Hesitant and spluttering at full throttle.

[Jrod]

1985 XR600.

When full throttle it is fine until youve had it pinned a while and its reaching highish speed (70ish)

Starts to splutter a bit and will get worse if you keep it pinned. When this happens it also pops and bangs when you back off the throttle for a few seconds and will stall if you pull the clutch in. Carry on riding at part throttle and it clears very quickly.

Brand new coil, cap and spark plug fitted. Also fitted new original sized jets today wich made it better but didnt cure it. (went from 148's to 122's!)

[finpos]

Sounds rather like it's not getting quite enough fuel at wide open throttle and it's leaning out the mixture. On a bike that age first thing to suspect is the fuel filter is full of snot. It'll probably be in the fuel tap, somewhere.

f.

[Jrod]

The tap was taken off and cleaned as was the tank. Carbs have been fully stripped and cleaned aswell.

[oldbiker]

Check the spark plug for any grey deposits on the centre insulator this would indicate that the timing was a little advanced,

Erosion or burning of the centre electrode would suggest that it was running a little weak on the mixture (try lifting the carb needle a notch or two).

very dark brown or wetness would suggest that it was running over rich (Lower the carb needle a notch or two)

And as the last post says check that the tank, float bowl and fuel lines are not full of snot.

is it possable that you may have altered that height of the float when you replaced the jets?
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[Alexio]

Air filter?
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will never give up his CG. I look at my fuel gauge more as a progress bar than a fuel gauge.
G: With my GSXR I do often effectively use it as a scooter with a clutch in town.
ms51ves3: why does it need 500 miles? Are you teaching it how to be a piston?

[Jrod]

New air filter. No i didnt touch the float levels when the jets were changed (as you don't need to take the carbs apart to swap jets, just 2 little access holes in the bottom)

Would the wrong float levels cause something along these lines as I've not checked them.

[Shreddie]

[oldbiker]

the sort of symptoms that you describe ( back fires, hesitant power when you drop the throttle) point towards the engine being very hot.
the most common causes are; timing being over advanced or wrong fuel \ air ratio,

if timing is ok, jets are correct (no engine or exhaust mods),
you are looking at something reducing the amount of fuel in the float bowl. could be crap in the tank, fuel lines, float bowl.

what was the last thing that you did to the bike before this started? and what was the problem that you were trying to solve then? that is what you must sort out.

the point about the air filter previously mentioned. If the air filter was clogged or replaced with a piece of card it would only make the bike slower, if the air filter was removed it would be unlikely to cause such obvious problems though it would make the engine run hotter.

is it possible that you may have an air leak somewhare between the carb and carb mounting?
____________________
It`s all powerfull white mans magic
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[finpos]

Have you checked you're getting decent enough flow of petrol out of the fuel line; should be pouring out. Check it with the fuel cap on and if is slows down after a while, take cap off (i.e. check the breather isn't blocked).

f.

[Jrod]

[temeluchus]

if its got a loud pipe it will need jetting.
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Some shite cruiser. Now with guns and FREEDOM!

[Jrod]

It has and it was jetted to suit (136 instead of 122.) I then went up to 148 and it was the same, now gone back to original 122s and its better but still there.

[temeluchus]

try lowering your float height, make sure its getting what it needs top end.
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Some shite cruiser. Now with guns and FREEDOM!

[Jrod]

The floats is my next step I tink as I've not touched these so they could well be wrong. The standard exhaust is also going back on as soon as I weld a small patch on.

[prawny1]

Does the xr have a cv type carb?

if it does check the needle slide diaphragm for splits etc, A very small split might not cause running trouble until your at full throttle/ high speed.

[Dustproof]

It sounds to me like the ignition is breaking down, replace the plugs if you haven't already. If this doesn't fix, it could be a coil breaking down. If it is arching to earth have a look at night and see if there are any electricity arching, if there is ANY sign of it replace the faulty coil.
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GSX1400 - Just like a magic carpet ride with a Rocket up it's arse

[Jrod]

[temeluchus]

[Vincent]

Sounds electrical to me too. You had a good look at all the ignition wire conecters? Made sure the flywheel is fitted ok? Does the engine misfire when you rev it high on the spot? Or only under load?

[Jrod]

[temeluchus]

ah you have the twin carb head.

Not under load-almost certainly float height.
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Some shite cruiser. Now with guns and FREEDOM!