1974 rd350b backfiring

[eddiekidd]

Hi Lads, I have a problem with my 350b running like the power of a 125 but sometime it runs good for a few seconds its as if its starving for fuel. I just had the carbs cleaned its on standard pipes and jets. I took it

 out for a spin this afternoon and noticed a backfire, I drove it back home and but it on the high stand ran it up and down the gears and in 6th gear it backfired a few times next thing it started revving full wack on its own I hit the kill switch and turned off the key to no avail next thing it cut out and wont start but if I kick it over a few times fast it back fires a bit but no start any help would be appreciated. Regards Eddie.                                                                                                                                                                                                                                                                       UPDATE////////////// just went back to the bike after it cooled down for an hour and first kick it started  perfect but running briefly on both cylinders and by giving a little throttle it runs intermittently on both  at approx  2500 revs . I turned it off again and when I started it again it revved out full speed again by its self shut it down again and again it wont start for me. Can any body help

[sispeed]

You write cleaned the carbs.
Float bowls swapped? Throttle bodies swapped?
Regards Siggi

[eddiekidd]

Hi siggi thanks for your reply. yes had the carbs professionally done. It started perfect this morning on both cylinders when cold but under load or when it starts to heat it goes intermittent on the second cylinder again, I'm think it may be a fuel supply to the second carb or a electrical fault.

[reedpete]

What colour is the plug on the dodgy side.
If it’s fuel starvation it’s going to be bone dry and pale but if it’s spark problem then you’d expect it to be wet.

[reedpete]

You’ll need to do a plug chop by cutting engine and coasting with clutch in to catch the condition. No point riding home and idle for a bit before you check.

[sispeed]

If problem starts when bike warm, I would point at the ignition and especial on the coils

[jonboy]

it is worth checking that the rectifier and regulator has no bad connections.. I worked on a 250 points model years ago which would drop on to one cylinder intermittently and then would suddenly chime in on two and then drop off again etc... it had a bad connection on the rectifier. sorting that connection sorted the issue... might not be that, but it is one to look out for. if its an electronic model, it won't have any effect as they will run with no battery or reg/rec

[beardy]

your issue has some similarities to an issue i`ve recently had with my 350lc. get an avo and check your hi and lo readings on the stator.
my readings were not as standard but it sometimes ran ok and at other times cut out and backfired. i`ve had the stator rewound and it appears to have fixed it.

[madmick]

Had exactly the same problem with my lc2... turned out to be the cdi.
I would say you have electrical gremlins. Go down that route.

M.M.

[stuzx4r]

Hi, the most likely cause would be condensers (and/or points), a defective condenser will very often work initially but will start to break down after being run for a while this leads to an erratic arcing at the points and an untimely spark at the plug creating a backfire. Both items are relatively cheap to buy thankfully. 

Good luck.

[copper99]

Start with the cheap stuff and go from there mate, for what its worth, when LC started back firing and mucking around last year, main cause was the stator.