ZXR750 running problems puzzler

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ZXR750 running problems puzzler

Okay here's a puzzler I need help with.

Kawasaki ZXR750 H1 running like shit. The bike runs on choke...revs high etc then sometimes dies.
Off choke, the bike hardly runs above 3k and the revs jump around like mad. Again, sometimes dies.
Original school of thought suggested valve clearances out, carbs gummed up or both.

The valve clearances were out (by quite a lot) and have been done. The carbs have been cleaned
out and blown through with jets checked for size etc. A compression test has been done and all
cylinders show good compression. A spark test has also been carried out and all sparks
present and correct.

So we have compression, fuel (off of a temporary supply) and a spark.

Any ideas?

have a '99 ZX7 - only time I have gotten erratic running is with electronics - is your ECU hosed???

how about worn emulsion tubes - also had/have probs with worn carbs...(independant of being balanced)...causing bogging gown, surges of fuel, jerking forward etc .etc.

What colour are the plugs after it's been run?

The bike runs on choke but wont run at low revs regardless of engine temp.I still suspects its either valve clearance or something is up with the idle circut of the carbs. I think Scoob is on the right lines, has the bike a race can or intake mods?Kev

if you have had a bike tested what where the compression figures.

Hithanks for the replies. A mechanic is actually looking at the bike and is a bit stumped because he was sure it would be the valves/carbs. The bike has a race can - but was running okay beforehand so I doubt it would be that. It has gone through one CDI since I owned it (and the wiring leaves alot to be desired) so not sure if it could be electrical. ???The mechanic is checking the fuel pump/filter as he thinks it could be that.

kris_gb20 wrote

The mechanic is checking the fuel pump/filter as he thinks it could be that.

But it runs ok at revs, nah its not the the fuel pump.

nah he said it doesnt run over 3k! fuel pump maybee, or huge carb failiure!how did this happen? what did you do before hand? did it suddenly happen or get worse over a period of time? Bought it like this? like this after lay up?

Dazed&Confused wrote

nah he said it doesnt run over 3k! fuel pump maybee, or huge carb failiure!how did this happen? what did you do before hand? did it suddenly happen or get worse over a period of time? Bought it like this? like this after lay up?

Bought the bike running fairly okay. (The bike would run fine but needed a bit of throttle to idle). After a few months began to play up getting harder to start. Sometimes it would fire first time then sometimes not. A couple of times I was riding along and the bike would die as if out of fuel. Then it would refuse to start for maybe 5-10 mins. Last time it happened it refused to start at all. But strangely after this it would run as before.Then it started messing around even more. The bike would run on choke then when warm I'd turn choke off and it would die. It would be like this for maybe 20 minutes refusing to run below 4k off choke.

sounds suspiciously like carbs to me (not that the zxrs ever work on choke btw, race or die, thats kwaker chokes for you) You sure they are spotless now, I assume you gave them a decent strip. Rubbers fine? Possible airleak somewhere? Did you check the pilot settings when you checked carbs? Can affect starting and tickover quite a lot, mine were way out (accidental rather than fiddling as one was way out others ok), sure float levels are ok and operating smothely. Of course not all of these should really alter much over time although temperature falling may cause symptoms to be worse.

Correct carb needles, clips/ spacers/ springs in the correct way? carb CV diaphragms OK? Mice in the airbox?

Over the summer I had similar problems with my ZX7R - very poor running, fuel starvation symptoms etc. It also ran very hot. In the course of troubleshooting I found:one blown fuel pump relay (smoking )one knackered fuel pumpearth wire from the loom that attaches to the -ve terminal on the battery had rotted awaythermostat was u/scoolant was long overdue a changeI fixed/replaced everything, cleaned the carbs out, checked the diaphragms for splits and so on and the problem went away.One thing I noticed was that, even with super-clean carbs, it still died when I gave it a handful. This stopped when I fitted a second-hand fuel pump (off a ZZR1100 BTW).Are you sure the carb diaphragms are OK (assuming they're CV carbs)?

tufty wrote

thermostat was u/s

do kwaker make them any other way, when I got mine max running temp (fan on) was 1/2 of scale, its now barely 1/4

Dazed&Confused wrote

do kwaker make them any other way, when I got mine max running temp (fan on) was 1/2 of scale, its now barely 1/4

Mine was the other way around - last one ran at 1/4 all day long and I only ever heard the fan in heavy traffic. After a while it started on 0/4, then shot to 3/4, thought about it, then settled down to 1/2, then decided it was time the fan came on ........ had a mind of its own.

Hi (a few quotes from the mechanic)"The fuel pump has been tested (and bypassed) and is fine. Relays etc are okay. The bike is running lean. The carbs have been balanced since the valve clearances have been done (definately not this anyway) Pilot/main jets have all been checked for size etc etc. Compression is good (all cylinders 175). Ignition system seems fine, as all sparks are there. "Bike is still running shite. I am trying to source a new set of carbs for it - as the mechanic seems to think it's worth a try. Other than that all he can think of is taking the head off and seeing if the gasket is weeping/leaking. The mechanic is totally stumped as to why it's not running right. booger

Tried another set of carbs. Very slight improvement but still unrideable and not running correctly. Any ideas? I'm at my wits end

E.C.U.

I take it the ECU is the same as the CDI unit?If so then we've tried a brand new one on it with no success.

um - yup - hehehe...

Ignition coil(s) maybe? Although there may be enough power in them to make a spark when the plugs are out of the bike, doing the same at 175psi takes quite a bit more welly.

Hi old thread I know but a

Hi old thread I know but a friend has the exact same symptoms with his zxr750 h1. Did you ever find out what was causing the problem? Cheers

In the bottom of each carb

In the bottom of each carb under the brass bush where the float needle sits is a filter and I wonder if one or more of these is blocked? I've had the same problem with a J1 and that fixed it.

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