Intermittently running on 3 cylinders *update video*

[demon_knight69]

hey all, haven't been active for quite a while. i've just finished my custom exhaust project using an r6 header and the end pipe of a gsxr600. unfortunately prior to starting the project, the bike started running very poorly. i figured it had been old gas that may have gummed up the carbs or some such, since the bike had been sitting for several months. this is definitely not the case. the bike is definitely running on 3 cylinders. the strange thing is it's only intermittent. if i'm at wide open throttle, the bike runs on all 4. but as soon as you let off the throttle its back on 3 cylinders again.

so, what i've done so far, without completely removing and cleaning the carbs, i've done the best i can to ensure that each cylinder is getting appropriate fuel. they all seem fine. i've tested each spark plug to ensure they're all firing, and they are. at this point i'm thinking perhaps the coils are not producing the appropriate amount of energy, or that the plug wire is going bad. i've seen this post viewtopic.php?f=8&t=6790&p=65823&hilit= ... ers#p65823. it seems to touch on the prospect that you can remove the plug wires from the coils. is there an easy way to do this? they really seem like they're hard wires together.

i guess i'm just looking for some additional information on the ignition system. it really seems to me like there's something going on with the plug wires or coils. any comments/suggestions are very welcome at this point.

and here's a teaser of the new exhaust.

i'll post a good video once i get the damn thing running on all 4 cylinders

[DonTZ125]

I'm going to say it IS your carbs -

if i'm at wide open throttle, the bike runs on all 4. but as soon as you let off the throttle its back on 3 cylinders again.

Ok, so your main jets are fine, but either your pilot or your needle on that cyl are completely messed up. Actually - if the SLIDE on that cyl is stuck open, the low and mid-range jetting will be butchered, but the WFO settings will be completely normal.

If you haven't already, pull, clean, and sync your carbs.

[jdugen]

Just rebuilt a wreck of a'91. Usual problems with carb jets blocked with stale fuel, cleaned them out but still had a problem at tickover/low speed with one cylinder. My problem (after much hair tearing) turned out to be the jet holder block GASKET on the erratic cylinder. Take the jet holder block off and dip the gasket in thinners, quickly, and wash in soapy water. This 'fattens' up the gasket enough to seal properly again and prove the point. New gaskets are advised.
If the bike has been stood on the sidestand for any length of time, it does seem to affect N0. 4 cylinders carb the worst.

[yamaha_george]

I'm going to say it IS your carbs -

if i'm at wide open throttle, the bike runs on all 4. but as soon as you let off the throttle its back on 3 cylinders again.

Ok, so your main jets are fine, but either your pilot or your needle on that cyl are completely messed up. Actually - if the SLIDE on that cyl is stuck open, the low and mid-range jetting will be butchered, but the WFO settings will be completely normal.

If you haven't already, pull, clean, and sync your carbs.

Unlikely to be ignition or 2 cylinders would not fire, I would however charge the battery overnight so you have full juice for diagnosis + fresh and checked gapped plugs.
Another poster said about far left carb taking abuse on side stand only bikes that seems common complaint.

[rotortech]

A lot of good advice posted here and should definitely be checked. I just wanted to add that it could be a faulty HT lead on one cylinder that is working intermittently. You might look into that if the carb work doesn't clear it up.

[demon_knight69]

thanks all, great advice. i'll be working on the bike over the next few days so i'll let you all know how it goes.

[ragedigital]

Love the exhaust, Demon. Glad to see you're still kicking the 96 around.

These guys are all incorrect - just replace the "flux capacitor" and you'll be fine.

darrin

[demon_knight69]

Love the exhaust, Demon. Glad to see you're still kicking the 96 around.

These guys are all incorrect - just replace the "flux capacitor" and you'll be fine.

darrin

, thanks darrin. yea amongst life in general, time for the bike has been limited, but it's still around. got lots more work to do still

[demon_knight69]

ok, time for follow up. after running the bike for a minute last night, we're sure it is the #1 cylinder that is having the issues (#1 being the far left while you are sitting on the bike). i'll start with spark since that was the easiest stuff to get to. tested resistance between 1&4 plug wires as well as 2&3, they're in spec. the caps are also in spec, they vary from 9000-11000 ohms. i have a couple new plugs (even though we were pretty sure that they aren't bad). when we pulled the plug and held it against the block and attempted to crank, you can see spark (although somewhat weak). still, as most have mentioned here, seeing as the bike runs fine when the throttle is most of the way open, it sounds more like a carb issue.

