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CraigF - 21/7/18 at 01:31 PM

Afternoon folks, sorry to come back again to ask the collective, but I am running out of ideas.

ZX9r engine on carbs.
car was sat for some time, went to take it to MOT station a couple of weeks ago and she would not run properly (would idle but die under load), so I thought it would be carbs.

Two weeks later and I have :
1. stripped the carbs twice and rebuilt
2. Checked float valves and heights
3. Checked needle valves and have them turned 2.5 out
4. put new plugs in
5. changed the fuel filter
6. put a new batter in
7. changed over the CDI and fuse boxes to known working versions

So today plugged the new batter in and tried to start her up,
she was spinning over but not catching, then she started to idle revved to about 2k and then suddenly stopped.
tried to start her again, and she was backfiring through the 3rd carb and through the exhaust, but she would not catch.
Now nothing, spins over but does not catch at all.

Please, what am I missing? what should I recheck as I feel as if I am going over the same stuff again and again. Any checks I can do to narrow causes down?


furryeggs - 21/7/18 at 02:23 PM

How olds the fuel?

CraigF - 21/7/18 at 04:24 PM

Not that old, about a couple of weeks.

just to add:
The fuel pump can be heard working
the coils are working ie you can see the spark when the plug is earthed to the block.

kingster996 - 21/7/18 at 04:26 PM

Bike carbs are notorious for “gumming up” if fuel is left in the float bowls for a long time (6 months or so)

Problem is they are very difficult to clean properly once this happens and can need ultrasonic cleaning.

Might not be the issue, but has happened to me in the past with a bike of this era and displayed similar symptoms.

CraigF - 21/7/18 at 05:01 PM

thanks Kingster996,

I did strip the carbs down completely twice, and left the various and bits in carb cleaner for over a week with regulator agitation each time. So appreciate that it could be gunk, but before I do rip down again, I want to make sure that I am not missing something simple. I keep stripping the carbs and rebuilding and it does not seem to fix the issue.


kingster996 - 21/7/18 at 05:41 PM

As I said Craig, might not be this, but in the past when I had a set of carbs gum up they just wouldn’t work no matter how many times there were stripped.

Can you get another set to try and eliminate them as the issue?

Also check the diaphragms in the top for any small years or holes. If they leak then they won’t lift the needles properly which again could cause similar symptoms.


CraigF - 21/7/18 at 05:56 PM

Kingster996, I have actually swapped during the process to a another set of carbs that I had in the garage, cleaned stripped and rebuilt those (they had been stored dry). It is these that are showing the symptoms I am describing.

Will look into ultrasound cleaning and see if I can find anyone local.

Will also look at the cams and make sure that the timing is still spot on and check the valve clearances.


Mark RSP - 19/1/20 at 07:31 PM

I had a problem on mine like the symptoms your describing and it turned out to be the fuel had water particles in it good flush out and new fuel sorted it