Hyo71
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I was going to ask the same question as I need to check mine. I was hoping they were 10mm as I already have a good range of those.
I’m only in to my second season, but they are into the 12th year/season for this class. We have 5 rounds a season with each round having a practice/qualifying session followed by 4 sprint races (6 laps). At each round, one of the races is a ‘Le Man’ style start which is fun. One of the rounds will also include a 1hr endurance race that can be riden either solo or with a partner that you swap with at 30mins. Race tracks are few and far between in New Zealand, so 4 of the rounds are held at the same track with 1 round being at another track 3.5hrs drive away. Other classes also run on the same day.
The aim of the class is to keep it cheap and fun and to get young racers started, give old hats a class to get back into racing as well as everyone in between looking for fun. So the bikes are stock and must run road legal tyres – no tyre warmers allowed. No mods to engine, suspension etc. Just remove road gear, lock-wire and go racing. You can add braided brake lines, fork fluid weight/vol is free to change, jets are free to change and thats about it. Because it is cheap to race, the field is large, which means there is lots of fun to be had! Doesn’t matter if your in the top 10 or last 5, there are battles to be had everywhere! You can pick up a race ready bike for between NZD$1,000-$2,000. I’m not sure what the numbers were before I joined, but last season there was about 40 of us, this season there is 50 – the track limit.
Look up ‘CTAS Live’ on Youtube – he live video streams the races and leaves them on his channel. Next round is 20th November.
Here’s the website for the cup https://www.ccmscup.co.nz/our-story
Or join the FB page to see all the race bike photos and video clips – Carl Cox Motorsport Cup
This is what 40 racing hyo’s look like in the Carl Cox Hyo cup in NZ at Hampton Downs. Round 2 of the 2022/2023 season
Have’nt touched the bike for a couple weeks as I needed to put the battery back into the race bike for a race that came up – I only have 1 battery between the 2 bikes.
In repsonse to your comments Marcel;
- The auxilary tank has a new inline filter on the feed hose.
- The air box and filter were fitted. I didn’t have a carb cleaner spray can at the time – will have to try this to see if there is a leak in this area.
- I only put my fingers over both inlet vacuum hoses at the same time when running – I’ll try plug them and clamp them tight.
- I had opened both fuel pumps at the time, and they were both clean and seemed to be functioning fine. Rubber seals all looked good.
- I haven’t opened the oil cap to smell for petrol but am familialr with this problem. I’ve had it on a dirt bike. – I’ll have a sniff to make sure it hasn’t occured.
- Compression – I just realised 2 mistakes I made, 1) I didn’t hold the throttle open when testing. 2) I hadn’t checked the valve clearances – I’ll have to check the clearances and re-do the test.
Hopefully get a chance to try this weekend.
Compression tester showed up yesterday. I got the below results on a hot engine with both plugs out when testing.
Front = 125 psi
Rear = 132.5 psi
Is that good or bad?
While I was waiting for the tester, I took out the jets for a 3rd time to triple check they were clear – they were. But I found that I missed the fuel inlet filter/gauze above the float stopper thingy. I took each of them out and one was semi-blocked with debris, the other was clear. Gave them a clean out, put the compressor blow gun on all holes and reassembled. Also made an auxiliary tank from a stainless steel water bottle so I can get the engine running without having to take the tank on and off everytime. This bypasses the ‘pump’ and goes straight to the carb inlet hose.
Few things I noticed:
- Good news is the bike will now rev to the limiter and everywhere inbetween as long as I keep the revs up, but it still dies at resting idle if I turn the choke off.
- It is also slow to decelerate when I release the throttle which I’m gussing is sticky slides/diaphragm? Odd as I cleaned all the sticky fuel residue off of them when I stripped the carbs. The throttle cable returns fine.
- As I bypassed the fuel pumps, I noticed the hoses from the inlet boots that create the vacuum for the fuel pump and the tank-tap pump had to be plugged well. They caused the motor to pop and cackle irregulary and the engine tune would improve when I blocked the hoses.
I’m not sure if it is running now due to the fuel inlet gauze being cleaned out in one of the carbs or it is because the fuel is gravity fed strainht into the carb hose. I need to hook the tank back up and see if the engine will still rev up. If it doesn’t, I think the pumps are the issue or the old vacuum hose’s have a leak in them (this is my pick).
Compression tester showed up yesterday. I got the below results on a hot engine with both plugs out when testing.
Front = 125 psi
Rear = 132.5 psi
Is that good or bad?
While I was waiting for the tester, I took out the jets for a 3rd time to triple check they were clear – they were. But I found that I missed the fuel inlet filter/gauze above the float stopper thingy. I took each of them out and one was semi-blocked with debris, the other was clear. Gave them a clean out, put the compressor blow gun on all holes and reassembled. Also made an auxiliary tank from a stainless steel water bottle so I can get the engine running without having to take the tank on and off everytime. This bypasses the ‘pump’ and goes straight to the carb inlet hose.
Few things I noticed:
- Good news is the bike will now rev to the limiter and everywhere inbetween as long as I keep the revs up, but it still dies at resting idle if I turn the choke off.
