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  1. Spark Plugs and Things
  2. Electronic Ignition
  3. Voltage Regulation and Rectification

Spark Plugs, Caps and Leads

One would think that the topic of spark plugs would not be interesting at all - heck they have been available and used in engines for over a century ! Not so - there is an emerging problem for older Japanese motorcycles as in some cases, the originally recommended plugs are just not being made. For example - my 1966 Yamaha YA6 calls for an NGK B7HZ spark plug - try to find one ! And if you own an RE5 then you have a real problem as the NGK A9EFP plug was only made for that model of machine, and has not been manufactured for years. And while in most cases it is possible to use a substitute spark plug type in place of the original, the range of options seems to be decreasing as it appears most plugs these days are 'resistor' plugs rather than the original non-resistor style spark plug.

All new engines use some sort of resistor in the high tension circuit to suppress RFI (radio frequency interference) caused by the spark as it interferes with TV and radio transmissions. Older Japanese motorcycles put the resistor in the spark plug cap, and have a metal core spark plug lead and a non-resistor spark plug. Cars generally use resistive spark plug leads (carbon) and resistor spark plugs with no resistor in the spark plug cap (not always true, but OK as a generalisation). Resistor style spark plugs started to become more common on Japanese motorbikes as electronic ignition systems (CDI) became more common and pretty much were standard by 1979 - points based ignition systems don't really care, and actually you do get a better spark with a non-resistive setup on the older bikes as the ignition coils were not that great.The best overview of the issues and options that owners of vintage motorcycles have that I've seen recently is here. In brief, as I am staying with points on my old bikes I need to find alternate non-resistor spark plugs - for the project bike, I do plan to use an electronic ignition so I just need to ensure that the spark plug cap at least is correct and is a resistive cap.

Decoding the spark plug types then is a useful thing to be able to do, and luckily there is a good chart available from NGK if, like me, you are using their plugs. I have it available here. This is a useful thing to have for example when trying to confirm the right plug to buy for my old Yamaha as NGK here in Canada was of no use at all - the kid on the customer support desk claimed they had never even offered a B7HZ plug and that I had the part number wrong ! It was almost enough to make me want to buy Champion plugs, but I'm not quite that desperate just yet.

First of all, if there is an 'R' in the spark plug label ahead of the number then its a resistor plug which I don't want. Using the B7HZ as an example, it decodes as follows:

Basically then, if a 'Z' plug is not available, a standard centre electrode plug should work fine (a B7HS with the 'S' being a 2.5 mm diameter centre electrode) - my assumption here is that the fatter centre electrode was wanted in 1966 as the injector oil fuel systems were new, and fouling would have been common. The injector oils available today are much better, so this shouldn't be an issue. Given my previous experience with a YA6 and holed pistons, I may actually start off with a colder plug and see how it works - this would be a B8HS.

For the GT750, the NGK B8ES series plugs are still available (the 'E' means it has a longer reach of 19 mm or 3/4 of an inch) - but I may stock up on them. I suspect they will eventually be phased out in favour of resistor style plugs as the general demand for non-resistor plugs declines over time.

For the project bike, I just need to ensure that I have the correct resistor caps, ideally with a lower resistance as the OEM ignition coils are not that great. NGK provides a PDF format reference sheet listing the available options which I've included here. Either the 1K ohm NGK part LB01E, or the 5K ohm NGK part LB05E caps should work fine, with the lower value probably being better to ensure the as much current reaches the plug as possible.

For the ignition leads themselves, generally speaking on older Japanese bikes these don't really wear out as they are wire cores, and are epoxied into the coils. At the resistor cap end, all that is required is to trim the end occasionally to ensure a good contact with the wire core and the cap. Obviously if you do this too often, you will end up with a very short lead, so it is possible to chip out the epoxy, and then install a new wire core ignition lead, and then re-epoxy the connection.

