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South Park Studios
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129 Posts
Discussion Starter #1
Hello,

Does anybody know where I could purchase a few Mikuni Main Jets for my FZR600? Or perhaps a shop (no dealers) where they could do the whole setup for me?
My bike is running really lean at full-throttle and although the person i bought it from claims it has a jet-kit, it really doesn't feel like it. Any help is greatly appreciated.
Thanks,

:rider
 

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Can you describe what it feels like at full throttle to make you say it's lean?

The reason I ask is that the guy may indeed have put a kit in there but he may have gotten greedy and just put the biggest jets in and perhaps it's actually running rich.

The sure sign of lean running is if you're at full throttle and the revs are over 8K and when you just start to roll off the bike either stays at full power for the very first part of the travel or else you actually feel it pick up just a tad before it starts to slow. And this is just the first few degrees of travel as it comes off the full on stop. On the other hand if it is actually running rough and takes a little bit of running to clear or keeps sort of gargling and sounds like it's almost missing then it's actually much too rich.

And this only applies when you're over 8K. If you're under then even though you have the grip full on it's actually the needles that are controlling the gas.

Sorry if this is old hat but just consider it a refresher if that's the case........
 

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South Park Studios
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129 Posts
Discussion Starter #3
Actually, when you put it that way, you may be right. I thought that with a rich condition the exhaust would be blowing a slight bit of black smoke.

Let me give an example of the acceleration.
Take-off is rather smooth, yet I need to rev the engine to around 2500-3000RPM before letting out the clutch otherwise it stalls. It goes well after initial take-off and at around 8,000RPM+ it begins to stumble and jerk all the way to redline.

I have changed the spark plugs, cleaned the K&N Filter, the exhaust is a Yoshimura slip-on, other than that its stock.

???? :confused
 

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You only get the black smoke if it's stupidly rich. Usually we are tuning somewhere closer to ideal than that.

Ok, it's time for more questions. Has it been like this since you got it or did it develop this or has it gotten worse with time? And more importantly what did your old plugs look like for color and any buildup of deposits? I'm assuming the valves are all in spec and you're not running the gas that's been in storage for 6 months or any thing else like that.....

And here's another test. When you start it up on a cool morning can you take it off the choke almost right away? Give that a try. It's not related to the top end thing but it'll check your pilot mixture and tell me more about the need to rev it that high for a simple departure.

We can work on the assumption it's the mixture for now but another item that is suspect is the spark leads. You can check these by pulling the fairings and spraying some water onto the leads with something like a Windex bottle while the bike is running. If it starts running very rough and / or you can see some sparks jumping from the wires to the frame and head or hear the little tick like cracks of the sparks if there's too much light then this could very well be the main problem.

This is more fun that cross word puzzles......... :thumbup
 

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South Park Studios
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129 Posts
Discussion Starter #5
It has been like this since I bought it, but was a slight bit better when I gave it a tune-up. The old plugs looked OK, the electrodes were slightly worn but the insulator was a nice light golden colour, apparently they were not changed for a very long time. (that's what the guy told me). I have already gone through three tanks of gas, thus year. I use Chevron Mid-Grade.

When I start it in the morning, if I take the choke off right away it will shut off. It usually needs about 30 seconds of choke before it's ready to go on its own.

About the Spark plug leads, I noticed on my tune-up that one of the leads actually came off from the wire that leads to the ignition. The inside of the wire where it connects to the lead was greenish and corroded. So I cleaned it up and re-screwed them back together. Just thought I'd mention that.

I appreciate all these ideas you're giving me, I have more experience with 2 stroke racing engines than the 4's.

:)
 

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Based on that lead you found I'd invest in a new set or at least get some new wire to use with the screw in ends. But if you can swing the extra cost then a whole new set of cables 'n caps is the best way. That green wire core is probably just a sign of a deeper cancer. That green is corroded copper which means there's been water inside the cables.

If you stay with the old ends then clean them well using a little stiff brush and a good degreaser like Simple Green or whatever and finish with lots of clear water and a blast of brake cleaner to totally clean and degrease and dry out the ends. Even a super light film of crud can cause the spark to jump the wrong way.

It may still be the carbs but you can't fight two problems at once. And without hearing the bike it sure sounds like that farting and missing could be spark related.