- It is also slow to decelerate when I release the throttle which I’m gussing is sticky slides/diaphragm? The throttle cable returns fine.
- As I bypassed the fuel pumps, I noticed the hoses from the inlet boots that create the vacuum for the fuel pump and the tank-tap pump had to be plugged well. They caused the motor to pop and cackle irregulary and the engine tune would improve when I blocked the hoses.
I’m not sure if it is running now due to the fuel inlet gauze being cleaned out in one of the carbs or it is because the fuel is gravity fed strainht into the carb hose. I need to hook the tank back up and see if the engine will still rev up. If it doesn’t, I think the pumps are the issue or the old vacuum hose’s have a leak in them (this is my pick).
I don’t have compression test gauges but wouldn’t mind investing in some. Do you know what size/pitch type fits the plugs?
The engine won’t rev to full throttle – it dies if I try get to 1/4 throttle. I am curious, how would the comprssion test results aid in determining an issue?
Cheers,
I’m leaning toward this as well… but I’m really not looking forward to trying to get the airbox/carb back on again – there was alot of swearing last time.
I’ve already stripped the carbs right down and cleaned all the fuel residue gunk from them. I was hoping pulling the main jets out and giving them a clean would solve it, but no such luck.
Hi,
That sounds odd, just few queries to get a bigger picture.
- So everything works fine when running? The horn, lights all work?
- Can the bike be riden normally right through the rev range?
- When running, if you stall the motor, will the dash still stay on and let you start again?
- Will it start after a certain amount of time has passed or if you take the key out and try a few times?
- When you say turn off – do you mean use the kill switch to turn the motor off, or do you mean turn the key off?
- Will it let you kill the bike with the kill switch and then start again or does the dash switch off when the bike dies?
Hey,
Yep, rediculously lucky with the auction. Once I get this back-up race bike ready, I’ll probably turn my attention to the new parts bike and see if I can get a 3rd race bike out of it – could start a little race team haha.
I tried the horn, and it’s as you described – the yellow brick thing made no difference to the horn. The bike also continued to run at an idle when I disconnected it – there was no effect on the running bike what so ever. I didn’t think to see if the bike would start with it disconnected.
In the video you can hear the bike about to die when I try rev it up but I release the throttle just before it cuts out. The bike starts easily now and once warm I try rev it up, but it still trys to die out. I’ll have to check the stator output next like you mentioned above to see if its cutting out when the revs rise – maybe the rectificer is toast. Will have to try the one on the parts bike to see if there is a difference.
Could it be the fact that I dont have an air filter on it? Would that cause it to run lean and die out? I’ve got a busy month ahead, so probably wont touch it for a while – probably start a new thread when I get back to it.
Thanks for the support on this spark issue, hopefully helps others.
Looking into this yellow thing a bit more… Since I’m getting continuity from the yellow thing to the horn plugs, it makes me think it has something to do with the horn. Doing a random ‘bike horn capacitor’ google search, I think it might be a ‘3-pin alarm boost inductor’ for the horn.
It’s a little hard to see in my photo earlier in the thread with the yellow thing circled, but I think the diodes are orientated in the direction of one ‘in’, and one ‘out’. Im thinking that the ‘in’ diode would allow a signal from the CDI to come ‘in’ and prevent a ‘boosted’ signal heading back to the CDI and blowing it. The ‘boosted’ signal would then go through the ‘out’ diode to the horn – I’m no electrician, this is just my loose understanding of diodes.
When I’m next in the shed, I’ll take the horn off my new “parts bike” plug it into the black plugs and see what happens when I unplug the yellow thing from its connector.
SOLVED!!
I put a stupidly low bid on a crash damaged 2008 GT250R on NZ’s equivalent version of ebay and somehow won the auction! I bought the bike back last night and swapped the CDI, and bingo! Spark against the cylinder.
The engine I put in was from a wrecker, so I still wasn’t entirely sure if there were any issues with it. After probably 20 attempts on the starter and a heap of fiddling with the choke slide by hand (the carb isn’t hooked up to cables or airbox), she fired a little burp. From here it took another few minutes of trying and she finally started and ran.
Still not sure what the yellow thing does. It is odd that it isn’t noted on the wiring diagram.
When testing the wires and looking at the wiring diagram, it seems the CDI deals with igniting the coils directly as well as sending signal to the tacho. Is this signal what tells the tacho what revs you are doing or does that come from the magneto signal?
That hint on the tacho and magneto is a good one, I’ll have to remember that for next time.
Yep, I think the black wires are for a horn as well.
Your assumptions are correct Marcel, the clutch, side stand and pick up sensor were some of first things I checked off when I started. The regulator rectifier I still felt wouldnt cause a non spark event so I left that off my list for the time being. The CDI was definitley on the list of things to try but it was the out of spec resistance readings on the secondary’s on the coils that led me to belive the coils were the culprit. Spec states the secondary’s should be 5.4 – 6.6 Kohm but I was getting around 14 Kohm. When I tried the replacement coils and they failed, I checked them, and they also tested to around 14 Kohm. Whether that has an effect on performance at the upper end of the rev range, I’m not sure, but I’ll find out.
