Strange engine behaviour

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Ewetea
zxr400 oc member
zxr400 oc member
Posts: 148
Joined: Mon Jan 12, 2009 12:04 pm
My Bike: ZXR400L5
Location: Newport Shropshire

Re: Strange engine behaviour

Post by Ewetea »

You must use water, because a liquid cannot be compressed (i.e. squeezed into say half it's normal volume, like a gas). When pressure is applied to a liquid it just transfers that pressure to the enclosure, trying to stretch it, albeit by a minute amount (in the bike, it would be the hoses expanding). I vaguely remember that the pressure in the coolant system of an engine is about 10 - 12 psi. Fill your system with water and then pressurize it to 10psi. If there is any leakage anywhere, just a drop of water loss will result in a significant fall, or even complete loss of pressure. If you used air to pressurize the system it would take ages to reduce with a small leak, and you couldn't be sure that the loss was not caused just by a change in temperature.
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

Thank you for advice! I found the details of this operation here (page 6): http://www.zxrworld.co.uk/Manuals/H%20M ... er%203.pdf
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

I just hit a dead end. I spent a bit of time trying to check and fix everything on my engine. So far...

- compression: OK
- valve clearance : OK
- spark plugs: OK
- carburetors: REBUILT (striped apart, cleaned, O-rings replaced)
- spark plug cables REPLACED

I decided skip the head gasket test for the moment because the compression and oil (no milky oil) seems fine.

And the engine still runs like crap...

https://www.youtube.com/watch?v=BY7hDy8UC3A

None of the spark plugs are wet or blacked. If I take out the spark plugs cables from #2 and #3 and start the engine it still runs, worse, but it runs. If I take out the cables from #1 and #4 the engine doesn't run at all if I try to start it. I switched the coils between them to rule out a bad coil possibility but no difference. If I take out the cables from each spark plug one at a time, the engine runs worse than with all four cables connected but at the same peace at each cable token out.

What can go wrong?
Last edited by Bogdan.V on Sun Mar 06, 2016 5:59 pm, edited 4 times in total.
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

Could this problem be because of unbalanced carburetors? Poor running is present at idle also at high revs. The carburetors was entirely striped apart (even main bodies one from each other) for cleaning and after that where balanced only visually on the table. I would like to balance them to rule out this problem but I don't have the tool yet. I also suspect that carburetors wasn't clean properly.
richyrd5
Posts: 63
Joined: Fri Feb 05, 2016 12:26 pm
My Bike: 400h

Re: Strange engine behaviour

Post by richyrd5 »

if you think they werent cleaned properly then get them apart again and give them a real good clean out(i have recently had to do this)..ran much better...also they will defitnatly need to be balanced properly with gauges if you have taken all the linkages apart...it will run real bad if there not bananced properly.. smiler
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

Does the unbalancing affect the engine run at high revs too? Shouldn't only affect the idle and low revs?
richyrd5
Posts: 63
Joined: Fri Feb 05, 2016 12:26 pm
My Bike: 400h

Re: Strange engine behaviour

Post by richyrd5 »

if they are out a lot it will affect them yes,,,try cleaning/balance then see how you go
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

I will balance them and if the problem still persist I will clean them again and come back with results. Thank you!
richyrd5
Posts: 63
Joined: Fri Feb 05, 2016 12:26 pm
My Bike: 400h

Re: Strange engine behaviour

Post by richyrd5 »

no problem..good luck and tells us how you get on,,its frustrating but you will get there in the end winks
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

By the way, could some possible problems to the alternator affect the engine performance in this way (like described above)? Although I have sparks to all spark plugs, I ask this because of desire to learn.
richyrd5
Posts: 63
Joined: Fri Feb 05, 2016 12:26 pm
My Bike: 400h

Re: Strange engine behaviour

Post by richyrd5 »

On some bikes,yes it can.(I have a vfr and the rectifier playing up can cause problems on one of these)but generally..no.but you could as a precaution check the voltage when its running.put lights on and rev to 5000..should be 13.8/14.3 volts across the battery terminals..but I think its more likely carb problems with yours...have you balanced them yet??
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

Not yet. Most probably the carburetors has some clogged air or fuel passes because I think the unbalanced carburetors cannot cause so much vibrations / poor running also on high revs and I don't want to spend money to balance them twice in case that the problem is clogged passes. Tomorrow I will soak the carburetor bodies for an hour in carburetor cleaner and blast the holes with compressed air after that to make sure they are clean. I would prefer an ultrasonic cleaner but I cannot find one in my area. Soaking the bodies in carburetor cleaner seems the best alternative for me. Last time I boiled them in water with lemon juice :pmsl but the lemon juice has left some sticky deposits on carburetor bodies. They where cleaned with a cloth and blasted with compressed air only the next day when they where dried so I think there are still some deposits inside air / fuel passes. After tomorrow cleaning I will balance them and see how it goes.
Bogdan.V
Posts: 37
Joined: Sun Jul 14, 2013 7:01 pm
My Bike: ZXR400 L5

Re: Strange engine behaviour

Post by Bogdan.V »

The engine runs fine now, at least below 4000 rpm. Most probably the carburetors wasn't clean properly last time. I just find out that my cam chain is loosen and I have to replace it so I didn't want to rev the engine higher. After I replace it I will come with the final results. I think the problem from the start was that my valve clearance where a bit too tighten and that caused the engine to start very hart at cold. Anyway, I learned a lot since then, I also made some little mistakes (but I guess everybody does at the beginning). I could not get this far without the help of this forum so thank you all for your support!
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