Ehh, those charts arent THAT accurate. IMO you would have seen a improvement with the Pilot if the air bleed would cure it. The needle is the only part that changes as you turn the throttle. Getting it the right diameter at the right point will fix your issues. You can even do some measuring of where the needles are at X throttle and compare numbers with what works and doesnt. Then get a needle that has the numbers that work. JMO
maybe redundant, but have you replaced the low speed air jet with the optional screw kit? finer adjustment.
Sounds like a PAJ issue. I usually end up with the PAJ about .5-1.0 turns out on most FCR's across a variety of bikes. That teeny-tiny throttle area you are having problems with, are where the PAJ's have the most influence. Also, seems like people always run FCR's with too fat pilots and too much slide height to compensate and get a decent idle. If the pilots are too fat and the slides too high, then you don't get enough vacuum at part throttle openings for good fuel pickup.
Yep. Keep thinking I missed something playing with pilot air and fuel. Out of the box was PFJ 45, PAJ 1.5, pilot screws 1. Tried a lot of combinations, but the richest I've gone with PAJ was .75, but I think that was with a 42 PFJ. When you say "slide height", you mean leaner on PFJ and the pilot screws so I have to open the throttle less with the idle speed screw to achieve correct idle speed (1000rpm)? And do you think the best way to go is dialing in mains and needles before adjusting pilot? Seems like the tricky part is due to the overlap of needle diameter and pilot air to maintain good AF from idle to 1/4-1/2 throttle. Right now I'm at PJF45 and PJA1.25, and there I have to go 2.5 turns out on the screws to get 12:5 AF at idle.
I think I might be onto something? I got this quote on a Norton Commando forum from a race guy dealing with FCRs, stacks and pods: "These long stacks tended to cause a stutter just off of idle that was very difficult, sometimes impossible, to tune out. On a racer this simply doesn't matter. On a road bike, its a real PITA." The more I research the more it seems FCRs are built to run with velocity stacks. The guy at Sudco pretty much said the same thing. My set came with the short/red (1 3/8" deep stacks), and I've already seen the major difference in main jetting using filters/adapters (138-128). The filter adapters I'm using are about the same length, but straight all the way, no taper. This guy is having the same problem I'm having with long stacks, possibly straight as deep as my adapters before the taper. Sounds too close to be coincidental, and it sure seems my problem is based on inadequate airflow to pull fuel from the pilot circuit off-idle. I'm gonna bolt on the stacks this weekend and see what happens before I go any further on jetting.
Exactly. It is very common on Ducatis with the FCR's because Sudco supplies their kit with huge PFJ's and the slides jacked up to compensate, and then everybody complains about the idle and off-idle response. I install much smaller pilots, lower the slides, play with the fuel and air screws, then they idle like a dream and pick up off idle fine. It's all about getting good vacuum across the idle circuit. I always start with the idle circuit when tuning because if they don't idle well, it's no fun doing everything else on the dyno... but that's just me. There is a small amount of overlap between PAJ and needle root diameter but it's usually a non-issue. [QUOTE="VTEC, post: 5403289, member: 65939" When you say "slide height", you mean leaner on PFJ and the pilot screws so I have to open the throttle less with the idle speed screw to achieve correct idle speed (1000rpm)? And do you think the best way to go is dialing in mains and needles before adjusting pilot?[/QUOTE]
Here's another quote from a Ducati forum. They use FCRs a lot. "you must use stacks as well, pods on the end of the carbs do not work well at all!" He's saying that if you use pods, you still need a velocity stack taper built into the adapter. I really think my straight adapter is hindering airflow and causing my problem. I'm headed for the garage right now. First I'm gonna run it with the filters off but straight adapters on to see if eliminating the filter restriction makes a difference. If not, I'll remove the adapters, install the v-stacks, and see what happens.
I've only run fcr's on a old f1 750 ducati with huge cams ( yes italian ) and no starter on track so idle is important on the starting line. First thing I was told is disconnect accelerator pumps while trying to jet low speed because the shot of gas with any throttle movement will confuse your tuning. I never reconnected them. Float fuel level height can make a difference and cheap other than time to do it. Different slide cutaway heights are shown in the manual but sudco says they aren't available. I think one slide is over half the price of a carb so if you want to try you can drill a hole and if you go too far epoxy a plug to remove it. I hope you get it right and would like to hear how you did it
Velocity stack filter adapters with air bleeds on the inside are available and what I would start with. Powernow ones with the blade in it.
I ran it with velocity stacks and no filters, and it did nothing to help the problem. So I'm going to re-focus on the pilot circuit. Right now I'm at 45pfj (original), 3/4 turn paj (1 1/2 original), and running 12 af with screws at 1 turn. Problem still there, maybe a little better full hot. Where should I go from here? 40pfj? I can feel the breakup in neutral at 1500-2k rpm. So next time I change pfj I'll leave the filter/adapters off so I can adjust paj in real time.
No, if you are trying to fix it with the Pilot circuit you need to adjust the fuel screws for max Idle rpm then drop the idle to where its supposed to be. If the problem is still there turn the PAJ in a half a turn and repeat the previous procedure and see if it helped. Forget about what the AF is reading at Idle and adjust for best idle. It will misslead you sometimes.
OK. Before going at the screw adjustment for highest idle (not so easy with 4 carbs), should I determine pfj by the stumble with the screws all the way in theory (not gonna stall one at a time with 4 cylinders)? Meaning if it stumbles below 1 turn and picks back up after one turn, I have the correct pfj. The only problem with that theory is what paj? Which I've discovered will have the same effect. Also, I understand that proper pilot circuit should have the screws between 1 and 2.5 turns. What if highest idle is at 3.5 turns?
If highest idle is at 3.5 turns you will need a larger pilot or smaller air bleed( i’m assuming you have screws). You have to get the idle right first. Like Hord said, if the slides are open to much to start with it doesnt get the proper draw through the idle circuit. Adjust fuel screws, drop idle to 1,000, repeat.
I spent the morning messing with the screws and pilot air. I noticed that the richer I go with pilot air, the higher rpm the breakup point is. Leaner pilot air starts breaking up at 1500, richer 2000. I think the best I got was 3/4 turn pilot air and 1 1/2 turns on the screws. Break up was less and at a higher rpm. But I think I'm too rich on pilot fuel. At 3/4 pilot air I can't get much rpm increase going out from 1/2 turn on the screws, and 1/2 turn pilot air, highest rpm is with the screws all the way in. Beginning to think my problem might be the need to have a more dominant rich pilot air to lean pilot fuel ratio. I think I should drop pilot fuel and do the routine again. I'm at 45, think I should drop to 42 or 40? 35 is as small as they go.
Ehh, that would be a waste of time IMO. If you cant get there with what changes you made you wont fix it with the pilot circuit. I would go to a richer needle and start over. Just a size smaller at the fattest part. Just a thought.... where is the ignition timing at and at what RPM does it advance?? Retarded timing will cause all sorts of jetting woes. Check that before moving forward.
Timing with the Dyna 2000 is at 38tdc max. They book says use the 5 setting with a peak at 6500rpm and 25 degree span, but it runs better down low at setting 4 maxing out at 3500rpm. Can't really view timing with a light at low rpm because the mark jumps all over the place. And Dyna says it's normal. Keep thinking about what Hordboy said about always using pilot air between .5 and 1 turn, and much leaner pilot fuel than out-of-the box to get it right. Right now with the 45 I'm too rich to get idle correct between .5 and 1 air. The smallest I have right now is 42, so I'm gonna put them in to see if there's any improvement. To keep my sanity I have to rule this out before going any further.
