lost my standard air box in moving.

Also full arrow exhaust.

[Efes123]

Ah, OK. Does it backfire when throttling off as well? It's basically when there's too much fuel going through it ends up in the exhaust, and then ignites.

Sorry, don't know the model too well. Have you tried screwing the mixture screws all the way back in, then taking them out half a turn at a time?
____________________
Honda Goldwing GL 1000 Current love
Honda VT500 ED - SOLD
Projects Suzuki GS125 Done, then stolen - Kawasaki GPX750R SOLD - Honda VF750S SOLD

[fully677]

Yeah back fires when throttling.

Tried screwing them in and half turns again no joy.

[Efes123]

The only thing I can suggest is a damn good clean of the carbs then, could be a stuck float. As I said, I don't really know the model, but I'd bet a pretty penny on it being carb related.
____________________
Honda Goldwing GL 1000 Current love
Honda VT500 ED - SOLD
Projects Suzuki GS125 Done, then stolen - Kawasaki GPX750R SOLD - Honda VF750S SOLD

[fully677]

I shall give it a clean and get back. Cheers

[G]

Once you've cleaned the carbs, check for air leaks - try spray some easystart, wd40 or similar around the carb area while idling and see if the revs rise.

Worth checking for compression.

Try covering some of the air box inlet - if it gets better it's running too lean. Putting the choke on may do the same thing.

[The other Paul Rudd]

One of my two strokes backfires like a mother when it's running low on fuel. Maybe check the float height if it's not a stuck float as mentioned above.

[fully677]

Well I would have thought the compression should be spot on with a full engine rebuild.

when you say test for air leaks, do you mean around the pipes?

at the moment, tick over seems fine, revving seems to be ok while in neutral as soon is I try to pull off its just wants to die.

unfortunately I only get to work on my bike at the weekend. so going to have to wait until next weekend now. I'll try get a vid.

thanks for the ideas so far, to me it defiantly seems like a carb issue.

[m3-paul]

Are you sure it is on standard jetting but you have a non standard filter and expansion chamber?

Have you taken all the jets out, stripped the carbs and soaked the jets in carb cleaner and blown the passageways out with cleaner?

If it is not picking up over idle then clean out the pilot jet and pilot circuit.

Possibly you need to get the carb back to the factory settings to get a baseline and work from there?
____________________
Yamaha TZR250 - love the smell of TTS!!!!
CBR900RR Fireblade - so much fun

[Ariel Badger]

A backfire is combustion in the exhaust, for combustion to take place you need three things heat fuel and oxygen. The first two are easy to explain but not the third, How good is the seal between the head and the pipe?
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Bikers make great organ donors, get 115 on your licence today.

[fully677]

well I have never changed the jets on my bike.

I have ordered some carb cleaner, so will try cleaning it all up good.

as for the connection from the head to pipe its a new gasket and tight fitting so id say pretty good.

[G]

Never found carb cleaner particularly useful.

Take the carb apart, take each jet out one at a time and blow through the holes - if needed for the really thin ones, use a thin bit of plastic (I nab a bit from a washing up brush) to poke any bits of stunk gunk out.

[fully677]

I might be able to get the carb out tomorrow, so will keep you posted.

P.S. Thanks for the help so far everyone

[Xenocide]

I'd check to make sure your tank isn't becoming pressurized causing the fuel to not flow to the carbs.
____________________
KTM LC4 400 | Honda VTR1000

[m3-paul]

My tzr250 was failing to fire on the left cylinder and if I could get it going would cut out when the throttle was applied.

I cleaned everything as best I could in the carbs but the problem always returned.

In the end I completely stripped the carbs and dropped the pilot jets in to a pot of carb cleaner and left them to soak for an hour. Suprisingly there was quite a bit of muck that had been washed out of them even though I was convinced they were clean.

Problem has never returned since then.
____________________
Yamaha TZR250 - love the smell of TTS!!!!
CBR900RR Fireblade - so much fun

[fully677]

Im not sure how I go about checking to see if the tank is becoming pressurized, any quick tips or is it a google search jobby. ('sorry at work atm')

its looking to be the carb to me in this instance by the sounds of things as everything but the carb and exhaust has been changed.