SlightlyOffAxis Posted May 29, 2010 Share Posted May 29, 2010 I have a 1984 FJ600 that ran perfectly until I did something, I’m not sure what. I pulled and cleaned the carbs (Mikuni BS 32 type 2) that are jetted Stage 3 with pod filters and a Kerker 4-1-2 system. Fuel mixture screw is 3 turns out, and jet needles are on the 3rd position as it has been for several years. I installed the larger main jet when I put the cone filters on and it ran well except for a slight flat spot just after ¼ throttle that cleared up before ½. The bike pulled hard all the way to redline in any gear. I adjusted the needles and fuel mixture screws and thing did not improve. I attempted to vacuum synch the carbs and in the process of all of this I ran into some issues that changed the throttle stop setting as well. I bench synced the carbs and cleaned them, I am meticulous, everything is cleaned and adjusted back to where it was but it will not start. It turns over fine. I have a suspicion it is how I have the throttle stop set that is making the difference. When I bench synced them yesterday I have them closed completely at the start position. Question 1. Is the throttle stop position correct? Question 2. Assuming the carbs are perfectly clean and there are no worn or dirty part what else should I look for. Question 3. I was able to get a copy of the Mikuni BS32 handbook that describes, among other things, how to vacuum sync their carbs and it is different than what Yamaha has in its service manual. Mikuni says you need to sync the #1 and #4 carbs to be even and slightly higher than the #2 and #3 carbs which would be level with each other. Yamaha says, as does everything else I have seen on the web, to sync them until they are all level based on the #3 carb setting as it is fixed. Why the difference? They way the carb appear to work to me is that I HAVE to adjust #2 to #3 first as #2 is only adjustable with the adjustment screw that adjusts the set, then adjust #4 to #3 and #1 to #2. Link to comment Share on other sites More sharing options...
Karen_Agusta Posted May 31, 2010 Share Posted May 31, 2010 I build race bikes and hot rods ... please consider this ... you are allowing far more fuel in ... you are moving far more air out ... yet your engine still thinks nothing has changed ... in other words ... imagine taking a Chevy 350, intalling a 1000 CFM dominator carb, A Single plane raised intake, high flow headers, and three inch exhaust ... while running a stock cam ... you will always have a flat spot ... Should you seek more information you may go to the following post ... ... and ... read the second Link down within it ... Also ... I would get a manual for the bike and synch it as it tells you then try it again ... of course ... all of these are thoughts and some ideas ... . ------------------------------------------------------------------------------------------------------------- http://www.megacyclecams.com/catalog/pages/page%2060.pdf YAMAHA 550 SECA, 600 FJ/FZ (1981—1992) and RADIAN (1986—1990) $399.00 Hardfaced cams per pair, on customer cores ... #105-Y R/D valve springs only ------------------------------------------------------------------------------------------------------------- CAM ----- VALVE -- DURATION -- LOBE ----- INTAKE OPEN/CLOSE --- RUNNING ---- DESCRIPTION NUMBER -- LIFT ----AT .040" -- CENTERS -- EXHAUST OPEN/CLOSE -- CLEARANCE -- APPLICATION 257-10 - .350 ---- 244 ------- 107 ------ 15 btc/49 abc ------- .005 ------- XJ550 OK w stk pstns / springs ---------.350 ---- 244 ------- 107 ------ 49 bbc/15 atc ------- .007 ------- Increased mid-range smooth idle ------------------------------------------------------------------------------------------------------------- CAM ----- VALVE -- DURATION -- LOBE ----- INTAKE OPEN/CLOSE --- RUNNING ---- DESCRIPTION NUMBER -- LIFT --- AT .040" -- CENTERS -- EXHAUST OPEN/CLOSE -- CLEARANCE -- APPLICATION 257-00 - .354 ---- 254 ------- 108 ------ 19 btc/55 abc ------- .005 ------- FZ-600 OK w stk pstns must use ---------.354 ---- 254 ------- 108 ------ 55 bbc/19 atc ------- .007 ------- 105-Y springs mid-range top-end ------------------------------------------------------------------------------------------------------------- . Ideas which hopefully may help a little . Karen I have a 1984 FJ600 that ran perfectly until I did something, I’m not sure what. I pulled and cleaned the carbs (Mikuni BS 32 type 2) that are jetted Stage 3 with pod filters and a Kerker 4-1-2 system. Fuel mixture screw is 3 turns out, and jet needles are on the 3rd position as it has been for several years. I