77 cb750f2 supersport breaking up in the mid/top range

specs on the ride.

engine: stock sohc750, kerker mac 4-1 header exhaust, dual mikuni vm34 carbs with pod filters, 240 main 35 pilot with the needle clip 1 position from full rich, new ngk plugs, checked/ adjusted my lifters, pints, and checked the static ignition timing

ignition system, besides a new voltage reg/rect from cyclex, is stock original equipment from 1977. its the only thing i havnt upgraded yet
im pretty sure the carbs are dialed in as best i can get them right now

3/4 and full throttle mostly 5k rpm and up it starts breaking up on me, im looking for someone to let me barrow a timing light to check and make sure my timing isnt retarded or too advanced

other than that im thinking the stock ignition system just isnt up to par, at first i thought i didnt have the carbs tuned right but the bike runs best where i have it set uo now,and im thinking my 35 year old coils and wires need to be upgraded along with possibly a new ignition

i was thinking about getting an electronic ignition setup from cycle x and possibly one of thier single phase batteryless charging systems

thought, questions, advice, tips anythings apprectiated at this point
btw this bike was sitting around in the garage for the past 20 some odd years and i just brought it back to life recently, the bike only has 2300 original miles on it

and for your view pleasures




and some new bars, so much moe comfortable to ride

A new set of points, condenser, coils and wires would be where I start, especially if they're that old. I don't think an electronic ignition is necessary, but if you got the $ to shell out for one, its not gonna hurt. I have a timing light if you want to swing by and use it. Once you're sure there's no ignition issues, then the carbs can be dialed in proper.

Start small. Make sure your advance unit is in good sahpe. As in make sure it's snappy. Adjust the points gap, then set your timing. Then try adjusting the carbs again. Do the plugs look good? Are they rich or lean?

I can tell you from experience, I had to bump my idle up a bit and run a little richer than I'de like (pulled the needle up a clip) and opened up the mixture screw to a full 1 1/4 turn out . Runs like a champ now. All the way through. My cb750 is a 1970. Cyclex carbs, cyclex charging system, dyna green 3 ohm coils, dyna s ignition. mac drags cut with wingnut baffles haha. You can dump a ton of money into an igntion system and coils. So shop around, check forums, don't buy used units.

Hondaman over at sohc4.com makes a transistorized unit that works off of the points, then there are also cyclex, dyna, and pamco I believe. I run NGK Iridium plugs with my hotter coils too. They seem to burn better.

good luck and nice ride

Easyspeed said it best...I would definitely change up to a Dyna 3ohm coil and e-ignition as well. Those carbs are a little finicky on the bike if you don't have the best spark you can give to your scoot. I wouldn't waste the scratch on a new charging sysrem from Cycle X yet, as long as you're running the combo you're all good.

thanks guys and easyspeed i think u answered my questions spot on, sounds like ur setup is similiar to mine and ur carbs sound to be set about the same as mine to, not sure what ur running for jets? im just gunna call up cyclex tomorrow and upgrade the ignition, screw it ive gone this far with the bike m not about to skimp out on my ignition system. im running the stock ngk plugs and they look to be burning well i think the mixtures good, just think the stock old ignition cant keep up

240 main?? needle is set at the 2nd ring from full rich. I have those chinsie ass v stacks too. Air screw is set 1 and 1/4 turn out. Not sure about you , but my bike sounds awesome at a low idle, unfortunately I've learned it's not the best way to run though. Turned it back up to what a 4 banger is supposed to idle at. seemed to help alot.

Here is my shit bird no fender shit slinging sled:



here is a small vid right after I got it running, before some tuning and with a lower idle. just bumped the idle screw in about a 1/2 turn each.
http://www.youtube.com/watch?v=FnsJZYeDMm8

hell yeah thats exactly how i have my carbs set too, i found it to be the best configuration, i just gotta fix this ignition. talked to roxy at cycleX this mornign and shes going to figue out a price for monday since theyre going out to race some bikes today. we talked about thier ignition kit #3 minus the start solenoid, voltage reg and ign switch since i already have those parts

sie note i got some 3" shorter fork tubes from them and im trying to put them on this morning, not sure if i should look for shorter springs from anther bike cause i can nt get these end caps on to save my life trying to compress 3" by hand is a nightmare, any suggestions??

3" under... cut 3 inches out of the springs or try and leave a little extra for preload. Like a 1/2" extra. I didn't use any extra when I lowered mine cause they are a bitch to get back together. that should do it. I used a cut off wheel on my springs

sweet bike man. glad to see somebody else without a rear fender.

actually ended up getting the fork tubes together without cutting the springs, wasnt easy but i got it done. bike rides and handles a million times better now

as it sits today...

sounds good and great looking ride btw, def one of my favorite cb's! i prolly would have kept my drag bars on like urs but it didnt feel comfortable with the forward controls, but hey if i get bored of this setup maybe ill put the drags back on and change my controls to some rear sets for hahahs

Originally Posted by easyspeed

240 main?? needle is set at the 2nd ring from full rich. I have those chinsie ass v stacks too. Air screw is set 1 and 1/4 turn out. Not sure about you , but my bike sounds awesome at a low idle, unfortunately I've learned it's not the best way to run though. Turned it back up to what a 4 banger is supposed to idle at. seemed to help alot.

Here is my shit bird no fender shit slinging sled:



here is a small vid right after I got it running, before some tuning and with a lower idle. just bumped the idle screw in about a 1/2 turn each.
http://www.youtube.com/watch?v=FnsJZYeDMm8

Big thanks to bambam for helping me with the timing light and more tuning on the carbs. The bikes running much better.. Still think I need to get atleast higher voltage coils an wires cause it bogs alittle if I open the throttle too fast from an idle and still breaks up some in the higher rpms.. It feels like the spark is weak and getting blown out but overall it's running great for whipping around town for now. Hopefully coils n wires will take cafe of the issue