Left Side Spark - Where The Hell Are You!!!

[grant81rs]

Gidday,

Here's a curly one for you!!

So when I first got this 78 RS the first item I brought was the pair of the spark plug extenders to short out the spark and tune the carbies by ear, you all know what I mean??

And before you continue reading yes I have spark at the plug as I removed the plug from the head and with the lead cap attached I laid it on the head and turned the engine over, it was sparking

Ok, so the left side spark plug (when sitting on the bike) will not short out at all, nope!!, nothing!! it just keeps running when I try to short it out.
The right side does as you would expect when the screw driver is placed across the extender and head and it stops the engine, but the left side nothing so today I -

Swapped over the spark plugs to different sides and still nothing on the left, so I swapped them back then I...

Swapped over the lead caps to different sides and still nothing on the left, so I swapped them back then I..

Swapped over the leads to different sides and still nothing on the left, so I swapped them back then I..

Installed two spare leads that SteveD lent me and still nothing on the left, then I cried!! jokes.

Next I removed the left side ignition coil and cleaned the inner section, reconnected and still the same.... NOTHING!!

Any ideas fellas as I am running out of options... Thanks

[2valve]

Hi Grant. Sounds like the L/H spark plug extender isnt letting the current flow throu the tool , may be give them a good clean back to bear metal for best conductor. Yep i know what the tools is, use to watch Don Wilson use them back in the days.

[SteveD]

...or just swap the tool to the other side to test the tool?

Grant also said that adjusting the idle speed on the left side seems to make no difference to anything, but the right side is nicely responsive. We're wondering why that might be happening? On both sides the adjuster just touches the adjustment arm.

There are two things we haven't checked.
1. The butterfly lever shaft o-rings
2. The weight of the floats. The left has been flooding lots. The floats are that darkened colour they go.

All accessible passages were sprayed and had fishing line thru them. The jet stack was removed and everything cleaned. The atomisers were stuck and full of junk.
New diaphragms, bowl gaskets, floats checked for shut off settings, float valves cleaned (lightly ridged), valve seat flushed and lightly lapped. All jets ultrasonically cleaned and new o-rings ...idle jet/mixture screw/the jet stock o-ring in the main jet stack.

On order: new float valves, new floats.

[grant81rs]

...or just swap the tool to the other side to test the tool?

Just tried that this morning and no difference...

[2valve]

Hi Grant. Would you mind asking easier questions to early in the morning for me !. How about this , wonder if the L/H side spark is weaker comparing the R/H side ? Has both sides has the same type of spark ? If its weak on the L/H side it wouldnt throw a good spark when shorted out and the current is still going to the spark plug via the shortest route?

[grant81rs]

Hi Grant. Would you mind asking easier questions to early in the morning for me !. How about this , wonder if the L/H side spark is weaker comparing the R/H side ? Has both sides has the same type of spark ? If its weak on the L/H side it wouldnt throw a good spark when shorted out and the current is still going to the spark plug via the shortest route?

Gidday..

Correct for an early riser!!

The left side when I touch the screwdrive does spark but only weak and will not stall the engine, I can prod about with the screwdriver at different spots, see spark there but no engine stall.

The right side only has to see the screwdriver approaching and it stops very fast and sudden, to a point of not even letting me hear a stumble or making the engine stall slowly as the stalling test is meant to do..

[SteveD]

Grants bike is a points bike. What is the recommended HT lead and plug cap setup?

The coil is a 3.0ohm coil and different from the later EI bikes.

How does the HT lead and spark plug cap differ from the EI bikes? We should probably ensure we've got this right before further troubleshooting.

On the POINTS airheads, especially the points models with two coils before 1979, the stock caps were about 1000 ohms in the earliest years, then later went to 5000 ohms. A change on only points models, from 5000 back to 1000 ohms MIGHT give some extra ignition performance, in the highest rpm area...near redline+-.....and probably help in starting in cold weather; and in other marginal situations. Thus, 1000 ohm caps are OK, in my opinion, for POINTS models. In fact, I recommend the 1K caps for POINTS models.

From about half way down this page..http://bmwmotorcycletech.info/sparkplugs.htm

[Rob]

I always went to MikesXS (Yamaha 650 twin) for my plug caps and wires for my R65 (points, dual coil).
Cheap, and fast delivery.
I used their 5K caps, because I liked the threaded spark plug connection better than the solid.

This is the page for their ignition stuff: http://www.mikesxs.net/products-27.html#products

Specifically:

wires: http://www.mikesxs.net/product/23-2902.html

NGK caps:
5K http://www.mikesxs.net/product/23-3113.html
5K http://www.mikesxs.net/product/23-3117.html
1K http://www.mikesxs.net/product/23-3116.html
Zero ohm http://www.mikesxs.net/product/23-3114.html

Also check out the tool page. Good stuff. http://www.mikesxs.net/products-49.html#products

[2valve]

On my OLD Points bike BMW 1976 90/6 it had 1k OHM O.E caps but later i fitted NGK 5 ohm caps after i was informed that the O.E caps short out in the heavy rain , but actually had more hassles with the NGK caps in the end for shorting out in the rain go figure !
The caps listed for grants bike is 5K OHM ,that's what they look like to me. They have that large rubber peice around the spark plug cap itself.
Personally I'd be sorting out the problem with the poor spark on the L/H Bank, poor spark equals crap running and tuning problems which you have at the moment.

[Rob]

I had those wet-riding issues when I was running the OEM metal-covered caps.
I switched to NGK, and never saw it again.