Now here is a baffling one...electrical gremlins might be at work

[JeremyW]

Right so I am having a small problem with my SRX400, other than this wee annoying problem she is a beauty.

The bike seems to cut out quite badly whenever I ride on the motorway or open road. When I use a reasonable amount of throttle (pretty much full on) for any more than about 10 seconds the bike will seem to miss badly and at any amount of throttle other than just cracked the bike will die.

This problem continues until I come to a stop and either just keep it running or it stops altogether.If it does stop it will start fine and 20-30 seconds later I ride away and everything is hunky dory.

WHAT!!!!???? I am a wee bit frustrated and would love it if someone could just give me their opinion on where I could start.

Spark plug cap is new, spark plug seems clean (brownish colour), not sure about cleanliness of carbs, plumbing seems fine and no funny smells.

[vifferman]

You seem to have ruled out electrical problems, so that leaves fueling and mechanical. Check for air leaks around the carb boot(s) and exhaust flange(s) and if you don't find anything untoward, carburetion may be the problem: crud in the carb or blocked filter being the most likely causes.

[idb]

Check that the air breather from the fuel tank is clear.

[tri boy]

Check that the air breather from the fuel tank is clear.

Catches alot of people out. Also drain the carb bowls.(water is a poor fuel).

[imdying]

Check for water, and replace your fuel filter.

[MSTRS:Me]

Water in carby bowl. Or the coil is breaking down.

[JeremyW]

Ah ha, these things I had never thought of! Thanks guys!

I have also found conflicting data on which plugs to use. Some are 7 heat, some are 8 heat (NGK) so I am a bit confused. I have a BPR8EA9 at the moment but if I did take the advice and go with a 7 I am worried about getting too hot and melting things....

Anybody with experience changing plug heat with big singles?

[Sketchy_Racer]

Sounds like you're using the fuel faster than what your float bowl is filling.

Check you fuel tap and make sure it is flowing freely, and then clean out your carb (throughly) and set the float level

Should go mint then

Also plug heat will make Sweet FA difference in a motor like that. Run what you got

[Moki]

If you've got CV carbs check the state of the diaphragms. Most likely fuel starvation though-Sketchy's said it already.

[JeremyW]

Ah ha I do have CV carbs, I will check that.

Well I drained the float, checked and replaced the fuel tank drain, checked the tap flow and cleaned the plug cap. Took her for a ride and it was much improved.... BUT it still misses when I open the throttle after being on the mway for a couple of minutes.

[Coldrider]

Sounds like my ZX9 when it is carb icing........the spark plug could be breaking down under load, cheap enough to replace & have a spare.

[smudge]

draining the carb bowls that could be a clue... when I drain carbs I try to catch the drained fuel so I can see what's in it.
Ignition problems usually show as a misfire under heavy load eg it will misfire like buggery going up a hill but run fine going down a hill. If the misfire depends on the throttle opening only it will be gas (or air) related. What is the history? Did it suddenly start misfiring?
I would check the fuel filter, if it wasnt that I would take the carbs apart. You would need to check the diaphragms, float valves (don't put them back upside down!) float levels and all the jets including the needle valves for crap. You need to take out the needle valve to check them properly as they have tiny holes radially throughout its length. Don't do silly stuff like changing the needle settings because they wont need to be changed unless your bike is modified in some way.

[Sully60]

Also check your float bowl vents, sometimes if they rubber hoses these can kink or the end becomes obstructed this can cause this as the vacuum created when this happens effectively stops fuel supply to the main jet.