Z250 Single

Another thing that comes to mind is the pilot screw

Yeh definitely, I will try playing with its adjustment when I next start the bike.

In the meantime, I've been reading up on how carbs work - these have been a great source of information:

carbkitsource.com/carbs/tech/articles/Tu...buretorTuneUp01.html - Too bad its missing the section on High Speed and power systems

and a 1980's Cycle World article called "In search of a Free Lunch" - www.mediafire.com/?7ttgomzmmjz

So I'm going to just think through what I understand, as there are some things which don't quiet make sense to me yet. Bear with me.

1. Carburetors operate on the difference in air pressure, with the low pressure spaces forming vacuums which suck at high pressure spaces.

2. Initially, the low air pressure formed in the carb throat/bore is caused by the intake of the engine, or the downward motion of the piston.

3. This low pressure affects the fuel in the float bowl and draws it through jets, starting the whole process.

4. This also relies on the Venturi Principle, which states that when an air passage narrows, moving air flows faster, making it an even lower pressure...


Now, in the context of jetting and pods:

1. Pods provides less restriction than stock air boxes, and more air gets to the carb bore. (More air does not equal lower pressure does it? So I am thinking that the issue why more air enters the carb is because there is more surface area for it to enter from, thus when the butterfly valve opens (controlled by the throttle) then more air is coming in...ok that seems to make sense.)

2. So then, shouldn't more air create a higher atmospheric pressure than before? Or is the low pressure even greater? I think what I'm asking is, does the engine suck in air at a greater rate because there is more air, or if the rate that air is sucked by the downward movement of the piston remains unchanged, which in my mind, means you will now have a higher low pressure than if you had an airbox, as there is now extra air?

3. Leaving that confusion alone:
lean - not enough fuel, too much air
rich - too much fuel, not enough air
It sounds like the mix of air and fuel occurs in the same volume - in the jet passages? so more air = a more air and hence less fuel. This is why carbs usually run lean. Hence jets have to be increased to allow more fuel to pass through. The aim of jetting therefore, would be to try to replicate the fuel/air ratio obtained when running the stock air box, at the different systems.

4. Therefore, if I'm running rich - I need to use smaller jets to decrease fuel flow. If it is the pilot system, I will also screw out the pilot screw.

5. If I'm running lean - I will need to use bigger jets to increase fuel flow. With the pilot system, I will be screwing in the pilot screw to also decrease air.


Symptoms of a rich running carb:
- boggy/sluggish acceleration
- black spark plugs

Symptoms of lean running carb:
- backfires when throttle is closing
- white/powdery plugs
- requires excessive choke to start


So at the end of all this, I am slightly confused because:

1. My spark plug shows I'm running rich.
2. My bike does not run without the choke on - it will stall

I'm thinking perhaps I'm not getting full power to my coils perhaps? That would explain the plugs.

The combination I'm running of the 130 main and 70 secondary seems to have worked for others on this site, so I'm not sure - I understand that jetting is particular to bikes and its not a one size fits all thing.

So, any advice would be great - and definitely let me know of errors in my thought process.

What was the issue with the STOCK AIR BOX? The bike would be running and riding by now.

Well really with a cv carb the problem u run in to with pod filters generaly is u lose restriction hence the classic "beer can fix" this being said a problem with alot of pod filters is that the rubber boot blocks the air port (kidney shaped passage at top of throat) preventing things from flowing proper for a more involved cv carb science lesson than I care to type here is a purty good article on cv40 carbs in operation they are the same as your cv 32 or any cv carb really www.gadgetjq.com/keihin_carb.htm

And one more thing on the pilot screw you want to make sure the o ring and washer are in good shape default setting is all the way in till just snug not tight then 1 1/2 turns out

Motorhead - the stock air box is fine, I just didn't know the air filter element was under a different code these days as it was listed as being obsolete - I bought a new pod filter and jets - and seeing as I have them, I want to at least get it running.

Joe - thanks for the article, it was quiet informative, especially in the tuning section. I did have a chance to look at the pilot screw, and tbh, I shouldn't have - I ended up dropping it and damaging the tip. Luckily, I had a kz400 carb one, which is similar, from the rebuild kit I've been using. The area of the thread and above is longer so it sits out from the carb now, but it seems to work. Adjusting the pilot screw seemed to work too - idled well at first. Could get power to the wheels without choke at less than 1/8 throttle - getting it to roll along the verandah, but when I revved it a bit harder, it stalled with a very loud metal clang.



Got more difficult to start after that, i tried adjusting the pilot screw a bit more while it was idling, but as I was doing so, it slowly stalled and white smoke came out from the pod filter.

And then starting getting more difficult from there on...

Until it pretty much refuses to start now.



The metal clang does keep happening when it stalls - I tried to record the sound, though its not as abrupt or loud in the moment I captured. Is it just the clutch?



The spark plug is fouled pretty bad. I'm thinking this might be the reason for the starting issues, though the metal sounds I'm hearing gets me a bit worried that there may be other issues internally as well.

