R75/7 Weak Spark

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mzmalc77
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R75/7 Weak Spark

Postby mzmalc77 » Mon May 21, 2018 8:09 pm

This is my first post. I am putting the 750 back to standard spec after removing a fairing and a lot of fun with the wiring. Everything is working but i have a puny spark at both plugs so no fire up. i am making up new HT leads to see if that helps but the machine has an old BB electronic ignition unit.
Should i junk it and go back to points or fit a newer version BB unit ? It was running when i got it but took a lot of persuading to start.

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Galactic Greyhound
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Re: R75/7 Weak Spark

Postby Galactic Greyhound » Mon May 21, 2018 8:42 pm

Hi,

See if you can identify your Boyer Bransden Ignition system from this link:

http://www.boyerbransden.com/index.html

If you can, tell us what type it is.

Have a go at getting the original system working before you think about changing it.
The problem could be just faulty connections or a component failure.

First, disconnect the HT leads from the Coil HT terminals (they pull out).

Carefully inspect the inside of each Coil HT terminal for corrosion and clean out with Contact Cleaner.

Check the ends of the HT leads where they are fitted into the Coils - there should be a clip which makes contact with the HT lead wire and this should also be free of any corrosion.


Re-insert the HT leads into the HT Coils making sure that you push them fully down and they fit with a distinct 'click'.

If you have a Multimeter, then remove both plug caps and measure the resistance from the inside of one plug cap (where the plug fits) to the inside of the other plug cap - expect to measure around 24 KOhms.

This will check the resistance of the Plugs Caps, HT leads and the HT Coil Secondary windings.
Let us know what reading you got.

See if the spark is any better.

See this similar thread and tests:

viewtopic.php?f=15&t=25936
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

mzmalc77
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Re: R75/7 Weak Spark

Postby mzmalc77 » Mon May 21, 2018 8:59 pm

Thank you .I have a meter and will run the diagnostics.I love a challenge . The last BMW i rebuilt (79 R100) had bean can ignition and was faultless,

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windmill john
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Re: R75/7 Weak Spark

Postby windmill john » Mon May 21, 2018 9:33 pm

By the way, I’ve had puny sparks on my R65 for the last 7 years, starts very well.

Is that Points or Electronic Ignition John?

Points ignition gives a weaker (lower energy) spark than Electronic Ignition.

With Electronic Ignition it is usual to get a much higher energy (Blue) spark.
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

Roy Gavin
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Re: R75/7 Weak Spark

Postby Roy Gavin » Tue May 22, 2018 12:11 am

Plug caps are service items and are not expensive to replace. If your coils are original they are probably over 40 years old,and might be on their way out.
You might find that the later Boyer kit which includes coils does not cost a lot more than other coils alone.
Ignition systems like full battery volts too, so check the voltage at the live coil terminal and if down consider feeding it direct from the battery through a relay triggered by the existing feed.
Simplest test of coils is if the spark will jump 8/10 mm consistently, not hard to rig up some form of dummy plug lead with a 8 mm gap and check.

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windmill john
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Re: R75/7 Weak Spark

Postby windmill john » Tue May 22, 2018 6:51 am

Whoa Phil, an unusual post with my name on it!!

Last night, I posted the line about weak spark, the one in quotes.

The post now shows it in quotes with three lines that I did not write!!

Obviously a glitch. Out of interest, who posted those three lines?
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

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Galactic Greyhound
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Re: R75/7 Weak Spark

Postby Galactic Greyhound » Tue May 22, 2018 8:21 am

John,

That was me!

Sorry - I have Moderator privileges and it looks like I selected EDIT instead of QUOTE when responding to your post!

The result was that I edited your post under your name instead of quoting it under my name.

I do apologise! :oops:
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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windmill john
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Re: R75/7 Weak Spark

Postby windmill john » Tue May 22, 2018 2:49 pm

Cor Ced, now you are impersonating me, have you not seen the GDPR rules :grin:

"Tonight Matthew, I'm going to be.... Windmill John" :grin:
http://www.kittos.co.uk
Best roads: 623 Burgos to Santander. A back road to Metz; can't remember which!
Schorsch 1978-80 R65 - bit of a Shetland pony; frisky and naughty.
Too many bikes have come and gone, trying to be sensible now!

mzmalc77
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Re: R75/7 Weak Spark

Postby mzmalc77 » Tue May 22, 2018 4:56 pm

Good Afternoon, I just want to thank everyone for advice and information. The beast is now up and running for the first time in 9 months . Despite 88500 miles it sounds great and pulls like the proverbial train.

I tested the circuit across the plug caps and got nothing . Removed caps and cut an inch of the HT leads and fitted new NGK caps , tested again and got
good reading plus healthy sparks. Spent an hour going over everything and fitted new air filter.

Taps on, choke on, pushed starter and bingo fired up straight away.

Now its in need of a good clean up ,more wiring tidy up and new tyres. Any tyre advice would be welcome , i am on original spoke wheels.

Thanks again . Malc.

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Galactic Greyhound
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Re: R75/7 Weak Spark

Postby Galactic Greyhound » Tue May 22, 2018 5:55 pm

Hi Malc,

Glad you got it sorted!
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!


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