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Here to F stuff up
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144 Posts
Discussion Starter · #1 ·
Ok cfers, I have a mission for you, should you choose to accept. I bought a 93 cbr f2 cheap non running, got it running. So far I have cleaned the carbs at least 5 times, re gasketed them, bench synced and set the idle air screws to stock. As far as the ignition, I have tested every piece short of the actual ignition box, and even replaced the plug wires with some big block chevy wires. It also has plugs that have less than 50 miles on them at all, almost brand new. Cold compression is the same on every cylinder, i adjusted the valves, and the cam timing is dead on, checked that multiple times. If I put new plugs in it, it will probably start up. However, to get it to start, I have to crank and blip the throttle until I can rev it up. Once it idles on its own, it runs amazing. I can't figure this starting thing out at all. Any suggestions?
 

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Here to F stuff up
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144 Posts
Discussion Starter · #3 ·
Stock header, d&d can. Stock airbox. I got it started, but here's the other issue I've been fighting. #1 doesn't fire at idle at all. Header temp sits at 150 mostly, and as soon as I open the throttle, #1 starts hitting. The bike runs good except if the throttle is barley open or closed. Then you can hear it missing. Idk at this point.
 

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Here to F stuff up
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144 Posts
Discussion Starter · #4 ·
Also, I put new plugs in and have them gapped at .030. Stock spec is between .030-.040. That's what got it running again.
 

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Sick of being frozen
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1,086 Posts
Have you checked the petcock? Or run it off another fuel tank? My cbr is a pain in the ass to get to run right.
I added a fuel filter and finally the carbs stay clean.
The fact that #1 isn't firing at idle is strange, Coils do fail, can you switch the coil from 1+4 to 2+3 and see if the miss moves?
The fact that it fires with throttle points to carbs though. make sure all of the parts are on your idle air screws and fuel screws, I can't remember exactly but I know some of those have super tiny o-rings that get destroyed/lost.
Lastly check your charging system/battery, cbrs act stupid at the slightest elecrical issues, load test your battery and check your regulator and wiring, they like to melt the large 3 prong plug by the regulator.
 

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Sick of being frozen
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1,086 Posts
Oh and older carbed bike are usually way lean at idle, I have fattened up the idle mixture on my cbr and 2 bandit 400s, just to get a nice smooth idle, no stalling when cutting throttle to stop fast.
 

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old fart
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3,716 Posts
check the pilot jet on no 1 carb, sounds like is letting gas through the needle when you use throttle, but cutting again when you shut it, which points to a blocked pilot.
 

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Here to F stuff up
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144 Posts
Discussion Starter · #8 ·
I've been through the whole pilot circuit 5 times, so I know that's clean as hell. I've also ran off an auxiliary fuel tank, no change. I'll try switching the coils tomorrow, we see what happens. What charging voltage should I be getting at idle with the headlight off?
 

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Active Member
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688 Posts
Any difference starting the bike on the side stand versus a center stand rear stand? Also, have you checked the plug on the #1 cylinder after trying to start it? Is it wet, fouled, dry? Have you verified float height as well as the float functioning as expected without leaking fuel?
 

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Premium Member
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If the cylinder chimes in with revs, it's almost certainly the carb. Try swapping the idle jets or whatever else from one to the other. Remember there are tiny passages that you can't easily get to which can get blocked with old fuel gum. Sonic cleaning may well be your answer, and at the least will save you getting dirty hands every time you take the carbs off ;)
 

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Here to F stuff up
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144 Posts
Discussion Starter · #11 ·
Side stand vs center stand no difference. Swapped pilot jets between bodies. For this carbs, floats are preset, can't adjust the height. I've cleaned up the seat and needle so that it seals like it should. At this point, idk what else to try. I know a guy that comes into my work a lot to buy parts, he might be able to hook me up with a sonic cleaning for cheap. I'll have to give it a try tomorrow. Thanks for the help guys. I know it's gotta be something simple, it's driving me bat shit crazy.
 

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Here to F stuff up
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144 Posts
Discussion Starter · #12 ·
anybody got anymore suggestions? im essentially back to the starting issue again. if i pull the plugs, theyre pretty dark, almost black, and usually wet with fuel. i think they keep fouling out. im so lost at this point.
 

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Here to F stuff up
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144 Posts
Discussion Starter · #13 ·


this is what the plugs look like when i pull them out. they have about 80 miles on them. i think theyre just rich fouled, i hope its not oil. what you guys think?
 

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Sick of being frozen
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The fact that you have to throttle it to start sounds like carbs still.
Does it start better with the choke on or off?
Does it run better with the choke halfway on or does that make it run worse?
Did you check the charging system?
Does your battery pass a load test?
In order to help we need more info, you say you've been through the carbs, were the small o rings on all the mixture screws?
 

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Here to F stuff up
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144 Posts
Discussion Starter · #15 ·
Well, i went all the way tonight boys.
Split and stripped dem bitches and got rough with them, soaked them down and let them sit in their own filth the rest of the night after I had my way with them.

Oh yeah, and I'm soaking the carbs in berrymans carb dip tonight. I did find one problem that could possibly be contributing to running crappy. Whenever I put the slide cover back on, I pinched the corner of it, causing it to not rise under vacuum. One problem down, hopefully the carb dip gets whatever shit is in the pilot circut out finally.
 

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DW is all that matters
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119 Posts
My f2's name was 'pita.' Carbs carbs and more work on the carbs. I don't know if you have compressed air, but blow out those little holes, using as much carb cleaner as possible. I picked up about 5 sets of carbs off ebay and built good sets. Balance & sync made huge difference initially when I figured out how (motionpro sync tool worked great for me). Had the cold cylinder problem before that which drove me crazy. Also had a bad coil that caused me grief till I pinned it down. Make sure your fuel screen is good inside the tank also. Those carbs were a pain in the a** for me and I can't say I miss them. F2 was my first built bike and I learned quite a bit on it, but damn annoying at times.
 

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Here to F stuff up
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144 Posts
Discussion Starter · #17 ·
well, even after splitting the bodies and soaking them in berrymans for 24 hours, plus shooting the passages with carb cleaner, plus blowing out EVERYTHING with compressed air, im still having the issue. plus in think cylinder 2 plug dropped this time. ugh, i want to throw this damn bike off a cliff and laugh manically as it tumbles to its doom.

as far as a filter, do you think itd be worth ditching the stock filter screen and just putting a small inline filter in that can filter a bit better? and ratfighter also pmed me a good point, that my cdi box could be bad, which i know a local guy that i could switch black boxes with to test that.

could the coils also be bad, but ohm out right when you take a dmm to them?

also, as for syncing, i usually just used some feeler gauges and benched synced them, usually worked fine enough to where i didnt dick around with using a set of vacuum gauges. maybe vacuum gauges are the right way to go here?

and i also just remembered this too. when i bought the bike, the throttle shafts were frozen in the bodies. while taking everything apart, i bent #1 throttle blade trying to get it out, since i have no experience and not a single clue what im doing. i bent it back as straight as i could in a vice, and checked it on a glass table, and i thought i got it completely flat. is it possible that its bent just enough that its still fudging up my idle and low speed running issues?
 
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