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Hello all!

I have a ZXR400 L5 with 40.000 km on board. The engine has a very strange problem. If is left for a day or two in the garage, when it is started for the first time, it will run with only three pistons (it makes that specific sound) even if it’s warm. The thing is that after I leave the engine to cool down and then I start it for the second time, after a couple of minutes the piston that is not working will have some attempts to work for some fractions of seconds (see this video: https://www.youtube.com/watch?v=GW00dvFMBEo - I managed to capture only the moments when that piston have attempts to work) and after another moments it will fully work.

Another problem is that even after the engine runs with all four pistons, if I fully rev it, it will stall for a fraction of second from around 11.000 rpm to around 9.000 rpm and then go again to 11.000 but not more (see this video: https://www.youtube.com/watch?v=3ZILXIjE4Po). The spark plugs are all new but they are blacked all the time.

Could be some problems with piston rings or carburetors?

I can’t send the bike to a mechanic for the moment because I’m too far away from one and is not worth for me to send it only for an inspection. First I want to figure out what budget I need to fix this problem.

most likely to be a blockage of the carbs, or a bad coil/HT lead/spark plug cap.

Cylinders 1 + 4 fire at the same time, and cylinders 2 + 3 fire at the same time, if cylinder 1 has the misfire try swapping the leads from cylinder 1 onto cylinder 4 and vice versa, if cylinder 1 still has a missfire it cant be the coil...these are the sort of things you need to test, noone on here can quote you a price/estimate the work that needs doing until you identify what the problem is - simple logic.

so if you trace it to a dead coil you can replace the coil pack, if it still gives you an issue then it could be the spark plug (i know they are new but new things can be broken) so swap it with cylinder 4 and see if it still has an issue - if the problem moves with the plug then the plug is dead, if it stays with cylinder 1 then its not coils or spark plugs, so its most likely carbs, i would be making sure that there are no blockages in the pilot air and fuel ways, and that your pilot fuel mixture screws all appear to be set similar and correctly.

you can check for low cylinder compression with a cylinder compression gauge, and once it fires up it would be a good idea to get the carbs ballanced - if they are vastly out of ballance this could also explain why its not firing correctly.

Thank you for replay!

The previous owner took out the gas filter (I don't know why...) so I also suspect a carbs blockage. At the moment I'm in the process of cleaning them. After that, if the problem still persist, I will test the coils, the spark plugs and the compression in the cylinders and come back with a replay.

I taken out the carburetors for a rebuild and now I waiting for new O-rings to arrive. Until then I want to check for low cylinder compression. In the workshop manual says that this procedure should be done with engine warmed up but because I don't have the carburetors I cannot do this. I wonder, it is really necessary to have the engine warmed up to do this?

you can do it warm or cold, doing it cold will result in lower psi values, what you are looking for is consistency across the board, if you get 90/85/100/20 then something is up with cylinder #4...

Today I find out that I need to replace basically all O-rings of the carburetors. As everybody knows, the original ones are pretty expensive so after looking on the web for some cheaper alternative I found those ones: http://litetek.co/Carb_Kit_Kawasaki_ZXR400.html

Has somebody have some experience with those kind of O-rings? Or maybe I can found somewhere some good alternatives at an affordable price besides http://www.kawasakioriginalparts.com and https://www.motorcyclespareparts.eu/kawasaki-parts.aspx ?

I use the litetek kits for all my carbs and they are top notch

I ordered LiteTek kit for carburetors but now I spot another problem. One of the cables from spark plugs have no contact with the coil pin. Does someone know where can I order some replacement cables with similar section and resistivity (without spark plug caps)?

Alot of spare coils for cheap on ebay- Was the bike running well before for u? Is your jetting way off in the carbs? U running standard air filter?

The bike had a hard/tricky start (only with cold engine) when I buy it. The problem described at the beginning of the topic appeared when I taken out the bike after last winter storing. I don't understand what "jetting way off in the carbs" means . I have standard air filter.

I just made a compression test and valve clearance check.

The compression test was made with cold engine (I taken out the carburetors for a rebuild). Here are the results:

#1: 136 PSI; 2# 130 PSI; #3: 137 PSI; #4 129 PSI; Some opinions? I wonder how much higher can be the compression with warm engine.

For valve clearance check I only had feeler gauge from 0.10 to 0.50 mm with 0.02 mm difference between them (0.10, 0.12, 0.14...) so if the 0.14 fits but 0.16 doesn't then it can be 0.14 or 0.15 or if the 0.10 doesn't fit is below 0.10 but I cannot find how much . Here are the results:

Exhaust: #1 18, 16; #2 14, 14; #3 16, 18; #4 18, 18;
Inlet: #1 12, 14; #2 10, 12; #3 16, 14; #4 below 10, 12;

I decided to replace exhaust shims from #2, first (from left to right) inlet shim from #2 and first inlet shim from #4.

I just realize what a dumb ass mistake I made... I removed some shims by moving the rocker arms to the side and after that I put the rocker arms back in place but without shims The reason of doing that was because I wanted to measure the shims but I didn't have a micrometer there. After that I wanted to remove some other shims but for that it was needed to rotate the camshafts. When the camshafts has been rotated, the cam lobes pushed directly on valves heads without shims between them. Could that damage the valves heads or rocker arms?

No

Before putting all the parts together (carburetors, top engine cover, fairings...), I want to make sure that my head gasket is fine. Can I diagnose it somehow without removing the engine top or starting the engine? The compression seams alright (see above).

you can put pressure on the cooling system. there is an adapter to mount on the radiator cap. if it holds the pressure the hg should be fine

So should I pump air or water until it reaches a certain pressure and wait to see if pressure drops over time? If so, what pressure should I put over the cooling system?