ZX7R Idle/firing problems

[climbatize]

Hey guys,

Idle has been a little rough on the ZX7R for a little while. It is possibly running on less than 4 cylinders at idle. Replaced the plugs to eliminate that problem but idle is still rough. Disturbing thing was that chamber 3’s plug was covered with oil and probably in turn not firing. There was also oil residue on the rocker cover, (up around the rubber tube insert, chamber 3), suggesting it had made its way past the seal. I had slightly over filled on the first oil change I gave the bike a month ago but I’m unsure if the oil can make its way up this path if too much oil is put into the engine and I thought that the oil would have burnt off by now anyway. So this leads me to believe there could be a possible break in one of the piston ring seals..?

I did a compression test with a ‘make do’ adapter and got back:
#1 120, #2 100, #3 120, #4 120 (PSI)
I’m not sure if these results are very accurate.. probably more of a very rough guide. Need to get the correct fitting.

ZX7R owner’s manual suggests usable compression is between 149-228 PSI.

Anyone care to shed some light or ideas where to approach this from?

Cheers

[climbatize]

Anyone??

[Gosling1]

the compression readings need to be within 5% of each other in a perfect world - being a bit 'under' spec is not the problem, but one pot being way lower than the others is....

From those readings, it doesn't look like you have any ring problems in #3.

If replacing the plugs has not cured the mis-fire, you could try checking all the plug leads and plug caps for any loose connections.

Throw a bottle of Wynns carbie cleaner into the tank as well - if any of the pilot jets or low-speed circuits in the carbies are blocked up or a bit gungy, a bottle of this shit in the tank will fix that straight away. Blockages in the low-speed circuits can often cause a mis-fire at low rpm's....

[Phil]

What altitude FFS

[Gosling1]

of course, I forgot the altitude !!!

[climbatize]

I don't live on everest.

I totally forgot to check the dizzy and the points. Thanks for the tips Gosling.. I wasn't sure about using additives but I guess it can't hurt too much. Motul also make one but could be a bit pricey.

[mike-s]

That was a reference to a shitfight of a thread that i must say Gos excelled at immersing himself in, if for no other reason to hang shit on someone for being totally wrong.