FZR 400RSP (2TK) running problems - CDI?

[goneleft]

Hi,

I have a 1987 FZR 400 RSP 2TK that I am really struggling with.

I bought the bike last year as a non-runner, it had sat for a while and the tank had rusted leading to the carbs getting gummed up. I cleaned the carbs thoroughly and replaced the tank and it's now running but is not very reliable.

The bike idles well once it has warmed up and riding around town it will be perfectly happy. When I take it out onto faster roads it will be sweet for a while and pull well through all the gears. However, if I ride for a while with the throttle wide open and the revs pretty high, when I come off the throttle it starts to run poorly. It will sometime cough and backfire a bit and then feel as though it is running on 3 cylinders. I can nurse it on for a while by blipping the throttle but it will always eventually die if it has to idle for at a set of lights/junction. It then won't start again no matter what I do with the choke or throttle. It will fire up again with no problem if I leave it for a few hours or overnight.

I've been through the carbs several times and rebuilt them with Litek seals. The float heights are set at 11mm and the fuel level looks when checked against the lines on the float bowl using a clear tube. The pilot screws are set to 3 turns out. I have synced them using a vac gauge.

I noticed the coils had cracks in them which lead me to believe it was an ignition problem, but even with new coils, the problem persists.

I've also re-shimmed all the valves and they are within spec, although towards the tight side.

I'm starting to think that I may have an issue with the CDI unit. Is there any way to test it? I was thinking of buying a 2nd had one from ebay and swapping it out. I can't find one for a 2tk and I wasn't sure whether it would be interchangeable with any other models (1WG/3EN1)?

Also if anyone has any further ideas on how to diagnose the cause of the issues it would me much appreciated as I'm pulling my hair out at the moment.

[MadMotoUK]

I'll be honest, I've never had a Yamaha CDI unit fail.

It sounds like it's dropping a cylinder, leading to unburned fuel going through the exhaust causing the pops and bangs.

What is the actual fuel level when you check it? It should be somewhere between, IIRC, 4 mm and 7mm.

What condition are the spark plugs in? Does one look different from the rest?

[MadMotoUK]

One other thing I'd suggest is making the valve clearances a little more towards the loose end of spec, they'll tighten up over time.

[Brandon88]

Any luck sorting the problem? Just wondering what fuel you’re using. Here in NZ I’m running my 3tj on 98. Only because I’m not sure what fuel is recommended and scared of pinging or detonation.

[kagari15]

Does it actually have CDI and not TCI? Can you read the label on it? See if it has been taken apart before like mine...and discover problems?

BUT - before that...are the fuel lines and the fuel pump and filter are clean and can supply enough fuel while going fast and revving high? That might be it.