installed the larger main jet when I put the cone filters on and it ran well except for a slight flat spot just after ¼ throttle that cleared up before ½. The bike pulled hard all the way to redline in any gear. I adjusted the needles and fuel mixture screws and thing did not improve. I attempted to vacuum synch the carbs and in the process of all of this I ran into some issues that changed the throttle stop setting as well. I bench synced the carbs and cleaned them, I am meticulous, everything is cleaned and adjusted back to where it was but it will not start. It turns over fine. I have a suspicion it is how I have the throttle stop set that is making the difference. When I bench synced them yesterday I have them closed completely at the start position. Question 1. Is the throttle stop position correct? Question 2. Assuming the carbs are perfectly clean and there are no worn or dirty part what else should I look for. Question 3. I was able to get a copy of the Mikuni BS32 handbook that describes, among other things, how to vacuum sync their carbs and it is different than what Yamaha has in its service manual. Mikuni says you need to sync the #1 and #4 carbs to be even and slightly higher than the #2 and #3 carbs which would be level with each other. Yamaha says, as does everything else I have seen on the web, to sync them until they are all level based on the #3 carb setting as it is fixed. Why the difference? They way the carb appear to work to me is that I HAVE to adjust #2 to #3 first as #2 is only adjustable with the adjustment screw that adjusts the set, then adjust #4 to #3 and #1 to #2. Link to comment Share on other sites More sharing options...
SlightlyOffAxis Posted June 1, 2010 Author Share Posted June 1, 2010 Thank you, all good points and thank you for the link , now I know were to go to get parts I feared would be impossible to find. After having bench synced the carbs again and double and triple checking all the jets, settings and connections, I can get the engine to turn over freely and on every third or fourth revolution I can hear the engine attempt to continue on its own, but it doesn't. I get a hazy smoke around the carbs and an occasional backfire. Then I get disgusted and walk away. Progress is slow indeed considering as it is set up right now it was running except or the flat spot at 1/4 throttle a few days ago. I build race bikes and hot rods ... please consider this ... you are allowing far more fuel in ... you are moving far more air out ... yet your engine still thinks nothing has changed ... in other words ... imagine taking a Chevy 350, intalling a 1000 CFM dominator carb, A Single plane raised intake, high flow headers, and three inch exhaust ... while running a stock cam ... you will always have a flat spot ... Should you seek more information you may go to the following post ... ... and ... read the second Link down within it ... Also ... I would get a manual for the bike and synch it as it tells you then try it again ... of course ... all of these are thoughts and some ideas ... . ------------------------------------------------------------------------------------------------------------- http://www.megacyclecams.com/catalog/pages/page%2060.pdf YAMAHA 550 SECA, 600 FJ/FZ (1981—1992) and RADIAN (1986—1990) $399.00 Hardfaced cams per pair, on customer cores ... #105-Y R/D valve springs only ------------------------------------------------------------------------------------------------------------- CAM ----- VALVE -- DURATION -- LOBE ----- INTAKE OPEN/CLOSE --- RUNNING ---- DESCRIPTION NUMBER -- LIFT ----AT .040" -- CENTERS -- EXHAUST OPEN/CLOSE -- CLEARANCE -- APPLICATION 257-10 - .350 ---- 244 ------- 107 ------ 15 btc/49 abc ------- .005 ------- XJ550 OK w stk pstns / springs ---------.350 ---- 244 ------- 107 ------ 49 bbc/15 atc ------- .007 ------- Increased mid-range smooth idle ------------------------------------------------------------------------------------------------------------- CAM ----- VALVE -- DURATION -- LOBE ----- INTAKE OPEN/CLOSE --- RUNNING ---- DESCRIPTION NUMBER -- LIFT --- AT .040" -- CENTERS -- EXHAUST OPEN/CLOSE -- CLEARANCE -- APPLICATION 257-00 - .354 ---- 254 ------- 108 ------ 19 btc/55 abc ------- .005 ------- FZ-600 OK w stk pstns must use ---------.354 ---- 254 ------- 108 ------ 55 bbc/19 atc ------- .007 ------- 105-Y springs mid-range top-end ------------------------------------------------------------------------------------------------------------- . Ideas which hopefully may help a little . Karen Link to comment Share on other sites More sharing options...
