ZZR400K serious bogging issue

[imthatguy]

Hey guys,

so my 1992 zzr400(k) is experience some serious surging / bogging with any sort of throttle.

It started last week when I was driving up to the coromandel, I filled up in Rotorua and almost immediately started noticing hesitation on acceleration, it got worse and worse throughout the day until by the time I reached Auckland (the next day) it was seriously effecting my driving.

It seems to happen at really any rpm with more then 10% throttle

Things I have tried so far:
- stripped and cleaned carbs and jets emulsion tubes etc
- checked for spark, measured resistance on ht leads (4.9k on all but one which is about 14k, but good spark on all of them)
- completely drained, flushed and replaced fuel
- checked a fixed a few minor air leaks
- tried numerous float heights (10m yielding the least hesitation but still not right)
- checked diaphragms for leaks, needles for wear, bombed the carbs with carb clean
- changed plugs

I should add that is starts, and idles fine - if a little slow when cold, but thats pretty normal.

Pretty much at my wits end here, Ive ordered another set of carbs to try but in the mean time has anyone got any other ideas?
Would I be able to borrow someones compression testing kit and / or ht leads to check if thats not the issue? (Medowbank area, Auck)

Cheers, guys - Aaron

[Zedder]

Hey guys,

so my 1992 zzr400(k) is experience some serious surging / bogging with any sort of throttle.

It started last week when I was driving up to the coromandel, I filled up in Rotorua and almost immediately started noticing hesitation on acceleration, it got worse and worse throughout the day until by the time I reached Auckland (the next day) it was seriously effecting my driving.

It seems to happen at really any rpm with more then 10% throttle

Things I have tried so far:
- stripped and cleaned carbs and jets emulsion tubes etc
- checked for spark, measured resistance on ht leads (4.9k on all but one which is about 14k, but good spark on all of them)
- completely drained, flushed and replaced fuel
- checked a fixed a few minor air leaks
- tried numerous float heights (10m yielding the least hesitation but still not right)
- checked diaphragms for leaks, needles for wear, bombed the carbs with carb clean
- changed plugs

I should add that is starts, and idles fine - if a little slow when cold, but thats pretty normal.

Pretty much at my wits end here, Ive ordered another set of carbs to try but in the mean time has anyone got any other ideas?
Would I be able to borrow someones compression testing kit and / or ht leads to check if thats not the issue? (Medowbank area, Auck)

Cheers, guys - Aaron

You filled up in Rotovegas! Well there's your problem...

But seriously, bad fuel could be the problem if it has just started. I had a 400k until recently so know them reasonably well but I'm not a motorcycle tech. How are the mixture screw settings? Apart from that, it looks like you've done all the right things so far.

I'd give George the Motorcycle Doctor a call if you have no further luck.

[FJRider]

But seriously, bad fuel could be the problem if it has just started.

Timing is everything ... any heavy flaking/rusting inside the tank may cause issues.

I'd let the bike sit for a while. Then empty the tank into a clear container. Water will be obvious as it looks like bubbles near the botton.

Remove and clean the filter inside the tank above the fuel tap. Flush out the tank.

Then drain the carbs.

Replace (or fit) an inline filter ...

[imthatguy]

Timing is everything ... any heavy flaking/rusting inside the tank may cause issues.

I'd let the bike sit for a while. Then empty the tank into a clear container. Water will be obvious as it looks like bubbles near the botton.

Remove and clean the filter inside the tank above the fuel tap. Flush out the tank.

Then drain the carbs.

Replace (or fit) an inline filter ...

Hey guys, thanks for your replies.

Just to reiterate I "have" completely flushed the tank of all the old fuel, and completely stripped the carbs to ensure there isn't any fuel left in there.
I completely drained the tank, then ran spirits through it to remove any residual water, then ran new fuel through it and flushed that a few times before refilling it with fresh fuel.

So I really don't think its fuel / water related..

