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Hello folks, So i have a 75 Honda cb306T, picked her up last year as a project. Heres a list of what I have done so far to the bike
- Cleaned / rejetted carbs
- new points, re-did timing to the T
- New tank, no rust. New side covers for air box's
- New tires / brakes
- New diagphrams
- New Spark Plugs
- New Oil / Fresh Gas
- New exhausts
the list goes on, I had her running perfect a week ago, took it out and put a good 30 miles on it before work, parked it put it on the charger and the next day I came out, started her up and i could tell she was only running on 1 cylinder. (the left one). I let it run for a solid 5 minutes revving it up, and noticed some back fire out of the right cylinder (the one that isnt running), this was only above 3k RPM's. I played with the adjusting screws on the carb because i thought maybe it was running to lean / rich. Pulled the spark plug cap off the dead cylinder and the bike still ran, checked the diaphrams and float levels, gas is getting into both carbs. then i noticed oil seeping out of the exhaust (where they connect) and dripping all over under the exhaust pipe. I shut the bike down and now im stuck. If there is anyone out there that knows the fix that'd be awesome!

Im thinking it could be a bad oring, or maybe my screen in my crankcase is filled with goop, any advice will help! thanks
 

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Is this for sure unburnt oil residue or is it a black liquid that resembles a mixture of unburnt fuel and black carbon? … and is the oil level in your bike dropping or holding steady?

I suspect it's just unburnt fuel washing carbon deposits out of your exhaust system. Also watch that you aren't forcing too much water into the muffler opening, that will sometimes flow out of the header connection because it's the lowest point on many muffler systems.


… just noticed you said the exhausts are new, the only previously accumulated carbon would have to be coming from inside the headers.
 

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Is this for sure unburnt oil residue or is it a black liquid that resembles a mixture of unburnt fuel and black carbon? … and is the oil level in your bike dropping or holding steady?

I suspect it's just unburnt fuel washing carbon deposits out of your exhaust system. Also watch that you aren't forcing too much water into the muffler opening, that will sometimes flow out of the header connection because it's the lowest point on many muffler systems.


… just noticed you said the exhausts are new, the only previously accumulated carbon would have to be coming from inside the headers.
Now that you say that it might be a mixture of unburnt fuel and black carbon, it was really black when i wiped it up with a rag, almost to dark to be fresh oil..I checked my oil earlier today and thought it looked a little low, but I havent changed the oil since last season ( which happened to be more then once)
 

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Step one download the service manual for free if you haven't already done so: http://www.carlsalter.com/pdfs/Honda_CB250.360.CL360.CJ250T.CJ360T.pdf

I expect you have no fire on the number 2 spark plug, the manual will help you trouble-shoot that. That's pretty much the only way you could have copious quantities of unburnt fuel passing through the cylinder.
Also make sure your crankcase venting is not compromised, that would create oil related problems. For unburnt oil to make it to the exhaust it would need to be coming down from the valves or up past the pistons oil ring, both highly unlikely.

Hope this helps some :|
 

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Is the battery fully charged / charging through the bike? These twins have a habit of dropping a cylinder if the charging system is not up to scratch.

Which would explain why there's unburnt fuel dumping out one cylinder and that taking off the spark plug cap does nothing.
 

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Discussion Starter #8
Is the battery fully charged / charging through the bike? These twins have a habit of dropping a cylinder if the charging system is not up to scratch.

Which would explain why there's unburnt fuel dumping out one cylinder and that taking off the spark plug cap does nothing.
yeah! I just put a brand new battery in, and everytime im not riding it its hooked up to the battery tender, and always at 100% before being started
 

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Try a new spark plug and check that side for spark as long as you have it out. Since you said you just set the timing, that is what I would check next. did a points screw back out? Always check whatever you fixed last.
 
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Check if you have a spark, pull the plug on the dead side and see if it's firing.
 

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Yep sounds like unspent fuel. As was mentioned, check the plug for spark, grounding it, turn it over in the shade and watch. I'd put a new one in anyway, they're cheap and you always need a spare. Fuel - spark - air, if you have'm you should be running. What did the plug you pulled look like? If you worked on the electrics that's where to look next. Hope it's a quick fix for ya.
 

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Yep sounds like unspent fuel. As was mentioned, check the plug for spark, grounding it, turn it over in the shade and watch. I'd put a new one in anyway, they're cheap and you always need a spare. Fuel - spark - air, if you have'm you should be running. What did the plug you pulled look like? If you worked on the electrics that's where to look next. Hope it's a quick fix for ya.
But ground it somewhere away from the hole for the cylinder which is suspected of dumping raw fuel...
 

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Discussion Starter #13
Just checked spark, it's very weak and a white spark, can barely see it, the plug is super black and sort of wet looking, I'll get a new plug here in a bit and see what I come up with
 

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Yep sounds like unspent fuel. As was mentioned, check the plug for spark, grounding it, turn it over in the shade and watch. I'd put a new one in anyway, they're cheap and you always need a spare. Fuel - spark - air, if you have'm you should be running. What did the plug you pulled look like? If you worked on the electrics that's where to look next. Hope it's a quick fix for ya.
I had the bike running, and noticed the back tail light wasnt working ( 2 of the wires had vibrated out) so I put them back in and crympted them down, the tail light then stayed on when the bike was running, so i unplugged it again, (This is prior to my bike only running on one cylinder) thats the only electrical work I've done on the bike this year, I dont think that would cause something shorting out up front causing one of the cylinders to dump, but hey ya never know!
 

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Discussion Starter #15
Put new plugs in and the right cylinder kicked on, here's a video of some of the smoke coming out, smelt alother like gas, thinking maybe time for an oil change.
 

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Looks like you have an exhaust leak, which won't help it.
Yeah i have one, couldnt find the right fitting for the exhaust the ones that came with it didnt fit snug, if there wasnt a leak it would just come out of the end of the exhaust, trying to make it stop before i fix the exhuast leak lol
 
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