Author Topic: idle to 4k rpm Misfires  (Read 3931 times)

Offline Amdalthon

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idle to 4k rpm Misfires
« on: June 21, 2012, 12:53:21 AM »
Today when i went to start my 1991 B4 after 2 weeks of sitting. I replaced all the orings 4 weeks ago had the pilot screw set at 2 1/2 turns, 15mm float height, and cleaned carbs also synched them then and it ran very nice. the tank was empty and so were the carbs so i had some gas in a jerry can and filled the tank up. the bike WOULD NOT run without the choke and wouldnt want to idle. so i took the carbs apart and saw that my pilot jets were plugged. i clean them out and all the passages in my carb and reassembled them. after putting everything back together i was able to start it and have it idle. i let the bike warm up for a good 5-10 mins and tried to go around the block. the bike has HORRIBLE misfires between idle and 4000 rpm. once i get past 4000rpm the bike pulls magically and does not have a dead spot at 6k. the bike is undriveable like this. so i took my carbs off and checked to make sure everything was good also checked the float level again and before i had the level set up to 15mm and now they are set at 14mm. i also cleaned everything again especially the pilot system. made sure that EVERYthing was clean. still the same problem... so i had some new plugs ordered and tried to see if that would help. it didnt. Has any 1 heard of these symptoms before? ive also tried the pilot screws from 1 1/2 turns - 3 turns and everything in between. if any 1 has any suggestions please let me know and ill try them out.

Offline pmackie

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Re: idle to 4k rpm Misfires
« Reply #1 on: June 21, 2012, 04:37:31 PM »
It sounds like your gas from the gas cans was dirty? Likely it also had some water in it. Hard starting could indicate low fuel vapor pressure.

I would drain and flush the tank, and start with fresh, clean, dry gasoline.
Paul
2002-GSF600S, Progressive Fork Springs, B12 Shock,
SS Brake lines, EBC HH pads, Leo Vince Ex & Kappa bags.
Ex Bike Mechanic (late 70's), somewhat rusty
32 years in the Fuel/lubes industry(Retired)

Offline Amdalthon

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Re: idle to 4k rpm Misfires
« Reply #2 on: June 21, 2012, 06:52:00 PM »
alright today i drained the gas in the tank and carbs. once i had that done i went and got fresh 87 octane gas. from canadian tire. i put 5 liters of fuel into the tank and tried to start it. it now starts without choke and run VERY rich it might be because my floats are at 14mm right now. but i is STILL Missing from idle to 4k. once you get past it its the same like before it will suck your eyeballs out. i also tried a set of CBR f2 ignition coils. this did not fix my issue. still the same thing. after a whole day of trying to get the bike right nothing worked. so AGAIN im taking off my carbs ( around 4 mins and there out! including the throttle cable.) im going to set the float height to around 15.6mm to lean it out which is the max called by the manual (  14.6 +or - 1mm)  i might also put the Stock needles back in to ensure that my mixture is not to rich. but first i will just try the float height. i also checked the cdi terminals to see if they were corroded or anything but they were not.

 I also check my R/R and i got 6.8-7k ohms resistance between the red and yellow(1,2,3) also did the same with the black. has any 1 check theres recently to see what they have? the manual calls for 3.5k ohms. when i tried to see the resistance between red and black i got nothing through all the multi meter ranges and it supposed to be 6k ohms

does any 1 know the symptoms of a bad cdi? would it effect my timing?

Offline Amdalthon

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Re: idle to 4k rpm Misfires
« Reply #3 on: June 26, 2012, 11:53:26 PM »
YAY! got the problem fixed now pulls from off idle all the way to redline with no hesitations or anything. i checked my valve clearances and they were all good except one intake but that wasn't the problem. i took the carbs out for the 7th time and did some more inspecting and once i pulled out my Pilot screw the needle was TAPERED!!!! so with initial settings(1 1/2 turns out) it was running SO rich because of the taper. i turned the pilot screws down to 3/4 of a turn and now it runs SUPER smooth. After messing around with all my electrical which wasnt the problem, im happy it was just my shitty carbs  :grin: damn these super SUPER sensitive carbs X_X my dads 1991 vfr 750 he just bought had the pilots screws at 5,4,4 and 7 turns out and it runs smooth  :grin: