Z250 Single

Hmmm...I just remember reading that a you should get a fresh or full battery before doing a compression test to get an accurate reading. I assume it's just to ensure the motor is turning over as efficiently as possible or something? Anyways, I am hoping that the battery strength does play a large part in the compression, or lack of, as today I am back to less than 30 PSI...

It was suggested to me to test my battery by turning all the lights and indicators on, and taking a measurement - I did this and found the battery had droppedg to 11.6V

I tried doing a wet compression test after that, putting a little engine oil down the spark plug, but the motor could barely turn over and as a result I got less than 30 PSI.

I measured the battery after that and got a reading of 11.96V, which according to the tables, means its pretty much now discharged...

Putting it back on the charger tonight.

Conclusion - so close yet no cigar. Assuming that tonight's compression test was ruined by the battery (and not some new issue) and that I should be able to get the bike started with a fresh battery (or just a running one)? Correct assumptions? Might try to borrow a car battery or something over the weekend - don't really want to spend on another new battery if I can't guarantee it will run. This current battery has seen 0 action.

Sham,
Is your Battery a Wet Lead Acid type? Have you checked the Electrolyte level? that's the Water/ Acid level. the plates should be covered, you can add a bit of distilled water if needed. Charge your battery at a slow rate, 2amps or less, don't use the 10amp or greater settings that most chargers have. One of your local Auto Electricians should be able to test your battery for you, fairly cheaply, maybe free, as a lot of shops would just be helpful.

Hey, been following your build as i'm trying to get mine gone again.
I've had a few of the same issues as you.
Battery loss , Does it hold the same charge left off the bike? (most shops will do a free test as mentioned)
have you tested the Regulator Rectifier and the stator?
I had a faulty RR on mine which caused charging issues that sound very similar to yours.
It's also worth checking the connections coming from the stator case back to the loom.
Battery should have no effect on the compression when it's not running.
The valves on these are probably going to be where your issue is as mentioned.
Did you find a Manual for the single in the end? I have one if you want any pages scanned.

Sorry for the lack of replies, been busy with work.

So...back to this..and I thought I was so close.

Motorhead - yeh its a wet lead acid battery. I ended up getting a ctek charger as I didn't want to run the risk of getting a new battery just to have it go flat as the bike sits and is unable to start again. The battery has charged up fine now.

scraps - thanks, I did get the manual and funnily enough (not that i'm laughing) I think it is a rectifier issue...I'll continue below. Did you manage to the ignition system working? I like the bobbed looked.

So after the success of the 103 PSI test and the subsequent failure which led me to believe I had a battery issue (as it was also reading below 12V), I got the charger as mentioned. I tried doing the wet compression test again and once again got the woeful 30 PSI and sporadic (and poor) starter motor turning. Add into this the smell of burning something and a hot key (though no sparks this time).

My guess for a culprit went to the rectifier. I tried running the resistance test between the red/white to yellow (2), and black to yellow (2) as specified in the manual. Not really understanding what it meant by testing both directions, I took a guess and performed the test first with the (+) tester lead on the red/white, going to each of the yellow wires, and then again with the (-) tester lead, and repeating for the black wire...

I did these tests focusing on the red/white and black wires coming out from the rectifier.

The results were suppose to be show one "direction" being 3x more than the other, but I didn't get that. In fact, I got no readings when I tested the yellow wires from the main wiring harness, regardless of whether it was with the red/white or black wire.

This leads me to believe I may have a defective rectifier, though I'm not sure if the 0 reaction to the rest of the wiring harness suggests that the issue may be elsewhere as well.

Next I tested the the resistance in the CDI - this yielded results totally different to that published in the manual. It was difficult to see what relation my figures had with the chart, if any. I'm also a bit worried that perhaps I fried the CDI if indeed I do have a defective rectifier.

Any tips?

Does my previous issues of sparking at the key, burning smell and sudden failure after testing 103 PSI help point to an issue with the rectifier, or could it be anything at all.

Thanks.

"So after the success of the 103 PSI test and the subsequent failure which led me to believe I had a battery issue (as it was also reading below 12V), I got the charger as mentioned. I tried doing the wet compression test again and once again got the woeful 30 PSI and sporadic (and poor) starter motor turning. Add into this the smell of burning something and a hot key (though no sparks this time)."

Sham, it sounds like your ground, negative battery cable does not have a good connection to the engine. You need to have the battery cable tight and in good condition, from the negative post down to the engine block. this carries the current for the starter motor, just as does the positive cable, which runs first to the starter solenoid then to the starter.
The burning smell is most likely the Black/ yellow wire which runs through the main harness. It is the main ground wire for the bike, and should have a frame attachment point as well as go to the negative battery post. Then each electrical Item plugs into the Black/ yellow for the ground circuit, but the high amperage from the starter must use the cables and not this Black/ yellow. Make sure of the cable connections.
You very well may have damaged the harness, and the insulation has been compromised. Wires can short together, which will cause more melting or fuse blowing. This would be my guess as to what happened to the Rectifier, the starter was looking for a ground, and went through the rectifier to get it, thus burning it out.

Motorhead - if this is the case and I haven't damaged the rectifier, this would be fantastic.

It sounds possible, as after I removed the air box, the negative battery cable had nothing to screw onto. I have screwed it down with a nut, but maybe its not tight enough as you say.

I will check this asap.

Do you have any suggestions as to the state of the rectifier? I just checked on ebay and I"m looking at $90 dollars...

New ones are available, around that price in USD. I wouldn't pay more than $50 for a used one. Thats a real gamble there, might be a waste of money. The bike doesn't need the rectifier to run, for a short period. Don't run it for a long period though, as the AC voltage from the stator will have no connection, and it could be harmed if run for extended periods. But just to find out if your bike will start and run, which I believe is where you are still, it will be OK.

Motörhead you're a genius.

It was the grounding cable - loose as you described.

Tightened it and ran quick compression test - 120 PSI!!!

Can't wait till Saturday - will try running it with petrol.

I'm not sure how the wiring has faired. Seeing as it hasn't been grounded properly for many attempts now and there has been a lot of burning, I imagine it's not the best. But for now it seems ok. Hoping to get it started and ride for a bit before redoing the harness and making some other changes.

Thanks heaps.

Good Luck Mate

Ive got a spare working R/R if you end up needing one, it's from the 80' but I think they are they same. Check the condition of connections from the stator to the R/R as well I've found these to be not the best and caused one issue on mine.
Had it running fine, but I've got a short somewhere and it won't charge with the lights on.

Woohoo - bike "started" for the first time today.

It only lasted for about a second (literally) - after the 3rd or 4th attempt at the starter button, it came to life with what sounded to me like a healthy rumble before dying again.

Fuel was pissing out from the overflow tube from the carb, so I'm thinking it died from an incorrect float level which resulted in the carb being flooded?

Hoping that's the issue, as I think I can deal with that.

Could it be anything else?

So scraps - for now, looks like my regulator is still ok, but I'll definitely be messaging you if it dies on me. Glad to hear you got it started at least

sham wrote: ...Fuel was pissing out from the overflow tube from the carb, so I'm thinking it died from an incorrect float level which resulted in the carb being flooded? ...Could it be anything else?....

Among other things, might be a leaking float valve, or possibly a cracked or loose overflow tube, or maybe an issue with float buoyancy or float function.

If not already done, would perform the clear tube test.

Good Fortune!