Help needed for SR250 spark or carb problem

[Timmay]

I have spent the day trying to sort out my mates SR250.

The problems are that it will idle fine when first started(1200rpm-ish) but once it has been reved or ridden it will only idle if the throttle is held open, otherwise it slows down and putters out. When riding at low revs it will sometimes start to jerk and misfire with no throttle response, then stall. Sometimes when the throttle is closed the revs stay high as well.

I have pulled apart the carb and cleaned everything, jets are round and clear, all galleries are clean, needle looks perfect.

I had trouble starting it once today so pulled the spark plug off and had a long spark (5-10mm) jumping from the lead to the spark plug to raise the voltage this managed to get it to start.

I will replace the plug and air filter tomorrow when red baron is open.

Nothing I have done today has seemed to change the nature of the problems.

Question 1: is the problem likely to be an old plug or is the slide sticking open and letting in excess fuel causing the engine to require high revs to run and causing misfires and stalling at low revs?

Second question: I had the pilot screw out today, I have it back in but there seems to be a wide range of adjustment where it will idle. What is the correct setting or adjustment method for this screw? I have read that it should be adjusted to allow quick pick up when the throttle is opened. Is this correct?

Thanks to all in advance

Timmmmmmmmmaaaaaaayyyyyyyyyyyyyyyyyyyyyy

[CookMySock]

does riding it around with varying amounts of choke do anything ? Because of the jerky nature of the fault, it sounds to me like an electrical problem.

DB

[Timmay]

Apparently there is a choke position which made it better but that was before I stripped and cleaned the carb, haven't tested it for this since. I guess I'll know more after putting a new plug and air filter in it. I just hope its not the lead or coil.

[skidMark]

It's running too rich/ choke problem

you sure you reassembled the carb correctly, thats your issue...

...check the choke isn't jammed or not fully shutting off...

Check that carb is assembled correctly, and check carb mixture is set correctly.

More likely choke stuck though.

Hope that helps.

Skid.

[skidMark]

Second question: I had the pilot screw out today, I have it back in but there seems to be a wide range of adjustment where it will idle. What is the correct setting or adjustment method for this screw? I have read that it should be adjusted to allow quick pick up when the throttle is opened. Is this correct?

Oh crap, thought so... lol

Generally most carbs are 1.5 full turns out (540 degrees)

Check owners manual/ find it on net.

[Timmay]

Thanks for the 540 degree tip. i'll try it tomorrow. I'm positive the carb is back togeather correctly, i have rebuilt plenty of carbs before and the problem is identical before and after. All the controls, choke, throttle, pilot screw function correctly

[Taz]

Have you checked valve clearances?

[TripleZee Dyno]

I have spent the day trying to sort out my mates SR250.

The problems are that it will idle fine when first started(1200rpm-ish) but once it has been reved or ridden it will only idle if the throttle is held open, otherwise it slows down and putters out. When riding at low revs it will sometimes start to jerk and misfire with no throttle response, then stall. Sometimes when the throttle is closed the revs stay high as well.

I have pulled apart the carb and cleaned everything, jets are round and clear, all galleries are clean, needle looks perfect.

I had trouble starting it once today so pulled the spark plug off and had a long spark (5-10mm) jumping from the lead to the spark plug to raise the voltage this managed to get it to start.

I will replace the plug and air filter tomorrow when red baron is open.

Nothing I have done today has seemed to change the nature of the problems.

Question 1: is the problem likely to be an old plug or is the slide sticking open and letting in excess fuel causing the engine to require high revs to run and causing misfires and stalling at low revs?

Second question: I had the pilot screw out today, I have it back in but there seems to be a wide range of adjustment where it will idle. What is the correct setting or adjustment method for this screw? I have read that it should be adjusted to allow quick pick up when the throttle is opened. Is this correct?

Thanks to all in advance

Timmmmmmmmmaaaaaaayyyyyyyyyyyyyyyyyyyyyy

Plenty of fuel flowing from the tank to the carb?
Float level OK an functioning?

[Timmay]

Hi, thanks to all for the replies. Its running better now, manifold leak was causing the petcock not to deliver fuel and that was causing the jerking.

Now the only problem is that it won't idle when it has been ridden. It starts fine and idles at rest although sometimes the idle goes from approx 1200rpm to 2000-2500rpm for no apparent reason. The bike rides fine but when stopping, at an intersection for a example, it putters out. The bike starts fine again immediately but wants a bit of throttle to stay running. Any ideas? For the time being my mate will just keep some throttle on at intersections.

Thanks

Tim

[The IT]

I'm resurrecting this thread to bring closure to it.

Firstly I should mention that the bike at hand is my bike, so thank you all who provided input to the problem, even though we were unable to diagnose the problem, Timmay taught me a lot playing around with the engine.

For anyone who thinks they have a similar problem to mine, I got the bike back from Spectrum in Takapuna, the bike now runs flawlessly, starts first time, idles flawlessly and has a lot more power too.

The issue was what they called the "compression screw" apparently it was too tight. So there you go, I hope this thread helps someone in the future and thank's again to everyone who helped out.