76 CB360T Driving me bonkers

[bikerbill2021]

Hey all

So Im not much of a poster here, but love this site, lots of bad ass bikes and props to all the riders on here. Posted this in the engine forums too, not trying to spam, just trying to get some answers.

Anywho, I'll get right into it. 1976 CB360T. Got it as more or less a basket case, been tinkering with it on the side in my shop (VW tech by day). Got it from a younger guy who got bored with it, he did a good job, but somethings were left undone/half done. Trying to get it running right, but it is driving me up the wall.

So I'll break it down, bear with me, as this is long, but I'm at a loss here, the bike is in "time out" at the moment while I figure this out/focus on my other projects.

Bike has stock air boxes, with what looks like some form of harley short pipes on it. I have no idea what the brand is, they have baffles in them, and they are quite loud. The kid had half the carbs apart, it looks like he either chemical dunked or media blasted one of them and left the other one dirty, Im leaning towards media blasting, as I've been finding small sand particles in the the clean carb.

So I tore them down, gave them a good cleaning, checked the jetting, which according to the Honda manual I have all is stock, except for the mains, which are 110s at the moment (Located in PHX AZ). Replaced the diaphragm of the dirty carb, as it was torn, diaphragm on clean carb was good. Fuel mixture screw at 1.5 turns out on each.

Hooked up a temporary gas tank with clean gas (tank is at the body shop), and fired the bike up. Thing was all over the place, idle was hanging/bike was revving out of control up to about 5k, only firing out one side, smoking bad etc. So I pulled the carbs back off the bike, in the process I found the intake boots were not tight to the head, inspected them for cracks and tightened them down, all is good. Back to the carbs, cleaned up the butterfly mechanism, as they appeared to be sticking open/not snapping back into place, bench synced them, and gave them a good cleaning once again.

Bike ran pretty decent after that, was firing on both cylinders, throttle was responsive, exhaust was a little smokey but not bad. Took it for a ride, pulled hard until about 6-7k, then started missing. Brought it back to my shop, damn thing started idling out of control again, couldn't get it to calm down unless running the choke at 3/4-max, and it seemed to be chugging gas. At this point I noticed some light smoke emitting from the breather tube, nothing crazy, just some light puffs of white, but enough to have me concerned.

So tore back into the bike, checked for compression on the hot/warm motor, was at 142 on the right and 137 on the left, was told around 170 is what a fresh motor will put out, so assuming thats good. Pulled the points assy and mechanical timing advance out, inspected them both, cleaned them up etc, everything seemed good, new battery in it as well, as I've heard these machines are not happy with a poor power supply. Pulled the carbs once more to check everything, and cleaned them again. (kept finding sand grains, which kept my prior assumption of media blasting strong).

Put it all back together, grabbed my shops emission tester to see exactly wtf was going on, and fired it up. The right bank, with the "clean" carb, was running way lean, almost 18% fuel trim, and hydro carbons were way high too, you could hear it missing/not firing properly as well. Hooked up the left bank with the "dirty" carb, and that one was pretty happy, around 13.5% on the fuel trim and much lower hydrocarbs, seemed that cylinder was basically carrying the whole engine.

So after these findings, I tried swapping coils to see if it was possibly ignition related, bike started idling super high again, and couldn't get it to calm down unless I ran it with 3/4 choke on again, and kept doing so once I switched the coils back to their original spot. And thats where I stopped for now.

So I'm at a loss now, this thing has a mind of its own. My thinking is the "clean" carb was possibly chemical dunked, and ate away some seals I'm missing on the inside, causing a leak? Is it possible I'm missing something on these carbs? It seems to be something internal causing a massive air leak on that "clean" carb, anything you guys can think of to help me would be great. Ive talked to a fellow tech at Honda whose worked on these things since new, he said these are some of the worst carbs Honda ever put on a bike, and I'd be better off just adapting some newer carbs to it, would rather not, but will if I have too.

heres a shot of the bike, maybe some one can identify the pipes

 

[jpmobius]

Sounds like you need to go back to the carbs. You said you "gave them a good cleaning", and then after some testing still found sand in the one. After a good cleaning???!!!! Might want to re-think the meaning of "good cleaning".

