Bike jerking at constant speed about 80mph??

[marsu11]

Hi.

Firstly i have to admit that i registered here because i bought the Varadero 1000 the carburators one and have a problem with it. I didn't have much money so i have been looking long time for Varadero and finaly got one for 1500. Yeah I know that cheep. It doesn't look the best but sounded sweet at least for a while.  Now when i ride with constant speed at about 80 mph bike keeps choking not all the time, it goes ok then sudenly is jerking for a couple of secounds then its ok for a bit and that keeps on repeating all the time making not very comfy ride. When i was checking bike in my garage and i kept it on neutral and reved it to 2500rpm and kept like it for a while it started doing that jerking thing as well.  Took it to the mechanic that checked it all and didn't know what is it, took it to another garage and they dont know as well. I checked the spark plugs, got new fuel pump started adjusting the carburators (according to haynes manual)  and nothing helps. I just dont know what to do?? Apart from that bit bike goes nice and accelerating great.  I appriciate any help.

Thank you.

[LazyRider]

If you 'blip' the throttle and it clears, it is probably Carb icing.   Try putting half a cup of methylated spirits in the fuel and see if that helps.
The Meths will also help clear any water droplets in the tank

[marsu11]

Thanks!!
I will try it.

[marsu11]

Its not carb icing 

[S Barker]

It has to be one of 3 things :

• Fuel
• Mechanical
• Ignition

If it was mechanical  (something seizing)  you would see other signs.

Fuel would have to be starvation or contamination. I'm assuming that you've eliminated contamination (the problem has existed over several tanks of fuel).

As the bike is a carb version and you mention "jerking" I don't think it can be the fuel pump causing starvation as the results of this would be a slower "fading". But as the only remaining cause is ignition and this will be expensive to track down it would be worth trying a few things to completely eliminate the fuel pump.

Does the problem ever occur when the tank is full ?

If so have you tried filling the tank and bypassing the fuel pump with a short length of hose (the pump is only needed once the level in the tank drops below the carb level).

Have you checked the carb floats and needle valves ?

[LazyRider]

Its not carb icing 

Well, it was worth a try!   I had the same problem with my first Varadero and the methylated spirits did not help on that either.  (It had resolved the problem on another bike .

On my Varadero, I resolved the problem by shutting the throttle occasionally ? to allow the fuel flow to 'catch up'.   That did work.

I agree with Stuart in that I think it is fuel related.  How much time you are prepared to spend resolving the problem is up to you.  But as it was only happening to me at constant speeds in excess of 80 mph I did not bother .  I just shut the throttle every now and again .

[Budgie446]

Hello Fella, I have a very similar problem, my bike runs very well untill im riding slow around town, if I sit at a set of traffic lights for to long it coughs and splutters like fuel starvation? but it only happens at low speed once the engine is hot, the temperature never go's up past three and the fan doesn't cut in but as I say it only happens when the bike gets hot and id riding slow, once i get it back on a straight road and open it up it eventually clears? I have no idea what it is, but my bike is fuel injected not carb? any idea's anyone? Andy