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[Jamesw]

I have a Crusader 250 and it has a persistent 'misfire'. It will tick over happily, even when throttle is adjusted for a faster speed, but when riding it falters - sometimes with a cough and other times dying for a second or two then picking up again.

I thought it may be electrics, so checked everything. Points seemed ok, plug lead looked a bit worn so I replaced it and when that didn't work I also replaced the coil. Problem still persists.

I am wondering if it could be something to do with carburation. I have considered water in the fuel, but it is kept under cover and never out in the rain.

It may or may not be relevant that first ride out after the winter I went about 10-12 miles before any misfire/faltering, though I managed to get home with just occasional misfire, but now it occurs before I have even gone round the block

So my dilemma is whether to pursue the electrical side or look at carburation, and where to look next?

[Gaz262]

Could it be ignition timing? I'm not familiar with Crusaders but do they have a condensor? - Could it be that?

[PeteF]

Is there sufficient fuel getting to the carb? Check the flow from the tap and/or any filters in line and on the carb banjo. Also worth checking the float height.

[Boxerman]

I had this problem with my bike after a period on non use. Turned out to be the ethanol in the petrol had combined with water [condensation?] in the tank to form thin gel which sank to the bottom. Drained the tank, let the fuel settle then siphoned the petrol off the top.
Frank

[jefrs]

Old school stuff - does it "dot" or does it "daw". If it "dots", cuts out suddenly, it's electrics. If it "daws", dies slowly, it's fuel.



Do you have a good spark?

It's the easy one to check.

If your sparks go missing it can cut out to nothing and then reconnect, on-off-on (dotting or kangaroo). Coil, lead lead, HT cap, plug, LT connections to coil (esp earth), condensor, contact-breaker gap (where applicable). The last thing to check is ignition +/- timing because that won't cause it to cut out.



Daawwwww-cough-cough-thump-thump-daawww. Fuel is usually it not getting to where it is supposed to be, clean all filters and float bowls and jets. If the valves are out but still opening and closing, it may run badly but won't cut out.

[jefrs]

Water in the fuel is not a good thing but it does burn, see water/methanol injection to increase power. Shake the tank well to mix it up. What can happen after standing idle is the water causes corrosion and then we get sediment blocking the tank filter. If fuel cannot get out of the tank it can feel like you're running out of petrol.

[Bullet Whisperer]

Water will dissolve in methanol and 'burn', but it will not dissolve in petrol and will just accumulate at all the lowest points of the fuel system, eventually getting to the area beneath the main jet and gradually blocking the flow of petrol through it - this becomes evident when the engine begins to misfire on ever decreasing amounts of throttle, until, eventually, it stops. Regards, Paul.

[Jamesw]

Thanks everyone. I decided to look at carburation because the faltering reminded me of one time a while ago when the filler cap breather was blocked and the engine faltered or died then picked up again. Also, the problem occurred after about 20 minutes riding on first run out after winter lay up. I have drained the tank and am currently cleaning the carburettor. Will post the result when done.

[Presto]

Water in fuel is not now only a case of the ingress of ‘alien’ water – i.e.rain – but as water is a component of ethanol water is now latent in all ethanol fuels. Ethanol, unlike petrol, is soluble in water. Straight petrol contains no water. The moisture content necessary for combustion is drawn from the atmosphere. Bio-fuel (ethanol) is able to absorb water and carry water.



Unlike petrol, ethanol is highly soluble in water. When the water content of the E5 blend (i.e. fuel with a 5% ethanol content; E10 = a 10% ethanol component) reaches a critical level the ethanol component and associated water will separate from the E5 blend and form an ethanol/water phase.



This will accumulate at the bottom of a tank leaving petrol (without the ethanol component) in the upper layer and is known as phase separation. On a motorcycle this effect may result in the carburettor being filled with ethanol/water and no petrol.



If phase separation occurs, when a bike with ethanol in the tank is left unused for a time, typically a few weeks, the process is essentially irreversible, there is no straightforward means of emulsifying - reblending - the ethanol back into the petrol. Shaking the bike in this case won’t help.

[Jamesw]

Update - drained the tank and cleaned out the fuel system and carburettor. Still no cure. That brought me back to electrical matters. I replaced the condenser and it appears - after a short test ride - to have solved the problem. Thanks for all the advice, some useful info about fuel which suggests that it may be wise to drain the tank before winter lay up in future.