I have a 2000 CBR F4, I have compression (155, 145, 155, 160) It seems like the plugs spark alot, more than once every two rotations, but I could be wrong. I have fuel in there as it will backfire like a shotgun everyonce in a while but it is random. I pulled the carbs and cleaned them, put them back and it coughed once but that was it. I have no idea what else to adjust or check/replace and my knowledge on bikes is small.

Any ideas?

Thanks,
Brad

 

Has the bike run ok previously? Are you absolutely sure you have connected the spark plug leads in the correct firing order? Sounds like a timing issue to me, hence the backfiring you are experiencing. I'm not sure of the firing order on your bike, but will be something like 1,3,4,2 or similar. Check your bike's handbook or a Haynes manual or ask a knowledgeable friend. I am pretty certain that if the leads were connected in the right order the bike would probably run, but not very well if there was another problem such as fuel starvation or an air leak somewhere.

 

firing order is 1-2-4-3.

If it is basically the same system as the F2/3 - one coil fires 1&4 and fires both plugs at the aem time, so it has to fire them once for cyl 1, and then again when Cyl4 is in compression, same for 2 & 3, meaning there is a lost spark for each cycle.

 

Back firing isn't a good sign bro ,, sounds like a timing or vacuum leak issue to me ,, you need to get the bike to a reputable bike shop if you don't know much about motorcycle engines , you will do some serious valve or head damage if its a slipped/jumped timing chain .
If you took the carbs off,,check the seal (O-Ring) at the mount of the carb to see if its sealed good ,,I've seen somebody mount the carb(s) and the o-ring fell off without them noticing . But this sounds like a timing issue , check the forum for a checking the timing segment . Better yet ,,you can download a manual via Haynes online (its in pdf format),,and its cheaper than the paperback . BTW ,Your compression is somewhat close to 10% of each other so it should fire and run . Someone may have one on here for that yr bike. But keep in mind ,, you can really make things worse if you don't have experience in these setup's . Not to say you can't do it,, Its just better to be safe than sorry on doing it wrong bro. When in doubt , have a pro do it. But rule of thumb is Fuel+spark+compression=BANG!! Not backfire. Even with a small vacuum leak,,it should still try to run,,like crap,,but run . Check the timing 1st,,or have it checked .
Keep us in the loop on how you get it worked out Bro. Would love to hear you got her back on the road.

 

definately timing is off . .my buddy had this probleme and he launched his exhaust baffle into orbit . . . . we never found it . . .it wasssssssss louuuuuuuuuud . . . does it turn over freely? if its cranking and it just cranks without probleme then you might have a crossfire issue . .with ur plugs . .generally when the timing is off ittl crank and then kinda stop then crank crank crank slow down KABOOOOOM!!!!!!!!!!!

 

Hey bainbridge,,,I experienced this last night similar thing last night doing a tuneup on my cbr1000,,lift the tank and see if the vacuum hose is hooked up to the tank dimple vent hose on the very bottom of the tank ,,on the righthand side. I was putting the plugs in and after I was done I buttoned up the tank and fired it up,,PUTT,,Sputt,,POP ,,clunk,,It was acting like a jumped timing,,,I asked my son if he touched anything,,He said,,yes,,the hose was hanging under the tank and I hooked it back up,,,I was like WHAT!!?? I lifted the tank up ,,AGAIN,,,and unhooked the hose,,,and waa laaa,,,it ran like a raped ape,,,wow,,a renewed power,,its runs so sweet. Anyways,,check that line to see if its hooked up,,,UNHOOK it if it is,,,my son attached it to the float over flow vacuum and it sealed of the carbs from flowing,,,flooded it . Check and see. Yours is a different bike ,,but check the vacuum routing to make sure your not choking the carbs off . Since you had the carbs off,,double check the vacuum lines,,that they are where theyre supposed to be . As for my son ,,,he's cleaning my dirt-bike for messing with things LOL!!
Good luck bro.

 

Did you end up solving this I have fuel spark and compression but it just won’t start she back fires like a shotgun randomly too also if I windher over long enough and use start ya bastard she will struggle to start, full throttle she sits on 1000 rpm and as I slowly over time back of the throttle she comes to life as soon as I let her sit she struggles to start and it’s for more than a hour she won’t start again