One cylinder running much cooler than the others on my GPz

[GPZ592]

Hi All - I've posted this over from my rebuild thread about a problem I have on my newly rebuilt GPz -

I've run the engine up to temperature a couple of times to heat cycle the engine, so I can check the head bolts, exhaust clamps, etc. Once hot, I used a IR thermometer to check the header pipe temperatures and I found cylinders 1,2 &4 were around 200 degree C, but cylinder 3 was only 90 The carbs have been ultrasonically cleaned and reassembled with all new O rings/gaskets, etc but retain genuine jets/needles/needle valves, etc. They are all set the same for float height, slow running mixture screw setting, etc. Obviously, the engine has been totally rebuilt and all 4 cylinders give 170 PSI on a compression test. All new spark plugs & caps have also been fitted. All the plugs look the same - i.e. no 3 is not fouled up or wet ( see photo below). I did try moving the plugs around just in case I had a faulty one, but the problem persisted on no 3. I can't hear any problem in the engine note - it sounds fine to me with no misfire or hesitation.

My next steps will be to swap coils & HT leads to try and eliminate an electrical issue before looking into the carbs further. However, if anyone has any suggestions/pointers/ideas, I'd be grateful to hear them

Thanks.

Mark.

[Al]

I had the same thing back in Feb, and it turned out to be one coil was internally shorted. They tell you to measure the HT side and the LT side but if you measure between them you should get infinite resistance. Looking at youre plugs, it seems the #2 isnt doing a lot of work so maybe a short between the LT and HT is not so mad.
Dont suppose you have a vacuum takeoff stub on #3 left open by any chance?
AL

[GPZ592]

Cheers Al

I'll check the coils tomorrow as you suggest and no, #3 stub was plugged

[Speedie]

Hi Mark
Just a comment, I have a similar issue on my recently rebuilt Zephyr 750 (same as you rebore/ultrasonically cleaned carbs all new parts and new OEM Jets/ needles etc etc etc. My no3 is also slightly down on temp, but only by about 10 degC not 110 like yours. I only have 300 miles on the engine and propose to wait until its over 5/600 and see what's happening. I also strangely have low vacuum across all four pots although the engine starts and runs fine. I have also carefully adjusted the individual air screws to obtain the highest revs/best running condition (changes are very subtle and a good ear is needed) As I say am going to wait until a few more running in miles on the engine before taking a second look.

Seems odd that you say N03 is the issue but your N02 plug electrode is the one showing that it may have a problem? Good idea to swap the coils and see if anything changes. On the Zephyr one coil supplies two cylinders (wasted spark) I guess this is the same on the Gpz? My thoughts are that if it was the coil you would get poor performance on two cylinders.
Could be a poor lead/cap connection? Will be interesting to see what you find!
Paul

[Gray17]

I agree with speedle, it seems to me that plug 2 in your photos shows no signs of heat or deposits, which to me indicates its not firing, this could be down to several reasons. As you probably know combustion needs 3 things to take place,
1. Fuel, mixed in the correct ratio with air. (Carburation)
2. Compression to compress the mix (piston and cylinder etc)
3. A spark at the correct moment to ignite the mix. (Spark plug, coil, timing etc) Take any of these elements away and that prevents detonation.
Assuming you have good compression and all is well with the piston etc then the coil would be the next likely suspect, but again the older Kawasakis run dual coils where one coil feeds the 2 outer cylinders and the 2nd coil feeds the 2 inner ones. Therefore as 3 cylinders run ok its not likely to be the coil itself more likely the plug lead or the cap itself as advised on cylinder 3. Try swopping the 2 centre cylinder leads around see if the problem swops to cylinder 2 which will prove the fault is the lead itself or cap.
Another issue may be carburation on that cylinder as if no fuel getting to plug it wont fire. Check if plug gets wet or bone dry. Check float height and jets for blockages on that cylinders carbs, also check mixture screws etc
Hopefully you will get it sorted

[zed1015]

I agree with speedle, it seems to me that plug 2 in your photos shows no signs of heat or deposits, which to me indicates its not firing.

It all depends on which way he's numbering the cylinders or whether 3 is a typo but #2 in the pic does appear to be the from the problem cylinder..
Cylinders should be numbered left to right when sat on the bike.

[GPZ592]

Thanks to everyone who responded with suggestions & ideas - I think I've now found the cause of the issue, but still a bit of fine tuning to do

Just to clear up a couple of points - It was definetely #3 that was cold and ,yes, I did count left-to-right while sitting on the bike I'm also sure I put the spark plugs into the card in the right order, but then you start to doubt yourself........................

Anyway, I re-checked the coils & HT leads and they all tested OK and within specification. I did swap the coils over anyway, just in case ! the plug caps were new, but I did swap them over too, but the HT leads are all different lengths, so not easy to swap. I then went around and re-torqued cylinder head nuts - all fine there. Then I checked the exhaust clamp nuts and whilst the ones on cylinder 1,2 & 4 went half a turn or so, cylinder 3 went a couple of turns !

After all that, I ran the bike up to temperature, balanced the carbs again, then checked the exhaust header temperatures and now all 4 were within 15 degrees of each other So, it looks like a slight blow by on the exhaust gasket was the culprit.

Here's the spark plugs now - still some fine tuning to do, as I said, but hopefully on the right track now.

Mark.

Spark Plugs 2.jpg (60.59 KiB) Viewed 10281 times