Farting around on a gpz 550

[davo231481]

So i rode down to bombala bike show last sat. On the way back to cooma the bike started to miss and not rev cleanly over 5k. So thinking it was possibly crap in the carbs i dropped it down to fifth and gave it a fistful of throttle:D . It responded and got up around 6-7 k so put it back into top. It didnt run well with a miss still present. Got it home and seemed to be running on 3 at idle with no improvement on throttle. Had a quick look at the plugs yesterday and 1 & 4 looked sooty. The coils are still original but have changed plugs leads and caps 12 months ago. Any ideas before i pull the carbs off yet avain. Btw tried fuel tap in various spots but made no difference.

[Gosling1]

check the charging voltage - this can sometimes fluctuate when the reg/rec gets hot and can cause voltage spikes etc - my z650 does the same thing every now and then.

What you can do to regulate the voltage received by the coils - is do the coil relay mod. Essentially - you use the +12v feed from the kill switch - which normally supplies the +12v signal to the coils - to a normal Bosch relay. Mount the relay up under the tank somewhere, where it won't get wet. You need to supply the coil with +12v straight from the battery through a fuse-holder. The 3rd relay pin is an earth - and the relay +12v output signal - is then split and fed to each coil.

This mod removes all the voltage drop you normally get on these old bikes, where the +12v signal has to go through the ignition switch via a couple of connector, then to the kill switch - then eventually back down to the coils. Its OK when the wiring and the bike is brand-new - but over time, connectors and switches build up resistance which results in less than +12v being received by the coils.....

here is the wiring diagram. Its a really easy mod, I have done this to all the zeds in the shed here....

[davo231481]

Cheers for that gos. Ill check voltage. Its got a charge meter on the tacho and see how that goes

[Gosling1]

If the voltage checks out OK - then I would check the coil resistance - these need to be in spec. Also - sometimes the igniter coils ( the ones down at the end of the crank) can and do fail - the most common symptom is the bike dropping from 4 cyl to 2 and then back. If only 1 cyl is dropping out - the problem is more likely to be with the plug/cap/lead, than the coil. Swapping the coils from one side to the other will show if the problem changes to a different plug.

I would be chasing electrical issues first, before worrying about the carbs at this stage.......

[davo231481]

My knuckles thank you.

[davo231481]

Heres a sit rep. Checked the caps. No probs. Checkdd leads. No probs. Checked the wiring from the connector to the coils no probs.. swapped plugs. Swapped the coils over to opposite sides and problem still existed but had worsened with it now backfiring at around 4k so stripped down carbs this arvo. Thank f it was warm and the rubbers were pliable. Ill fire it up tomorrow and see how it goes.

[Gosling1]

mm OK hope you can find it mate. Carbs can be a right pain in the arse sometimes. Have you got an air-duster to blow them clean ?

[davo231481]

Yeah it was just shit in the carbs. Took it for a spin and ran a lot better. Jush got to find a yoshi to fit as it sounds awesome with the one i got for the suzuki.

[Gosling1]

good to hear its fixed