She won’t start on the button !

[1975-S1C]

Morning folks.

I have a KZ900 that is fitted with Boyer Bransden electronic ignition (not my choice, it was fitted when I bought it about 8 years ago).

I replaced the battery maybe 5 years ago with a Motobatt.
Up till now all has been well and the bike always started up on the button no problem after the Winter lay-up.
This year it wouldn’t start on the button, but eventually I started it using the kicker, but it ran terribly when I took it round the block, coughing and backfiring. I recall reading somewhere that BB ignition systems need a good battery so I bought a Motobatt charger and sure enough the battery was down on charge. Once fully re-charged I fitted it to the bike and tried again.

Once again it wouldn’t start on the button (though it seems to turn the bike over ok), but it started on the kick start after a few kicks, and actually seemed to run a bit better, though I haven’t taken it for a run to try it properly yet.

I measured the voltage of the battery after I’d been cranking the bike over for a while and it’s at 12.2v.

My question is, is it possible that the battery has enough snot to turn the bike over but not for the BB to work properly ? And therefore I should just go buy a new battery and all will be well ? Or does that sound too simple and my problem is likely somewhere else ?

I’d appreciate your thoughts / suggestions

Thanks
Paul

[warren3200gt]

Low battery voltage/amps will cause all kinds of odd symptoms from weak spark to poor starting and everything in between. Just because you have 12+ volts across the poles doesn't mean your getting adequate amp out put.
At 5 yo the battery is the likely cause and I would replace that first anyway.

[kev edwards]

Yes Boyers need a good electricity supply, but then all ignitions need a good supply, you said after the lay off, so you may have a pilot circuit problem instead, Boyer's are good, been around a long time, I've had them on a good few bikes and have never been let down by them.

[1975-S1C]

Thanks chaps. Really appreciate the replies.

I’ve taken Warren’s advice and just placed an order for a new battery. Might as well take that out of the equation to start with, and hopefully that fixes it.

I’ve given the carbs a thorough clean Kev, as I did think pilot circuit in the first instance. What makes me think battery is that it’ll start on the kicker but not on the button. Presumably the starter is putting a load on the battery and it doesn’t have enough snot to produce a spark, or at least a decent one !

[Big Fluff]

To me it sound more like blocked pilot jets. The pilot jet bore size is miniscule and takes next to nothing to block them up.
Use a wire prong from a traditional wire brush to gently twixt through the jet prior to cleaning with brake spray and compressed air.
We get 50+ bikes in every year with carb issues, most of them due to winter lay-ups and not draining the fuel out before hibernating.

Agree that some ignition systems needs a strong battery supply. The ZRX1100/1200 bikes won't run below 12.4v.
BB systems can be somewhat questionable regarding reliability issues..... Dyna-S is the aftermartket standard.

[1975-S1C]

Already cleaned the carbs, it seems to run ok now once started. It’s the starting that’s the issue. Starts on kicker, won’t start on starter motor, so I’m thinking battery. I’ve got a new one on order so that’ll eliminate battery from the equation anyway. Fingers crossed all will be well, we’ll see I guess !

[1975-S1C]

Bit of an update.

New battery arrived, fitted, fires up on the starter pretty much straight away. Therefore I conclude my main issue was indeed the original battery not having enough snot to both turn the engine over and provide a spark at the same time.

So far so good. But ….

Ever since I owned this bike it has always run Rich. The plugs are generally very sooty, it has a little splutter when I open the throttle from idle, and folks that follow behind me report black smoke and a petrol smell when I open the taps !

I’d like to resolve this, so next dim question is:

Should I adjust the air screws out a small amount at a time until (hopefully) it’s dialled in ? At present they are at about 1 1/2 turns out.

Cheers

[warren3200gt]

Airscrews out will lean it off on the idle pilot circuit but not really any other rev range. 1 1/2 to 2 turns out is within the normal setting range which suggests the main issue lies elsewhere.
Assuming jetting is standard I guess your old choke plunger seals are shot creating a rich mixture throughout the full rev range.
Rob (zed1015) does a seal replacement service using viton seals.

[1975-S1C]

Thanks Warren.

I guess I’ll get in touch with Rob. It sounds like that could be a likely cause, and won’t hurt to rule it out anyways.

The Mains are 115 and the pilots are 17.5 which I think is standard for the bike.
What isn’t standard is that it was bored out (1015 I believe) by the previous owner, and also has a non-standard air box. The air box is essentially the same shape but made of aluminium, but the back is open and it has a car air filter in it. Again, from the previous owner. I guess I’ll work my way through that at some point, but makes sense to get the choke plunger seals sorted first and work from there.

Thanks again
Paul

[warren3200gt]

Car air filter could also be your problem then. Car filters are pretty restrictive as they don't need to allow huge air flow due to only revving to half the rpm a bike engine does. That'll affect the entire rev range. Try running it without the filter in place and leave the air box open. That will lean off the mixture somewhat. If you can get good plug colour without the air filter fitted that's another thing that needs addressing. In fact I'd try that before the plunger seals.
You might find the new battery also helps as a weak spark will cause sooty plugs.

[1975-S1C]

Thanks Warren. I will definitely try your suggestion ref the air box. I actually have a Z1 air box and filter that I plan to put on at some point.
I’ve already messaged Rob about the choke plunger seals and to be honest I think I’m going to get them done anyways, as that’ll rule them out of being the cause.

[kev edwards]

I guess while carbs are off it would be better to put original air box on, carbs that old choke plungers are a must.

[1975-S1C]

You’re right Kev. I looked at the plunger seals last night and they definitely need doing.
I’ve got them all packaged up and will be on their way to Rob as soon as the post office opens.

I’ll put the new air box and filter on when it all goes back together.

While the carbs are on the bench I’m also going to have a quick peak to check which groove the c-clip on the jet needle is in.I believe it should be the 3rd groove from the top.

[kev edwards]

What carbs do you have, 26 or 28, fuel or air screw?

[1975-S1C]

26’s I believe Kev