I have a 416 with stage 2 cam. The 39 fcr i put on my bike gave me an extra 3hp and the accelaration it gained was awesome. I would consider it a good choice.

 

How do you know it gave you 3 hp? And where?

 

Scrambler, don't take this the wrong way, but you don't know what you are doing if you tried that many jets and were still looking at the plug color. Plug color has little or nothing to do with jetting any more. The ground strap has a spot where the color changes, that is about the only way you can get any info from the plug. You want the change in color to be right at the 90. Did you even mess with any of the other circuits? I happen to have a FCR on my Z, and I had one on my EX, and trust me, there is power to be gained, if you can tune it. And its not tougher to tune than any other carb, its simple, here let me help....

Choke system:

The choke system’s purpose is to provide the rich air/fuel mixture an engine needs to start and run reliably when cold. The choke is designed to work correctly with the throttle closed. Opening the throttle greatly reduces the action of the choke.

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Idle System:
(Idle - 1/8 throttle)

Tunable components: the Pilot Air Screw and the Pilot Jet. The air screw’s purpose is to fine-tune the mixture at idle. The pilot jet controls the total amount of fuel passing through the idle system.

So, we learn that the Pilot Jet is the metering device and that the screw is simply a fine tuning device. Can we fine tune a pilot jet that’s too large or too small? Yes, but there is an optimum setting for the air screw and if proper idle is not achieved with that optimum setting or near it, the pilot jet must be changed.

How to tune Idle System:

What should the engine do @ idle? Idle smoothly, without hesitations, surges, etc. Standing and listening to an engine idle, we all have a pretty descent idea of what it should sound like. For my intentions and purposes, I don’t really care that much about idle. If it’s close I’m cool. I don’t let the machine run @ idle. I’m either moving or the machine’s off. You be the judge of how you want to idle.

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Main System:
(Off-idle – 1/4 throttle)

Tunable components: the straight diameter of the Jet Needle controls mixture from off idle to 1/4 throttle.

If part-throttle/off-idle acceleration is flat (not enough fuel), you are too lean i.e. the straight diameter is too large. If cold engine, off-idle acceleration is crisp (kinda like the choke system), you are too rich i.e. the straight diameter is too small.


How to tune the off-idle – 1/4 throttle system:

Tuning here is done with a focus on the top portion of the jet needle. Flat acceleration or crisp acceleration w/ a cold engine must be dealt with by substituting a smaller or larger straight-sectioned jet needle. Again, this must be done by feel/sound.

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Main System:
(1/4 throttle – 3/4 throttle)

The tapered portion of the needle or in other words from where the straight part of the needle ends to the “point”


How to tune the 1/4 throttle – 3/4 throttle system:

Tuning here is just simply a function of needle taper. If acceleration is flat (lean) you must remove the needle clip and place it in a lower position. If, while closing the throttle from approximately 3/4 to 1/2 and the engine loads or surges, you are probably to rich. You must then move the clip to a position at least one higher that it’s current spot.

You may not get the perfect off-idle thru 3/4 throttle combination in the same needle, but you’ll need to get as close as possible, because there are no 2-piece needles. Well maybe there are… who the hell knows.

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Main System:
(3/4 throttle - WFO)

There are (3) ways to test the main:

#1: Dyno
#2: Roll-off throttle
#3: Roll-on throttle (takes multiple people & timing devices - not practical for selector and won't be covered)

Test #1: Dyno

Got a dyno? I don’t – we’re done here.

Test #2: Roll-off

You’ve already settled on the lower throttle settings and are satisfied w/ them. Fit what you think is the correct main and get somewhere that you can ride and WFO for several seconds at least and have some decent run-off room too. Get to WFO and run there for several seconds, then let off to about 7/8 throttle. If you seem to gain power, you’re too lean – install a larger main and retest. Why would you gain power by letting off the throttle? If you’re too lean, closing the throttle from WFO to 7/8 or so, will have and “extra” bit of fuel delivered thus creating the feeling of gaining power. Actually that extra bit is the perfect amount, but it’s being delivered at the wrong time.

If you back off to 7/8 throttle and the engine hesitates, you are too rich. Why? Again, backing off of WFO still has a touch of fuel in the process of being burned. Well this time it’s a bit too much and as such is more than the engine wants to burn.

Working this method will have your carb within (1) size of the correct main jet and I'm sure you can fine tune it to the proper main from there.



Its common knowledge, and proven by many dynos, that a FCR, or any flat slide, carb will give you gains in the 2-3 hp range, through the band, although mostly on the top end. I have seen in certain cases, depending on port work, compression, ect, where bottom end actually suffers, but top end is always a plus.

 

I know all of that. my carb is now giving me some gains but it would not when my bike was relatively stock. And the plug now looks perfect and it runs good so how does that have nothing to do with jetting?

 

Just get the FCR, you won;t be dissapointed, its no harder to jet than stock. Same deal, there is a needle, a main jet,a pilot jet, and a air/fuel screw adjsutment.
It WILL make more power.
Scrambler, I am not, was not, trying to argue with you.
Its just ignorant to say
[quote]
I have a 39fcr on my z-400 all it did was take forever to jet no real performance gains.[/Q

 

 

I dynoed my bike at 37hp before the carb and with the carb it made 40.There is not much that i havnt modded in the motor and obviously it was restricted by the stock carb.Its not the fact of making the extra hp but how fast it accelarated that impressed me.

 

what jetting you running??

 

you know any thing about this KGB??

 

The washer fis betweenthe spring and teh rubber diaphragm in the accel pump. If you remove the cover, a spring will pop out, it seats ont eh rubber, place a small washer in between the two, it should be roughly the same size as the spring. I was told that the Factory whatever cap, woudl lean it out even more thatn the washer. Again, contact Sudco. They pointed me in the direction I needd to go. The accel pump wheel has a few adjustmenst in it as well. I had to do alot of messing with mine, but I had a weird build (14.1 comp, and crazy porting). I got it dialed in and working fine. I have another FCR on my wifes Z. I have the washer in the accel pump, and I have it set at factory settigns on the wheel. I do not know anything about using RC parts to change accel pump ratios, but I can see how that might work.