Karen_Agusta Posted June 2, 2010 Share Posted June 2, 2010 A backfire and the symptoms you are describing are almost always ignition related ... did you work on the ignition / timing at all? Thank you, all good points and thank you for the link , now I know were to go to get parts I feared would be impossible to find. After having bench synced the carbs again and double and triple checking all the jets, settings and connections, I can get the engine to turn over freely and on every third or fourth revolution I can hear the engine attempt to continue on its own, but it doesn't. I get a hazy smoke around the carbs and an occasional backfire. Then I get disgusted and walk away. Progress is slow indeed considering as it is set up right now it was running except or the flat spot at 1/4 throttle a few days ago. Link to comment Share on other sites More sharing options...
Kelly Corey Posted September 6, 2010 Share Posted September 6, 2010 Hi, I have the same bike and have been working with carb issues for part of the summer. I have made some advances this weekend, I vacuum synced the carbs using the two-bottle method, which works really well if your carbs are way off like mine were - no fluid gets sucked up! Anyway, my Haynes manual says to sync 1&2, 3&4 and then 1+2 & 3+4. The adjusting screws are super sensitive btw. My exhaust is a Yoshi 4-1-1, and I have been having issues with plugs carbon-fouling. I have it narrowed down to plugs #1 and #4; the inside plugs seem fine. I haven't been meticulous enough to see where on the throttle the fouling occurs, but I suspect it is lower range rather than upper. I have my pilot screws set to 1 turn out each right now, I have experimented as far up as 2 1/2 turns without much real difference. I have gone with a hotter plug on the outside which seemed to make a bit of difference. The bike runs well except for a stutter in 6th gear between 5500-6000 rpm. After 6000 it pulls hard and fast as far as I want it to go. I am not sure if this is an ignition issue or a carb issue, I am leaning more towards an ignition issue since it is the same coil for plugs 1 & 4 and those are the ones that are fouling. And the problem seems more rpm/engine load related rather than throttle position. I had a small leak on intake boot #2, so I took them all off and sealed them up around where the band clamp goes, some minor cracks on each. I also found that carb #2 should have a #7 jet needle, the other carbs have a #3. Someone had the #7 in carb 1, whether this makes a huge difference or not I don't know. Anyway, replaced the boots and the carbs last night, it started up fine and rev'ed smoothly. Took it for a short test down the road, runs about the best i have had it running all summer right now. I will take it out for a longer ride and come back with my findings on the stutter and plug fouling. I want to re-sync the carbs with the freshly sealed boots anyway. I found a stock exhaust for sale, I am thinking I may need to swap out the 4-1, I suspect too the carb issues I am having are somehow tied into the yoshi setup. All carbs jets are stock, and maybe I need to change the main jet to accommodate the yoshi. A lot of trouble for a 26 year old bike, but it is my first and I want it to run the best it can. It has under 26K km's and is in good shape overall. Also thinking about changing my plug boots, removing the 10k ohm stock boots with some 0 ohm boots, haven't made that leap yet. Link to comment Share on other sites More sharing options...
Kelly Corey Posted July 5, 2011 Share Posted July 5, 2011 After settling for status quo for the remainder of 2010 and now this far into 2011, I took off the carbs again a couple of weeks ago and found the main jets were all #115. Stock should be #105 in #1 and #2 and #102.5 in #3 & #4. The jet needles are also wrong, 4CP3 in 1, 3, & 4 and 4CP7 in #2. Should be 4CP4 and 4CP6 according to Haynes. Anyway, I found some smaller main jets (thanks to J&R Cycle in Stayner!), went with #110 in #1 & #2 and 107.5 in #3 & #4. Still need the jet needles on the top clip setting, but the bog is almost completely gone. The previous owner must have tried to compensate for the 4-1 Yoshi pipe with the larger jets, but I think they way overcompensated... Just did this work this morning and ran it around for a bit on the local roads. Seems a whole bunch better in the 3/4 to full throttle range. Re-synced the carbs, will hopefully get to test it out on a longer run tomorrow if the weather holds. Getting tired of yanking the carbs, it is rough on the intake and exhaust boots, harder each time to get the all-important seal. Thinking of going for the pod filters... Link to comment Share on other sites More sharing options...
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