Intermittently running on 3 cylinders *update video*

[jdugen]

Had a very similar fault. Motor would rev fine, but cut to three at tickover.
On mine (after making sure that the carbs were balanced, there were no airleaks from cracked inlet rubbers, that the float height was correct, that the plug was clean and new), turned out to be the jet holder block. This is held in place by a hex nut, undo this and the whole block will come away. There is a neophrene gasket that seals between pilot and main jet passages. Mine had gone leaky.

I proved this by swapping the jet holder block between working and non working cylinders, the fault moved with the jet block.

To make life easier, you do not have to keep removing the carbs to do these tests, the float bowls will seal well enough with two screws holding them, which makes swapping these components a much easier job with the carbs in situ. (you must replace all screws when the fault has been cured... of course).

I have found these motors to be VERY fussy about pilot jet mixture settings, although a bit awkward, adjust the mixture on a warm engine untill a steady tickover is achieved, made much easier by the use of a digital thermometer (very cheap and very worthwhile).

[yamaha_george]

I popped the covers off of mine and found them all at different positions.

Not unusual since each carb & each cylinder set up is unique, Infra red Thermometer and those floppy things either side of your head will let you know about your idle state PLUS fresh plugs used for a plug read.

The figure of 3.5 turns is NOT cut in stone !! it is just a suggested base line to work from.

Another thing that should be checked is the float height.

+5 on that with FZR's 1mm off can with some engines make a great deal of difference, see a post by RAGE DIGITAL on how to make your own carb float tool

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.

Music wire will scratch / cut brass & castings like a file would, if you are checking passages & jets use Nylon music strings or plastic fishing line PLEASE.

Jet sizing is inaccurate enough with out making the problem worse see:-

http://www.saltmine.org.uk/martin/jet_sizing.html


PS:- leaving the caps off is not a problem since removing them usually "cattle trucks" them.
A dab of nail polish on the carb castings thread SPARINGLY applied after it is correctly adjusted will stop it from backing out and causing a major problem when adjusting at a later date.

[demon_knight69]

hrm, for some reason my post from last night doesn't appear to have actually posted. at any rate bike is FIXED. running on all FOUR cylinders now. problem appears to have been the idle mixture screws. i took them all out last night, cleaned out the passageways and the screws themselves. one screw was almost all the way in and had a bit of gummy crud on it, and the other screws were around 2 turns out. after cleaning everything i put them all in and have them backed out to 3 turns (the bike ran a bit rich as it was, so i figured that 3 turns wouldn't make it much worse (especially as one screw was almost all the way lean). after everything was put back together the bike fired up with no problems and is purring like a kitten.

a big THANK YOU to everyone for the great advice! after work today i'll be taking the bike through emissions. i'll try to take some video this evening as well so everyone can hear the new exhaust

[DonTZ125]

Jet sizing is inaccurate enough with out making the problem worse see:-
http://www.saltmine.org.uk/martin/jet_sizing.html

Hi, George. I saw this years ago, and I've always been skeptical. First, he's comparing Mikuni and knock-offs. Second, he's using RZ500 #195s as an example - I've seen several people comment that the RZ500 mains were #165s deliberately mislabeled, so that when people tried to rejet slightly leaner they would actually go RICHER, thus preventing very expensive burn-downs and warranty claim hassles.

[demon_knight69]

just went through emissions and passed with no issues. and since i promised, here's a crappy video of the new pipe:

[apsolus]

its gonna look perfect with some side fairings on it

[demon_knight69]

its gonna look perfect with some side fairings on it

i've got a complete set of fairings sanded down waiting for some paint. i'll be going with a matte black color. once that's done i'll be doing my yzf swingarm/r6 wheel project. one of these days it'll be somewhat done

[blensen]

I really, really like that exhaust! *quickly runs to ebay...*

[Kyle844]

when you guys say 3.5turns is the baseline adjustment for the adjustment screws with the brass caps, are you meaning full 360* turns or a 180* turn of the screw driver, i just adjusted mine 3 turns 360* out and when i rev it up it will come back to around 3k rpm false idle for a second or two then drop to 1200rpm idle. Is this a sign of running too lean? The choke when on blasts rpm up to 5k rpm. K&n drop in filter, exup valve removed, jardine rt-1 slip on. all modifications were from previous owner so now it's time to get it running top notch.

[DonTZ125]

You've got an air leak - "the choke when on blasts up to 5k rpm."

[Kyle844]

looks like the piece that connects the carb to the head, i guess it'd be an intake manifold/plenum has cracks. can you just fill those cracks with epoxy or silicone or can u find those reletivly easy

[demon_knight69]

I really, really like that exhaust! *quickly runs to ebay...*

thanks! i'm pretty pleased with how it turned out. the r6 header was modded by thatkid, and a good chunk of everything else was my resourceful brother in law. we had to create a custom mid-pipe to go from the header to the end of the gsxr600 pipe, which took the bulk of the time, but it definitely turned out great