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Triumph TR7 spluttering (misfiring?) at high speeds?

2K views 6 replies 6 participants last post by  Old Cafe Racer 
#1 ·
My TR7 (1973) still splutters at high speeds (gradually accelerating) or with quick acceleration. This doesn't seem to be the case if I open the throttle in neutral/clutch pulled in. I fitted the new MKIV Boyer ignition unit about 6 months ago now...surely if this was faulty it wouldn't be running smoothly at idle. Also...this phenomena is a little tempremental. The back was splutering at 90km/h on the motorway for 20mins and then after that it calmed down (not 100% however).

The fuel lines and carburettor have been checked and there are no blockages and a steady flow of fuel. I'm suspecting whether there is an electrical problem (spark plug caps? ignition unit? vibrations causing on/off in circuit).

Anyone else have any experience with this or ideas?
 
#2 ·
First up, check your alternator output (14.5 volts @3000rpm)

13.5 volts is not good enough, has to be 14.5.

If ok, fit new plugs & go for a run in third gear, constant throttle at 100kph. Stop after a mile & remove & check spark plug colour.

Grey/brown OK, Black sooty too rich or oil burning.

If bike still misfiring, remove air cleaners & try again.

Misfiring is usually caused by weak ignition (spark), fuel starvation feels like loss of power & no response to throttle.
 
#3 ·
I would also run it with the ignition switch out of circuit.These switches get all shook up as Elvis said.
Just connect the Boyer supply direct to the main fuse for a run.Just be aware that after it starts,you cannot stop the engine without disconnection.
 
#5 ·
Agree with Rambo about bypassing the ignition switch. If you hotwire it as Rambo says you'll bypass the kill switch too, which is another possible source of intermittent connection/disconnection. New plugs is a must!

If it isn't igniton it'll be carburation, but it can be hard to tell without going through the process of eliminating one possibility before starting on the other. What have you checked & eliminated so far?
 
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