Getting frustrated as it won’t start.

Robin Webster

Robin Webster

Hero member
Location
Silverstone
‘76 3C , I went for a ride on the 12th July and after 10 miles the bike lurched a few times popped and a bang then the engine stopped and I coasted off a duel carriage way and haven’t been able to get it running since. I’ve been away from home and couldn’t make the 75th meet at the weekend so only just today fitted the new RR.
There is spark and I’ve fitted brand new spark plugs, a battery - 12v 32Ah, and a new Reg/Rec. There is also fuel in the tank!

Cone filters off and you can see the accelerator jet squirting in fuel when you open the throttle.

Engines need spark, fuel, compression and timing so the next thing would be timing but it was running well enough.. The compression is a little low at 105, 105 and 117.5 but it should still run.

Where should I look next?
Robin
 
Coil one (next to Bosch unit ) to plug 1 on left of bike as you sit on it.
Coil nearest headstock to plug 2 (middle cylinder)
Rear most coil to plug 3 on right of bike..
Robin
 

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Check Ignition timing really. Check the wires from the pickups, they are known to lose their insulation which shortens the wires to the engine case... This can result in sparks, but at the wrong timing... Had that one a 1000 SFC Classic that I bought. Was running a DMC 1.0 (silver box). Did not want to fire up, although everything was checked, carbs were ultrasonic cleaned, new leads and spark-plug caps, new plugs etc.

soldered in some new wires from the pickups to the DMC in this case and - voilà - solid spark, and a bike barking into live again! 😉
 
Laverdalothar said:
Check Ignition timing really. Check the wires from the pickups, they are known to lose their insulation which shortens the wires to the engine case... This can result in sparks, but at the wrong timing... Had that one a 1000 SFC Classic that I bought. Was running a DMC 1.0 (silver box). Did not want to fire up, although everything was checked, carbs were ultrasonic cleaned, new leads and spark-plug caps, new plugs etc.

soldered in some new wires from the pickups to the DMC in this case and - voilà - solid spark, and a bike barking into live again! 😉
Click to expand...
Thanks I’ll take a look. Got to go and pick up my daughter from work now.
Robin
 
The breakdown of insulation on the stator coils is almost certain if it is original. I have one from an engine that has done hardly any miles and been unused for a long time. The insulation disintegrates as soon as you touch it.
 
It's likely a silly fault.
An errant earth on the ignition circuit?
The accelerator jets pumping fuel doesn't mean that the engine is being fuelled as it should. Are the plugs wet or dry?
Is the plastic tube linking the carbs intake side in place?
Paul
 
The coil wire insulation was crumbling when I got it, I covered it with a rubber goo from a tube. The bang was a back fire.
Got to move on to the car now, rear engine front radiators; water pipes are leaking at the joins.
 
Easy things first, there are two types of engine stop relays on a HKZ ( which is what you have, well done you BTW.. ancient now ) one early type open circuits part of the twin pickups ( or 300Vac exciter coil, forgotten which it is as i type ) and the other places a short on the said pickups, if original barrel relay then that is where i would start ( no pun intended ), need a relevant factory wiring diagram, lads here will know what lurks in the website library. Be careful as you investigate, moving wires and connectors around with old wiring, ie introducing new faults while seeking the original cause.

Next, my inclination is the red exciter wire from the under magnet stator plate, sits under the bucking regulator ( read you have a proper RR? ) may be open circuit. Tricky diagnosing exciter issues, given it wont work without the magnet and you need to remove the magnet to investigate. HTH j
 
Robin Webster said:
‘76 3C , I went for a ride on the 12th July and after 10 miles the bike lurched a few times popped and a bang then the engine stopped and I coasted off a duel carriage way and haven’t been able to get it running since. I’ve been away from home and couldn’t make the 75th meet at the weekend so only just today fitted the new RR.
There is spark and I’ve fitted brand new spark plugs, a battery - 12v 32Ah, and a new Reg/Rec. There is also fuel in the tank!

Cone filters off and you can see the accelerator jet squirting in fuel when you open the throttle.

Engines need spark, fuel, compression and timing so the next thing would be timing but it was running well enough.. The compression is a little low at 105, 105 and 117.5 but it should still run.

Where should I look next?
Robin
Click to expand...
Just re-read, you have spark, consistent spark? Dependant on accuracy of the compression gauge, those are really low readings, borderline cold crank start, rich cylinder fuel load, for a normal start. Needs to be over 150psi, dry and 200 thereabouts wet. running on low compression can be done, though cold crank starts are impeded ie need to start to overcome the low compression, if that helps. Are the plugs wet after unsuccessful starts? j
 
Yes, the plugs are wet but next time I get to fiddle I will have the carbs off and have a good look through them. They were in poor condition when I got the bike early May. After that it will be diving into the ignition circuit.

Thanks all.
 
Your ignition system is 48 years old. You've already made 1 repair. That was a warning to replace the system! As John has pointed out, there are all sorts of potential issues lurking. Unlikely to be carbs IMHO
 
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