so let's move on to carbs. took them off last night, took the float chambers apart, cleaned everything that could be easily seen (took out the jets and cleaned them as well as the passageways). took the front of the carbs with the diaphragms off, made sure they didn't have any holes or tears, checked the needles as well. there was a small hole underneath the covers with a small o-ring, made sure that was all clean as well. i think that's about it. basically took all the easy stuff apart and made sure they were clean. there was nothing that looked even remotely blocked/gummed up. the only thing that we didn't get to was the emulsion tubes. i did take some of that apart and clean it, but the emulsion tubes were not removed. it seems to me that we cleaned pretty much everything. after putting the carbs back together and put them on the bike, gave it a bit of choke to start and it sounded like it was firing on all four (although it definitely could have been our imagination). it then was definitely still running on 3.

so...what have i missed? we're going to take the carbs back out today and mess with the emulsion tubes, but is there anything else carb related that we've missed? or anything spark related that we may have missed? i don't like the weak spark from #1, and just for the hell of it i'd like to change the plug wire. does anyone know how to remove the plug wires from the coils? the last thing i want to do is break something up there. i keep staring at the carbs and coils and i KNOW i have to have missed something, i just can't think of what it is :-/

[kilika2]

Did you check your Idle Mixture Screws (IMS) too? I've heard of them turning in on their own from engine vibration, which would make the bike lean and therefore not fire completely. I had largely the same problem once and after fogging the system it cleared up. Do you have an infared thermometer that you can put on the header. Or have you checked compression too?

But first I would get the IR therm on there first and see where the IMS's are too.

Chris.

[demon_knight69]

Did you check your Idle Mixture Screws (IMS) too? I've heard of them turning in on their own from engine vibration, which would make the bike lean and therefore not fire completely. I had largely the same problem once and after fogging the system it cleared up. Do you have an infared thermometer that you can put on the header. Or have you checked compression too?

But first I would get the IR therm on there first and see where the IMS's are too.

Chris.

no, i'll add that to the list of things to check tonight. are you talking about the synchronizing screws? or something else. i've been wanting to get an IR thermometer for a while, so maybe this will be excuse enough to get one. after letting the bike idle for a minute last night we could definitely tell that the #1 cylinder was -warm- to the touch, while the others were quite hot.
we haven't measured compression, so we can do that. putting a hand over the top of each intake you can definitely feel sucking.

[kilika2]

No the synch screws are different than the IMS. There is a picture on here somewhere I'm trying to find it.


This isn't the one I was going for but it will work. This is from megaloxana's gallery but I think it's rage's pic. But circled in read in the picture there is the idle adjustment screw and above that (in the image not on the bike) is a small flathead screw, one per carb.



In this crappy picture from me (keep in mind this picture is upside down) you can see the 2 "nipples" on the back of the carb. And just above that, towards the black carb boot, you can see a brass cap that is hiding those screws.

But stock the IMS screws are 3.5 turns out and out equals rich and in equals lean.

Chris.

[demon_knight69]

This is from megaloxana's gallery but I think it's rage's pic. But circled in read in the picture there is the idle adjustment screw and above that (in the image not on the bike) is a small flathead screw, one per carb.

In this crappy picture from me (keep in mind this picture is upside down) you can see the 2 "nipples" on the back of the carb. And just above that, towards the black carb boot, you can see a brass cap that is hiding those screws.

But stock the IMS screws are 3.5 turns out and out equals rich and in equals lean.

Chris.

ah ha, those are caps. i was wondering wtf those were. been too long since i've messed with the fzr. thanks chris.

-nick

[rotortech]

+1 to idle mixture screws - especially if they are still covered by the brass caps. I popped the covers off of mine and found them all at different positions. Another thing that should be checked is the float height. If you go to the trouble of getting the carbs out take all the jets out and the emulsion tubes and check every passage with a piece of music wire.

[demon_knight69]

+1 to idle mixture screws - especially if they are still covered by the brass caps. I popped the covers off of mine and found them all at different positions. Another thing that should be checked is the float height. If you go to the trouble of getting the carbs out take all the jets out and the emulsion tubes and check every passage with a piece of music wire.

yea the caps are still on. it's been so long since i've looked at fzr carbs i completely forgot that they covered the screws
can the caps be left off when i'm done messing with them? that shouldn't cause any adverse effects should it?