The choke thing sounds normal but you may be able to fine tune the pilots for a better light throttle takeoff. If they are too lean then your bike will tend to bog a little from cruise to light acceleration at low rpms'. If it's too rich then the it'll tend to pause with more of a gargle and then pick up under the same situation and may need more throttle opening to respond at all. Too lean will also cause the engine to surge, pause, surge along with steady throttle at lower rpms. Too rich and it'll run with a sort of stuttering sound and have a surge as well but it'll be much less repetitive. More of a random "miss". It's hard to describe but easy to feel the difference. Keep the rpms down to about 2500 to 4000 for these tests.

The good thing is that it's easy to play with the pilot screws to set the low rpm and low throttle thing. You'll need a manual (or a good guess) to find the pilot screws and it helps to find out if the screws control the air bleed or fuel flow. Both types of carbs exist. The ones with the screws down by the float bowl are the fuel control types and the ones on the sides or up by the vacumn pistons are the air bleed types. I'd start with opening them up 1/4 turn at a time until you feel a drop in response. Then close them back 1/4 to 1/2 turn to optimum. If it gets worse with the first 1/4 turn opening then it's too rich and you need to go back by 1/2 turn so it's 1/4 closed. Here again keep going until you notice that lean surging and then open it to the last point where you liked how the bike feels. This adjustment only affects the lower rpm range and throttle openings up to about 1/4 throttle so ride like a grandma to set these.

And keep notes. After the 4th change it's hard to figure out where you are. Also before you start turn all the screws in lightly until they bottom (DON'T TORQUE DOWN ON 'EM EITHER) while counting and recording the openings. They should all be the same or very close to it. Do this counting to a 1/4 turn resolution. Yes it's that critical. I'm telling you to do this counting because with the screws upside down it's VERY easy to get confused and turn them the wrong way.

I actually use a hex screwdriver bit to do my adjusting and count the flats of the hex as they go by so I work to the nearest 1/6 turn. This works very well and the screwdriver bit is small enough to fit under the carbs without having to pull stuff off.

Phew, that was a long one........
 

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South Park Studios
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129 Posts
Discussion Starter #7
WOW!! Thanks for the in-depth info.
With your assitance during my "Wallow in Corners" Problem and now this, I feel you should be sending me an invoice :)

I'll start with the spark plugs wires (replacement) and see how that goes.

I'll post my result when I do that...

Thanks again...:thumbup
 

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Apollo said:
WOW!! Thanks for the in-depth info.
With your assitance during my "Wallow in Corners" Problem and now this, I feel you should be sending me an invoice :)

I'll start with the spark plugs wires (replacement) and see how that goes.

I'll post my result when I do that...

Thanks again...:thumbup
I'll pass on the invoice but a pint of dark ale at one of our dinners wouldn't go unappreciated......... :D
 

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Hey, very interesting reading your putting up BMathews. Thanx. I noticed that you asked if his bike runs fine after initial startup with choke.

In the morning, I need to start the bike with choke, but I wait about 5 or 10 seconds until the Rpms start to rise on their own and then I can kill the choke and it's fine.

What exactly is that testing for? After tuning by Bk I also noticed the low end gurgling and decelerating at 2500rpm. Brian, one of their best carb guys took my bike for 3 or 4 runs with different settings and improved it imensely, but I still found the low rpm stutter.

It's sort of important because you will usually get off the line feathering the clutch from 3krpm. When you let the clutch out a little more the rpms will drop below the majic spot and when you try to accelerate it softens up first and then picks up again.

You've got another beer lined up if you can answer this question. Maybe some nacho's if you don't wanna get too loaded at the next meet.
 

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The test of how fast it can come off the choke is to learn just how rich the pilot mixture is. If it's too rich then you can let off right away or within a few seconds much like you can in your description.

I suspect that Brian was playing with the pilot adjustment to fine tune the idle mixture much as per what I mentioned above. You can do this too just as I described. It's not rocket science. I did mine on the 9R this morning and it took all of 10 minutes to lift the seats, undo and prop up the gas tank rear with a block of wood, make the adjustment and put it all back together and start it up.

If Brian got it pretty close then you want to make very small adjustments. From the sound of it I'd go 1/6 turn leaner first off. follow that by another 1/6 if it gets better or has no change. Keep going until you notice a change for the better or the worse. If it's worse then bring it back to where it was originally and go 1/6 more open at a time. When fine tuning it you may only want to go half a flat on the hex bit.

There may be some other transition problems but this is the best you can do without getting a decent jet kit or Ivan's needles and other stuff like that.
 
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