Hey Guys. I could really use some help on this one. I have a set of 4 FCR35 on a KZ1000 "J" engine. Bored 1075cc, 10.5:1 MTC pistons, Ape 410 street cams, pods and a Kerker with 2" baffle. Just off-idle, slow accel, 1500-2k rpm, it surges/breaks up. It's continuous so not from a mis-timed pump shot. Can even feel it in neutral with no load. Idles fine (every pilot change trying to maintain reasonable idle A/F between 1 and 2.5 turns). Above 2.5k rpm no problems. Using Innovate LM-2 and see the lean spike when it happens, also improves when full-hot so I know it's a lean spot. Tried every pilot fuel and air combo to no avail. If I go 3 steps rich on needle diameter I can almost completely kill the lean spot, but then I'm way too rich at cruise. Someone suggested checking the vacuum release plate seals, and they were somewhat degraded on the edges, but replaced and didn't help. Carbs are about 5 years old with low miles. This FCR set was made/tuned for my engine with open exhaust and velocity stacks. Out of the box jetting: Main: 138 Main air:200 Pilot fuel: 45 Pilot air: 1.5 turns (about a 125) Needle: EMQ (center clip) Pilot screw: 1 turn Float: 9mm Down to a 128 main to get about 13 A/F at WOT. I believe because I'm using pods as opposed to the stacks the carbs were tuned for. Any suggestions would be great. Thanks.
Forget about Idle A/F, try a 50 pilot and adjust air screws for best idle(akahighest idle speed). If that wont get it done you may need to go back up on the main and put bigger main bleeds to get the A/F where you want it.
Hey Danny, It seems the screws only affect idle. Had 50s in there, 3 turns out (could no longer get a stumble running the screws all the way in), and the problem was still there. And the lean spot was there from the beginning running the 138 mains. Still thinking I might need the perfect balance of pilot fuel and air, but running out of combinations. Wish there was a chart telling me what pfj with what paj. Seems as if the lean spot is where pilot fuel decreases and needle diameter fuel increases.
From my experiance on bigger bikes like that Pilots have a pretty significant crossover to cruise very light throttle rideability. It may be time to put some tape and marks on the throttle and see exactly what throttle opening the problem is happening... many times at Cruise the throttle is open VERY little. If it is open enough you will need to go to a richer needle (IE smaller at the fattest part) and then adust its height to obtain A/F at larger throttle openings.... May want to make sure the needles arent currently bottoming in the mains as that can cause issues like you are having also....
Good idea on marking the throttle to be more accurate on throttle position. Incase I didn't explain it right, the problem isn't at cruise, it's slight part throttle from a stop. But everything I try to richen up and fix the problem at slight throttle, makes it too rich at cruise (11:1 range). Slight throttle is like 1/16 at 2k rpm in 1st gear (the problem spot), and cruise is like 1/8 or a little more, 4500rpm in 5th gear. Right now I can't correct the the problem with the pilots, but with 3 or 4 steps richer diameter needles I can, but again way too rich at cruise. Suck down a tank of gas in no time. Here's where I'm at right now. Main:128: (13:1 WOT) Main air: 200 Pilot fuel: 45 Pilot air: 120 EMQ needle (center clip) I have lots of jets, but here's what I have on needles right now. EMM (kills the problem, too rich at cruise) EMN (almost kills the problem, too rich at cruise) DVP (richer one step on diameter, leaner one step on L1 and taper. No affect with same pilots) My plan was to install the DVP needles, up the pilot fuel to 48, and and decrease pilot air to 100). Trying to get a little richer on both pilot and needle at part throttle. Let me know if you have any other suggestions, and I will mark the throttle for the next run. Thanks.
I have a lot of experience tuning Keihin CRs and they are sensitive to needle taper. At that RPM you are just coming off the idle circuit and coming onto the main jet. Try raising the needles, if that does not work get ones with less of a taper.
Run the EMM needles and raise the clip until cruise is good. If that wont get where you need to be then try a ENM needle in the middle position.
K. I'll run the EMMs with the clip in the top grove and see what happens. Because I know they were way too rich at cruise in the 3rd.
Just got off the beast. Jetting: 128 main 200 main air EML needles at top clip.(I was mistaken. I have EMM, and EML). 45 Pilot 1 1/4 turns pilot air 2.5 turns out on screws Marked the throttle. The breakup is at 1/16 to 1/8 throttle, 1st/2nd gear (up to 12.5 AF, 100% better with the rich diameter needles, but still noticeable cold) , 2k rpm. Cruise is 1/8 to 3/16 throttle, 5th gear, 4500 rpm (11:1). 1/2 throttle is about the same. 3/4 throttle at 12.5: 1, and WOT at 13.2:1. Seems like I need to find the perfect (crazy) combination of pilots and needles.
So I might be wrong but you might have to readjust float heights? Those carbs are sitting back a little when they should be tilted forward? Just my .00002 cents
https://thumpertalk.com/forums/topic/544643-fuel-flow-diagram-keihin-fcrs/ The problem is where pilot and needle diameter interact. I think I still need more from pilot to fix the problem without going too rich at cruise. Cruise is almost the same throttle position as my problem, but higher rpm.
http://www.bulldock.jp/gtm/ These guys build some serious modified classics. They use FCRs on almost every bike.
Since you didnt see a improvement with the Pilot the problem is the fat part of the needle was too large. With the changes you made you are now WAY rich in the middle. A change leaner in taper and possibly L1 will fix that. Its best to be a bit lean at cruise IMO like 13.7-14.0.
Hey Danny, Take a look at the fuel flow chart. https://thumpertalk.com/forums/topic/544643-fuel-flow-diagram-keihin-fcrs/ The needle diameter fuel covers the 1/8 throttle problem, peaks at 1/4 throttle, ends at 1/2. But look at needle clip, L1 and taper. No effect at all until 1/4 throttle. Meaning if I go rich on diameter, and lean on clip, l1 or taper to compensate it's not going to help the rich cruise at slightly above 1/8. And I think that showed on the last run with EMLs at the top groove still being way too rich all the way to 1/2 throttle. Still think pilot air is the root of the problem, and maybe I missed the perfect combination. See how slow air begins just off idle and increases from there. Anyway. I'm thinking of going the old faithful route. Start with getting the main perfect, the taper, then L1 working down in throttle position. Then diameter, which I want perfect at 1/4 throttle where it peaks. After all that is set in stone, tackle pilot air and fuel. I think going with the 128 mains and EMQ needles (center clip) would be a good place to start and evaluate adjustments. It looks like evaluating at highest rpm in 5th gear at the throttle position that peaks for each adjustment might work well. Like taper just above 1/2 throttle, clip/L1 just before half throttle, diameter at 1/4 throttle. What do you think?