I glass bead carb bodies all the time with no issues (but I actually do give them a good cleaning afterwards ;D), but no telling what media may have been used on yours. Walnut shells can be a lot of trouble for instance. Certainly you need to learn the function of every passageway so you can know all are clear and working properly. Seals and gaskets all need to work correctly. Check all jets and needles to be original OEM manufacturer. If aftermarket, toss them and get original factory parts so you know what you are starting with. I have seen many motorcycle carbs "re-built" with aftermarket kits that could not be made to work. Swap out all the new brass for the old and instant repair - believe it. If you have OEM jets and needles, keep them and look elsewhere for the trouble. Your carbs obviously are at least a part of the problem, maybe the whole problem. Take your time to get them back to original. Most times (but not always) there is just one problem. Leave no stone unturned on the carbs before looking elsewhere.

 

[irk miller]

When right, these are good carbs. They can be modded to significantly improve performance. It's not a kit method, but it can be done. Go with JBM diaphragms, as other manufactured options are known to have common pin hole issues. I don't see where you synced the carbs. Has this been done yet? It requires a special tool. Are those pipes baffled? Too little restriction will cause these carbs to lean out, and there's no pumper to compensate.

Assuming all of the gaskets are replaced and/or reinstalled, there are other places where common vacuum leaks occur on these carbs: the intake boots, the cap over the diaphragm, and around the throttle blade shaft where it's pressed into the body.


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[Sonreir]

Sounds like multiple problems.

The high revving is a common symptom of an air leak. Over tightening the manifolds to either the carbs or the head will cause as many problems as under tightening them. I use a thin layer of Vaseline on the inside of the boots when the fit over the carbs and I also use a thin layer of Three Bond between the manifolds and the heat.

Hunting idle is usually a sync issue. Bench sync is good, but that gets you close enough to do a proper sync with vacuum gauges. If your linkage is loose, you can easily go out of sync.

Compression is kind of low. If you can get it to idle and warm up well, repeat your tests. Poor compression will hurt idle and throttle response.

Double check your ignition timing using a strobe light.

 

[DohcBikes]

This is my reply to your identical thread in the engine section about 6 hours ago. The duplicate caused me some major confusion and damn near ended up with a not so pretty post and an undeserved comment or two, which has been removed. Try not to cross post:


You still have air leaks and dirty carbs. Address this first.

Hold the slide diaphragms up to a light source and look for holes.

Your pipes are too short, this will not cause your major issues but it will exacerbate them.

Bench sync is unreliable, especially when dealing with a worn engine. Having the benefit of only having two cylinders, you can make a sync tool out of easily sourced items such as a yardstick, tape, some atf and about 8 feet of clear line.

 

[irk miller]

I'm intrigued by the setup those things can make. I was referring the this tool:

Which goes through the hole in the frame at the back of the tank, loosens or tightens the locknut and turns the screw to sync. Also, these Keihins have an odd thread size, so many get these nipples for the vacuum ports:

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[DohcBikes]

I'm intrigued by the setup those things can make. I was referring the this tool:

Yep those tools along with several other special carb tools are handy. Motion Pro sells several. Not what I was mentioning though.

I ran across this page years ago and used this method to sync several twins before I bought a 4 port sync tool. It works beautifully. He suggests two stroke oil as a fluid. The tiny amount that it takes to fill the tube is not a concern, and Ive never seen it get sucked in anyway.

http://www.powerchutes.com/manometer.asp

 

[Trevor May]

I was going to post this earlier. I have a CJ360T, fraternal twin to yours. My machine ran horribly and sporadically before I employed all of the above tools to tune the carbs. I also used a timing light to set the ignition as well. As a result of getting the ignition proper, I could get it to idle long enough to balance the carbs with the manometer and the little nozzles, purchased from CrazyPJ. Balancing the carbs using that fancy screwdriver and wrench tool improved the reliability of my bike so significantly that I have taken it on several jaunts through back roads alone or with friends, and managed to put on almost 500 miles this year. Its been a whole different machine. My bike has lower compression, and I know that it needs a top end before I get the best out of her, but she pulls me along mostly due to finally getting some proper work accomplished. All these things listed above are worth the price to get that bike to finally perform reliably.

Edit: I changed the o-ring between the manifold and the engine but didn't use vaseline or threebond; I didn't know about those until just now. Sonreir, which threebond do you use?

 

[trek97]

http://www.dotheton.com/forum/index.php?topic=63133.0

 

[Sonreir]

Edit: I changed the o-ring between the manifold and the engine but didn't use vaseline or threebond; I didn't know about those until just now. Sonreir, which threebond do you use?

I use the 1104. Mainly that's because what was recommended to me. I have no experience with the other varieties.