Z250 Single

What really? I've never heard of these? The thumb throttle sounds like the best solution, as I'd want to avoid any unnecessary pressure on the wrist. This sounds amazing.

Yeh our laws are much more stringent than that of the states. A lot of the bikes I see on sites like exif etc wouldn't really be legal here...

I'm starting to look into rego and it sounds like a pain - there's a chance the RTA will want to inspect my bike as it hasn't been registered for so long - that might cost $421????

Yes the RTA will require a Rego inspection. I believe any licensed inspection station should be able to do it, if they have a mechanic with the certificate for Bikes.
Any Mods will have to be certified by an engineer. That's a real pain, I've seen a lot of what we here in the USA consider a Normal Mod, be required to have an Engineers certificate there in NSW. But this can be obtained, there are lots of Toys running around heavily modified. You don't want a Defect Notice from the Coppers!

So just a question - the spark plug keeps fouling and I'm starting to think this is related to the overfilling of engine oil when I first got the bike started.

So what happened was the bike was originally filled with the right amount of oil but it wasn't showing in the viewing window, so my friend suggested we fill up more. For I believe we filled about an extra 3L or so.

The symptoms of the extra engine oil have been present - the white smoke from the exhaust, and from time to time when the bike stalls, a white puff of smoke from the air filter. I've only just realized the latter is a sign of too much engine oil.

With that in mind, can I assume that this may be a reason for my spark plug fouling and how the bike doesn't run smoothly and likes to stall or bog down after revving the bike?


Image of oil spilling out from the spark plug hole.


New spark plug after running the bike in neutral after less than 5 minutes.

Otherwise it looks like it might be piston rings and valve seats

1.6 litters = full + 3 litters = wow! Lol that could very well be an issue this also reminds mi is there an easy way to clean 30 yr old oil stains off the oil window lol

Lol yeh - bit excessive aye?
No idea how to clean oil stains - does yours take a long time to get to the actual window?
Oh and compression with a warm engine was 125 PSI...

Not great right?

Don't know how long it takes on mine the window stays black empty or full lol 125 I have seen worse not sure off the top mi head wat our lil 250 should be

Ha I have the opposite problem to you - my oil window doesn't get any oil to it unless its super full.

So here's the deal now - I know I overfilled about 3L, I have drained 2 of that (putting it into a 2L milk container) but no matter how straight or sideways I put the bike, the oil won't get to the oil window.

Before I drained it, I had the bike upright and the level was definitely over...

So, should I be trusting "the window" or the manual - if the manual says 1.4, is 1.4 enough, or is it based more on how the oil is flowing in the engine and into the window?

From what I've read, for compression it seems like 130 PSI is the desired minimum. Don't thin the manual states a minimum but.

Your checking the oil in the sight window with the engine off, on the center stand, or level, right?
That plug looks heavily oil fouled for running only a couple of minutes. Reset the oil level and get it going again, it may take a bit for any excess oil to burn away, so it may still smoke. Get it to temp, and let it run awhile, and see how it goes. You may get to tear into it yet Sham.

Ah Motor Head, you just answered my observation from tonight.
With my fail wrists, I can't get the bike on the centre stand, but I have managed to get it level using a small brick and some wood.
So, having done that, finally got the oil level right, drained it and starting from scratch.
Then I decided I should get onto the float levels again as I was never sure about it and was always judging it off side stand - and managed to get it within 1mm of the gasket level, which I'm pretty happy with for tonight. The manual does ask for 2.5 +/- 1mm, but close enough?

The bike now starts super easily, hear the starter motor go twice and it's running.

Idles well around the 1.2/800 mark - starts off around the 1.2 and slowly drops lower. First time round I let it idle for a couple minutes and it slowly revved slower and slower until it stalled. Second time around I let it idle and revved it when it started dipping to about 800 and it would pop back up to 1.2k. I'm thinking with some tweaking of the pilot screw that might be fixed?