FJRider; I haven't changed the mixture screws yet as once I play with them ill need to rebalance (and I don't have any gauges) but I haven't changed them so I assume they should be fine..

[FJRider]

So I really don't think its fuel / water related..

Then it must be electrical.

A short in the HT leads maybe.

An Auto sparky might test a few other things too ...

[Gadget1]

Hey guys, thanks for your replies.

Just to reiterate I "have" completely flushed the tank of all the old fuel, and completely stripped the carbs to ensure there isn't any fuel left in there.
I completely drained the tank, then ran spirits through it to remove any residual water, then ran new fuel through it and flushed that a few times before refilling it with fresh fuel.

So I really don't think its fuel / water related..

FJRider; I haven't changed the mixture screws yet as once I play with them ill need to rebalance (and I don't have any gauges) but I haven't changed them so I assume they should be fine..

I've got two ZZR400s and have stripped and cleaned both carbs. You don't neccessarily need the gauges and can do a bench sync/balance if you change the mixture screw settings. Google it and you'll see. However, I'd go with the Motorcycle Doctor option at this stage too.

[GSF]

Know anyone who has a matching CDI box you could borrow and try? My Yamaha's stator went kaput, fried my reg/rec and CDI which cause some very interesting surging/bogging issues (ignition breaking down as CDI shat the bed) until I found the fault.

[Zedder]

I've got two ZZR400s and have stripped and cleaned both carbs. You don't neccessarily need the gauges and can do a bench sync/balance if you change the mixture screw settings. Google it and you'll see. However, I'd go with the Motorcycle Doctor option at this stage too.

Two ZZR400s ay? I've got lackabikealosis and have been hiring them lately. Wanna sell one?

[imthatguy]

Then it must be electrical.

A short in the HT leads maybe.

An Auto sparky might test a few other things too ...

Yeah Ive suspected as much.. Electrics are a bit of a black art to me tho, but Ive checked the most common things - Its definitely getting spark, the spark is strong and will jump around 11mm to the frame with the plug removed. The coils are getting 12.46v (which is exactly the battery voltage).

I can definitely give the motorcycle doc a call, the only issue is last time I asked he was booked out for almost a week an advance and I suspect ill have the same issue..

[imthatguy]

Know anyone who has a matching CDI box you could borrow and try? My Yamaha's stator went kaput, fried my reg/rec and CDI which cause some very interesting surging/bogging issues (ignition breaking down as CDI shat the bed) until I found the fault.

Hmm not really ay, I don't know anything else with this bike anywhere actually

It could be I suppose.. Don't suppose theres any way I could test that without another one is there?

The R&R has been recently replaced and seems to be working perfectly

[FJRider]

Yeah Ive suspected as much..

Shorts show up well in the dark.


But have you checked your Air Filter .. ??? Dirty air filters will cause all you describe.

[imthatguy]

Shorts show up well in the dark.


But have you checked your Air Filter .. ??? Dirty air filters will cause all you describe.

Its actually filthy, but I tried running without it and it doesn't seem to have made any difference

[Gadget1]

Yeah Ive suspected as much.. Electrics are a bit of a black art to me tho, but Ive checked the most common things - Its definitely getting spark, the spark is strong and will jump around 11mm to the frame with the plug removed. The coils are getting 12.46v (which is exactly the battery voltage).

I can definitely give the motorcycle doc a call, the only issue is last time I asked he was booked out for almost a week an advance and I suspect ill have the same issue..

George has given me advice over the phone a couple of times, however, I've actually had my 'bike in at his workshop in the past.

[Gadget1]

Two ZZR400s ay? I've got lackabikealosis and have been hiring them lately. Wanna sell one?

I'll PM you.

[GSF]

Hmm not really ay, I don't know anything else with this bike anywhere actually

It could be I suppose.. Don't suppose theres any way I could test that without another one is there?

The R&R has been recently replaced and seems to be working perfectly

Unfortunately they're not really testable unless you have very special gear as far as I know. Main way to test one is to swap it out for one you know is good.