Now I can progress putting this bike back together..
Evening,
I thought I would bring the problem solving for the spark issue back to the Tech Help section so as to help any others that may have a similar issue in future (as opposed to the Project thread I have).
I had a chance to check the 3x yellow wire plug (Charge coil). I got 109 ohm. Spec tolerance 90-110 ohm. So ok there.
The Blue + Green wire plug (pick up coil). I got 0.6 ohm. Spec tolerance 0.6-0.9 ohm. So ok here as well.
I hadn’t seen your post Marcel so have’nt taken the stator cover off for a photo. I’ll pop it off next time I’m in the shed. I had already sort of checked the CDI/loom, but I only checked using the continuity function (the buzzer), not the resistance like you mentioned. Is chekcing with resistance better?
Using the buzzer there doesn’t seem to be any breaks in the loom and the wires align with the wiring diagram (mostly). I’m getting continuity from my CDI to all of the key components regarding ignition/spark. Likewise for the regulator rectifier.
I tried my replacement coils but that didn’t solve the issue, so back to the drawing board.
I tested the rear ‘brick’ diodes with the 3 wires (Blue/yel, Blue, Green/red) and came up with the following readings on the diodes;
- B/y = 0.512v
- B = N/A (signal to CDI)
- Gr/r =0.576v
I opened up the mystery black ball thing which had a yellow sensor (?) thing and 2x diodes. It has 3 wires (Black/brown, Black, Black/white) and testing them I came up with the folling readings on the diodes;
- Blk/brwn = 0.190v
- Blk = 0.185v
- Blk/wh = NA (earth from yellow brick thing, to earth for rear coil)
When I carried out a buzz test on the 2x diode wires, they colour match 2x black rubber covered plugs that pop out the front of the frame and buzz. They almost look like wires for a horn but they don’t align with the colours on my wiring diagram for the horn. Being a race bike all road items (horn, lights, indicators etc) where removed and I can’t find the corresponding plugs – could they be for a 2x wire indicator relay? I’ve had them before but the wiring diagram shows a 3x wire relay at the rear of the bike. These wires are at the front.
I carried out a resistance test on the CDI using the pin table in one of the manuals I found on this forum. I’m not getting a single match. For reference, my multimeter is auto ranging.
My next steps are to borrow a CDI off a known running bike and take the cover off the stator for a photo. Failing those, I’ll try source another loom/harness.
Any ideas people?
All the pen ‘ticks’ are the wires I’ve checked for continuity. 
Neutral diode circled in red. 
Mysto yellow sensor with 2x diodes. This was heavily wrapped in a black ball of heatshrink. Red and green lines just to give you an idea of wire runs goining into harness and coming back out to the 2x rubber plugs. Note Blk/wht wire from yellow sensor going to earth at rear coil earth. 
This is where the 2x mysto wires/plugs come out. I dont have corresponding plugs. I hope the harness isn’t the issue, that’ll mean more cold nights in the garage! Or a replacement harness from a wrecker, they’re about NZ$15 here (GBP $7). Nothing to say that it wouldn’t have issues either though – luck of the draw I guess.
Thanks for the heads up on the diodes, I’ll have to look into them to get a better understanding. I had an issue with a KTM 450 motard a couple years ago where I had issues with both the left and right LED indicators turning on at the same time whenever I used the indicator. I traced it back to the indicator lamp on the dash – the dash indicator lamp shared the common wire and the LED’s allowed the power to flow both ways causing them to both switch on. After a bit of research all I had to do was put a NZ$0.65 diode in the common line in the dash and it solved my problem – I saw it as type of 1-way valve.
Yep, the neutral sensor was confirmed early as it was showing on the screen and it would go ‘out’ when I put it in gear.
Are these the diodes wrapped up in the photos below? The front one is in a heatshrink cacoon and the rear one is a rectangular brick – is that right?
Little bit of progress.
I’ve carried out a couple other checks with the electrics and I think my coils are my problem. I tested the resistance on my magneto pick up coil and charging coil and they are both within spec (0.6 ohm and 109 ohm). I was also getting a small voltage through the coil primary wire when pressing the starter for a couple seconds, so I’m hoping that means my coil theory is right. I have ordered a pair of coils from a wrecker, so hopefully show up next week.
Also put my forks on and discovered why the bike came with 3x fork legs…… 1 is bent! If I can be bothered, I’ll have to get around to painting the leg bottoms both black.
While I’m waiting for the coils, next on the list is to look at the rear brake system.
Black fork, silver fork. 
Starting to resemble a bike. 
My process of elimination list. Yea, the laid out parts turned into a photo op – my work benches where full of crap and the floor was the only empty space.
Avalon was before my time, but I too had noticed her. Not sure what she is racing now. There are only around 5-7 GD bikes in the field and I think it just comes down to cost – they are a little more.
Thanks for the welcome.
The class (otherwise known as the Carl Cox Hyo cup – sponsored by UK DJ) has just completed it’s 11th year and has the biggest field in NZ – around 40 riders on the grid on race day. It’s a stock class open to any year Hyo GT250 and is one of the cheapest classes to race in – hence the high field count.