The second thing was the white smoke, which surprised me as I know the oil levels are good - dead on centre between the two lines. So perhaps it just needs to burn off. Only let it idle for about 5-10 minutes all up.

What a big differences these little things make. And how ironic its taken this long, essentially fidgeting with the same several elements.

After last night's goodness, all has reverted back to normal in the non working sense.

I started the bike up in the morning and let it idle, just to see how it would perform. Started off great - it always seems to idle a bit higher at the beginning before quickly coming down to just below 1k. I messed around with the idle screw to get it to the 1.3k mark the manual recommends, and it was happy with that. All the meanwhile, white smoke continued to come out from the exhaust.

Revved it a bit and noticed 'dirty' smoke coming from the exhaust around the 3k mark. Not sure if its brown or black but lots of it, after which, the bike started to want to die on itself, and while I could keep it running by revving it more, it got harder and harder until it died.

Pulled the spark plug out again and noticed it was carbon fouled. Reasons for this seems to be the following:
1. rich mixture
2. weak ignition
3. poor compression

I tested my compression and got 110 PSI, which seems to be what I'm getting these days with a warm engine.

Cleaned the spark plug (just brushing some of the carbon off) and tried starting again. Bike did not want to start and I believe started backfiring. I'm calling it backfiring because I saw fuel mist shoot out from the jets holes in the carb, on the intake end, after removing the pod filter. This action produces a far amount of force and even managed to shift the carb loose from the manifold...

So reasons for backfiring according to a quick search on the internet are:
1. lean mixture
2. incorrect ignition timing

So continual issues which I am now facing are:
1. Bike idles fine, but has a tendency to want to die after giving it substantial throttle and revving past the 3k mark. As I am running the pod filter this most likely has to do with my jetting (running 130 main/68 secondary - originally 98 main/68 secondary)
2. White smoke, initially thought to be a result of overly high levels of oil, but after running it for a good 10 minutes or so on idle, the smoke is still there. May be pointing to issues with piston rings or valve seals?
3. Starting is unreliable and gets more and more difficult after each attempt.

Having seen the big difference the correct oil levels made to starting the bike, and seeing the continual white smoke, and linking that with the difficulty in starting (but not the backfiring, which is the main issue now) I'm thinking there may be an issue with the oil seals? I have read that I should be able to read the oil levels on the bike after letting it cool down for a couple minutes, but my oil levels never seem to return to the gauge very quickly - could this be pointing to an issue to how the oil may be impeded from returning back down?

Anyways, I think I should look into the backfiring first. Will try changing the secondary jet back to the 70 (one size up) and try to check the ignition timing. However, the manual says I need a strobe light, so I'll have to look into it. It also confuses me why this might happen now, when it was starting fine before. It definitely isn't the spark plug, as even though its fouled, I can see a clear spark from it.

For motivation, a kz250 featured on pipeburn, from an Aussie builder!

Sham,
Changing the float height/ fuel level as you have, would have more fuel in the bowl, which sounds like it should be correct now anyway/ Before, checking the level with the bike on its side stand, was a No No. Hopefully changing back to some leaner fuel jets will get it closer. Yes a strobe Timing Light is needed to set up the ignition, those can be had pretty inexpensively. Your "Super Cheap Auto" will sell on pretty cheap.
110lbs of compression warm? Well if that is accurate then that is pretty low, but it will run like that. It won't have the power it should, and may well burn some oil. But then it might run like that for quite awhile, who knows. The smoke would be the concern, as you over filled the oil and the exhaust will be having it inside for a while. You need to get it out and run it to get enough temp in the pipes to burn it out.
So don't give up yet there Sham, that little bike will be an enjoyable ride once you get a few more things straight.

Well it is atleast making steps forward when I first got mine it would idle all day long and it would drive as long as u was super gentle with the throttle rev it to fast or to high and insta stall but over time as I ran it more it got better and better know have new tires on the way still need to find a front brake cable and muffler but meh I will get muffler next week.and meybe find a brake cable that will work