Poor running below 2000 rpm

[Al]

I have a set of working CV 34 mm's from my J which you are welcome to borrow just to swap over if you can work out how to collect and return to North Hampshire unless you can find some nearer to you.

AL

[Taffus]

Check you are getting 12V at the coils if not try this

[njwmct]

I have a set of working CV 34 mm's from my J which you are welcome to borrow just to swap over if you can work out how to collect and return to North Hampshire unless you can find some nearer to you.

AL

Thanks for your kind offer - I may well take you up on this

[debben1]

When you adjusted the valve clearances did number 1 cylinder need adjusting by much ? could be a valve not seating properly, if so no amount of carb cleaning/swaping/ jet changing will help, Regards, Steve

[njwmct]

When you adjusted the valve clearances did number 1 cylinder need adjusting by much ? could be a valve not seating properly, if so no amount of carb cleaning/swaping/ jet changing will help, Regards, Steve

Hi Steve,
The valve clearances on no.1 were fine / on the bottom end of the tolerance so I don't think it's a valve not seating.

[njwmct]

This is really starting to drive me crazy now!
Z1000 MKII - very low mileage motor - only 4,900 miles genuine.
Bike will not pull cleanly until it's above 2000 rpm.
Cylinder 1 plug is sooty all the others are fine.
Here's what I've done to try & solve the problem.
New Plugs.
Carbs stripped & cleaned about 4 times - all the following renewed, pilot jets, Main jets, Needle valves & seats, all o-rings replaced.
Choke plungers are all free.
Service Fuel level checked & adjusted 2 times.
Inlet rubbers removed , checked & resealed at head.
Carbs balanced.
Valve clearances checked & adjusted.
Anyone experienced a similar problem?

Forgot to say:
Engine idles nicely & pulls nicely from 2000 rpm up!

Over the weekend it's been suggested to me that this problem could be down to the needle or needle jet - does that make sense to anyone?

[njwmct]

Z1000 MKII - very low mileage motor - only 4,900 miles genuine.
Engine idles beautifully but when you ride it & try to pull away it stumbles &
will not pull cleanly until it's above 2000 rpm.
Once it clears it runs great above 2000 rpm.
Cylinder 1 plug is sooty all the others are fine.
Here's what I've done to try & solve the problem.
New Plugs.
Carbs stripped & cleaned about 4 times - all the following renewed, pilot jets, Main jets, Needle valves & seats, all o-rings replaced.
Choke plungers are all free.
Service Fuel level checked & adjusted 2 times.
Inlet rubbers removed , checked & resealed at head.
Carbs balanced.
Valve clearances checked & adjusted.
Anyone experienced a similar problem?

Hi Guys,
Still trying to solve this problem!
I've done a bit more investigation as follows:
Checked out the ignition side with a multimeter & all of the following OK:
healthy 12v to both coils, ballast resistor OK, coil primary windings & secondary windings OK.
swapped over the leads 1&4 but problem still on no.1
Also tracked down a new needle & changed that on no.1 carb.
Re-balanced the carbs.
But here's the interesting bit:
Borrowed a Colourtune & set up the mixture at idle on all cylinders then used it cylinder by cylinder to see what's happening.
It confirmed a problem on no. 1 it's going rich at 1250-1500 rpm (just where I get the stumble) & stays rich (yellow burn) if you hold the rpm at this level - nice bunsen blue flame at idle & on constant throttle above 2500 rpm.
Any ideas what the cause might be?

[morten]

Understand that you start to be confused but don't give up be angry instead and give that bike a real kick in the ass

I read that the compression is ok an all cyl., but is the compression holding or do you perhaps have a small leak on no1. ???

I suggest you cut and try solving a little further on that no1. carb. Seems to me that the problem maybe has to be in the pilot circuit of that carb in a way. I would have tried to swop no1. and no4 carbs in the row just to see if the problem moves over to no.4. That is easy to do for a test. If this solve things on no1 your carb no1 has to be changed it is then worn out in a way and can not be trusted.

If not try to borrow a complete carb. set and see if this solve your problem just to eliminate the carbs!!

If still not solve anything you most certain have a leak in a way on cylinder no1. since your ignition seems ok. I presume that your inlet manifolds are not leaking?

[z1bman]

hi have the mixture screws got any o rings fitted not sure whether they are fitted on the mk2 ? if they have ? have you replaced them ? you mention that you have changed the pilot jets. have you tried swapping them over with no 4 cylinder. what size are the pilot jets

[njwmct]

hi have the mixture screws got any o rings fitted not sure whether they are fitted on the mk2 ? if they have ? have you replaced them ? you mention that you have changed the pilot jets. have you tried swapping them over with no 4 cylinder. what size are the pilot jets

Yes the MKII has o-rings on the mixture screws which I have renewed.
The pilot jets are 15.
I have'nt tried swapping 1 & 4 over (I guess you're thinking there might be a faulty jet) - it's worth a try I guess.

[z1bman]

you have probably already checked this but make sure there is no obstruction in the mixture screw hole like remains of an old o ring. try squirting some wd40 into the mixture hole + see were it comes out it should come out through the air jet in the rear of the carb

[RAYZ1]

you have probably already checked this but make sure there is no obstruction in the mixture screw hole like remains of an old o ring. try squirting some wd40 into the mixture hole + see were it comes out it should come out through the air jet in the rear of the carb

I had a problem on one of my Z1s. Cyl 3 ran rich, no amount of cleaning , setup, ignition tweaks, swapping leads, coils, colour tuning made any difference whatsoever

Carb 3 body had a problem, hairline crack/defect - probably the result of poor ultrasonic cleaning, New carb body and problem solved

Ray

[njwmct]

Spent a bit of time on the Mark11 again today trying to cure the dreaded off-idle stumble.
I found that by adjusting the slide height on cylinder no.1 with the screw adjuster on the top(raising the slide) then I could get rid of the stumble!!!
However, at the same time it's caused the bike to go rich & produce black smoke at the exhaust.
Does this give anyone any clues?

[LTD Project]

Just out of interest, did you ever get this sorted?

If so what the hell was it?

[njwmct]

Just out of interest, did you ever get this sorted?

If so what the hell was it?

Yes just sorted it out last weekend - only took 10 months to get there!!

Turned out to be a dodgy needle jet on carb no.1 - replaced it with one that had a clean bore & bingo problem solved.