Buccaneer
XS400 Enthusiast
Hi all,
As some may know from other threads, last year I got a 1980 XS400 US Custom (UK model, like Special). This has points ignition on SOHC engine.
It has always been hard to start, and iffy idling. It will often die at the lights ...embarrassing!
After doing all the obvious battery charge, points, timing, valve clearances etc...
Last year I gave it a huge carb clean (boil) and added a fuel filter, which seemed to cure it ... for a day or two, then al the symptoms came back almost as bad as before. Since then I've scoured the web for info, the carbs have been off again for a very thorough second clean. Carb cleaner shoots out of all the right places, orifices have been carefully poked through with a bit of fine brass wire, etc etc. It is really hard to believe there could be any dirt left in the carbs, the second time I knew there was a really insidious problem and was done so carefully and thoroughly... however, one additional symptom is this: idling is much more reliable with the 'choke' (enrichener) on its first stop rather than off, even in warm weather.
Last time I checked the plugs, they looked OK indicating a bit rich (sooty) if anything, but I had been leaving the choke on quite a lot and only shutting it down when on the open road (not very often round here in UK!).
So my thoughts turned to electrics again. Measuring the voltage at the twin bullet connector where the coils plug into the wiring loom, with the engine static I see only around 8.5 Volts even though the battery is freshly charged (doing around 12.5 V under ignition load, 12.8 off load and 14.5 under charge). This voltage at the bullet connector rises to over 13 with the engine running at about 2000 rpm.
OK so I am assuming this 8.5V is because of the current draw of two coils permanently 'on', and V drop due to resistances in the wiring loom. Then when the engine is running, the average current draw here is way down due to the duty cycle of the ignition, so the voltage drop almost disappears... correct?
Question: is that 8.5V ish at coils with engine static normal, or do I have excessive voltage drop in the wiring loom? If it's abnormal, any ideas where to look first? Connectors for Ignition key / Engine Kill switches in the headlight shell?
I tried the obvious thing and ran a thick clip wire around a couple of foot long directly from the battery +ve to the coils. This upped the volts at the coils to within around 0.2V of the battery volts even with engine static, as expected. It seemed to have no positive effect on starting or idling performance, which leads me back to carburation problems again. Drat!! My pilot mixture screws are about 3.5 turns out for best idle (still poor and unpredictable though), so I suppose upping the pilot jet size is next on the list to try? Exhaust is Norton peashooters stuffed with wire wool. Main difference to stock is no balance pipe, is this likely to be a big problem?
Any help will be much appreciated!
As some may know from other threads, last year I got a 1980 XS400 US Custom (UK model, like Special). This has points ignition on SOHC engine.
It has always been hard to start, and iffy idling. It will often die at the lights ...embarrassing!
After doing all the obvious battery charge, points, timing, valve clearances etc...
Last year I gave it a huge carb clean (boil) and added a fuel filter, which seemed to cure it ... for a day or two, then al the symptoms came back almost as bad as before. Since then I've scoured the web for info, the carbs have been off again for a very thorough second clean. Carb cleaner shoots out of all the right places, orifices have been carefully poked through with a bit of fine brass wire, etc etc. It is really hard to believe there could be any dirt left in the carbs, the second time I knew there was a really insidious problem and was done so carefully and thoroughly... however, one additional symptom is this: idling is much more reliable with the 'choke' (enrichener) on its first stop rather than off, even in warm weather.
Last time I checked the plugs, they looked OK indicating a bit rich (sooty) if anything, but I had been leaving the choke on quite a lot and only shutting it down when on the open road (not very often round here in UK!).
So my thoughts turned to electrics again. Measuring the voltage at the twin bullet connector where the coils plug into the wiring loom, with the engine static I see only around 8.5 Volts even though the battery is freshly charged (doing around 12.5 V under ignition load, 12.8 off load and 14.5 under charge). This voltage at the bullet connector rises to over 13 with the engine running at about 2000 rpm.
OK so I am assuming this 8.5V is because of the current draw of two coils permanently 'on', and V drop due to resistances in the wiring loom. Then when the engine is running, the average current draw here is way down due to the duty cycle of the ignition, so the voltage drop almost disappears... correct?
Question: is that 8.5V ish at coils with engine static normal, or do I have excessive voltage drop in the wiring loom? If it's abnormal, any ideas where to look first? Connectors for Ignition key / Engine Kill switches in the headlight shell?
I tried the obvious thing and ran a thick clip wire around a couple of foot long directly from the battery +ve to the coils. This upped the volts at the coils to within around 0.2V of the battery volts even with engine static, as expected. It seemed to have no positive effect on starting or idling performance, which leads me back to carburation problems again. Drat!! My pilot mixture screws are about 3.5 turns out for best idle (still poor and unpredictable though), so I suppose upping the pilot jet size is next on the list to try? Exhaust is Norton peashooters stuffed with wire wool. Main difference to stock is no balance pipe, is this likely to be a big problem?
Any help will be much appreciated!
). Time to find out where one gets those screws for the butterfly rebuild. Also, is a special tool required to splay the ends of the threads again? It sure looks like it, as I wouldn't want to start hitting the carb internals with hammer blows, especially when the things are assembled! (Lordy, that would do my soul good though, after over 12 months of this 'stuff'!!!! 
)
