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Z650F3 running poorly despite lots of attention!

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Stagman
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Z650F3 running poorly despite lots of attention!

#1 PostAuthor: Stagman » Tue Aug 27, 2019 12:00 pm

Hi Guys,

Really struggling with a problem I hope you may be able to give me a steer on?

I bought a Z650F3 with a knackered cam bearing bolt being the only problem with it (ha ha….not quite but there we are – buyer beware an all that).

So I repair the thread, and rebuild it, only to find on running it won’t pull at all cleanly and is reluctant to rev, exhibiting signs of running lean, such as popping back through the carbs when you are stood by it (can’t feel this on the road), and the electrodes on the plugs look a bit lean.
The engine has had the valves shimmed during the rebuild and shows about 150 psi compression across all cylinders so that seems fine. The carbs were according to the PO, ultrasonically cleaned (receipt was provided), but the tank was full of crappy liner and rust so I have treated that, and at the same time I stripped the carbs and cleaned them all out as there was a reasonable amount of fine crud in them from the tank pre me sorting it out. I set the floats carefully to the F3 dimension and have since checked the fuel level with a tube, ranging from about 2 mm below the carb bowl join, or almost level with it, so I doubt that is influencing it.
All jets were cleaned out during my strip, and were OK anyway.
I have carefully inspected the diaphragms and they are sound.
I checked the ignition timing and that is OK too, and even the carbs seem very well balanced!
The intake rubbers are also new and I have checked these for leaks during running with WD 40 and can see nothing untoward.
I get the feeling because the PO had fitted new intake rubbers, had the carbs ultrasonically cleaned and had also fitted a new coil, he was investigating the same thing, and tried shimming the valve clearances and buggered up the thread, then gave up.

Basically guys I am at a loss as to what might be causing this so any pointers would be most welcome!

Thanks in advance

Regards
Mark

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Re: Z650F3 running poorly despite lots of attention!

#2 PostAuthor: Philippe » Tue Aug 27, 2019 4:26 pm

Hi Mark
I think your bike is running too lean. An obstruction in one of the fine passage ways in the carbs might be the problem. When you cleaned them, did you use compressed air to clean all the passages in the carbs?
Is there enough fuel coming from the tank to the carbs? Did you clean the fuel tap? Is the little vent hole in the fuel tank cap not obstructed so the tank doesn't get sucked vacuum when the engine is running?
Sometimes little things can cause major problems.
I hope you find the solution! Good luck with it!
GrtZ
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Re: Z650F3 running poorly despite lots of attention!

#3 PostAuthor: z1bman » Tue Aug 27, 2019 10:21 pm

what is the spark like if you remove the plug cap & hold the HT lead to the engine then gradually move it away?

Stagman
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Re: Z650F3 running poorly despite lots of attention!

#4 PostAuthor: Stagman » Wed Aug 28, 2019 5:51 am

Hi guys,

Yes I blew all passages out with compressed air, and ran it without the fuel cap closed to check for vacuum. Also I refurbished the tap and it runs fine on all 3 settings.
I have taken the plug caps off while running to see the effect but not with the cap removed so will try this.

Maybe I need to separate all the carbs and clean them myself again in the ultrasonic tank, despite the PO having a receipt for it being done

Thanks for the replies guys. Much appreciated.

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Re: Z650F3 running poorly despite lots of attention!

#5 PostAuthor: Mathh » Wed Aug 28, 2019 7:43 am

Ultrasonic cleaning became much more difficult since ethanol has been added to fuel. Years ago I used to clean carbs by putting them in the tank for about 20 minutes, nowadays I do them completely dismantled for 2 x 60 minutes at 65 degrees celcius using triple the amount of Tickopur in the fluid and in some cases even that is not enough. On Ebay I bought some sets of carb cleaning brushes in all sizes and clean every single opening that is in the carbs and double check with air. If that does not help garages use extremely powerful carb cleaner not available for non professionals. Maybe try to find some of that. Good luck!

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Re: Z650F3 running poorly despite lots of attention!

#6 PostAuthor: Stagman » Wed Aug 28, 2019 8:38 am

Good advice thanks. I think I will separate them completely, strip again and soak for a morning!

Followed by copious compressed air blow through!

