750 Sf1 troubleshooting - A/R unit ?

N

NeilD

Junior member
Location
on the road to Skegvegas, Lincs
well, i had to push the bike most of the way home tonight...  :( fortunately i hadnt gone very far!

anyway, symptoms as follows..

ever since i've had it, on occasion it would feel really 'flat' when first started -  not missfiring, running on both cylinders, but relucant to pull above 4000 rpm... whenever it did this it usually cleared within a mile or so of leaving home. 
Tonight it didnt and after filling with fuel it wouldnt start. didnt have many tools with me but pulled the points cover off and the points didnt appear to have closed up and were sparking  when opened with a screwdriver.
Eventually started and headed back home, still as flat as a witches appendage.. then it would just stop dead.. i'd push for a while, it would restart  then die again after a few mins.

so... i'm assuming electrical as both cylinders appear affected in equal measure concurrently.. the general lack of go is making suspect timing, and a quick search on here shows the A/R unit as a common problem...

is it likely to be anything else that would affect both cylinders? I'm just in the process of getting my Ducati on the road so am tempted to sort that out and leave the SF and eventually go for one of the electronic ignitions.. the bike is due a good look over as since i've had it all i've done is put petrol in it, check the oil and tyres and ride it..  :-[

Neil

 
 
I was about to ask what the A/R unit was but plc answered that before I looked stupid :o :o

To check the fuel flow take the 2 float bowl covers off, put out your cigarette then turn the fuel taps on, the fuel should piss out the bottom of the carbs. If it doesn't then the filters on the inlet of the carbs may be clogged or the ones on the fuel taps.
 
From your description of how the problem started, I would suggest checking the choke plungers and idle mixture screws/passages/o-rings etc. as problems in this area can cause bad running and fouling until the engine is hot, then eventually it won't start at all.  But if the plugs are not nasty and black then please ignore!
 
Unlikely to actually stop if advance/retard not working. As mentioned a look at the plugs may tell you something about the problem i.e. wet/sooty or dry. Ignition feed is common to both cylinders with a blue wire to first coil - after that things are separate for each cylinder and again it would be unlikely to stop dead if only one cylinder cut out. Most ignition or fuel problems would cause a misfire first but you say this does not happen. You could try a  'hot wire'  feed from the battery positive to the coil feed -that way you eliminate all ignition and kill switch contacts - check the engine is properly earthed to the battery negative as well.
Do you know how to check the points timing correctly?
 
Have you checked your tank breather isn't blocked? Mate of mine's bike had similar symptoms, and that was the cause.
 
I had a similar issue with my 71 in Italy on my way to France via Genoa (got within 50 KM of making it before I turned around and headed back to Napoli). Found the spark plug caps were shorting out internally which eventually was killing the spark. Found it by getting the bike to run and then removing one of the plug caps and getting my arse zapped (2AM at a Agip station in Pisa), thought the old men watching me were going to die laughing. At the time I didn't see the humor in it but have since found it to be a good one to tell after a few long necks. I ended up leaving the caps off and just sticking the plug wire to the top of the plug after I took the screw on cap off.

Just a thought  >:D
 
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