The Metal noise you hear when the bike stalls, thats the one-way starter clutch, and that is Normal.
If the plug is fouling, you should check the Voltage from the Ignition to the coil primary side. The WG Coil Mod is a much debated topic here, like the Pod Air filters. In reality if you have low voltage getting to a circuit, like your coils, you probably have low voltage elsewhere. This can cause a multitude of other problems. It is best to track down then issue causing the voltage issue and repairing it. That way the other issues don't become problems.
Now that it is running, at a reasonable Idle RPM, instead of revving high. Can you do another compression test, with the Throttle fully open, engine warmed up?
There is a lot of good reading in the File base on KZR, upper right corner of the page. Under Non Specific models there's a bunch of carb tuning info.
Your pilot screw will be a Mixture Volume Screw, so turning out will add fuel mixture to the pilot circuit, thus richening the mixture. Maybe with the bigger pilot jet, and the screw out, its to rich. Turn the screw in, till the RPM drops, then back it out 1/4 to 1/2 turn. See how that does, you may need to increase the Idle speed adjustment to get the tach to around 1100 first. Then once you have it set, the pilot screw, shut it off and then check how many turns out you are at. If between 1-1/2 to 3 turns out the pilot jet size should be OK.
This is of course if the coils voltage, compression, fuel level, etc is correct.
That Pod filter, did you OIL it? If so, as they need oiling, is it over oiled, as this can act like a Choke and en-richen the Mixture through out the carb settings.
another thing I just though of, if you pull the carb off again, look and see where the throttle valve/ butterfly is at. It should be nearly closed, with only a small gap to see light through. If it is open much more than say the thickness of a small paperclip, it could be pulling fuel out of the next circuit in the carb. This can lead to issues also, and is from something not set up right, like engine compression possibly cam timing.

Well glad to hear ya got that lil shella to half way cooperate for a bit droping yer screw sounds like something I would do and I am noticing we seem to share some issues when I first got mine if you revved it very hard at all it would die a quick replacement of the petcock screen and washer fixed that the screen had somewhat corroded meybe not to mention was kind of waded lol I would like to say that this discovery was due to brilliant deduction but honestly I just wanted to check the sediment bowl the tank only had minor bits of rust specs that I could see and I wanted to know if there was signs of major sediment and as motor head mentioned I forgot to mention with your richer jetting a turn or so in from default is likely needed I failed to remember your rejet

Motorhead - thanks for identifying that and sharing the info. I actually didn't know I had to oil the pod filter lol, so its definitely not oiled. I will definitely check the voltage from the ignition to the coil, and recheck compression when I get time.

The plan is that after I get my Ps (which is now looking unlikely as I have another 2 weeks to go and my wrists still aren't up to it) I was planning to redo the wiring loom next - cos you're definitely right in that there will be other issues - I've already noticed reliability issues with lights and indicators, and I swear I saw an orange flame/spark come from the fuse box once...so in light of that, do you think its worth doing the WG coil mod? The strange thing is the bike started fine yesterday and I got to ride it around a bit, so perhaps its just the fact I kept starting and stalling on Saturday that affected my starting?

Joe - that's funny, because I'm thinking I need to fix up my petcock too. When I was adjusting the pilot screw, I noticed that fuel was seeping through the screws which are holding the petcock to the tank. I'm also thinking that, as I've been running the bike with the petcock on the reserve setting rather than on, perhaps fuel flow is a bit slow? Seeing as I didn't ride it the first time round and didn't get to experience how the bike wouldn't go without the choke, I think the adjustments to the pilot screw has already improved that a lot, based on how I felt the bike road (albeit only across a short patch of driveway)...

So seeing as its so cold and the bike is now outside, I've been compiling a list of things to buy - the pesky fuel tank cap gasket, some jets, a new pilot screw and other carb bits (rubber cap, o rings)...the list goes on.

Hopefully can get it running a bit better soon.

If you do the WG Coil Mod, consider it a temporary mod, and get yourself ready for spending the time to find the issue and repair it correctly.
Fuel leaking from petcock, have you had the petcock off and clean out your Tank? That bike sat for quite awhile didn't it? You don't want to be out somewhere and have fuel issues, clean out the tank and petcock if you haven't yet.
Good to here that you've ridden some, so you still have L plates? Next is the P Plates? You will have to have the P's for what 1 year? Or is it only 6 months?

Ps for 1 year I believe. Ls have a max limit of 1 year and no extensions, problem being with my wrist and bike issues, I haven't been able to ride. Even know I can't fully turn the throttle. I'm looking into getting a straight bar or something with minimal rake to see if that will be any better, as it's the angle that's affecting me.

I cleaned the tank out again recently and it's good. Still clean. Also using an inline filter, so perhaps its just all a bit too slow in getting to the engine atm? It's not dripping or anything, just wet if you get what I mean.

That's one thing I remember very well from living in NSW, the rules/ laws are very strict.
You may find one of the home made throttle levers could help, they also sell some. They just go over the tube/ grip, and let you push down with the palm of your hand, at the wrist area. Or you could swap to a Quad Bike 4 wheeler thumb throttle, instead of the twist type.