Cheers guys

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Re: Z650F3 running poorly despite lots of attention!

#7 PostAuthor: Stagman » Mon Sep 09, 2019 1:38 pm

Guys,
I think I may have got to the bottom of the poor running (severe spitting back through the carbs on idle, general lack of responsiveness). I noticed the slides barely lift when revving it at a standstill. On closer examination of the slides, there is a fair amount of clearance between slide and body. Could it be that they have worn sufficiently to prevent the pressure differential from occurring to allow them to lift?
If so I am still wondering why they are spitting back on idle when the slides won’t normally be lifted, making me think there may be another issue? If you put your hand on them its quite a heavy knock.
If it’s a wear issue, the previous owners must have put up with poor performance over a long period for them all to wear to the point where they no longer lift, making me doubt my diagnosis.
The diaphragms are all fine and the hole in the slides are clear.
If the consensus is worn carbs, then does anyone have a good set for sale please?
Will non CV carbs fit is I can’t get a decent CV set please?
Thanks as always
Regards

Mark

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Re: Z650F3 running poorly despite lots of attention!

#8 PostAuthor: Charlie » Mon Sep 09, 2019 4:07 pm

I have never been a big fan of CV carbs. They are OK on newer bikes but once they have a few years and some wear and tear they can be hard to set up.

The earlier 650's had VM24 carbs, you will find those around, although they will likely need a strip and rebuild too. You will then have a problem as the inlets and carb rubbers will need to be for the earlier carbs...maybe even the airbox, I have not done a conversion myself on that bike.

You may find it easier to graft some Z750 CV carbs in there if you can find a good set, the F4 is almost a Z750 anyway, it was a three-quarter way house with the Hyvo camchain etc.

How good are the diaphragms on your current set ? If they are baggy or split - that will def give issues.

You will get good model specific help and maybe even find parts you need on http://z650.proboards.com/

Its focussed on Z650's specifically and Alex on there is nothing short of a wizard in anything Z650 :D
Why do I persist in debating with idiots ? I really should know better :)

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Re: Z650F3 running poorly despite lots of attention!

#9 PostAuthor: Stagman » Mon Sep 09, 2019 5:58 pm

Many thanks for great advice Charlie

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Re: Z650F3 running poorly despite lots of attention!

#10 PostAuthor: z1bman » Mon Sep 09, 2019 9:49 pm

are the passageways in the carb body close to the throttle butterfly's clear ? if you squirt some wd40 through the pilot system it should come out the small hole in front of the butterfly valves

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Re: Z650F3 running poorly despite lots of attention!

#11 PostAuthor: Stagman » Tue Sep 10, 2019 5:55 am

Hi,

Thanks for suggestion. Yes everything is clear. 100%. Looking at my diaphragms, they do seem quite baggy. This may well be the problem?

Regards

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Re: Z650F3 running poorly despite lots of attention!

#12 PostAuthor: Charlie » Tue Sep 10, 2019 8:20 am

If you or someone else has sprayed carb cleaner in the vicinity of those diaphragms, it will cause them to "grow". If you do use carb cleaner, never get it anywhere near diaphragms. It ruins them.
Why do I persist in debating with idiots ? I really should know better :)

Stagman
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Re: Z650F3 running poorly despite lots of attention!

#13 PostAuthor: Stagman » Tue Sep 10, 2019 9:01 am

Can I ask what kind of slide to carb bore clearance is acceptable please? I don't have a new standard to judge against, or much previous experience as most of my previous stuff / existing stuff is old fash slide carbs or injection. My slide to bores are a reasonably rattly fit but I see no signs of wear.

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Re: Z650F3 running poorly despite lots of attention!

#14 PostAuthor: z1bman » Tue Sep 10, 2019 6:34 pm

if you blow through the oval airway at the top rear end of each carb you should hear the slide go up the carb bore? if the slide does go up there is nothing wrong with the slide. the clearance in the slide will have little or no effect on the running performance

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Re: Z650F3 running poorly despite lots of attention!

#15 PostAuthor: Stagman » Wed Sep 11, 2019 8:14 am

Thanks for the answer, its re-assuring to know the clearance has little performance affect. I learnt this blowing in the hole trick after I re-installed them for the 3rd time after cleaning them. May have to remove them again to check.

Cheers for now


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