Breaking down under load

[SCARFEY]

Some of those things are impossible to find.

I had an R80 BMW that would cut out at about 100 kmh and I couldn't work it out for ever.

Turns out the owner had lowered the float levels to a point that at certain revs the vibration from the motor turned the fuel in the bowls to foam. Of course when you backed off for a split second the problem disappeared.

Only by resetting everything including replacing all the electrical bits did I twig to the problem.

[makzy]

True. Should have been more specific. Set the dial to 20k, they should read at least 5 point something.
Car type leads? Mine would hardly run 15 years ago when I tried silicon carbon leads.
And are the spark plug caps motorcycle resister type or car type?

[Christian Raith]

Yeah, well, have you tested the plug caps? 5 ohm. Have you put new plugs in it? Breaking down at high rpm sounds electrical or spark, I recently purchased a top quality timing light that also doubles as a dwell metre, advance angle metre and Taco, it does from 2 cyl to 12 cyl, as well as a really good professional multi metre and mercury rod vacuum gauges, my old girl has never run better after a whole day in the shed, 1 plug cap was down to 3 ohms, the carbs were all over the place but it still sounded ok and I thought it was running ok, the timing was out by about 3 degrees.
I thought to myself that it just shows how finnicy these bloody things can be!
Keep tinckering, you’ll get there.

Plug caps are 5K ohms

[Jonesy :-)]

New spark plugs, leads are car type with rubber boots, checked out Ok.
Yes, its back up on the bench for more tinkering

[makzy]

Yeah, well, have you tested the plug caps? 5 ohm. Have you put new plugs in it? Breaking down at high rpm sounds electrical or spark, I recently purchased a top quality timing light that also doubles as a dwell metre, advance angle metre and Taco, it does from 2 cyl to 12 cyl, as well as a really good professional multi metre and mercury rod vacuum gauges, my old girl has never run better after a whole day in the shed, 1 plug cap was down to 3 ohms, the carbs were all over the place but it still sounded ok and I thought it was running ok, the timing was out by about 3 degrees.
I thought to myself that it just shows how finnicy these bloody things can be!
Keep tinckering, you’ll get there.

[Jonesy :-)]

Thanks makzy,
Thought fixing those wires was going to stop it breaking down but no. It still misses, stutters at about 6000 rpm with a full throttle. Under fuelling?,jammed advance bob weights?

[makzy]

Very inventive, well done. I hate soldering, I have all the good gear for light and heavy jobs but I’m too blind and shake to much so I got a piece of flat timber and screwed 2 small alligator clamps to it about 20 mm apart to hold the wires steady while I soldered, works good.
But that situation is a bit different, very cleaver.

[Jonesy :-)]

Hands free solder holder

[steptoe]

In the video, I think I just stripped and fed together, gave them a little twist to hold them and soldered

[Jonesy :-)]

got the wires stripped and tinned for re-soldering, need to fab up a little tool of some sort to hold the wires together hands free while i do the solder join. Thinking paper clips and a conduit saddle clamp

[steptoe]

It’s often the simple things in life

[Jonesy :-)]

 Oldest one in the book, found both wires broken on the top pickup coil right where the little OEM clip is. Thank goodness, wasn't looking forward to pulling the carbys off again. I,ve had these wires brake before (on another bike) and it's complete loss of power on 2 pots. This one must have been ok until fully advanced

[Jonesy :-)]

Roger that Steptoe comprenday, I,'ll check it out, good layman's explanation
Makzy I agree, doing the easy stuff first before carbs come off, other bikes have sat just as long with no problems?

[steptoe]

Super easy Jonesy, even I can do it, jam one end of multimeter up the cap, shove the other up the other end, put the multi into the earmuff looking symbol and they should read 4.8  or 5,,
If they take ages to settle they’re buggered

[makzy]

It’s hardly likely that all 4 plug lead caps all at once, but they do fail, it might be only one, that’s enough to make you think everything’s gone wrong.
If it was running fine when you parked it a little while back it could be either faulty contacts somewhere or even fuel laquere, ( can’t spell the bloody word!) build up in your carbs somewhere. choke Pistons can get sticky, fuel journals can block.
It’s a hard one to diagnose without hearing.
Start somewhere and eliminate one thing at a time, good luck.