August 29th Update - I managed to connect with Carrie and Brandon from the US NGK Customer and Technical Support teams, and Brandon has confirmed that, as I'd guessed, the B7HS was the correct NGK plug for my old Yamaha. I still haven't heard a peep out of the Canadian branch of NGK which is disappointing, but at least I have an answer.

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Electronic Ignition

There are several electronic ignition options available for the GT750 and include the Boyer Bransden, Newtronic, and roll your own as described on the Pink Possum web site.

If you search the web, the kit that seems to have the best reviews is the Newtronics kit as it is packaged as a Suzuki specific item - for example you supposedly do not need to butcher your wiring to install it. See Gunner's write up on the Newtronic unit here. However, as of this writing Newtronic are no longer in business, although their SU6 kit can still be found if you look and the new owner - Autocar - may start selling them again. Given availability issues, I went with the Boyer Bransden unit which I bought from Walridge Motors who are the Boyer distributors here in Canada. Walridge Motors is actually a vintage British motorcycle supplier, and they were very easy to do business with, and quite helpful. They also stock the old style metal core ignition wire which is handy for repairing old Suzuki ignition coils if you have the need.

Update January 2015: There have been a few changes since 2008 - both Newtronic and Boyer Bransden are still supplying product, but my current preferred choice for ignitions is the Accent unit from Germany. These units fit very neatly under the points cover plate, no wiring modifications are required and installation can be done in as little as 30 minutes. * Packaged ignition units are also available from Marcel in The Netherlands

I won't repeat what Gunnar has mentioned about the Boyer Bransden model KIT00083 kit to fit the Suzuki triples, other than to agree that it is disappointing as it is actually a made over kit intended for a Kawasaki and as such it lacks the correct mounting plate, the correct wiring diagram information or even what I'd call 'good' set-up information. Having said that, it wasn't too hard to figure out and install. I did have to modify the Suzuki mounting plate as the rotor supplied in the Boyer kit was too big for the hole in the centre of the points mounting plate as seen to the left - I opened the hole up with a step drill bit. I also made a rubber pad from an old inner tube to fit under the Boyer contact plate which was probably not really required, but seemed like a good idea as the Boyer supplied plate is not very rigid. The mounted point plate can be seen in the photo below.

On the plus side - once I had it installed, the bike did start up with no trouble at all so my first impressions are positive. The folks here in Calgary that I've spoken to who have the Boyer Bransden unit installed, all seem happy with the product, and several of them have had years of use with no problems at all, so we will see how it goes.

It should be mentioned, that a decent dial gauge is a must for doing the initial setting of the timing, and a good list of available options is offered on Gunnar's site. I actually built my own dial gauge shown to the right using a cheap unit from Princess Auto (part 2970986) which was on sale, and an old NGK spark plug which I modified to be a holder. It has worked well for me for many years now at a total cost of less than $10 CDN.

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Voltage Regulation and Rectification

As I looked at the 33 year old rectifier and voltage regulator, I felt a bit uncomfortable - they looked like they would work, and they checked out OK electrically, but having just updated the ignition to be electronic and having got rid of the points, they both seemed a bit tired in comparison. As I looked around for at least a new voltage regulator, I saw several NOS regulators for sale, but the cost seemed high, especially when you considered you were still buying an old style mechanical device that frankly was not that accurate under load. Then I stumbled across a small outfit in the USA called Oregon Motorcycle Parts that not only sold solid state regulators, but also had new rectifier units to fit the GT750 ! And all of this at a very reasonable price for both the units and shipping, which is where you normally get hosed by eBay for example.

The items arrived very quickly and were easy to install - the voltage regulator (the silver coloured item seen to the left in the photo above, and part number VR3-SGT) is solid state and barring a major electrical fault in the wiring harness, should last forever. It is adjustable - there is a small pot on the wire harness side of the regulator which can be adjusted with a small screw driver if required to set the voltage (roughly 14.2 V at 1500 RPM). The rectifier was just a 'drop in' fit - quite painless.

So now that the GT750 electrics have been updated, we can move to the End Game.

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