Cb360 starting/running issues. Fresh 378 rebuild

Yeah that's how I've been doing it. "By the book". But I thought this method was interesting and that's not the first time I've heard the gap isn't really important. I guess with new points you can do this method but as your points start to age you definitely want to start checking gaps


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That's just to get you close, anyways. You should really check it with a strobe once you get it running to make sure it's firing on the dot at full advance.

Any progress getting it to run? Try hooking it up with a bottle and see if the plugs get wet when you crank it over.


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No luck yet. I have clear fuel lines so I can see the fuel flowing when I open the valve. Also if I blow air into the kidney part of the carbs the slide operates and fuel sprays out of the jets. Double checked compression today and in 3 kicks I'm at 180 on both cylinders


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Sprayed some starter fluid in the carbs. It started right up and died. Definitely a fuel issue


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Disconnected the fuel lines from the carbs and a bunch of fuel came out the fuel supply bung on each carb. Probably half an ounce came out of each carb. Is that normal? I wonder if it's because I blew air into the kidneys and that caused them to take more fuel


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Holy crap she's running strong now! Cleaned the fuel valve, went through the carbs again, and set float height to 18mm. There was a little gunk in the fuel valve but not enough to prevent flow. Maybe it was just enough to make it finicky. There was also a little oil on the carb slide. Im wondering if that might have put more resistance on it than it's supposed to have. I'm also wondering if changing the float height made a big difference.

Now my issue is that it started revving higher and higher without me pulling on the throttle. I just cut it off at that point because I got freaked out. I might have left the choke half on. Maybe that caused it. The bike is crazy loud so I'm stopping for the night. I'm just so excited it's running! And it started on the first kick!

Thanks everyone for your help!


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Decided to start it one more time. Ok this bike just really scared me for the first time ever. Revvs climbed super fast again. This time with choke off. Throttle closed too. Idle mix is 1/2 turn out, verified the butterflies are closing when throttle is released, and checked idle screw to make sure throttle is actually closing. I have new manifolds so there shouldn't be a vacuum leak.


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Check cable to see it's routed properly, but chances are intakes are leaking... Make sure the clamps between the intakes and carbs are not too loose or too tight. Spray carb. cleaner or wd40 around the intakes. Carbs. are sensitive. Did you check the idle adjustment? Turn it down if possible to get an idle of some sort, the do the leak test. Your intakes maybe new, but all it takes is them to slightly leak to drive you nuts.
 
Well, I didn't have filters on the carbs. But that shouldn't cause rpms to climb like crazy should it? Seems impossible if the butterflies are shut


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This climbed to probably 6,000 rpms in about 3 seconds before I cut it off


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thrillseeker said:
This climbed to probably 6,000 rpms in about 3 seconds before I cut it off

Yeah that has nothing to do with air filters. That sounds like your idle screw is off, your sync, or a vac leak if those two are in line. Bench sync ain't shit, do a proper vac sync.
 
Idle mixture screw or do you mean the throttle stop screw? I plan on syncing the carbs but want to make sure it's not going to blow up idling first


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You said the intakes are new, so I wanted to say something. The intakes I'm sure are good, but they could puckered if the clamps aren't quite right or they aren't bolted quite right to the heads. I've never worked on a 360 but take it for granted they are similar to other vintage bikes. Is there gaskets between the intakes and heads? Are they seating properly? Sometimes there is an O-ring between the intake and head, are they new/supple? I know this is frustrating for you, but to let you know, I had an 850 once that I had to mount the carbs. about 15 times before they seated properly. Drove me nuts for a week, but once the were right, the bike ran fine. There isn't a whole lot of things that can cause this. Focus on getting them mounted properly and the symptoms should fade.
 
thrillseeker said:
Idle mixture screw or do you mean the throttle stop screw? I plan on syncing the carbs but want to make sure it's not going to blow up idling first

Yeah the throttle stop screw, not the air/fuel screws. Those will only give you a few hundred RPM variance, if that. Back the throttle stop off all the way, then screw it in until it just engages the throttle assembly. I usually go about 1/2 turn from here and then adjust from there but that should give you a good starting point, at least you can rule that out.
 
Throttle stop. Get it to an idle that won't cook things, then start with the leak test. If that does what I think, then the intakes need to be attended to.
 
Another thought, after the intake test are exhausted and the bike is still doing the high idle thing, check the slide gaskets to make sure they are seated properly to the top pf the carb. See where this is going? What's happening (if not cable related) is a leak. Find the leak, fix the issue...
 
Thanks guys. I'll try to find time to investigate further tomorrow. I did make sure the slide assembly was put together right and sealing this last time I reassembled the carb.


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If you can get it down to a steady idle, even if its high (under 2500), vac sync it. I replaced the boots/2 sets of intake gaskets on my 360 thinking the same thing as Bill is suggesting, and it turned out to be a 1/4 turn on the sync screw was the difference between a 2k idle and a 1200 idle. The 360 carbs are SUPER sensitive to a bad sync when running with pods.
 
Here's what I learned on multi carbed bikes. First I want to say, that everybody, and I mean everybody on this site, has more talent and knowledge than I do. I learn from my mistakes and listening to talented people.

Vacuum synching can help hide issues. Don't get me wrong, vacuum synching is the goal to get your bike to it's optimum. But here's where it gets sticky. If there is a leak somewhere, synching can help hide it. You get an idle, you synch and your bike runs well, then you notice it idles funny when hot, or cold, or the idle changes every time you start the bike, it might fade on top end or bog on shift changes. It could lag off idle or flat spot at different RPM's.

So as bad as I fought it for years, the reality is, there are dozens of places your carb can leak. Slide rubbers, screw rubbers, intakes etc. but here's one almost everybody misses. The linkage that goes in the side of the carbs usually have gaskets and sometimes neopreme or plastic washers. I can say as truth, every time I've replaced them, the bikes ran better. Along with a rebuild (many carb kits don't come with these rubbers or washers) the bike then runs like new or better.

Once all the leaks are found, the synch brings everything to the balance the bike needs. I own a good synch, and for years I played Mr. synch for all my buddies. Everybody thought I was a genius, until I hung with some old dudes who put me to shame. They sat down and showed me the theory that doing things out of sequence will bite you in the ass. Synching is the goal, the finish line, but showed me on several occasions that the synch was hiding issues I didn't want to deal with. Who the hell wants to take the things all the way down, when I can hide the issue and go riding.

Lets get to the synch, but lets make sure everything else is proper to get there. I mean no disrespect to anybody, this is just something a hack like me has to do to keep from spending $ and time chasing ghosts...
 
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